RU2116370C1 - Method for production of copper-base dispersion-hardened materials - Google Patents

Abstract

FIELD: production of dispersion-hardened materials; may be used in manufacture of thermally-stressed parts of welding equipment and engines. SUBSTANCE: powders of copper, oxide- and carbide-forming elements and carbon are placed into attritor and subjected to mechanochemical activation by grinding in air atmosphere. In so doing, carbon is introduced in the amount exceeding its stoichiometric needs for complete carbonization of oxide- and carbide-forming elements of not in excess of 0.5 wt.%. Oxide- and carbide-forming elements are used in the form of metals taken from groups III, IV, V and VI of the Periodic System. EFFECT: simplified technology of production of blanks from the offered material and higher safety. 13 cl, 3 dwg, 2 tbl

Description

 The invention relates to powder metallurgy, and in particular to methods for producing dispersion-hardened materials with a high temperature of recrystallization, which can be used in heat-stressed parts of welding equipment, as well as engines.

Parts that are intended for welding production, work under the influence of high loads and temperatures of 600 - 900 ^o C). Parts intended for engine construction are also used under high loads while exposed to high temperatures (400 - 800 ^o C).

 Thus, the material of all these parts must have high resistance to softening at high temperatures, the characteristic of which is the temperature of recrystallization of the material.

 Known methods for producing materials used under conditions of exposure to high loads and temperatures, which consist in mixing powders of the base metal, such as copper with tungsten and nickel powders, subsequent pressing and sintering [1].

 However, these materials have a very high cost, due mainly to the use of expensive materials for their manufacture, in particular tungsten. In addition, the technological process of this method is quite complicated and expensive, since it requires the use of protective media during sintering.

Known methods for producing dispersion-strengthened materials based on copper by mixing powders of copper and oxides of Al ₂ O ₃ and SiO ₂ with a content of up to 12 vol.%, Subsequent hydrostatic cold pressing of the powder mixture, sintering of the pressing at temperatures of 500 and 1000 ^o C and hot pressing at a temperature of 760 ^o C [2, 3]. At the same time, in order to protect the copper contained in the compacts from oxidation and, consequently, reduce the physicomechanical properties of the material, for example, electrical conductivity, sintering is carried out in a hydrogen medium, which imposes high safety and labor protection requirements on the technological process, which are further tightened if note that in order to achieve the effect of hardening of the material, the powders of the hardening phases must have sizes less than 1 μm, which means that they have high pyrophoricity. All this leads ultimately to the high cost of the material and technology for its production.

 Known methods for producing copper-based material containing hardening phases, such as ceramic, and used at elevated temperatures, which include the introduction of carbon or carbon-containing components as the main additives [4, 5]. Carbon is introduced with stirring of the starting components and, forming a film on the surface of copper particles, prevents the oxidation of copper, promotes the formation of a material structure that provides improved material properties. However, the particles of the strengthening phases introduced into the initial powder composition initially have rather large sizes and are prone to further coagulation, which negatively affects the properties of the materials.

 Methods are also known involving the use of carbon as a carbide-forming element for additives in the form of powders of carbides of various elements, for example titanium [6] to copper powder. However, as in the previous case, carbide particles have rather large sizes, which also negatively affects the properties of these materials.

There is a method of producing dispersion-hardened materials from powders of an alloy of copper and alloying elements, in which, along with other operations inherent to it, produce "internal oxidation" of the powder of the alloy of copper and alloy metal [7]. "Internal oxidation" is the oxidation of a powder of an alloy of copper and an oxide-forming metal, for example aluminum, having a high affinity for oxygen. During subsequent heat treatment in a reducing medium, the copper powder is reduced from copper oxides, and the oxide-forming metal remains in the form of finely dispersed and evenly distributed particles of its oxides, in particular Al ₂ O ₃ . The recrystallization temperature of materials obtained by this method reaches 0.75 of the melting point of copper.

 This method does not allow to obtain materials with a high content of particles of phase hardeners, which is necessary to increase the strength properties of materials at high temperatures. This is because when the content of the oxidizable element is more than 0.5 wt.%, It remains in solid solution or in the form of compounds with copper, and the released oxide particles are large, which significantly impairs the properties of the materials.

A known method of producing a dispersion-strengthened material based on copper, including mechanochemical activation by grinding a mixture of powders of copper and aluminum in a ball mill in an oxidizing atmosphere [8]. But such a method for the recovery of oxidized copper requires subsequent diffusion annealing of the obtained granules at 700 ^o C and reductive annealing in a mixture of water vapor and hydrogen at a ratio of 100: 1 at 700 ^o C. To obtain blanks for parts operating at high temperatures, the obtained after this treatment, the granules must be compacted into briquettes cold and extruded into a rod or profile at a temperature of 750 - 850 ^o C (see Fig. 1).

 Due to the mechanochemical activation of the powder components during grinding in a ball mill, the time for the occurrence of redox reactions is significantly reduced in comparison with the method involving "internal oxidation", and the temperature at which they occur is reduced. However, the method remains complex and expensive, quite long, requires the use of protective atmospheres and environments with a strictly defined ratio of oxidizing agent and reducing agent.

 The prototype of the invention is a method for producing dispersion-strengthened copper-based materials [9], including mechanochemical activation, in which the first stage is separately processed by grinding in an argon medium, for example, in a ball planetary mill, copper powder and a mixture of copper, oxide and carbide-forming powders elements, such as titanium, and carbon. In this case, carbon is taken in an amount stoichiometrically necessary so that all of it will form carbides, for example, TiC without residue. In addition, the method also provides additives in the form of metal oxides, which are also poured into the mill along with oxide and carbide-forming elements.

 At the second stage, also in argon medium, the powders passed through the first stage of processing are milled together. It is well known that the content of the hardening phase in the material should be in the range of 0.5-5.0 vol.%. This method does not require diffusion and reductive annealing, in contrast to the previously described methods. However, the need for a long multi-stage separate processing of powders in a ball mill to ensure complete interaction of oxide and carbide-forming elements with carbon and uniform distribution of the product of this interaction (hardening phase), as well as the use of an inert gas, significantly reduces productivity and increases the cost of materials obtained way.

 In addition, to obtain blanks for parts operating at elevated temperatures, it is necessary, as in the previous method, to pre-compress the granules of the material obtained by the prototype method, to deform (hot extrusion, rolling, etc.) also in shielding gas environment, which also increases the cost of dispersion-hardened materials, complicating the process (see Fig. 2).

 The invention solves the problem of creating a method for producing dispersion-strengthened materials based on copper, providing these materials with high temperatures of recrystallization while simplicity, high productivity, safety, efficiency. The technical result of the proposed method is to simplify the technology for producing workpieces of parts from material obtained using the method, increasing safety.

 This result is achieved by the fact that in the method for producing dispersion-hardened materials based on copper, mainly for parts operated at elevated temperatures, including mechanochemical activation by grinding powders of copper, oxide and carbide-forming elements, carbon and oxides, the mechanochemical activation is carried out in one step in air , while the oxides are obtained by filling in the grinding zone of the oxide and carbide-forming elements, and carbon is introduced in an amount exceeding no more than 0.5 wt.% stoichiometric cally necessary amount for its complete carbonization oksido- and carbide-forming elements. As carbide and oxide-forming elements, metals selected from groups III, IV, V and VI of the Periodic Table of Elements D.I. can be used. Mendeleev.

The difference of the proposed method from the prototype is to carry out all operations of the technological process of obtaining materials in air without the use of any oxidizing, reducing or protective gases (see Fig. 3). This advantage, which is manifested in a significant simplification and cheapening of the technological process (cf. FIGS. 2 and 3) and, accordingly, reduction in the cost of the materials obtained by this method, is achieved by introducing into the materials such an amount of carbon that is at most 0.5 wt.% Higher than the stoichiometrically necessary amount for complete carbidization of alloying elements. Due to this, heating in air of a product of mechanochemical activation - granules does not lead to oxidation of the copper contained in them, since the residual ultrafine and evenly distributed carbon in them in free form binds air oxygen in the furnace with the formation of CO and CO ₂ gases. Moreover, carbon at the same time restores copper oxidized during mechanochemical activation. The carbon dioxide generated in this process leaves the pores of the briquette and further prevents the ingress of air oxygen into them. In addition, carbon interacts with alloying elements with the formation of finely dispersed carbides.

 Thus, these excess, in contrast to the method selected as a prototype, the introduction of carbon into the powder mixture not only makes it possible to obtain the required dispersion-hardened material structure, but also provides copper recovery and its protection from oxidation in them, which makes it possible to avoid long and expensive redox annealing in the environment of special (explosive) gases, and the whole process is carried out in air.

 In addition to these functions, free carbon, the particle sizes of which after mechanochemical activation of steel, as shown by studies, 0.01-0.05 μm, has two more functions: it acts as an additional hardening phase in the material and as a kind of dry lubricant, increasing material its anti-friction and anti-adhesive properties, which is also very important for products of the above applications.

 The implementation of mechanochemical activation in air, in contrast to the method selected as a prototype, also has, in addition to simplicity and lower cost of operation, another advantage: atmospheric oxygen reacts with oxide and carbide-forming elements and forms their oxides, which are the same as and carbides, additionally harden the material.

 The presence of simultaneously heterogeneous hardening phases (oxides, carbides, and carbon) in materials, as is known [7], significantly reduces their tendency to coagulate, compared with the case when the materials contain only one homogeneous hardening phase, which prevents softening of materials at high temperatures and provides them with high temperatures of recrystallization.

Thus, in the process of obtaining dispersion-hardened materials according to the claimed method, the following basic chemical reactions and interactions proceed:
a) in the process of mechanochemical activation:
- reactions of copper and the oxide and carbide-forming element Me with oxygen in the air:
Cu + O ₂ _ → CuO (CuO ₂ ) - a chemical compound that adversely affects the physical and mechanical properties of the material;
Me + O ₂ _ → MeO (MeO ₂ , Me ₂ O ₃ , etc.) - hardening phase;
- carbon balance:
C _ → C ′ + C ″,
Where
C 'is the amount of carbon required for complete carbidization of the oxide and carbide-forming element (stoichiometrically necessary amount);
C '' is the excess carbon in the granules; during processing in a ball mill it is only crushed.

- матрица материала;
- взаимодействие углерода с кислородом воздуха:

- защитная атмосфера.- reactions of the oxide and carbide-forming element with carbon C ':
Me + C ′ _ → MeC (Me ₄ C ₃ , Me ₃ C ₂ and others) - hardening phase;
b) in the process of heat treatment of briquettes before extrusion:
- excess carbon balance C '':
C '' = C '' _b + C '' _a + C '' _c
where C _b '' is the amount of excess carbon consumed at
heating the briquette before extrusion to restore copper from its oxides;
C _a - the amount of excess carbon spent on the formation of a protective atmosphere when heating briquettes before extrusion;
C _c - the amount of excess carbon in the material in a free ultrafine state and acting as an additional phase hardener, as well as anti-friction and anti-adhesive additives;
- reactions for the reduction of copper from its oxides:

- material matrix;
- interaction of carbon with oxygen:

- protective atmosphere.

 As a result, the dispersion-hardened material obtained by the claimed method and containing in the initial state only one oxide and carbide-forming element Me and carbon C, represents the following system.

Cu - MeO - MeC - C _c '',
which simultaneously contains three hardening phases: oxide, carbide and excess carbon. In the material obtained by the prototype method when introducing into powder copper also one oxide and carbide-forming element and carbon, in the end there will be only one strengthening phase, namely carbide. Due to the fact that the mechanochemical activation by the prototype method is carried out in an argon medium (i.e., the absence of air, which means oxygen in it), the oxide and carbide-forming metal, for example titanium, cannot form its own oxide. In order for the final material to contain oxide, it is necessary to add the powder of this oxide to the initial powder mixture.

Obviously, if not one oxide and carbide-forming element is introduced into the initial powder mixture, but two at once (for example, titanium and aluminum), then the material obtained by the prototype method will have two heterogeneous strengthening phases (in this case, TiC and Al ₄ C ₃ ), while in the material obtained by the claimed method, the number of phase hardeners will be five (in this case, TiC, TiO ₂ , Al ₄ C ₃ , Al ₂ O ₃ and excess carbon).

 Since all five of these strengthening phases are heterogeneous, the material containing them will have virtually no softening due to coagulation of particles of the strengthening phases and will have high values of the recrystallization temperature.

 As oxide- and carbide-forming elements, elements of groups III, IV, V or VI of the periodic system of elements D.I. Mendeleev, in particular boron, aluminum, scandium, yttrium, lanthanum, silicon, titanium, hafnium, thorium, vanadium, niobium, chromium, molybdenum, tungsten, forming oxides and carbides stable at high temperatures.

 In the table. 1 presents the data of a comparative analysis of technological processes for the preparation of preforms, for example, rods for parts from dispersion-hardened copper-based materials used at elevated temperatures, using the method described in [8] (Fig. 1), the prototype method [9] ( Fig. 2) and the claimed (Fig. 3).

 From the table. 1 it follows that the technological cycle of manufacturing blanks using the proposed method is two operations shorter than the technological cycle of manufacturing blanks by the method described in [8], and by the method selected as a prototype.

 The total machine time of the technological process according to the claimed method is 6.2 - 6.7 times less than the machine time of the technological cycle using the method described in [8], and is as much less than the method selected as a prototype.

 In addition, in the technological process using the proposed method there are no operations in which protective gases are used, whereas in technological processes using other methods of such operations, four.

 The foregoing makes it possible to assert that the claimed method is much simpler, more productive, and safer than the method selected as a prototype, and the cost of billets made of dispersion-strengthened materials based on copper using this method is significantly lower than the cost of billets made by the prototype method.

где
A_c - атомный вес углерода;
A_э - атомный вес легирующего элемента;
K_с и K_э - коэффициент формулы, химической реакции между углеродом и легирующим элементом соответственно для углерода и легирующего элемента.Example. According to the prototype method (see Fig. 2), hot-pressed bars with a diameter of 16 mm were made, where titanium was the oxide- and carbide-forming element, and its amount was such that ultimately 3.0 was contained in the material; 4.0 and 5.0 wt.% Reduced titanium, while the carbon content was the stoichiometrically necessary amount for the complete carbidization of titanium, which was calculated by the well-known formula:

Where
A _c is the atomic weight of carbon;
A _e is the atomic weight of the alloying element;
K _c and K _e are the coefficient of the formula, the chemical reaction between carbon and the alloying element, respectively, for carbon and the alloying element.

 According to the claimed method (see Fig. 3), hot-pressed bars of dispersion-hardened materials with a diameter of 16 mm were manufactured, where the oxide and carbide-forming elements were metals of groups III, IV, V and VI of the periodic system D.I. Mendeleev, respectively, aluminum, titanium, vanadium and chromium. The content of the above elements in the original powder mixture was 3.0; 4.0 and 5.0 wt.%. The initial carbon content exceeded the stoichiometrically necessary amount for their complete carbidization by 0.1; 0.2; 0.3; 0.4 and 0.5 wt.%. The stoichiometric amount of carbon C 'in this case, necessary for the complete carbidization of the alloying element, was calculated by the above formula.

The technological process for the production of rods consisted in grinding the initial powders in an attritor in an atmosphere of air, cold compaction into briquettes in air, heating in air to 750 ^o C and extrusion from this temperature into rods.

The following main reactions proceed between these elements and carbons:
4Al + 3C = Al ₄ C ₃ ;
Ti + C = TiC;
V + C = VC;
3Cr + 2C = Cr ₃ C ₂ .

 The presence of carbides of the above types, as the main ones formed during the reaction of these elements with carbon, was subjected to x-ray phase studies of the materials obtained.

 Based on these reactions, the stoichiometric amount of carbon C 'required for complete carbidization of 1 g of aluminum, titanium, vanadium and chromium is 0.334, respectively; 0.250); 0.236 and 0.154 g.

 The resulting rods of all materials were tested, the purpose of which was to determine the temperature of their recrystallization.

 The research results are presented in table. 2.

 From the table. 2 shows that in the entire investigated range of contents of the oxide and carbide-forming element and carbon, the temperature of recrystallization of the materials obtained by the claimed method is higher than the materials obtained by the prototype method. This is due to the presence in the materials obtained by the claimed method of heterogeneous hardening phases that are less susceptible to coagulation and agglomeration processes than homogeneous: in the entire range of studied contents of oxide and carbide-forming elements and carbon, the average particle size of the hardening phases in the materials obtained by the claimed method, less than the materials manufactured by the prototype method.

Sources of information taken into account during the examination
1. Sintered materials for electrical engineering and electronics. Reference book / G.G. Gnesin, V.A. Dubok, G.N. Braterskaya et al. - M.: Metallurgy, 1981, p. 344.

 2. Zwilsky K.M. a.o. J. Metals, 1957, v. 9, p. 1197-1201.

 3. Zwilsky K.M. a.o. Trans. AIME, 1961, v. 221, p. 371-377.

 4. Copyright certificate of the USSR N 1016067.

 5. Copyright certificate of the USSR N 1222698.

 6. RF patent N 2015851.

 7. Danelia E.P., Rosenberg V.M. Internally oxidized alloys. - M.: Metallurgy, 1978, p. 232.

 8. Oppenhein H. Herstellung, Eigenschaften und Verwendungs-moglichkeiten von dispersionsgehartetem Kupfer. Z. Metallkunde, 74, 1983, p. 319-322.

 9. Offenlegung BRD DE 4418600 A1, 11/30/95. Verfahren zur Herstellung von dispersionsverstarkten metallischen Werkstoffen, insbesondere Kupfer und Silber. Kieback B., Kubsch H., G., Sauer C. Aktenzeichen P4418600.2, 05.27.94.

Claims (2)

 1. A method for producing dispersion-strengthened copper-based materials mainly for parts operated at elevated temperatures, including mechanochemical activation by grinding powders of copper, oxide and carbide-forming elements, carbon and oxides, characterized in that the oxides are obtained by filling in the grinding zone powders of oxide and carbide-forming elements, the process is carried out in one stage in an atmosphere of air, and carbon is introduced in an amount exceeding no more than 0.5 wt.% stoichiometrically necessary to lichestvo for complete carbonization oksido- and carbide-forming elements.  2. The method according to claim 1, characterized in that as the oxide and carbide-forming elements use metals selected from groups III, IV or VI of the Periodic Table of Elements D. I. Mendeleev.

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