Classifications

• • 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
  • B22F3/10—Sintering only
  • B22F3/1003—Use of special medium during sintering, e.g. sintering aid
  • B22F3/1007—Atmosphere
• • 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
• • 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
• • 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
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/02—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working in inert or controlled atmosphere or vacuum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
  • C22F1/18—High-melting or refractory metals or alloys based thereon
  • C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon
• • 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
• • 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
  • B22F2301/205—Titanium, zirconium or hafnium
• • 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
• • 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
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/25—Process efficiency

Definitions

• the present invention relates to a method for powder metallurgical production of a component made of titanium or a titanium alloy, wherein first formed by using titanium powder or titanium alloy formed metal powder, a green part and this compacted and solidified in a subsequent sintering step.
• titanium component there are various powder metallurgical processes for producing true-to-scale titanium components (with "titanium component” are simplified here and below
• Green part produced and this is compacted and solidified in a sintering process.
• the production of the green part can take place in different ways, in particular by means of additive manufacturing processes, metal injection molding,
• the powder-metallurgical production of titanium components is becoming increasingly important due to the excellent properties of the material titanium paired with the economic and economical production method.
• the good biocompatibility and high specific strength of titanium material play especially in the application areas of medical technology and aerospace play an important role.
• the most economically important alloy, with sales of more than 50% of the total titanium market, is Ti6AI4V.
• the aim of the shaping is to bring the titanium powder particles in near dense packing in close to net shape.
• additives are used which must be removed in one or more subsequent debindering step (s).
• s subsequent, often final, process step, sintering, the powder particles are consolidated by material transport.
• Titanium has two crystal modifications.
• the hexagonal ⁇ -phase which is pure titanium and atmospheric pressure up to a temperature up to 882, 5 ° C, and the cubic body-centered ß-phase, which occurs at pure titanium and normal pressure above the temperature described above.
• the presence of the different phases at room temperature is used to classify titanium alloys into a-Ti, (a + ß) -Ti and ß-Ti alloys.
• Ti6Al4V is an (a + ß) alloy, ie at room temperature both phases are stable in the microstructure.
• Microstructure has a ß-grain size of about 1 50 / vm.
• ß-grain size of about 1 50 / vm.
• a standard adjusting structure is one with Titanium powders commonly used in the art (with powder particles of sizes ⁇ 45 / vm) and Ti6Al4V samples sintered under sintering conditions typically used in the art are shown in FIG. It can be seen there the typical for powder metallurgically produced and sintered titanium components lamellar formed from ⁇ -phase and ß-phases mixed structure, the (a + ß) -fabric, with a mean primary ß-phase grain size (D) of about 1 90 / vm.
• D mean primary ß-phase grain size
• a further procedure for producing fine-grained titanium or titanium alloys by powder metallurgy is described in WO 201 2/1 48471 A1.
• a green part of titanium (alloy) powder with particle sizes below 325 mesh (below 44 / vm) is produced and then subjected to a multi-stage process for compaction and grain remodeling.
• the green part in a hydrogen atmosphere at temperatures of 1 1 00 to 1 500 ° C, in the embodiments is always referred to as process temperature 1 200 ° C, sintered. This produces titanium material of the ß-phase.
• a phase remodeling takes place in which the ⁇ -grains undergo a restructuring which results in a phase mixture of fine ⁇ -grains, ⁇ -grains and ⁇ -phases.
• the hydrogen must then be expelled from the resulting component, which is done by applying a vacuum.
• the use of hydrogen in particular is problematic, since this gas from the finished component can be driven only with great effort and often not completely.
• negative influences on the material properties and the stability of the material are attributed.
• outgassing of residual hydrogen from the finished component in various applications is anything but desirable.
• An objective generally pursued by the invention is now to provide a possibility for powder-metallurgically produced and sintered titanium components to manipulate the microstructure and to optimize the material properties.
• a crucial prerequisite for the implementation of the method according to the invention and for the creation of the possibility of influencing the material properties in the sintering process is the use of metal powder formed from titanium or titanium alloys with a mean particle size ⁇ 25 / vm, so-called fine powder.
• the maximum particle size may be in particular ⁇ 30 / vm.
• the maximum particle size is specified by the manufacturers of such fine powder as a limit. Nevertheless, a small proportion of particles in such a charge may still have particle sizes above this limit. Such a proportion is usually specified with a maximum of 1 to a maximum of 5% by weight.
• the mean particle size can advantageously be even lower, in particular at ⁇ 20 / vm, with advantage ⁇ 10 / vm and particularly preferably even ⁇ 5 / vm.
• the smaller the particle size of the metal powder the sooner high end densities can be achieved even at sintering temperatures which are significantly reduced compared with the comparatively high sintering temperatures used hitherto.
• the measurement of the particle sizes essential for the invention and their distribution is carried out by means of a particle size analysis by means of laser beam scattering according to the ASTM B822-10 (published in 2010) valid at the time of priority of this application.
• the distribution of the particle sizes is determined by weight% and according to D 10 / D50 / D90, where D50 is the mean particle size.
• the particle sizes reported herein were determined in carried out by the Applicant comparative tests by measurement with Particle size analyzers COULTER ® LS manufacturer Beckman Coulter and evaluation using the Fraunhofer theory by ASTM B822- 10 degrees.
• the particle size in the sense of the invention is determined by the particle diameter in the case of spherical particles.
• the particle size corresponds to the projected maximum particle dimension.
• the unconsolidated component increases the surface available for the sintering process and thus also the stored surface energy. Since the reduction of this energy is the driving force in the sintering process, the sintering process can then proceed with the use of low thermal energy.
• a further advantage of using fine powders sized as described above for molding the green parts is that more powder particles can be introduced per unit volume. In addition to the increased surface area, this leads to a higher number of contact points of the particles per unit volume, as illustrated in FIG. 3. There, the influence of a halving of the particle size (on the example of spherical particles) on the number of particles for filling a defined volume is illustrated in a schematic representation.
• the contact points of the particles are in turn starting point and a necessary condition for the sintering process, which is driven by diffusion processes.
• the increase in the number of such contact points per unit volume thus provides an improvement in the starting conditions for the sintering process.
• the ideal packing density apart from the stated advantages, also results in the consequence that the volume enclosed by the powder particles, as shown in FIG. 4 idealized is reduced.
• FIG. 4 illustrates, in a schematic representation, the reduction of the cavity between adjoining particles by halving the particle size (using spherical particles as an example). Since this cavity must be closed by material transport during the sintering process in order to achieve the high density of material desired for the component obtained after the sintering process, a smaller volume to be bridged represents a further decisive reason for an improvement of the method result.
• the sintering step typically takes place in a reduced pressure atmosphere.
• This can be a vacuum with a pressure of ⁇ 10 3 mbar, in particular ⁇ 10 "5 mbar, but it can also be an inert gas atmosphere with a reduced pressure of, for example, ⁇ 300 mbar.
• the sintering temperatures according to the invention are below 1 100 ° C. In particular, they can be at a maximum of 1 050 ° C., a maximum of 1000 ° C., even a maximum of 950 ° C.
• the sintering temperature should advantageously not be chosen below 860 ° C for achieving a good sintering result.
• the sintering temperature can be maintained evenly. In particular, however, it is also possible and within the meaning of the invention to vary the temperature during the sintering process.
• the sintering temperature is here the temperature which has experienced the workpiece to be sintered.
• an adapted process temperature will have to be selected in its control, as it may happen that the process temperature measured at a process temperature remote from the workpiece differs from the sintering temperature experienced by the workpiece.
• the sintering time can be in particular ⁇ 3.5 hours, often ⁇ 3 hours or even ⁇ 2.5 hours. However, it has been found that, as a rule, for achieving good results, the sintering time should be at least 1 hour, preferably at least 2 hours.
• titanium or titanium alloy components produced by the process according to the invention generally have a final density of> 97%. It can also be reached final densities are above 98%, yes even> 99% amount.
• the titanium components were sintered below the ⁇ -transus temperature (e.g., at a temperature 30 ° C below the ⁇ -transus temperature).
• components with a final density of> 97% were produced at a sintering temperature of 950 ° C. below the ⁇ -transus temperature and with a sintering time of less than three hours. These had a globular structure with an average particle size of 10, 1 / vm and a max. Size of 29 / vm on. The structure of this material is shown in FIG. 5 shown. These particle sizes are of the order of magnitude of the powder particles used.
• the ⁇ -transus temperature of Ti6AI4V is according to the literature in the range of 985 ° C to 1 01 5 ° C [3; 5]. This comparatively wide range stated in the literature is due, on the one hand, to the distribution of the alloying elements in the titanium alloys. On the other hand, the ambient pressure is another influencing factor. For example, Huang et al. Describe that a reduction of the a-Transus temperature can be observed for the alloy Ti46AI8Nb due to increased process pressures (1 500 bar) [6].
• the components were sintered near the ⁇ -transus temperature but still below it.
• first samples were prepared by sintering the titanium components at a sintering temperature of 1000 ° C. (FIG. 6). This sintering temperature was still below the .beta.-transus temperature, although only marginally, as shown by investigations of the samples obtained with regard to the structure formed in the sintered alloy.
• the resulting bimodal microstructure consists of a globular ⁇ -microstructure and small proportions of lamellar (a + ⁇ ) -surfaces, where the average ⁇ -grain size is 81 / vm.
• Density was measured according to ASTM B962 and ASTM B31 1 specifications. The determination of the grain sizes was carried out in accordance with the provisions of ASTM E1 1 2.
• the components were largely, ie. the predominant time, below the ⁇ -transus temperature, but with a minimum hold time, which was below 30 min, preferably below 20 min remained, in particular less than 10 min, in phases also above the ⁇ -Transus temperature , Sintered so that completely the ß-phase is present, so as to produce just the lamellar structure, but the primary ß-phase grain does not exceed the size range mentioned in claim 1 6.
• the sintering above the ⁇ -transus temperature with a minimum retention time was carried out in any case at a temperature above 101 5 ° C. In each case, this temperature was kept below 1 080 ° C, was advantageously below 1040 ° C and was selected in particular ⁇ 1020 ° C.
• powder metallurgical shaped bodies of titanium and titanium alloys are sintered below the sintering temperatures which are usually above 1 100 ° C., generally at 1200 ° C. and above, advantageously below the ⁇ -transus temperature and thereby components with good structural and other material properties can be obtained. It could be shown that, compared to the sintering temperatures which are generally lower in the state of the art, significantly lower sintering temperatures are set-unexpectedly-components with high end densities of> 97% can be obtained.
• the method according to the invention allows the structure of the titanium components to be varied in the sintering process and the grain size to be drastically reduced, whereby the mechanical properties of the components, for example tensile strength, ductility and fatigue strength, can be optimized.
• a particularly low temperature for sintering may be chosen, e.g. a temperature of below 950 ° C, and it can, if in such a sintering step the desired material density in the finished component (usually> 97%) is not reached, a further compression of the material in a subsequently performed pressing step are carried out in the material is subjected to pressure and possibly a temperature, in particular by cold isostatic pressing (CIP) or by hot isostatic pressing (HIP).
• CIP cold isostatic pressing
• HIP hot isostatic pressing
• components produced by the process according to the invention may be subjected to further thermal aftertreatments subsequent to the sintering step in order to influence the properties of the material even further to take.
• Such further thermal aftertreatments may be, for example, one or more of the following processes: hot isostatic pressing (HIP), quenching, uniform rapid quenching (URQ).
• the sintering temperatures reduced according to the invention compared with the sintering temperatures used in the prior art give rise to further ecological / economic and process engineering advantages. On the one hand, less thermal energy is needed in the sintering process, which leads to lower costs but also shorter process times. On the other hand, the process carried out according to the invention with reduced sintering temperature makes it possible to use hot-wall oven concepts, which in turn are more cost-effective than ovens designed for process temperatures> 1100 ° C. and which are classically cold-wall furnaces.
• the targeted combination of fine powders with average particle size ⁇ 25 / vm, preferably also with maximum particle sizes ⁇ 30 / vm, and reduced compared to the prior art, to be classified as low sintering temperatures allows the unique manipulation of the structure and thus the material properties.
• FIG. 1 shows a representation of a lamellar (a + ⁇ ) layer of a Ti6Al4V sample with a description of the structure fractions according to Sieniawski et al. [3];
• FIG. 2 shows a microscopically enlarged photograph of a powder-metallurgically produced and standard sintered Ti6Al4V sample using powder particles ⁇ 45 / ⁇ m and for this a lamellar (a + ⁇ ) -fabric;
• FIG. 3 shows a schematic representation of the influence of the halving of the particle size (on the example of spherical particles) on the number of particles for filling a defined volume
• Figure 4 is a schematic representation of the reduction of the cavity between adjacent particles by halving the particle size (the example of spherical particles).
• Fig. 5 shows a microscopically enlarged micrograph of a powder metallurgically produced and sintered Ti6Al4V sample using powder particles ⁇ 20 / vm, which demonstrates the formation of a globular ⁇ -microstructure
• FIG. 6 shows a microscopically enlarged micrograph of a powder metallurgically produced and sintered Ti6Al4V sample using powder particles ⁇ 20 ⁇ m, which demonstrates the formation of a bimodal microstructure with globular ⁇ structure and lamellar ( ⁇ + ⁇ ) microstructure.

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