EP2600996B1 - Process for producing a cu-cr material by powder metallurgy - Google Patents
Process for producing a cu-cr material by powder metallurgy Download PDFInfo
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- EP2600996B1 EP2600996B1 EP11751787.0A EP11751787A EP2600996B1 EP 2600996 B1 EP2600996 B1 EP 2600996B1 EP 11751787 A EP11751787 A EP 11751787A EP 2600996 B1 EP2600996 B1 EP 2600996B1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
- B22F1/052—Metallic powder characterised by the size or surface area of the particles characterised by a mixture of particles of different sizes or by the particle size distribution
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- B22—CASTING; POWDER METALLURGY
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- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
- B22F3/1017—Multiple heating or additional steps
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/12—Both compacting and sintering
- B22F3/16—Both compacting and sintering in successive or repeated steps
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/24—After-treatment of workpieces or articles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/0425—Copper-based alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/045—Alloys based on refractory metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
- C22C27/06—Alloys based on chromium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C9/00—Alloys based on copper
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H1/00—Contacts
- H01H1/02—Contacts characterised by the material thereof
- H01H1/0203—Contacts characterised by the material thereof specially adapted for vacuum switches
- H01H1/0206—Contacts characterised by the material thereof specially adapted for vacuum switches containing as major components Cu and Cr
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H11/00—Apparatus or processes specially adapted for the manufacture of electric switches
- H01H11/04—Apparatus or processes specially adapted for the manufacture of electric switches of switch contacts
- H01H11/048—Apparatus or processes specially adapted for the manufacture of electric switches of switch contacts by powder-metallurgical processes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/24—After-treatment of workpieces or articles
- B22F2003/248—Thermal after-treatment
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2301/00—Metallic composition of the powder or its coating
- B22F2301/10—Copper
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2301/00—Metallic composition of the powder or its coating
- B22F2301/20—Refractory metals
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2304/00—Physical aspects of the powder
- B22F2304/10—Micron size particles, i.e. above 1 micrometer up to 500 micrometer
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
- B22F2998/10—Processes characterised by the sequence of their steps
Definitions
- the present invention relates to a method for the powder metallurgical production of a Cu-Cr material for a switching contact, in particular for vacuum switches. It involves the production of a high-performance Cu-Cr material.
- the switching contacts require a switching capacity that is as constant as possible over the service life, a high dielectric strength and the lowest possible burnup.
- the aim is to achieve a high erosion resistance, a good electrical and thermal conductivity, the lowest possible tendency to weld during the switching operation and a high dielectric strength and a sufficient mechanical strength of the switching contact.
- Copper-chrome contacts for vacuum switches are thereby produced by producing a thin copper-chromium sheet as the starting material for the contacts by means of a casting or spraying process with subsequent rapid cooling. In this case, concentration profiles set in a direction perpendicular to the belt direction. A state diagram of the Cu-Cr system is also shown and described.
- the EP0469578 A2 describes a method for producing a Cu-Cr contact material according to which an alloy of copper and chromium is melted and atomized, and the recovered Cu-Cr alloy powder is sintered in a copper matrix.
- the WO2010050352 A1 describes a method for producing a material for switch contacts, according to which atomized Cu-Cr alloy powder is mixed with Cr powder and Cu powder, compacted and sintered.
- the method for powder metallurgy producing a Cu-Cr material for a switching contact comprises the following steps: pressing a Cu-Cr powder mixture formed from Cu powder and Cr powder, sintering the pressed Cu-Cr powder mixture to the material of the Cu-Cr switch contact.
- the sintering and / or a subsequent thermal treatment process is carried out with an alternating temperature profile in which the Cu-Cr powder mixture or the Cu-Cr material is heated at least twice alternately above an upper temperature limit and cooled again below a lower temperature limit. All steps are performed at temperatures that do not form a molten phase.
- the entire manufacturing process of the Cu-Cr material is thus carried out purely by powder metallurgy at temperatures below the temperature of the eutectic (1075 ° C) of the Cu-Cr system, so that no forms molten phase.
- the term "pure powder metallurgy" in this case refers to a process in which there is no formation of a molten phase.
- Either sintering or a subsequent thermal treatment process (or both) with an alternating temperature profile is performed.
- An alternating temperature profile is understood here to mean that an increase in temperature and a decrease in temperature take place alternately, wherein a temperature increase and a temperature decrease occur in each case at least twice.
- the temperature increase and the temperature reduction preferably take place at least three times.
- the alternating temperature profile can be traversed, for example, during the sintering of the pressed Cu-Cr green body. However, it is also possible, for example, to expose the already (conventionally) sintered Cu-Cr material to the alternating temperature profile in a subsequent thermal treatment process.
- the upper temperature limit can preferably be chosen so that the greatest possible solubility of Cr in Cu is given in solid solution.
- the lower temperature limit may preferably be chosen to provide a significantly lower solubility of Cr in Cu in solid solution than at the upper temperature limit.
- the production of the Cu-Cr material may be e.g. such that already the finished switching contact is provided in its final form, or e.g. also such that the switching contact is given its final shape only by suitable post-processing.
- the Cu-Cr material By purely powder metallurgical production of the Cu-Cr material can be provided in a particularly economical manner. Due to the alternating temperature profile (pendulum annealing) it is achieved that many Cr grains with grain sizes with a cross section between 0.1 ⁇ m 2 and 50 ⁇ m 2 (measured in the micrograph) are formed in a Cu matrix.
- the Cu-Cr material formed thus has a particle size distribution of the Cr grains measured in the micrograph, which has a first maximum in the range of grain sizes with a cross section between 0.1 ⁇ m 2 and 50 ⁇ m 2 .
- the determination of the particle size distribution is carried out microscopically in a grinding by measuring the surfaces of the respective Cr grains. Microscopic is understood here by light microscopy and electron microscopy.
- a Cu-Cr material is provided for a switching contact, which is produced in a very economical manner while high erosion resistance, good electrical and thermal conductivity, a low tendency to weld in the switching process and a high dielectric strength and sufficient mechanical Strength of the switch contact achieved.
- the advantageous particle size distribution described is also achieved without difficulty if relatively coarse Cr powder (for example having particle diameters between 20 ⁇ m and 200 ⁇ m) is used as the starting material.
- the resulting Cu-Cr material has a microstructure in which in the micrograph in a Cu Matrix are present in addition to some smaller Cr grains relatively large Cr grains with a grain diameter in the range between 100 microns and 150 microns. This then typically results in a unimodal grain size distribution with a maximum, for example, with grain sizes in the range between 100 ⁇ m 2 and 25000 ⁇ m 2 . This suggests that the particle sizes of the Cr powder as the starting material in the resulting Cu-Cr material are substantially maintained unless the alternating temperature profile is traversed.
- the method for producing the Cu-Cr material With the method for producing the Cu-Cr material, a low porosity, a high density, an extremely low degree of impurities, finely and homogeneously isotropically distributed Cr grains in a Cu matrix and a uniform homogeneous chemical composition of the Cu-Cr Material reached.
- the resulting Cu-Cr material is ideal for switching contacts for use in vacuum switching technology, both as a circuit breaker in the high and medium voltage range and as a vacuum contactor switch in the low voltage range.
- the upper temperature limit is in a range between 1065 ° C and 1025 ° C and the lower temperature limit is at least 50 ° C below the upper temperature limit.
- the lower temperature limit is preferably at least 100 ° C below the upper temperature limit.
- the upper temperature limit is in a temperature range just below the temperature of the eutectic (1075 ° C), that is, a range in which up to about 0.7 at% Cr can be dissolved in the Cu matrix in solid solution. This corresponds to the range in which the maximum solubility of Cr in Cu is given in solid solution.
- the upper temperature limit is far enough below the temperature of the eutectic that the formation of a molten phase is reliably prevented even with slight temperature fluctuations.
- the lower temperature limit is well below the upper temperature limit, ie in a range in which (in thermal equilibrium) a significantly smaller amount of Cr in the Cu matrix can be dissolved in solid solution.
- Cr in the case of heating above the upper temperature limit Cr, it is enriched in the material of the Cu matrix (up to a maximum of approximately 0.7 at%).
- the amount of Cr dissolved in solid solution exceeds the solubility corresponding to this lower temperature value, which is significantly less than 0.7 at%. Consequently, Cr is precipitated from the Cu matrix and Cr grains with small grain sizes are formed. In a repeated passing through the alternating temperature profile, the number of Cr grains formed with small grain sizes increases first.
- the method further comprises the step of: mixing Cu powder and Cr powder into a Cu-Cr powder mixture.
- the Cu-Cr powder mixture can be easily provided by using conventional Cr powder and Cu powder.
- the Cu particles in the Cu-Cr powder mixture have a particle size distribution with a maximum particle diameter ⁇ 80 ⁇ m, preferably ⁇ 50 ⁇ m, on.
- a maximum particle diameter is determined by means of a sieve analysis. In this case, a sieve with a corresponding mesh size (eg 80 microns or 50 microns) is used and only particles that fall through the sieve are used.
- the Cr particles in the Cu-Cr powder mixture have a particle size distribution with a maximum particle diameter ⁇ 200 ⁇ m, preferably ⁇ 160 ⁇ m, on.
- the maximum particle diameter is again determined with a sieve analysis with a corresponding mesh size of the sieve.
- the value for the maximum particle diameter is small enough so as not to form excessively large Cr grains in the Cu-Cr material.
- the individual particles can also be formed large enough so that no excessive risk of contamination by oxides occurs and in conventional production plants, a high density and a low degree of porosity can be achieved.
- the Cr particles in the Cu-Cr powder mixture have a particle size distribution with a minimum particle diameter ⁇ 20 ⁇ m, preferably ⁇ 32 ⁇ m.
- the minimum particle diameter is also determined with a sieve analysis (with a mesh size of, for example, 20 ⁇ m or 32 ⁇ m), but in this case only the particles which do not fall through the sieve are used. In this case, the minimum particle diameter is large enough so that there is no excessive risk of oxide contamination, and high density and a low degree of porosity can be achieved in conventional production equipment.
- the Cu-Cr powder mixture has a Cu content between 30% by weight and 80% by weight and a Cr content between 70% by weight and 20% by weight. In this case, it is achieved that both a high erosion resistance and a low tendency to weld as well as good electrical and thermal conductivity and sufficient mechanical strength can be provided. If the Cr content exceeds 70% by weight, this leads to a marked deterioration of the thermal and electrical conductivity. If the Cr content is less than 20% by weight, no satisfactory burn-off resistance and welding tendency can be obtained.
- the powder-metallurgically produced Cu-Cr switch contact has a Cu content between 30 wt .-% and 80 wt .-% and a Cr content between 70 wt .-% and 20 wt .-%.
- the Cu-Cr switch contact has Cr grains in a Cu matrix.
- a particle size distribution of the Cr grains measured in the micrograph has a first maximum in the range of particle sizes with a cross-sectional area between 0.1 ⁇ m 2 and 50 ⁇ m 2 .
- the switching contact is made by a powder metallurgy process of Cu powder and Cr powder without formation of a molten phase. It is thus a purely powder metallurgically produced Cu-Cr switching contact.
- the Cu-Cr switch contact may be designed for vacuum switch.
- a Cu matrix is understood to mean a material which mainly consists of Cu but may also have a small proportion of Cr in solid solution. There may also be traces of impurities.
- Cr grains are formed.
- the grain size distribution of the Cr grains is determined as follows: A micrograph of the Cu-Cr material of the switch contact is made and analyzed microscopically. In the micrograph, the Cr grains are identified and the cross-sectional areas of the Cr grains are measured. The evaluation is carried out over a sufficiently large surface area or different surface areas, which form a sufficiently large total area, so that a representative, statistical statement is possible. The evaluation can be done eg by hand or supported by a suitable software.
- the particle size distribution is seen.
- the particle size distribution has a maximum in a range of particle sizes with a measured cross-sectional area between 0.1 ⁇ m 2 and 50 ⁇ m 2 .
- the powder-metallurgically produced Cu-Cr switch contact achieves the advantages described above with respect to the method of powder metallurgy producing a Cu-Cr material for a switch contact. Due to the pure powder metallurgical production a particularly economical production is possible. Because of the grain size distribution with the maximum in the range of grain sizes with a cross-sectional area between 0.1 ⁇ m 2 and 50 ⁇ m 2 , the Cu-Cr switch contact has a large number of fine Cr grains. The fine Cr grains are largely homogeneously distributed. In this way, a very good erosion resistance is achieved.
- the Cu-Cr switch contact is obtainable by a purely powder metallurgical process in which sintering or a subsequent thermal treatment process is carried out with an alternating temperature profile in which a Cu-Cr powder mixture or the material of the Cu-Cr switch contact alternates at least twice is heated above an upper temperature limit and cooled again below a lower temperature limit, and wherein all steps are carried out at temperatures, where no molten phase is formed.
- the production in a purely powder metallurgical process can be seen on the Cu-Cr switch contact.
- the grain size distribution of the Cr grains has a second maximum in the range of grain sizes with a cross-sectional area between 100 ⁇ m 2 and 10000 ⁇ m 2 .
- a bimodal Cr phase distribution which has two maxima, a first maximum for grain sizes with a measured cross-sectional area between 0.1 ⁇ m 2 and 50 ⁇ m 2 and a second maximum for grain sizes with a measured cross-sectional area between 100 ⁇ m 2 and 10000 ⁇ m 2 .
- This particle size distribution results from the purely powder metallurgical production process using coarse Cr powder, for example with particle diameters between 20 .mu.m and 200 .mu.m.
- the number of Cr grains corresponding to the first maximum is greater than the number of Cr grains corresponding to the second maximum, ie, there are more grains having a grain size corresponding to the first maximum than grains having a grain size corresponding to the first maximum have second maximum corresponding grain size.
- the Cu-Cr switch contact has a relative density> 90%.
- good electrical and thermal conductivity and high mechanical strength are reliably provided.
- Such a high specific gravity can be reliably achieved by using relatively coarse Cr powder and Cu powder in conventional production equipment.
- relative density is meant the ratio between the density achieved and the theoretically achievable density for the composition.
- the Combination of this high density and the high proportion of fine Cr grains in the Cu matrix can be achieved by combining a use of coarse Cr powder (with particle diameters between 20 ⁇ m and 200 ⁇ m) and using an alternating temperature profile alternating at least twice a warming above an upper temperature limit and again a cooling below a lower temperature limit, reach.
- a first step -S1- Cu powder having a maximum particle diameter of preferably at most 50 ⁇ m with Cr powder having a maximum particle diameter of at most 200 ⁇ m (preferably at most 160 ⁇ m) and a minimum particle diameter of at least 20 ⁇ m (preferably at least 32 microns) mixed into a Cu-Cr powder mixture.
- Cr powder having a maximum particle diameter of at most 200 ⁇ m (preferably at most 160 ⁇ m) and a minimum particle diameter of at least 20 ⁇ m (preferably at least 32 microns) mixed into a Cu-Cr powder mixture As an example, a first Cu-Cr powder mixture having a Cr content of 25% by weight and a Cu content of 75% by weight and a second Cu-Cr powder mixture having a Cr content of 43% by weight have been exemplified .-% and a Cu content of 57 wt .-% produced.
- a second step -S2- the Cu-Cr powder mixture is pressed.
- the Cu-Cr powder mixture is compacted by cold pressing at a compression pressure in a range between 400 MPa and 850 MPa.
- the green compact formed in this way is sintered in a sintering process at temperatures in a temperature range well below the temperature of the eutectic (ie, significantly below 1075 ° C.).
- the sintering process can be carried out, for example, at temperatures in a temperature range between 850 ° C and 1070 ° C. The temperatures must be high enough so that the sintering process proceeds sufficiently and with sufficient speed, and low enough that no molten phase forms even with unavoidable temperature gradients.
- FIG. 2 An exemplary light microscopic micrograph of a powder-metallurgically produced Cu-Cr material after step -S3- is in Fig. 2 shown.
- Fig. 2 It can be seen that Cr grains with different grain sizes are incorporated in a Cu matrix.
- FIG. 1 An evaluation of the grain size distribution of the Cr grains in the thus prepared Cu-Cr material is shown in FIG Fig. 1 represented by a solid line.
- a micrograph of the Cu-Cr material was prepared and the size of the Cr grains was examined microscopically and measured. 10 different regions of the Cu-Cr material were analyzed to obtain a statistically meaningful distribution.
- Fig. 1 is the measured on the horizontal axis Cross-sectional area of Cr grains in ⁇ m 2 plotted on a logarithmic scale. On the vertical axis, the corresponding number of grains normalized to a unit area of 1 mm 2 is also shown in a logarithmic representation. As in Fig.
- the Cu-Cr material in this stage of the process has a monomodal particle size distribution with particle sizes in a range between about 10 microns 2 and 25000 microns 2 .
- the particle size distribution has a maximum, which is at a particle size> 100 microns 2 .
- the Cu-Cr material is then subjected to a thermal treatment process with an alternating temperature profile, as will be described below.
- the Cu-Cr material is alternately heated to a temperature above an upper temperature limit and cooled to a temperature below a lower temperature limit.
- the alternating heating and cooling take place at least twice. In these process steps, too, care is taken that no molten phase is formed, i. the Cu-Cr material is kept at temperatures below the temperature of the eutectic (1075 ° C) of the Cu-Cr system. This will be described in more detail below.
- the Cu-Cr material is heated to a temperature above the upper temperature limit.
- the upper temperature limit is preferably relatively close below the temperature of the eutectic of the Cu-Cr system, so that the Cu-Cr material is brought to a temperature just below the temperature of the eutectic, but far enough away from the temperature of the eutectic that forming a liquid phase is reliably prevented.
- the upper temperature limit value is thus preferably in a range between 1025 ° C and 1065 ° C.
- the Cu-Cr material is cooled to a temperature below a lower temperature limit.
- the lower temperature limit is preferably in a range which is at least 50 ° C below the upper temperature limit, more preferably in an area more than 100 ° C below the upper temperature limit.
- the lower temperature limit is preferably at most 250 ° C below the upper temperature limit, more preferably at most 180 ° C below the upper temperature limit.
- the lower temperature limit should be chosen so that there is a much lower solubility of Cr in solid solution in Cu than at the upper temperature limit. The reason for this choice will be explained in more detail.
- the Cu-Cr material can be cooled to temperatures in the range of about 850 ° C. It is recommended not to set the lower temperature limit too low to ensure a sufficient degree of diffusion processes in the Cu-Cr material. At the upper temperature level and the lower temperature level, the Cu-Cr material is held for some time each.
- the step -S4- is repeated, i. the Cu-Cr material is again raised to a temperature above the upper temperature limit.
- the step -S5- is repeated, i. the Cu-Cr material is again cooled to a temperature below the lower temperature limit.
- the steps -S4- and -S5- are repeated a total of n times, but a total of at least twice, preferably at least three times. It has been found that when the steps -S4- and -S5- are passed through from 2 times to about 6 times (2 ⁇ n ⁇ 6), an improvement of the Cu-Cr material is achieved and with a larger number of repetitions no further improvement is expected.
- the Cu-Cr material is thus exposed to a pendulum annealing. At least steps -S4- and -S5- are carried out in a protective gas oven under reducing atmosphere and / or in a vacuum oven to avoid unwanted oxidation with oxygen. Subsequently, the manufacturing process is terminated.
- Fig. 3 shows a light microscopic micrograph of powder metallurgically produced Cu-Cr material after passing through the described alternating temperature profile.
- Fig. 3 It can be seen that, after performing the pendulum annealing, the content of Cr grains having a small cross-sectional area compared with the state before the pendulum annealing (cf. Fig. 2 ), clear has increased.
- a closer analysis of the grain size of the Cr grains reveals that a bimodal grain size distribution has been established which has two maxima.
- Fig. 1 is shown as a dashed line, the determined particle size distribution after passing through the alternating temperature profile.
- the grain size distribution was determined in the same manner as above with respect to the solid line of Fig. 1 has been described. It can be seen that, after the pendulum annealing, instead of the previously existing monomodal particle size distribution (solid line), there is a bimodal particle size distribution.
- the particle size distribution has a first maximum in a range of grain sizes with a cross-sectional area between 0.1 ⁇ m 2 and 50 ⁇ m 2 . Furthermore, the particle size distribution has a second maximum in the range of grain sizes with a cross-sectional area between 100 ⁇ m 2 and 10,000 ⁇ m 2 .
- the number of Cr grains corresponding to the first maximum is greater than the number of Cr grains corresponding to the second maximum.
- the number of Cr grains corresponding to the first maximum is larger than the number of Cr grains corresponding to the second maximum by a factor> 5.
- there is a very homogeneous distribution of the Cr grains in the Cu matrix The proportion of Cr grains with a cross-sectional area ⁇ 10 ⁇ m 2 measured in the micrograph is thus very high.
- the thermal treatment with the alternating temperature profile thus achieves a shift to a high proportion of very small finely divided Cr grain precipitates in the Cu matrix.
- the described starting materials having a relatively coarse particle size of the Cr powder, it is possible to produce very dense Cu-Cr materials with low porosity in a purely powder metallurgical process with conventional production plants, which also have a low level of impurities.
- the pure powder metallurgy production is recognizable on the Cu-Cr material. Due to the very finely distributed Cr grains, the purely powder-metallurgically produced Cu-Cr material has a high erosion resistance, a high dielectric strength and a sufficient mechanical strength of the switching contact.
- the formation of the finely divided Cr grains in the Cu matrix can be with regard to the example in the aforementioned DE 10 2006 021 772 A1 illustrated Explain the state diagram as follows: At temperatures above the upper limit of the temperature in a region near below the temperature of the eutectic, up to about 0.7 at% of Cr can be dissolved in solid solution in the material of the Cu matrix (in thermodynamic equilibrium). Upon cooling of the Cu-Cr material to a temperature below the lower temperature limit, the material is brought to a temperature at which only a much smaller proportion of Cr in solid solution in the material of the Cu matrix can be dissolved in the thermodynamic equilibrium. Upon cooling, Cr is thus precipitated out of the material of the Cu matrix and this precipitation takes place in the form of small grains.
- the temperature change between the high and the low temperature level in the pendulum annealing should be chosen to be sufficiently slow that Cr is reliably precipitated from the Cu matrix on cooling, but not too slow so that larger Cr grains are not produced again by grain coarsening.
- the treatment with the alternating Temperature profile only after the step -S3- of the sintering in the Cu-Cr material
- the pressed Cu-Cr green compact is already repeatedly subjected to steps -S4- and -S5 during the sintering process.
- the separate step -S3- is omitted and the sintering takes place during the steps -S4- and -S5-.
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Description
Die vorliegende Erfindung betrifft ein Verfahren zum pulvermetallurgischen Herstellen eines Cu-Cr-Werkstoffs für einen Schaltkontakt, insbesondere für Vakuumschalter. Es handelt sich dabei um das Herstellen eines Hochleistungs-Cu-Cr-Werkstoffs.The present invention relates to a method for the powder metallurgical production of a Cu-Cr material for a switching contact, in particular for vacuum switches. It involves the production of a high-performance Cu-Cr material.
Es ist bekannt, als Material für Schaltkontakte, insbesondere im Einsatzbereich des Vakuumschaltprinzips, Cu-Cr-Werkstoffe einzusetzen. Das Vakuumschaltprinzip hat sich im Bereich der Mittelspannung, d.h. im Bereich von ca. 7,2 kV bis 40 kV, bereits weltweit als führendes Schaltprinzip durchgesetzt und es ist auch ein Trend zu einem Einsatz bei höheren Spannungen ersichtlich. Derartige Schaltkontakte kommen dabei z.B. sowohl bei Vakuum-Mittelspannungs-Leistungsschaltern als auch bei Vakuumschützen zum Einsatz.It is known to use Cu-Cr materials as material for switching contacts, in particular in the field of application of the vacuum switching principle. The vacuum switching principle has been found in the range of medium voltage, i. in the range of approx. 7.2 kV to 40 kV, already established as the leading switching principle worldwide, and there is also a trend towards use at higher voltages. Such switching contacts come here, e.g. used in both vacuum medium-voltage circuit breakers and vacuum contactors.
Von den Schaltkontakten werden unter anderem ein über die Lebensdauer möglichst gleichbleibend hohes Schaltvermögen, eine hohe dielektrische Festigkeit und ein möglichst geringer Abbrand gefordert. Es wird erstrebt, eine hohe Abbrandfestigkeit, eine gute elektrische und thermische Leitfähigkeit, eine möglichst geringe Verschweißneigung beim Schaltvorgang sowie eine hohe dielektrische Festigkeit und eine ausreichende mechanische Festigkeit des Schaltkontakts zu erzielen.Among other things, the switching contacts require a switching capacity that is as constant as possible over the service life, a high dielectric strength and the lowest possible burnup. The aim is to achieve a high erosion resistance, a good electrical and thermal conductivity, the lowest possible tendency to weld during the switching operation and a high dielectric strength and a sufficient mechanical strength of the switching contact.
Wie aus dem Zustandsdiagramm ersichtlich ist, existiert in der festen Phase nahezu keine Mischbarkeit zwischen Cu und Cr. Lediglich in einem kleinen Bereich unterhalb des Eutektikums, das sich bei einer Temperatur von ca. 1075 °C befindet, existiert ein Bereich, in dem eine geringe Löslichkeit von Cr in fester Lösung in Cu gegeben ist. Die maximale Löslichkeit von Cr in Cu in fester Lösung ist im thermodynamischen Gleichgewicht mit ca. 0,7 at.-% bei 1075 °C gegeben. Zu niedrigeren Temperaturen nimmt die Löslichkeit von Cr in Cu ab und bei 400 °C sind im thermodynamischen Gleichgewicht nur noch 0,03 at.-% Cr in Cu in fester Lösung gegeben. Ein detaillierteres Zustandsdiagramm des Cu-Cr-Systems ist z.B. in dem
Aus dem Zustandsdiagramm ergibt sich, dass bei Cu-Cr-Werkstoffen mit einem typischen Gehalt von 30-80 Gew.-% Cu und 70-20 Gew.-% Cr bei Temperaturen unterhalb des Eutektikums Cr-Körner in einer Cu-Matrix vorliegen. Aufgrund der geringen Löslichkeit von Cr in Cu in diesem Bereich, kann dabei in der Cu-Matrix ein geringer Anteil von Cr in fester Lösung vorliegen. Im Folgenden wird der Begriff Cu-Matrix auch dann verwendet, wenn ein geringer Anteil von Cr in fester Lösung in dem Cu vorhanden ist.It can be seen from the state diagram that, for Cu-Cr materials with a typical content of 30-80% by weight of Cu and 70-20% by weight of Cr, at temperatures below the eutectic, Cr grains are present in a Cu matrix. Due to the low solubility of Cr in Cu in this range, a small amount of Cr can be present in solid solution in the Cu matrix. In the following, the term Cu matrix will be used even if a small amount of Cr is present in solid solution in the Cu.
Zur Herstellung von Cu-Cr-Werkstoffen für Schaltkontakte für die Vakuumschalttechnik sind rein pulvermetallurgische Verfahren, Sinter-Tränk-Verfahren und auch schmelzmetallurgische Verfahren bekannt.Pure powder metallurgical processes, sintered impregnation processes and also melt metallurgical processes are known for the production of Cu-Cr materials for switching contacts for vacuum switching technology.
Die
Die
Aufgrund des komplexen Zustandsdiagramms des Systems Cu-Cr, ist die direkte Herstellung von homogenen Schmelzwerkstoffen nicht möglich. Aus diesem Grund werden häufig für hochwertige Cu-Cr-Werkstoffe für Schaltkontakte für Vakuum-schalter sogenannte Umschmelzwerkstoffe eingesetzt, wobei z.B. ein Umschmelzen unter Verwendung eines Lasers oder eines Lichtbogens zum Einsatz kommen kann.Due to the complex state diagram of the Cu-Cr system, the direct production of homogeneous fused materials is not possible. For this reason are often used for high quality Cu-Cr materials for switching contacts for vacuum switches so-called remelting materials used, for example, a remelting using a laser or an arc can be used.
Eine rein pulvermetallurgische Herstellung von Cu-Cr-Werkstoffen für Schaltkontakte für Vakuumschalter (im Folgenden auch: Vakuumschaltkontakte) stellt sich, verglichen mit einer schmelzmetallurgischen Herstellung, wesentlich wirtschaftlicher dar. Es hat sich jedoch gezeigt, dass die pulvermetallurgisch hergestellten Cu-Cr-Werkstoffe bisher noch nicht in zufriedenstellendem Maße die gewünschten Eigenschaften aufweisen.A purely powder metallurgical production of Cu-Cr materials for switching contacts for vacuum switches (hereinafter also: vacuum switching contacts) is compared to a metallurgical production, much more economical. However, it has been shown that the powder metallurgically produced Cu-Cr materials so far not yet to a satisfactory extent have the desired properties.
Es ist Aufgabe der vorliegenden Erfindung, ein Verfahren zum pulvermetallurgischen Herstellen eines Cu-Cr-Werkstoffs für einen Schaltkontakt bereitzustellen, das sowohl eine hohe Abbrandfestigkeit, eine gute elektrische und thermische Leitfähigkeit, eine möglichst geringe Verschweißneigung beim Schaltvorgang sowie eine hohe dielektrische Festigkeit und eine ausreichende mechanische Festigkeit des Schaltkontakts bereitstellt als auch eine wirtschaftliche Herstellung ermöglicht.It is an object of the present invention to provide a method for the powder metallurgical production of a Cu-Cr material for a switching contact, which has both a high erosion resistance, good electrical and thermal conductivity, the lowest possible tendency to weld in the switching operation and a high dielectric strength and sufficient provides mechanical strength of the switch contact as well as economic production allows.
Die Aufgabe wird durch ein Verfahren zum pulvermetallurgischen Herstellen eines Cu-Cr-Werkstoffs für einen Schaltkontakt nach Anspruch 1 gelöst. Vorteilhafte Weiterbildungen sind in den abhängigen Ansprüchen angegeben.The object is achieved by a method for the powder metallurgical production of a Cu-Cr material for a switching contact according to
Das Verfahren zum pulvermetallurgischen Herstellen eines Cu-Cr-Werkstoffs für einen Schaltkontakt, insbesondere für Vakuumschalter, weist die folgenden Schritte auf: Pressen eines aus Cu-Pulver und Cr-Pulver gebildeten Cu-Cr-Pulvergemischs, Sintern des gepressten Cu-Cr-Pulvergemischs zu dem Werkstoff des Cu-Cr-Schaltkontakts. Das Sintern und/oder ein nachfolgender thermischer Behandlungsprozess wird mit einem alternierenden Temperaturprofil durchgeführt, bei dem das Cu-Cr-Pulvergemisch bzw. der Cu-Cr-Werkstoff zumindest zweimal abwechselnd über einen oberen Temperaturgrenzwert erwärmt und wieder unter einen unteren Temperaturgrenzwert abgekühlt wird. Sämtliche Schritte werden bei Temperaturen durchgeführt, bei denen sich keine schmelzflüssige Phase ausbildet. Der gesamte Herstellungsprozess des Cu-Cr-Werkstoffs wird somit rein pulvermetallurgisch bei Temperaturen durchgeführt, die unterhalb der Temperatur des Eutektikums (1075 °C) des Cu-Cr-Systems liegen, sodass sich keine schmelzflüssige Phase ausbildet. Der Begriff "rein pulvermetallurgisch" bezeichnet dabei vorliegend einen Prozess, bei dem es nicht zur Ausbildung einer schmelzflüssigen Phase kommt. Es wird entweder das Sintern oder ein nachfolgender thermischer Behandlungsprozess (oder beides) mit einem alternierenden Temperaturprofil durchgeführt. Unter einem alternierenden Temperaturprofil wird dabei verstanden, dass abwechselnd eine Temperaturerhöhung und eine Temperaturerniedrigung stattfinden, wobei eine Temperaturerhöhung und eine Temperaturerniedrigung jeweils zumindest zweimal erfolgen. Bevorzugt erfolgen die Temperaturerhöhung und die Temperaturerniedrigung zumindest dreimal. Das alternierende Temperaturprofil kann dabei z.B. bereits bei dem Sintern des gepressten Cu-Cr-Grünlings durchlaufen werden. Es ist z.B. aber auch möglich, den bereits (konventionell) gesinterten Cu-Cr-Werkstoff in einem nachfolgenden thermischen Behandlungsprozess dem alternierenden Temperaturprofil auszusetzen. Der obere Temperaturgrenzwert kann dabei vorzugsweise so gewählt werden, dass eine möglichst große Löslichkeit von Cr in Cu in fester Lösung gegeben ist. Der untere Temperaturgrenzwert kann vorzugsweise so gewählt werden, dass eine deutlich niedrigere Löslichkeit von Cr in Cu in fester Lösung gegeben ist, als bei dem oberen Temperaturgrenzwert.The method for powder metallurgy producing a Cu-Cr material for a switching contact, in particular for a vacuum switch, comprises the following steps: pressing a Cu-Cr powder mixture formed from Cu powder and Cr powder, sintering the pressed Cu-Cr powder mixture to the material of the Cu-Cr switch contact. The sintering and / or a subsequent thermal treatment process is carried out with an alternating temperature profile in which the Cu-Cr powder mixture or the Cu-Cr material is heated at least twice alternately above an upper temperature limit and cooled again below a lower temperature limit. All steps are performed at temperatures that do not form a molten phase. The entire manufacturing process of the Cu-Cr material is thus carried out purely by powder metallurgy at temperatures below the temperature of the eutectic (1075 ° C) of the Cu-Cr system, so that no forms molten phase. The term "pure powder metallurgy" in this case refers to a process in which there is no formation of a molten phase. Either sintering or a subsequent thermal treatment process (or both) with an alternating temperature profile is performed. An alternating temperature profile is understood here to mean that an increase in temperature and a decrease in temperature take place alternately, wherein a temperature increase and a temperature decrease occur in each case at least twice. The temperature increase and the temperature reduction preferably take place at least three times. The alternating temperature profile can be traversed, for example, during the sintering of the pressed Cu-Cr green body. However, it is also possible, for example, to expose the already (conventionally) sintered Cu-Cr material to the alternating temperature profile in a subsequent thermal treatment process. The upper temperature limit can preferably be chosen so that the greatest possible solubility of Cr in Cu is given in solid solution. The lower temperature limit may preferably be chosen to provide a significantly lower solubility of Cr in Cu in solid solution than at the upper temperature limit.
Das Herstellen des Cu-Cr-Werkstoffs kann dabei z.B. derart erfolgen, dass bereits der fertige Schaltkontakt in seiner Endform bereitgestellt wird, oder z.B. auch derart, dass der Schaltkontakt erst durch eine geeignete Nachbearbeitung seine endgültige Form erhält.The production of the Cu-Cr material may be e.g. such that already the finished switching contact is provided in its final form, or e.g. also such that the switching contact is given its final shape only by suitable post-processing.
Durch die rein pulvermetallurgische Herstellung kann der Cu-Cr-Werkstoff in besonders wirtschaftlicher Weise bereitgestellt werden. Durch das alternierende Temperaturprofil (Pendelglühen) wird erreicht, dass viele Cr-Körner mit Korngrößen mit einem Querschnitt zwischen 0,1 µm2 und 50 µm2 (gemessen im Schliffbild) in einer Cu-Matrix ausgebildet werden. Der gebildete Cu-Cr-Werkstoff weist somit eine Korngrößenverteilung der Cr-Körner gemessen im Schliffbild auf, die ein erstes Maximum im Bereich von Korngrößen mit einem Querschnitt zwischen 0,1 µm2 und 50 µm2 aufweist. Die Bestimmung der Korngrößenverteilung erfolgt dabei mikroskopisch in einem Schliff durch Ausmessen der Flächen der jeweiligen Cr-Körner. Unter mikroskopisch wird vorliegend lichtmikroskopisch und elektronenmikroskopisch verstanden.By purely powder metallurgical production of the Cu-Cr material can be provided in a particularly economical manner. Due to the alternating temperature profile (pendulum annealing) it is achieved that many Cr grains with grain sizes with a cross section between 0.1 μm 2 and 50 μm 2 (measured in the micrograph) are formed in a Cu matrix. The Cu-Cr material formed thus has a particle size distribution of the Cr grains measured in the micrograph, which has a first maximum in the range of grain sizes with a cross section between 0.1 μm 2 and 50 μm 2 . The determination of the particle size distribution is carried out microscopically in a grinding by measuring the surfaces of the respective Cr grains. Microscopic is understood here by light microscopy and electron microscopy.
In dieser Weise wird ein Cu-Cr-Werkstoff für einen Schaltkontakt bereitgestellt, der in sehr wirtschaftlicher Weise hergestellt ist und dabei gleichzeitig eine hohe Abbrandfestigkeit, eine gute elektrische und thermische Leitfähigkeit, eine geringe Verschweißneigung beim Schaltvorgang sowie eine hohe dielektrische Festigkeit und eine ausreichende mechanische Festigkeit des Schaltkontakts erzielt. Durch die Realisierung des alternierenden Temperaturprofils wird die beschriebene vorteilhafte Korngrößenverteilung auch dann problemlos erreicht, wenn relativ grobes Cr-Pulver (z.B. mit Partikeldurchmessern zwischen 20 µm und 200 µm) als Ausgangsmaterial verwendet wird.In this way, a Cu-Cr material is provided for a switching contact, which is produced in a very economical manner while high erosion resistance, good electrical and thermal conductivity, a low tendency to weld in the switching process and a high dielectric strength and sufficient mechanical Strength of the switch contact achieved. As a result of the realization of the alternating temperature profile, the advantageous particle size distribution described is also achieved without difficulty if relatively coarse Cr powder (for example having particle diameters between 20 μm and 200 μm) is used as the starting material.
Bei einem rein pulvermetallurgischen Herstellungsverfahren ohne Durchlaufen des alternierenden Temperaturprofils, bei dem z.B. Cu-Pulver und Cr-Pulver mit maximalen Partikeldurchmessern bis etwa 200 µm eingesetzt wird, weist der resultierende Cu-Cr-Werkstoff eine Gefügestruktur auf, bei der im Schliffbild in einer Cu-Matrix neben einigen kleineren Cr-Körnern relativ große Cr-Körner mit einem Korndurchmesser im Bereich zwischen 100 µm und 150 µm vorhanden sind. Es ergibt sich dann typischerweise eine unimodale Korngrößenverteilung mit einem Maximum z.B. bei Korngrößen im Bereich zwischen 100 µm2 und 25000 µm2. Dies lässt darauf schließen, dass die Partikelgrößen des Cr-Pulvers als Ausgangsmaterial in dem resultierenden Cu-Cr-Werkstoff im Wesentlichen erhalten bleiben, wenn nicht das alternierende Temperaturprofil durchlaufen wird.In a purely powder metallurgical production process without passing through the alternating temperature profile, in which, for example, Cu powder and Cr powder is used with maximum particle diameters up to about 200 microns, the resulting Cu-Cr material has a microstructure in which in the micrograph in a Cu Matrix are present in addition to some smaller Cr grains relatively large Cr grains with a grain diameter in the range between 100 microns and 150 microns. This then typically results in a unimodal grain size distribution with a maximum, for example, with grain sizes in the range between 100 μm 2 and 25000 μm 2 . This suggests that the particle sizes of the Cr powder as the starting material in the resulting Cu-Cr material are substantially maintained unless the alternating temperature profile is traversed.
Eine Verwendung von deutlich feinkörnigerem Cr-Pulver als Ausgangsmaterial würde hingegen zu weiteren Problemen führen. Der Herstellungsprozess würde deutlich erschwert. Feinkörnige Cr-Pulver haben einen deutlich höheren Sauerstoffanteil als grobkörnige Pulver. Dadurch wird die Einbindung der Cr-Phase in das Cu-Matrixmaterial erschwert, was eine höhere Porosität nach sich zieht. Es hat sich zudem gezeigt, dass der Grad an Verunreinigungen durch Oxide in feinen Cr-Pulverfraktionen höher ist, als in grobkörnigen Pulvern. Eine weitere Schwierigkeit bei der Verarbeitung von feinen Pulvern sind die Handhabung bezüglich der Vermeidung der Sauerstoffaufnahme während des Herstellungsprozesses sowie die Gewährleistung einer ausreichenden Arbeitsplatzsicherheit. Desweiteren würde zum Erreichen einer zufriedenstellenden Dichte und einer geringen Porosität des Werkstoffs ein höherer Pressdruck erfordert oder eine Kaltverformung des gesinterten Werkstoffs würde nötig. Mit den angegebenen Verfahrensschritten können die gewünschten Eigenschaften des Cu-Cr-Werkstoffs hingegen unter Verwendung konventioneller Produktionsanlagen in wirtschaftlicher Weise erreicht werden.On the other hand, using significantly finer-grained Cr powder as starting material would lead to further problems. The manufacturing process would be much more difficult. Fine-grained Cr powders have a significantly higher oxygen content than coarse-grained powders. This complicates the incorporation of the Cr phase into the Cu matrix material, resulting in a higher porosity. In addition, it has been found that the degree of contamination by oxides is higher in fine Cr powder fractions than in coarse-grained powders. Another difficulty in the processing of fine powders is the handling of the Avoiding oxygen uptake during the manufacturing process and ensuring adequate job security. Furthermore, to achieve a satisfactory density and a low porosity of the material, a higher compression pressure would be required or cold deformation of the sintered material would be necessary. By contrast, with the given process steps, the desired properties of the Cu-Cr material can be achieved economically using conventional production equipment.
Mit dem Verfahren zum Herstellen des Cu-Cr-Werkstoffs werden eine geringe Porosität, eine hohe Dichte, ein äußerst geringer Grad an Verunreinigungen, fein und homogen isotrop verteilte Cr-Körner in einer Cu-Matrix sowie eine gleichbleibende homogene chemische Zusammensetzung des Cu-Cr-Werkstoffs erreicht. Der resultierende Cu-Cr-Werkstoff eignet sich hervorragend für Schaltkontakte für die Anwendung in der Vakuumschalttechnik, sowohl als Leistungsschalter im Hoch- und Mittelspannungsbereich als auch als Vakuumschützschalter im Niederspannungsbereich.With the method for producing the Cu-Cr material, a low porosity, a high density, an extremely low degree of impurities, finely and homogeneously isotropically distributed Cr grains in a Cu matrix and a uniform homogeneous chemical composition of the Cu-Cr Material reached. The resulting Cu-Cr material is ideal for switching contacts for use in vacuum switching technology, both as a circuit breaker in the high and medium voltage range and as a vacuum contactor switch in the low voltage range.
Gemäß einer Ausgestaltung liegt der obere Temperaturgrenzwert in einem Bereich zwischen 1065 °C und 1025 °C und der untere Temperaturgrenzwert liegt zumindest 50 °C unterhalb des oberen Temperaturgrenzwerts. Der untere Temperaturgrenzwert liegt bevorzugt zumindest 100 °C unterhalb des oberen Temperaturgrenzwerts. In diesem Fall liegt der obere Temperaturgrenzwert in einem Temperaturbereich knapp unterhalb der Temperatur des Eutektikums (1075 °C), also einem Bereich, in dem bis zu etwa 0,7 at-% Cr in der Cu-Matrix in fester Lösung gelöst werden können. Dies entspricht dem Bereich, in dem die maximale Löslichkeit von Cr in Cu in fester Lösung gegeben ist. Andererseits liegt der obere Temperaturgrenzwert weit genug unterhalb der Temperatur des Eutektikums, sodass das Ausbilden einer schmelzflüssigen Phase selbst bei leichten Temperaturschwankungen zuverlässig verhindert wird. Der untere Temperaturgrenzwert liegt deutlich unterhalb des oberen Temperaturgrenzwerts, also in einem Bereich in dem (im thermischen Gleichgewicht) eine wesentlich geringere Menge Cr in der Cu-Matrix in fester Lösung gelöst werden kann. Somit wird bei der Erwärmung über den oberen Temperaturgrenzwert Cr in dem Material der Cu-Matrix angereichert (bis auf maximal ca. 0,7 at-%). Bei dem Abkühlen unter den unteren Temperaturgrenzwert (was einer senkrechten Bewegung in dem Zustandsdiagramm entspricht) übersteigt die in fester Lösung gelöste Cr-Menge die diesem tieferen Temperaturwert entsprechende Löslichkeit, die deutlich geringer als 0,7 at-% ist. Folglich wird Cr aus der Cu-Matrix ausgeschieden und es bilden sich Cr-Körner mit kleinen Korngrößen aus. Bei einem wiederholten Durchlaufen des alternierenden Temperaturprofils nimmt zunächst die Anzahl der gebildeten Cr-Körner mit kleinen Korngrößen zu.In one embodiment, the upper temperature limit is in a range between 1065 ° C and 1025 ° C and the lower temperature limit is at least 50 ° C below the upper temperature limit. The lower temperature limit is preferably at least 100 ° C below the upper temperature limit. In this case, the upper temperature limit is in a temperature range just below the temperature of the eutectic (1075 ° C), that is, a range in which up to about 0.7 at% Cr can be dissolved in the Cu matrix in solid solution. This corresponds to the range in which the maximum solubility of Cr in Cu is given in solid solution. On the other hand, the upper temperature limit is far enough below the temperature of the eutectic that the formation of a molten phase is reliably prevented even with slight temperature fluctuations. The lower temperature limit is well below the upper temperature limit, ie in a range in which (in thermal equilibrium) a significantly smaller amount of Cr in the Cu matrix can be dissolved in solid solution. Thus, in the case of heating above the upper temperature limit Cr, it is enriched in the material of the Cu matrix (up to a maximum of approximately 0.7 at%). In which When cooled below the lower temperature limit (which corresponds to a vertical movement in the state diagram), the amount of Cr dissolved in solid solution exceeds the solubility corresponding to this lower temperature value, which is significantly less than 0.7 at%. Consequently, Cr is precipitated from the Cu matrix and Cr grains with small grain sizes are formed. In a repeated passing through the alternating temperature profile, the number of Cr grains formed with small grain sizes increases first.
Gemäß einer Ausgestaltung weist das Verfahren ferner den Schritt auf: Mischen von Cu-Pulver und Cr-Pulver zu einem Cu-Cr-Pulvergemisch. In diesem Fall kann das Cu-Cr-Pulvergemisch in einfacher Weise durch Verwendung üblicher Cr-Pulver und Cu-Pulver bereitgestellt werden.According to one embodiment, the method further comprises the step of: mixing Cu powder and Cr powder into a Cu-Cr powder mixture. In this case, the Cu-Cr powder mixture can be easily provided by using conventional Cr powder and Cu powder.
Gemäß einer Ausgestaltung weisen die Cu-Partikel in dem Cu-Cr-Pulvergemisch eine Partikelgrößenverteilung mit einem maximalen Partikeldurchmesser ≤ 80 µm, bevorzugt
≤ 50 µm, auf. In diesem Fall wird bei dem Sinterprozess eine zuverlässige Ausbildung der Cu-Matrix ermöglicht und der Cu-Cr-Werkstoff kann zuverlässig mit geringer Porosität und hoher Dichte bereitgestellt werden. Der maximale Partikeldurchmesser wird dabei mittels einer Siebanalyse bestimmt. Dabei wird ein Sieb mit einer entsprechenden Maschenweite (z.B. 80 µm bzw. 50 µm) verwendet und nur Partikel, die durch das Sieb fallen, werden verwendet.According to one embodiment, the Cu particles in the Cu-Cr powder mixture have a particle size distribution with a maximum particle diameter ≦ 80 μm, preferably
≤ 50 μm, on. In this case, in the sintering process, reliable formation of the Cu matrix is enabled, and the Cu-Cr material can be reliably provided with low porosity and high density. The maximum particle diameter is determined by means of a sieve analysis. In this case, a sieve with a corresponding mesh size (eg 80 microns or 50 microns) is used and only particles that fall through the sieve are used.
Gemäß einer Ausgestaltung weisen die Cr-Partikel in dem Cu-Cr-Pulvergemisch eine Partikelgrößenverteilung mit einem maximalen Partikeldurchmesser ≤ 200 µm, bevorzugt
≤ 160 µm, auf. Der maximale Partikeldurchmesser wird wiederum mit einer Siebanalyse mit einer entsprechenden Maschenweite des Siebs bestimmt. In diesem Fall ist der Wert für den maximalen Partikeldurchmesser klein genug, um zu erreichen, dass in dem Cu-Cr-Werkstoff keine übermäßig großen Cr-Körner ausgebildet werden. Andererseits können die einzelnen Partikel auch groß genug ausgebildet sein, sodass keine übermäßige Gefahr von Verunreinigungen durch Oxide auftritt und in konventionellen Produktionsanlagen eine hohe Dichte und ein geringes Maß an Porosität erreicht werden können.According to one embodiment, the Cr particles in the Cu-Cr powder mixture have a particle size distribution with a maximum particle diameter ≦ 200 μm, preferably
≤ 160 μm, on. The maximum particle diameter is again determined with a sieve analysis with a corresponding mesh size of the sieve. In this case, the value for the maximum particle diameter is small enough so as not to form excessively large Cr grains in the Cu-Cr material. On the other hand, the individual particles can also be formed large enough so that no excessive risk of contamination by oxides occurs and in conventional production plants, a high density and a low degree of porosity can be achieved.
Gemäß einer Ausgestaltung weisen die Cr-Partikel in dem Cu-Cr-Pulvergemisch eine Partikelgrößenverteilung mit einem minimalen Partikeldurchmesser ≥ 20 µm, bevorzugt ≥ 32 µm, auf. Der minimale Partikeldurchmesser wird dabei ebenfalls mit einer Siebanalyse (mit einer Maschenweite von z.B. 20 µm bzw. 32 µm) bestimmt, allerdings werden in diesem Fall nur die Partikel verwendet, die nicht durch das Sieb fallen. In diesem Fall ist der minimale Partikeldurchmesser groß genug, sodass keine übermäßige Gefahr von Verunreinigungen durch Oxide auftritt und in konventionellen Produktionsanlagen eine hohe Dichte und ein geringes Maß an Porosität erreicht werden können.According to one embodiment, the Cr particles in the Cu-Cr powder mixture have a particle size distribution with a minimum particle diameter ≥ 20 μm, preferably ≥ 32 μm. The minimum particle diameter is also determined with a sieve analysis (with a mesh size of, for example, 20 μm or 32 μm), but in this case only the particles which do not fall through the sieve are used. In this case, the minimum particle diameter is large enough so that there is no excessive risk of oxide contamination, and high density and a low degree of porosity can be achieved in conventional production equipment.
Gemäß einer Ausgestaltung weist das Cu-Cr-Pulvergemisch einen Cu-Gehalt zwischen 30 Gew.-% und 80 Gew.-% und einen Cr-Gehalt zwischen 70 Gew.-% und 20 Gew.-% auf. In diesem Fall wird erreicht, dass sowohl eine hohe Abbrandfestigkeit und eine geringe Verschweißneigung als auch gute elektrische und thermische Leitfähigkeit und eine ausreichende mechanische Festigkeit bereitgestellt werden können. Wenn der Cr-Gehalt 70 Gew.-% übersteigt, führt dies zu einer merklichen Verschlechterung der thermischen sowie elektrischen Leitfähigkeit. Wenn der Cr-Gehalt kleiner als 20 Gew.-% ist, können keine zufriedenstellende Abbrandfestigkeit und Verschweißneigung erzielt werden.According to one embodiment, the Cu-Cr powder mixture has a Cu content between 30% by weight and 80% by weight and a Cr content between 70% by weight and 20% by weight. In this case, it is achieved that both a high erosion resistance and a low tendency to weld as well as good electrical and thermal conductivity and sufficient mechanical strength can be provided. If the Cr content exceeds 70% by weight, this leads to a marked deterioration of the thermal and electrical conductivity. If the Cr content is less than 20% by weight, no satisfactory burn-off resistance and welding tendency can be obtained.
Der pulvermetallurgisch hergestellte Cu-Cr-Schaltkontakt hat einen Cu-Gehalt zwischen 30 Gew.-% und 80 Gew.-% und einen Cr-Gehalt zwischen 70 Gew.-% und 20 Gew.-%. Der Cu-Cr-Schaltkontakt weist Cr-Körner in einer Cu-Matrix auf. Eine Korngrößenverteilung der Cr-Körner gemessen im Schliffbild weist ein erstes Maximum im Bereich von Korngrößen mit einer Querschnittsfläche zwischen 0,1 µm2 und 50 µm2 auf. Der Schaltkontakt ist durch einen pulvermetallurgischen Prozess aus Cu-Pulver und Cr-Pulver ohne Ausbildung einer schmelzflüssigen Phase gefertigt. Es handelt sich somit um einen rein pulvermetallurgisch hergestellten Cu-Cr-Schaltkontakt. Der Cu-Cr-Schaltkontakt kann für Vakuumschalter ausgebildet sein.The powder-metallurgically produced Cu-Cr switch contact has a Cu content between 30 wt .-% and 80 wt .-% and a Cr content between 70 wt .-% and 20 wt .-%. The Cu-Cr switch contact has Cr grains in a Cu matrix. A particle size distribution of the Cr grains measured in the micrograph has a first maximum in the range of particle sizes with a cross-sectional area between 0.1 μm 2 and 50 μm 2 . The switching contact is made by a powder metallurgy process of Cu powder and Cr powder without formation of a molten phase. It is thus a purely powder metallurgically produced Cu-Cr switching contact. The Cu-Cr switch contact may be designed for vacuum switch.
Unter einer Cu-Matrix wird dabei ein Material verstanden, das hauptsächlich aus Cu besteht, jedoch auch einen geringen Anteil an Cr in fester Lösung aufweisen kann. Es können ferner auch Spuren an Verunreinigungen vorliegen. In der Cu-Matrix sind Cr-Körner ausgebildet. Die Korngrößenverteilung der Cr-Körner bestimmt sich dabei wie folgt: Von dem Cu-Cr-Werkstoff des Schaltkontakts wird ein Schliffbild angefertigt und mikroskopisch analysiert. Im Schliffbild werden die Cr-Körner identifiziert und die Querschnittsflächen der Cr-Körner werden ausgemessen. Die Auswertung erfolgt dabei über einen ausreichend großen Flächenbereich bzw. verschiedene Flächenbereiche, die eine ausreichend große Gesamtfläche bilden, sodass eine repräsentative, statistische Aussage ermöglicht ist. Die Auswertung kann z.B. per Hand oder aber auch durch eine geeignete Software unterstützt durchgeführt werden. Bei einer graphischen Auftragung mit der gemessenen Querschnittsfläche auf der x-Achse und der zugehörigen Anzahl der ermittelten Cr-Körner mit der jeweiligen Querschnittsfläche pro Einheitsfläche (z.B. pro mm2) auf der y-Achse (bevorzugt jeweils in logarithmischer Darstellung), ist die Korngrößenverteilung ersichtlich. Die Korngrößenverteilung weist ein Maximum in einem Bereich von Korngrößen mit einer gemessenen Querschnittsfläche zwischen 0,1 µm2 und 50 µm2 auf.A Cu matrix is understood to mean a material which mainly consists of Cu but may also have a small proportion of Cr in solid solution. There may also be traces of impurities. In the Cu matrix Cr grains are formed. The grain size distribution of the Cr grains is determined as follows: A micrograph of the Cu-Cr material of the switch contact is made and analyzed microscopically. In the micrograph, the Cr grains are identified and the cross-sectional areas of the Cr grains are measured. The evaluation is carried out over a sufficiently large surface area or different surface areas, which form a sufficiently large total area, so that a representative, statistical statement is possible. The evaluation can be done eg by hand or supported by a suitable software. In the case of a graphical plot with the measured cross-sectional area on the x-axis and the associated number of Cr grains determined with the respective cross-sectional area per unit area (eg per mm 2 ) on the y-axis (preferably in logarithmic representation), the particle size distribution is seen. The particle size distribution has a maximum in a range of particle sizes with a measured cross-sectional area between 0.1 μm 2 and 50 μm 2 .
Mit dem pulvermetallurgisch hergestellten Cu-Cr-Schaltkontakt werden die oben in Bezug auf das Verfahren zum pulvermetallurgischen Herstellen eines Cu-Cr-Werkstoffs für einen Schaltkontakt beschriebenen Vorteile erreicht. Durch die rein pulvermetallurgische Herstellung ist eine besonders wirtschaftliche Herstellung ermöglicht. Aufgrund der Korngrößenverteilung mit dem Maximum im Bereich von Korngrößen mit einer Querschnittsfläche zwischen 0,1 µm2 und 50 µm2 weist der Cu-Cr-Schaltkontakt eine große Anzahl von feinen Cr-Körnern auf. Die feinen Cr-Körner sind dabei weitestgehend homogen verteilt. In dieser Weise ist eine sehr gute Abbrandfestigkeit erreicht. Der Cu-Cr-Schaltkontakt ist durch ein rein pulvermetallurgisches Verfahren erhältlich, bei dem Sintern oder ein nachfolgender thermischer Behandlungsprozess mit einem alternierenden Temperaturprofil durchgeführt wird, bei dem ein Cu-Cr-Pulvergemisch bzw. der Werkstoff des Cu-Cr-Schaltkontakts zumindest zweimal abwechselnd über einen oberen Temperaturgrenzwert erwärmt und wieder unter einen unteren Temperaturgrenzwert abgekühlt wird und wobei sämtliche Schritte bei Temperaturen durchgeführt werden, bei denen sich keine schmelzflüssige Phase ausbildet. Die Herstellung in einem rein pulvermetallurgischen Prozess ist an dem Cu-Cr-Schaltkontakt ersichtlich.The powder-metallurgically produced Cu-Cr switch contact achieves the advantages described above with respect to the method of powder metallurgy producing a Cu-Cr material for a switch contact. Due to the pure powder metallurgical production a particularly economical production is possible. Because of the grain size distribution with the maximum in the range of grain sizes with a cross-sectional area between 0.1 μm 2 and 50 μm 2 , the Cu-Cr switch contact has a large number of fine Cr grains. The fine Cr grains are largely homogeneously distributed. In this way, a very good erosion resistance is achieved. The Cu-Cr switch contact is obtainable by a purely powder metallurgical process in which sintering or a subsequent thermal treatment process is carried out with an alternating temperature profile in which a Cu-Cr powder mixture or the material of the Cu-Cr switch contact alternates at least twice is heated above an upper temperature limit and cooled again below a lower temperature limit, and wherein all steps are carried out at temperatures, where no molten phase is formed. The production in a purely powder metallurgical process can be seen on the Cu-Cr switch contact.
Gemäß einem Beispiel weist die Korngrößenverteilung der Cr-Körner ein zweites Maximum im Bereich von Korngrößen mit einer Querschnittsfläche zwischen 100 µm2 und 10000 µm2 auf. Es liegt somit eine bimodale Cr-Phasenverteilung vor, die zwei Maxima aufweist, ein erstes Maximum bei Korngrößen mit einer gemessenen Querschnittsfläche zwischen 0,1 µm2 und 50 µm2 und ein zweites Maximum bei Korngrößen mit einer gemessenen Querschnittsfläche zwischen 100 µm2 und 10000 µm2. Diese Korngrößenverteilung resultiert aus dem rein pulvermetallurgischen Herstellungsprozess unter Verwendung von grobem Cr-Pulver z.B. mit Partikeldurchmessern zwischen 20 µm und 200 µm.According to one example, the grain size distribution of the Cr grains has a second maximum in the range of grain sizes with a cross-sectional area between 100 μm 2 and 10000 μm 2 . There is thus a bimodal Cr phase distribution which has two maxima, a first maximum for grain sizes with a measured cross-sectional area between 0.1 μm 2 and 50 μm 2 and a second maximum for grain sizes with a measured cross-sectional area between 100 μm 2 and 10000 μm 2 . This particle size distribution results from the purely powder metallurgical production process using coarse Cr powder, for example with particle diameters between 20 .mu.m and 200 .mu.m.
Gemäß einem weiteren Beispiel ist die Anzahl der dem ersten Maximum entsprechenden Cr-Körner größer als die Anzahl der dem zweiten Maximum entsprechenden Cr-Körner, d.h. es liegen mehr Körner vor, die eine dem ersten Maximum entsprechende Korngröße aufweisen, als Körner, die eine dem zweiten Maximum entsprechende Korngröße aufweisen. In diesem Fall liegen im Verhältnis zu der Gesamtzahl der Cr-Körner viele feine Cr-Körner mit Querschnittsflächen zwischen 0,1 µm2 und 50 µm2 vor. Es wird eine besonders vorteilhafte Abbrandfestigkeit erreicht. Wenn die Anzahl der dem ersten Maximum entsprechenden Cr-Körner um einen Faktor > 5 größer als die Anzahl der dem zweiten Maximum entsprechenden Cr-Körner ist, liegt ein besonders vorteilhafter Anteil an feinen Cr-Körnern mit kleiner Querschnittsfläche vor.According to another example, the number of Cr grains corresponding to the first maximum is greater than the number of Cr grains corresponding to the second maximum, ie, there are more grains having a grain size corresponding to the first maximum than grains having a grain size corresponding to the first maximum have second maximum corresponding grain size. In this case, in relation to the total number of Cr grains, there are many fine Cr grains having cross-sectional areas between 0.1 μm 2 and 50 μm 2 . It is achieved a particularly advantageous erosion resistance. If the number of Cr grains corresponding to the first maximum is greater than the number of Cr grains corresponding to the second maximum by a factor> 5, a particularly advantageous proportion of fine Cr grains having a small cross-sectional area is present.
Gemäß einem Beispiel weist der Cu-Cr-Schaltkontakt eine relative Dichte > 90 % auf. In diesem Fall werden zuverlässig eine gute elektrische und thermische Leitfähigkeit sowie eine hohe mechanische Festigkeit bereitgestellt. Eine derart hohe relative Dichte lässt sich zuverlässig bei der Verwendung von relativ grobem Cr-Pulver und Cu-Pulver in konventionellen Produktionsanlagen erzielen. Unter relativer Dichte wird dabei das Verhältnis zwischen der erreichten Dichte und der theoretisch erreichbaren Dichte für die Zusammensetzung verstanden. Die Kombination aus dieser hohen Dichte und dem hohen Anteil feiner Cr-Körner in der Cu-Matrix lässt sich durch die Kombination einer Verwendung grober Cr-Pulver (mit Partikeldurchmessern zwischen 20 µm und 200 µm) und Nutzung eines alternierenden Temperaturprofils, bei dem zumindest zweimal abwechselnd eine Erwärmung über einen oberen Temperaturgrenzwert und wieder eine Abkühlung unter einen unteren Temperaturgrenzwert erfolgt, erreichen.According to one example, the Cu-Cr switch contact has a relative density> 90%. In this case, good electrical and thermal conductivity and high mechanical strength are reliably provided. Such a high specific gravity can be reliably achieved by using relatively coarse Cr powder and Cu powder in conventional production equipment. By relative density is meant the ratio between the density achieved and the theoretically achievable density for the composition. The Combination of this high density and the high proportion of fine Cr grains in the Cu matrix can be achieved by combining a use of coarse Cr powder (with particle diameters between 20 μm and 200 μm) and using an alternating temperature profile alternating at least twice a warming above an upper temperature limit and again a cooling below a lower temperature limit, reach.
Weitere Vorteile und Weiterbildungen des Verfahrens ergeben sich aus der nachfolgendenFurther advantages and developments of the method will become apparent from the following
Beschreibung unter Bezugnahme auf die Figuren.
- Fig. 1
- zeigt eine Korngrößenverteilung der Cr-Körner bei einem pulvermetallurgisch hergestellten Cu-Cr-Werkstoff im Ausgangszustand (durchgezogene Linie) und nach Durchlaufen eines alternierenden Temperaturprofils (gestrichelte Linie).
- Fig. 2
- zeigt ein lichtmikroskopisches Schliffbild eines pulvermetallurgisch hergestellten Cu-Cr-Werkstoffs.
- Fig. 3
- zeigt ein lichtmikroskopisches Schliffbild eines pulvermetallurgisch hergestellten Cu-Cr-Werkstoffs nach Durchlaufen eines alternierenden Temperaturprofils.
- Fig. 4
- zeigt schematisch die Verfahrensschritte eines Verfahrens zum pulvermetallurgischen Herstellen eines Cu-Cr-Werkstoffs für einen Schaltkontakt.
- Fig. 1
- shows a grain size distribution of the Cr grains in a powder metallurgically produced Cu-Cr material in the initial state (solid line) and after passing through an alternating temperature profile (dashed line).
- Fig. 2
- shows a light microscopic micrograph of a powder metallurgically produced Cu-Cr material.
- Fig. 3
- shows a light microscopic micrograph of powder metallurgically produced Cu-Cr material after passing through an alternating temperature profile.
- Fig. 4
- schematically shows the process steps of a method for powder metallurgy producing a Cu-Cr material for a switching contact.
Im Folgenden wird unter Bezug auf die
In einem ersten Schritt -S1- wird Cu-Pulver mit einem maximalen Partikeldurchmesser von bevorzugt höchstens 50 µm mit Cr-Pulver mit einem maximalen Partikeldurchmesser von höchstens 200 µm (bevorzugt höchstens 160 µm) und einem minimalen Partikeldurchmesser von mindestens 20 µm (bevorzugt mindestens 32 µm) zu einem Cu-Cr-Pulvergemisch vermischt. Es wurden z.B. als Beispiele ein erstes Cu-Cr-Pulvergemisch mit einem Cr-Gehalt von 25 Gew.-% und einem Cu-Gehalt von 75 Gew.-% und ein zweites Cu-Cr-Pulvergemisch mit einem Cr-Gehalt von 43 Gew.-% und einem Cu-Gehalt von 57 Gew.-% erzeugt.In a first step -S1-, Cu powder having a maximum particle diameter of preferably at most 50 μm with Cr powder having a maximum particle diameter of at most 200 μm (preferably at most 160 μm) and a minimum particle diameter of at least 20 μm (preferably at least 32 microns) mixed into a Cu-Cr powder mixture. As an example, a first Cu-Cr powder mixture having a Cr content of 25% by weight and a Cu content of 75% by weight and a second Cu-Cr powder mixture having a Cr content of 43% by weight have been exemplified .-% and a Cu content of 57 wt .-% produced.
In einem zweiten Schritt -S2- wird das Cu-Cr-Pulvergemisch gepresst. Bevorzugt wird das Cu-Cr-Pulvergemisch durch Kaltpressen mit einem Pressdruck in einem Bereich zwischen 400 MPa und 850 MPa verdichtet. In einem nachfolgenden Schritt -S3- wird der derart gebildete Grünling in einem Sinterprozess bei Temperaturen in einem Temperaturbereich deutlich unterhalb der Temperatur des Eutektikums (also deutlich unterhalb von 1075 °C) gesintert. Somit bildet sich bei keinem der Schritte -S1- bis -S3- eine schmelzflüssige Phase in dem Cu-Cr-Pulvergemisch bzw. in dem gepressten Grünling aus. Der Sinterprozess kann zum Beispiel bei Temperaturen in einem Temperaturbereich zwischen 850 °C und 1070 °C durchgeführt werden. Die Temperaturen müssen dabei hoch genug sein, dass der Sinterprozess in ausreichendem Maß und mit ausreichender Geschwindigkeit abläuft, und niedrig genug, dass sich auch bei unvermeidlichen Temperaturgradienten keine schmelzflüssige Phase ausbildet.In a second step -S2- the Cu-Cr powder mixture is pressed. Preferably, the Cu-Cr powder mixture is compacted by cold pressing at a compression pressure in a range between 400 MPa and 850 MPa. In a subsequent step -S3-, the green compact formed in this way is sintered in a sintering process at temperatures in a temperature range well below the temperature of the eutectic (ie, significantly below 1075 ° C.). Thus, in any of steps -S1- to -S3- forms a molten phase in the Cu-Cr powder mixture or in the pressed green body. The sintering process can be carried out, for example, at temperatures in a temperature range between 850 ° C and 1070 ° C. The temperatures must be high enough so that the sintering process proceeds sufficiently and with sufficient speed, and low enough that no molten phase forms even with unavoidable temperature gradients.
Ein beispielhaftes lichtmikroskopisches Schliffbild eines pulvermetallurgisch hergestellten Cu-Cr-Werkstoffs nach dem Schritt -S3- ist in
Eine Auswertung der Korngrößenverteilung der Cr-Körner in dem derart hergestellten Cu-Cr-Werkstoff ist in
Der Cu-Cr-Werkstoff wird anschließend einem thermischen Behandlungsprozess mit einem alternierenden Temperaturprofil unterworfen, wie im Folgenden beschrieben wird. Dabei wird der Cu-Cr-Werkstoff abwechselnd auf eine Temperatur oberhalb eines oberen Temperaturgrenzwerts erwärmt und auf eine Temperatur unterhalb eines unteren Temperaturgrenzwerts abgekühlt. Dabei erfolgen das abwechselnde Erwärmen und Abkühlen zumindest zweimal. Auch bei diesen Prozessschritten wird darauf geachtet, dass sich keine schmelzflüssige Phase ausbildet, d.h. der Cu-Cr-Werkstoff wird auf Temperaturen unterhalb der Temperatur des Eutektikums (1075 °C) des Cu-Cr-Systems gehalten. Dies wird im Folgenden noch eingehender beschrieben.The Cu-Cr material is then subjected to a thermal treatment process with an alternating temperature profile, as will be described below. In this case, the Cu-Cr material is alternately heated to a temperature above an upper temperature limit and cooled to a temperature below a lower temperature limit. The alternating heating and cooling take place at least twice. In these process steps, too, care is taken that no molten phase is formed, i. the Cu-Cr material is kept at temperatures below the temperature of the eutectic (1075 ° C) of the Cu-Cr system. This will be described in more detail below.
In einem Schritt -S4- wird der Cu-Cr-Werkstoff auf eine Temperatur oberhalb des oberen Temperaturgrenzwerts erwärmt. Der obere Temperaturgrenzwert liegt dabei bevorzugt relativ nah unterhalb der Temperatur des Eutektikums des Cu-Cr-Systems, sodass der Cu-Cr-Werkstoff auf eine Temperatur knapp unterhalb der Temperatur des Eutektikums gebracht wird, allerdings weit genug von der Temperatur des Eutektikums entfernt, dass ein Ausbilden einer flüssigen Phase zuverlässig verhindert ist. Der obere Temperaturgrenzwert liegt somit bevorzugt in einem Bereich zwischen 1025 °C und 1065 °C.In a step -S4-, the Cu-Cr material is heated to a temperature above the upper temperature limit. The upper temperature limit is preferably relatively close below the temperature of the eutectic of the Cu-Cr system, so that the Cu-Cr material is brought to a temperature just below the temperature of the eutectic, but far enough away from the temperature of the eutectic that forming a liquid phase is reliably prevented. The upper temperature limit value is thus preferably in a range between 1025 ° C and 1065 ° C.
Anschließend wird in einem Schritt -S5- der Cu-Cr-Werkstoff auf eine Temperatur unterhalb eines unteren Temperaturgrenzwerts abgekühlt. Der untere Temperaturgrenzwert liegt dabei bevorzugt in einem Bereich der sich zumindest um 50 °C unterhalb des oberen Temperaturgrenzwerts befindet, mehr bevorzugt in einem Bereich um mehr als 100 °C unterhalb des oberen Temperaturgrenzwerts. Der untere Temperaturgrenzwert liegt dabei bevorzugt höchstens 250 °C unterhalb des oberen Temperaturgrenzwerts, mehr bevorzugt höchstens 180 °C unterhalb des oberen Temperaturgrenzwerts. Der untere Temperaturgrenzwert sollte so gewählt werden, dass bei diesem eine deutlich geringere Löslichkeit von Cr in fester Lösung in Cu gegeben ist, als bei dem oberen Temperaturgrenzwert. Der Grund für diese Wahl wird noch eingehender erläutert. Z.B. kann der Cu-Cr-Werkstoff auf Temperaturen im Bereich von ca. 850 °C abgekühlt werden. Es empfiehlt sich, den unteren Temperaturgrenzwert nicht zu niedrig zu wählen, um ein ausreichendes Maß an Diffusionsprozessen in dem Cu-Cr-Werkstoff zu gewährleisten. Auf dem oberen Temperaturniveau und dem unteren Temperaturniveau wird der Cu-Cr-Werkstoff jeweils für einige Zeit gehalten.Subsequently, in a step -S5-, the Cu-Cr material is cooled to a temperature below a lower temperature limit. The lower temperature limit is preferably in a range which is at least 50 ° C below the upper temperature limit, more preferably in an area more than 100 ° C below the upper temperature limit. The lower temperature limit is preferably at most 250 ° C below the upper temperature limit, more preferably at most 180 ° C below the upper temperature limit. The lower temperature limit should be chosen so that there is a much lower solubility of Cr in solid solution in Cu than at the upper temperature limit. The reason for this choice will be explained in more detail. For example, the Cu-Cr material can be cooled to temperatures in the range of about 850 ° C. It is recommended not to set the lower temperature limit too low to ensure a sufficient degree of diffusion processes in the Cu-Cr material. At the upper temperature level and the lower temperature level, the Cu-Cr material is held for some time each.
Anschließend wird der Schritt -S4- wiederholt, d.h. der Cu-Cr-Werkstoff wird wieder auf eine Temperatur oberhalb des oberen Temperaturgrenzwerts erhöht. Nachfolgend wird der Schritt -S5- wiederholt, d.h. der Cu-Cr-Werkstoff wird wieder auf eine Temperatur unterhalb des unteren Temperaturgrenzwerts abgekühlt. Die Schritte -S4- und -S5- werden insgesamt n-mal wiederholt, jedoch insgesamt zumindest zweimal, bevorzugt mindesten dreimal. Es hat sich gezeigt, dass bei 2-maligem bis ca. 6-maligem (2 ≤ n ≤ 6) Durchlaufen der Schritte -S4- und -S5- eine Verbesserung des Cu-Cr-Werkstoffs erreicht wird und bei einer größeren Anzahl von Wiederholungen keine weitere Verbesserung zu erwarten ist. Der Cu-Cr-Werkstoff wird also einem Pendelglühen ausgesetzt. Zumindest die Schritte -S4- und -S5- werden in einem Schutzgasofen unter reduzierender Atmosphäre und/oder in einem Vakuumofen durchgeführt, um eine unerwünschte Oxidation mit Sauerstoff zu vermeiden. Anschließend wird der Herstellungsprozess beendet.Subsequently, the step -S4- is repeated, i. the Cu-Cr material is again raised to a temperature above the upper temperature limit. Subsequently, the step -S5- is repeated, i. the Cu-Cr material is again cooled to a temperature below the lower temperature limit. The steps -S4- and -S5- are repeated a total of n times, but a total of at least twice, preferably at least three times. It has been found that when the steps -S4- and -S5- are passed through from 2 times to about 6 times (2≤n≤6), an improvement of the Cu-Cr material is achieved and with a larger number of repetitions no further improvement is expected. The Cu-Cr material is thus exposed to a pendulum annealing. At least steps -S4- and -S5- are carried out in a protective gas oven under reducing atmosphere and / or in a vacuum oven to avoid unwanted oxidation with oxygen. Subsequently, the manufacturing process is terminated.
In
Mit den beschriebenen Ausgangsmaterialien mit einer relativ groben Partikelgröße des Cr-Pulvers lassen sich in einem rein pulvermetallurgischen Verfahren mit konventionellen Herstellungsanlagen sehr dichte Cu-Cr-Werkstoffe mit geringer Porosität herstellen, die zudem ein geringes Maß an Verunreinigungen aufweisen. Die rein pulvermetallurgische Herstellung ist an dem Cu-Cr-Werkstoff erkennbar. Aufgrund der sehr fein verteilten Cr-Körner weist der rein pulvermetallurgisch gefertigte Cu-Cr-Werkstoff eine hohe Abbrandfestigkeit, eine hohe dielektrische Festigkeit und eine ausreichende mechanische Festigkeit des Schaltkontakts auf.With the described starting materials having a relatively coarse particle size of the Cr powder, it is possible to produce very dense Cu-Cr materials with low porosity in a purely powder metallurgical process with conventional production plants, which also have a low level of impurities. The pure powder metallurgy production is recognizable on the Cu-Cr material. Due to the very finely distributed Cr grains, the purely powder-metallurgically produced Cu-Cr material has a high erosion resistance, a high dielectric strength and a sufficient mechanical strength of the switching contact.
Die Ausbildung der fein verteilten Cr-Körner in der Cu-Matrix lässt sich im Hinblick auf das z.B. in der eingangs genannten
Es hat sich gezeigt, dass für eine zufriedenstellende Bildung von feinen Cr-Körnern zumindest zweimal der obere Temperaturgrenzwert überschritten und der untere Temperaturgrenzwert unterschritten werden sollte. Ab einer gewissen Anzahl von Wiederholungen bei dem Pendelglühen kann allerdings keine Verbesserung der Struktur mehr beobachtet werden. Die Temperaturänderung zwischen dem hohen und dem niedrigen Temperaturniveau bei dem Pendelglühen sollte ausreichend langsam gewählt werden, dass Cr zuverlässig beim Abkühlen aus der Cu-Matrix ausgeschieden wird, andererseits aber auch nicht zu langsam, damit nicht durch Kornvergröberung wieder größere Cr-Körner entstehen.It has been found that for a satisfactory formation of fine Cr grains at least twice the upper temperature limit should be exceeded and the lower temperature limit should be exceeded. From a certain number of repetitions in the pendulum annealing, however, no improvement in the structure can be observed more. The temperature change between the high and the low temperature level in the pendulum annealing should be chosen to be sufficiently slow that Cr is reliably precipitated from the Cu matrix on cooling, but not too slow so that larger Cr grains are not produced again by grain coarsening.
Es wurden auch Versuche mit Cu-Cr-Pulvergemischen mit anderen Verhältnissen zwischen Cr und Cu durchgeführt, die ebenfalls zu vergleichbaren Ergebnissen führten. Auch Versuche mit einem Cr-Gehalt von 70 Gew.-% und einem Cu-Gehalt von 30 Gew.-% führten in Bezug auf die feinen Cr-Ausscheidungen zu einem vergleichbaren Ergebnis.Experiments were also carried out with Cu-Cr powder mixtures with other ratios between Cr and Cu, which also led to comparable results. Also, experiments with a Cr content of 70 wt .-% and a Cu content of 30 wt .-% resulted in respect to the fine Cr precipitates to a comparable result.
Obwohl beschrieben wurde, dass die Behandlung mit den alternierenden Temperaturprofil erst nach dem Schritt -S3- des Sinterns bei dem Cu-Cr-Werkstoff erfolgt, ist es z.B. auch möglich, bereits den Sinterprozess selbst mit einem alternierenden Temperaturprofil durchzuführen. In diesem Fall wird bereits der gepresste Cu-Cr-Grünling während des Sintervorgangs den Schritten -S4- und -S5-wiederholt unterworfen. In diesem Fall entfällt der separate Schritt -S3- und das Sintern erfolgt während der Schritte -S4- und -S5-.Although it has been described that the treatment with the alternating Temperature profile only after the step -S3- of the sintering in the Cu-Cr material, it is also possible, for example, already perform the sintering process itself with an alternating temperature profile. In this case, the pressed Cu-Cr green compact is already repeatedly subjected to steps -S4- and -S5 during the sintering process. In this case, the separate step -S3- is omitted and the sintering takes place during the steps -S4- and -S5-.
Claims (7)
- A process for producing a Cu-Cr material by powder metallurgy for a switching contact, in particular for vacuum switches, comprising the steps of:(S2) pressing a Cu-Cr powder mixture formed from Cu powder and Cr powder,(S3) sintering the pressed Cu-Cr powder mixture to form the material of the Cu-Cr switching contact,characterized in thatthe sintering and/or subsequent thermal treatment process is carried out with an alternating temperature profile, in which the Cu-Cr powder mixture or the Cu-Cr material is heated above an upper temperature limit value (S4) and cooled again below a lower temperature limit value (S5) at least twice in alternation and in which all of the steps are carried out at temperatures at which no molten phase forms.
- The process as claimed in claim 1, characterized in that the upper temperature limit value lies in a range between 1065°C and 1025°C and the lower temperature limit value lies at least 50°C below the upper temperature limit value, preferably at least 100°C below the upper temperature limit value.
- The process as claimed in claim 1 or 2, characterized in that the process also has the step of: (S1) mixing Cu powder and Cr powder to form a Cu-Cr powder mixture.
- The process as claimed in one of the preceding claims, characterized in that the Cu particles in the Cu-Cr powder mixture have a particle size distribution with a maximum particle diameter of ≤ 80 µm, preferably ≤ 50 µm.
- The process as claimed in one of the preceding claims, characterized in that the Cr particles in the Cu-Cr powder mixture have a particle size distribution with a maximum particle diameter of ≤ 200 µm, preferably ≤ 160 µm.
- The process as claimed in one of the preceding claims, characterized in that the Cr particles in the Cu-Cr particle mixture have a particle size distribution with a minimum particle diameter of ≥ 20 µm, preferably ≥ 32 µm.
- The process as claimed in one of the preceding claims, characterized in that the Cu-Cr powder mixture has a Cu content of between 30% by weight and 80% by weight and a Cr content of between 70% by weight and 20% by weight.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT0048410U AT11814U1 (en) | 2010-08-03 | 2010-08-03 | METHOD FOR THE POWDER METALLURGIC MANUFACTURE OF A CU-CR MATERIAL |
PCT/AT2011/000319 WO2012016257A2 (en) | 2010-08-03 | 2011-08-01 | Process for producing a cu-cr material by powder metallurgy |
Publications (2)
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EP2600996A2 EP2600996A2 (en) | 2013-06-12 |
EP2600996B1 true EP2600996B1 (en) | 2018-06-06 |
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EP11751787.0A Active EP2600996B1 (en) | 2010-08-03 | 2011-08-01 | Process for producing a cu-cr material by powder metallurgy |
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US (2) | US20130140159A1 (en) |
EP (1) | EP2600996B1 (en) |
CN (1) | CN103201059B (en) |
AT (1) | AT11814U1 (en) |
ES (1) | ES2686421T3 (en) |
WO (1) | WO2012016257A2 (en) |
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WO2014084315A1 (en) * | 2012-11-28 | 2014-06-05 | 古河機械金属株式会社 | Thermoelectric conversion module |
US9992917B2 (en) | 2014-03-10 | 2018-06-05 | Vulcan GMS | 3-D printing method for producing tungsten-based shielding parts |
CN104232961B (en) * | 2014-09-10 | 2016-09-21 | 华南理工大学 | A kind of high-strength height hard Cu-Cr composite and its preparation method and application |
CN105018815B (en) * | 2015-07-31 | 2017-03-08 | 陕西斯瑞新材料股份有限公司 | A kind of high-Cr, high withstand voltage copper-chromium contact material and preparation method thereof |
RU2645855C2 (en) * | 2016-06-28 | 2018-02-28 | Федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский технологический университет "МИСиС" | Method for producing electrocontact composite material based on copper containing clusters containing clusters based on refractory metal particles |
US10468205B2 (en) * | 2016-12-13 | 2019-11-05 | Eaton Intelligent Power Limited | Electrical contact alloy for vacuum contactors |
CN109351977B (en) * | 2018-10-18 | 2020-03-31 | 西安交通大学 | Preparation method of iron core-containing copper-chromium contact material |
CN111266585A (en) * | 2020-03-02 | 2020-06-12 | 合肥尚德新材料有限公司 | Method for preparing liquid-phase-immiscible metal composite material |
CN113695594B (en) * | 2020-07-28 | 2022-05-31 | 中南大学 | Method for evaluating selective laser melting aluminum alloy |
CN112375942B (en) * | 2020-10-26 | 2022-02-22 | 宁波德业粉末冶金有限公司 | Combined type intelligence bumper shock absorber piston |
CN112391556B (en) * | 2020-11-17 | 2022-02-11 | 中南大学 | High-strength high-conductivity Cu-Cr-Nb alloy reinforced by double-peak grain size and double-scale nanophase |
CN112553500B (en) * | 2020-12-11 | 2022-04-05 | 中南大学 | Method for simultaneously improving strength and conductivity of Cu-Cr-Nb alloy |
CN112985052A (en) * | 2021-04-09 | 2021-06-18 | 江西科技学院 | Tunnel type continuous sintering furnace and sintering method thereof |
CN114769585B (en) * | 2022-04-20 | 2024-01-05 | 中铝科学技术研究院有限公司 | Cold spray forming method of Cu-Cr-Nb alloy |
CN114951665B (en) * | 2022-05-17 | 2024-04-16 | 浙江省冶金研究院有限公司 | Preparation method of low-cost high-density high-conductivity copper-chromium contact |
CN115323217A (en) * | 2022-08-23 | 2022-11-11 | 陕西斯瑞新材料股份有限公司 | Preparation method of low-cost CuCr25 contact material |
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2010
- 2010-08-03 AT AT0048410U patent/AT11814U1/en not_active IP Right Cessation
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2011
- 2011-08-01 CN CN201180038423.7A patent/CN103201059B/en active Active
- 2011-08-01 US US13/813,996 patent/US20130140159A1/en not_active Abandoned
- 2011-08-01 ES ES11751787.0T patent/ES2686421T3/en active Active
- 2011-08-01 EP EP11751787.0A patent/EP2600996B1/en active Active
- 2011-08-01 WO PCT/AT2011/000319 patent/WO2012016257A2/en active Application Filing
-
2015
- 2015-12-21 US US14/976,553 patent/US20160107237A1/en not_active Abandoned
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US20160107237A1 (en) | 2016-04-21 |
WO2012016257A3 (en) | 2012-11-01 |
AT11814U1 (en) | 2011-05-15 |
WO2012016257A2 (en) | 2012-02-09 |
CN103201059A (en) | 2013-07-10 |
CN103201059B (en) | 2016-06-29 |
EP2600996A2 (en) | 2013-06-12 |
ES2686421T3 (en) | 2018-10-17 |
US20130140159A1 (en) | 2013-06-06 |
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