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
  • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
  • B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
• • 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
  • B22F3/001—Starting from powder comprising reducible metal compounds
• • 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
  • B22F3/1017—Multiple heating or additional steps
  • B22F3/1021—Removal of binder or filler
  • B22F3/1025—Removal of binder or filler not by heating only
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B23/00—Obtaining nickel or cobalt
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B34/00—Obtaining refractory metals
  • C22B34/30—Obtaining chromium, molybdenum or tungsten
  • C22B34/34—Obtaining molybdenum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B5/00—General methods of reducing to metals
  • C22B5/02—Dry methods smelting of sulfides or formation of mattes
  • C22B5/12—Dry methods smelting of sulfides or formation of mattes by gases
• • 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

Definitions

• the present invention relates to a powder metallurgical process for the production of metal parts.
• the parts accessible by the classic PM process are characterized by simple geometries, which are unidirectionally pressed from relatively coarse powders and avoid thin bars, narrow bores, as well as bevels and undercuts.
• Typical part weights range from a few grams (e.g. locking nuts in the lock industry) to around one kilogram in the automotive sector (e.g. oil pump rotor, sprockets, ABS sensors).
• the manufacturing costs of such parts are low.
• the low mechanical strength of classic PM parts is particularly disadvantageous. They generally have densities below 7 g / cm 3 and thus have a considerable pore volume. This leads to a strong notch sensitivity, which does not allow the use of classic PM parts in applications subject to alternating loads (e.g.
• MIM metal powder injection molding
• finely divided metal powders particles diameter typically ⁇ 22 ⁇ , 90% point
• feedstock a binder to a homogeneous mass
• the proportion of binder is Dependence on particle density and morphology in general at 5 to 15 wt.%.
• the binder which no longer occurs in the actual end product (sintered steel part), takes on the task of encasing the metal particles in the process sequence and making the mass homogeneously flowable without any noteworthy segregation.
• Most of the binders used industrially are based on the interaction of the following three components, as explained below: removable component (K1), polymer (K2) and surface-active auxiliary (K3).
• This feedstock which has the flow properties of a filled thermoplastic, is processed to shaped bodies (green compacts) on conventional injection molding machines, this sub-step of the process corresponding to the molding principles of plastic injection molding and thus allowing the production of geometrically complex shaped bodies.
• component K1 the predominant part of the binder is removed from the green compact of the process, a porous part being obtained (brown compact), the external geometry of which is practically identical to that of the green compact and the shape of which is formed by a polymer (component K2 ) is held together.
• component K2 pores are created which, during the subsequent pyrolysis of the polymer skeleton, allow the pyrolysis gases that are formed to escape to the outside without building up internal pressure (i.e. without damaging the component through bubbles and cracks).
• Both binder mixtures are known in which K2 and K1 are homogeneously soluble in one another, and those in which these form two discrete phases after cooling / Lit5 /.
• Component K1 can be removed thermally, chemically, microbially or solvent-based.
• component K2 comprises polymers from the following classes: polyolefins, polystyrene, polyamides, acrylates, cellulose acetate, polyacetals.
• a further component K3 is often added to the binder as a flow improver which has surface-active properties and thus allows the surface of the metal particles to be wetted as homogeneously as possible.
• the brown product obtained is then sintered in the presence of H2, H2 / N2 mixtures or in vacuo at temperatures below the melting point of the alloy.
• the components K2 and K3 decompose and the Braunling shrinks under internal compression by the original volume fraction of the binder.
• the shrinkage in the x, y, z direction is approximately isotropic and, depending on the binder content and composition, is approximately 13-20%.
• EP-PS 125 912 describes a method in which K2 one of the above-mentioned thermoplastics is processed with a wax K1.
• EP 0465 940 B1 is a thermoplastic composition in which component K2 is a polyolefin and K1 is a polyoxymethylene, K1 being removed by acid catalysis and K2 then being expelled pyrolytically.
• K1 is made from the Braunling by solvents e.g. Alcohols and or chlorinated hydrocarbons are extracted.
• US 4,445,936 and US 4,404,166 describe one possibility of increasing the accuracy of MIM parts by compressing them after inserting into a press die after sintering at 2150 ° F (1177 ° C) with plastic deformation of the metallic matrix formed during sintering ,
• high accuracies are achieved without the formation of cracks, the density increasing minimally compared to the sintered parts. If oxides are used as a component of the feedstock, then when sintering under hydrogen at approx. 1200 ° C (2150 ° F), parts that can be deformed with the hammer are obtained, the volume of which has shrunk considerably compared to the originally shaped starting geometry. Stressed and described only molded parts are first sintered and then calibrated, ie the end product is the calibrated sintered body whose geometry corresponds exactly to the geometry of the calibration mold.
• the present invention has therefore set itself the task of creating a possibility to significantly expand the technically / economically conditioned component upper limit for MIM parts by using cheaper starting products instead of the expensive, finely divided metal powders previously required and at the same time significantly reducing the shrinkage during sintering.
• the solution to this problem is achieved by incorporating the corresponding unreduced metal compounds (for example, as inexpensive oxides) into the binder instead of the finely divided metal powders and only after the shaping of the green body while largely maintaining the initial geometry with a reducing gas at elevated temperature, definitely reduced to metal below the sintering temperature.
• the minimum temperature required depends on the redox potential of the cation under consideration and increases with the increasingly base character of the metal, e.g. from Cu (approx. 270 ° C) to Ni (approx. 650 ° C) to Fe (approx. 700 ° C).
• the reduced moldings have a high, precisely controllable porosity and a correspondingly low density. They can be manufactured inexpensively using simple principles within narrow geometric tolerances.
• any reducible metal cations can be used in free or complex-bound form with any inorganic or organic anions, such as oxides; which form volatile or non-disruptive end products under the reduction conditions; Hydroxides, sulfides, nitrates, carbonates, formates, oxalates, acetates or metallates (eg paratungstate) and mixtures of such compounds are used.
• oxides or mixtures of different oxides and ammonium metallates are preferably used, especially since their metal content based on the initial volume of the metal compound used is comparatively high.
• the composition of the binder is not subject to any technical restriction. It is therefore possible to use commercially available binder systems, and in particular the principle well known from MIM technology can be used to construct the binder from an easily removable (e.g. extractable) component in combination with a crackable polymer. Since the metal particles are incorporated into the binder in oxidized form, water-extractable binder systems can be used without corrosion problems.
• the removal of the binder can be carried out in any manner known per se, with the dimensional stability of the shaped bodies formed by reduction, in contrast to the conventional MIM process, being removed by removing the crackable binder components under oxidizing conditions in air or a water vapor-containing atmosphere at temperatures between about 400 and 950 ° C has proven to be advantageous. With this measure, partial sintering of the highly porous matrix, which is under volume shrinkage, as well as its expansion, is avoided. continuous carburization avoided, so that the porous matrix formed by reduction provides dimensionally stable parts.
• the two-stage reduction can be made possible in a simple manner by adding a low-molecular-weight organic compound to the reactor in the first sub-step (reduction under a carbon-containing atmosphere), e.g. a lower alcohol is added with the addition of aqueous ammonia solution and is only reduced with hydrogen after a certain (component-dependent) partial conversion has been achieved.
• a low-molecular-weight organic compound e.g. a lower alcohol is added with the addition of aqueous ammonia solution and is only reduced with hydrogen after a certain (component-dependent) partial conversion has been achieved.
• the porous shaped bodies formed by reduction can be any porous shaped bodies formed by reduction.
• the present invention thus circumvents the disadvantages of the prior art and describes a process which reduces the raw material costs of the MIM process to a negligible proportion and only requires minor additional investments. This is achieved by using the unreduced metal compounds (eg as inexpensive oxides) as the basic component of the feedstock instead of expensive, finely divided metal powder these are reduced to metal only after the shaping of the green compact.
• the unreduced metal compounds eg as inexpensive oxides
• This method is not restricted to special binders, and is described below using an example of a commercially available binder composition (model binder).
• the possibility of using water-soluble binders is advantageous, since the oxidic particle matrix does not cause any corrosion problems here.
• Green parts with a part weight of 10.49 g are injected from this feedstock on a conventional injection molding machine. After removing component K1 by extracting component K1 in acetone for 12 hours, the brown body is kept in the presence of hydrogen or hydrogen-containing gases for several hours at temperatures between 550 and 1250 ° C. and thus converted into a porous matrix.
• the extent of this shrinking process essentially depends on the reduction temperature, the duration of the reduction, the gas composition and the specific gas feed (I H2 / h / Kg Braunling).
• the SF value the quotient between the currently considered length and the associated output length in the green compact.
• the transition temperature is kept below 600 ° C, the pre-sintered parts are mechanically very susceptible, since due to the low surface diffusion at these temperatures, hardly any sintering processes take place.
• the three-dimensional network of metal particles that forms is therefore held together only by very weak forces.
• the temperature profile during the reduction of the metal connections has to be adapted to the part geometry, whereby high wall thicknesses rather require a slow rise in temperature in order to achieve a conversion that is as uniform as possible within the matrix. If the temperature is increased too quickly, the reaction rate in the outer areas is very high, while the comparatively slow diffusion of the hydrogen into the interior of the part and the diffusion of the water vapor formed in the opposite direction mean that the almost completely reduced areas near the wall are still largely faces the original output matrix inside the part.
• the different density between the starting and the end product leads to stresses in the part, which either show as cracks or as faults in the pre-sintering.
• a temperature profile has proven itself, in which the temperature is increased from 550 ° C to 800 ° C within 3 to 8 hours. Since the reduction of the metal oxide is an equilibrium reaction, it makes sense to drive with an excess of hydrogen during the conversion and to discharge the water formed in the reaction in a circuit. To achieve a complete conversion of the oxide used, the highest possible final temperature should be selected.
• the pre-sintered product obtained in the manner described above can now be sintered into the end product analogously to the classic MIM process either in a separate process step or directly by further increasing the temperature.
• the brown compact which was reduced at 850 ° C., was sintered in a vacuum at a temperature of 1280 ° C. for 30 minutes.
• the final density achieved at 7.55 g / cm 3 corresponded to that customary in the MIM process.
• the conversion shrinkage also occurs in the process according to the invention.
• This high total shrinkage is uncontrollable, especially in the case of parts with different wall thicknesses, especially if one takes into account that the attack of the hydrogen takes place from the outside and thus internal tension in the part is pre-programmed.
• the problems associated with the high shrinkage of the warpage and the high dispersion of the target dimensions can be greatly minimized if the sequence of the process steps is reversed, as explained in Example 2.
• a sintered body (hereinafter referred to as invert sintered body) is first produced from the chemically precisely defined Braunling of Example 1 without the addition of reducing gases.
• the Fe3O4 brown body is heated to 800 to 1360 ° C under nitrogen or vacuum (30 min holding time at maximum temperature).
• a gas evolution is observed in the temperature range of approx. 350-500 ° C, above approx. 750 ° C by reaction of the cracked residual polymer from the Braunling with the Fe3O4. This reaction leads to a weight loss which is due to the fact that the cracked residual polymer reduces part of the Fe304 to FeO / Fe.
• the conversion due to this reaction depends on the invert sintering temperature and the gas atmosphere set and is e.g. in vacuum depending on the maximum temperature approx. 4% (850 ° C) and 28% (1360 ° C). If you use an inert gas (e.g. N2), the sales are slightly lower.
• an inert gas e.g. N2
• the invert sintering essentially consists of the sintered starting product (here Fe3O4 with Ni), which, depending on the maximum temperature of the invert sintering, has a residual porosity of approx. 8% by volume (1360 ° C) to approx. 32% by volume (850 ° C) ) has.
• the invert sinterling is mechanically extremely stable, especially at higher sintering temperatures (from approx. 900 ° C) and shows no deformation or cracks despite the relatively high wall thickness.
• SF value is between 1.01 (800 ° C) and 1.15 (1360 ° C) (see Fig. 3).
• the statistical distribution of dimensions for different parts of the same series is strikingly narrow with a maximum of +/- 0.4% of the mean.
• the micro density of the open-pore structure increases due to the parallel partial reduction of Fe3O4 with increasing invert sintering temperature from 5.2 g / cm 3 (invert sintering temperature 700 ° C) to 5.5 g / cm 3 (inverting sintering temperature 1360 ° C), the macro density increases in the same Direction from 3.6 to 5.1 g / cm 3 .
• the invert sinterling is reduced to iron in analogy to example 1.
• the conversion at approx. 900 ° C in the H2 / N2 mixture has proven to be favorable.
• the required reaction time depends on the wall thickness of the parts and is usually around 3 to 7 hours.
• the shrinkage which occurs when the invert sinterling is reduced to the outside is comparatively low at temperatures below 1000 ° C.
• the SF value between invert sinterling and Braunling is only approx. 1.005 to approx. 1.030 depending on the maximum temperature passed. This is due to the fact that during the previous sintering of the unconverted Fe304 brown body (invert sintering) a mechanically stable skeletal structure with an internal residual porosity of approximately 8-32 vol.% Depending on the temperature used is formed.
• Example 1 In contrast to Example 1, the shrinkage resulting from the conversion of the oxide therefore does not manifest itself to the outside, but, while maintaining the outer shape, leads to an increase in the internal porosity of approximately 32% by volume and thus (depending on the previous invert sintering temperature) reduction is 43 to 65% by volume. In contrast to the directly reduced brown compacts from Example 1, the converted invert sinterings are largely free of cracks and warpage due to the skeleton structure mentioned, even at a comparatively low transition temperature.
• the macro density of the reduced invert sinterlings was around 2.6 to 4.2 g / cm 3 , depending on the conversion conditions.
• the micro density was independent of the Invert sintering temperature of approx. 7.5 to 7.7 g / cm 3 is approximately the theoretically maximum possible value.
• the tensile strength of the reduced (converted) invert sintered blocks corresponds approximately to that of plastics, but the fracture behavior is without elastic components.
• the tensile strength increases with increasing invert sintering temperature and reaches a typical value of approx. 70 N / mm2 at 1345 ° C (invert sintering temperature) after reduction in the H 2 stream (900 ° C; 3 hours).
• invert sintering temperature invert sintering temperature
• the strength of the parts increases to approx. 300 N / mm2 with a macro density of approx. 5.3 g / cm , The residual porosity of these parts is around 25%.
• Example 2 In contrast to Example 2, the temporal and spatial separation of invert sintering and reduction is eliminated in this concept, which means that, due to the lack of intermediate cooling, comparatively low invert sintering and transition temperatures remain manageable without cracks.
• a batch of the brown pieces from example 1 consisting of 150 parts is run into the hot belt furnace in a stream of N2.
• the set temperature of the 5th Heating zones (300/600/900/900/900 ° C) and the belt speed are calculated as a heating rate of approx. 20 ° C / min.
• the belt advance was put out, kept under N2 for 30 minutes and then the oxide components of the brown body were reduced to iron within 2 hours at this temperature by adding 1.5 Nm3 H2 / h.
• a mixture of hydrogen and nitrogen with a circulatory procedure with simultaneous removal of the water formed has proven to be advantageous.
• DI sintered parts show approximately the same geometric dimensions as the brown parts used at a temperature of 900 ° C, whereby the SF values can be controlled within certain limits without cracks by appropriate gas and process control .
• the pore volume resulting from the volumes of the former binder components and the conversion shrinkage (reduction of Fe3O4 to Fe) is in the range from 60 to 70% by volume, i.e. the removal of the binder and the conversion take place with appropriate process control while largely maintaining the outer geometry while simultaneously building up a high, homogeneously distributed inner porosity.
• the Dl sintered products produced in this way have a low tensile force of approx. 10 to 20 N / mm2, but are promising candidates in such applications in view of the low macro density of approx. 2.6 g / cm 3 where metal foams (e.g. hot gas filters; crash absorbers) are discussed. These metal foams have so far not been made of steel but, due to the process, only accessible from alloys that have comparatively low melting points. (e.g. decomposition of TiHx in Al and Zn melts)
• the DI sinterings produced according to Example 3 were sintered at high temperatures (for example 1320 ° C. for 1 hour in a vacuum). As expected, the parts shrank and the macro density increased to approx. 7 g / cm 3 . At the same time, the tensile strength that can be achieved increases to approx. 400 N / mm2.
• the tolerances of the final sintered parts can be set within relatively narrow limits despite the shrinkage factors above 1.3.
• the statistics of the dimensions of +/- 0.7% are not worse than those of the usual MIM method, despite the significantly higher shrinkage.
• the DI sintered compact (density 2.74 g / cm 3 ) thus obtained had practically not shrunk compared to the green compact and had a diameter of 26.85 mm and a height of 25.0. It was placed in a press die (diameter 27 mm and pressed with upper and lower punches at a given press pressure.
• PDI Pressure after Direct Inversion
• the hardness increases to 52 HRC with a simultaneous increase in tensile strength to> 1000 N / mm 2 .
• the toughness and notched impact strength of the materials produced according to Example 5 are high. Even if the pressure applied to the PDI is only 2.6 t / cm 2 and the sintered density is only around 6.95 g / cm 3 , the tensile strength is over 500 N / mm2. In contrast to conventional PM materials with a comparable density, these parts are surprising because of the significantly higher tensile strength and the significantly lower sensitivity to notch impact, which is due to the extremely fine-grained structure.
• the method according to the invention can thus be used to achieve material properties at comparatively low pressures, which are clearly superior to the conventional PM parts produced using comparable pressures. For a given press output, significantly larger parts can be produced using the method according to the invention than is possible with the classic PM.
• the porosity of the DI sintered body is increasingly eliminated by compression in the Z direction.
• the porosity remaining in the molded body after pressing disappears during the ters to the final density and leads to a sintering shrinkage that occurs evenly in the first approximation in the x, y and z directions.
• the underlying presses and tools are accordingly very complex and It becomes particularly critical if, instead of two or three-height molded parts, geometries with a continuous change in height (eg an oblique edge) or undercuts in the pressing direction are to be produced. manoeuvrable tools or mechanical reworking of corresponding blanks.
• Example 7 The ductile flow behavior mentioned in Example 7 makes it possible, within certain limits, to fill in the press die such material contours whose material is not pre-formed in the porous molded body inserted into the mold. That the porous molded body need not necessarily represent the shape of the pressed body expanded in the pressing direction.
• a PDI insert A, compression density 6.4 g / cm 3
• a porous DI manufactured according to Example 3 is then placed on this PDI and, using the ductile flow behavior, pressed in a form-fitting manner with insert A transversely to the pressing direction.
• the two parts connected by pressing technology are now sintered together. Since both part geometries (assuming the same pre-compression) shrink identically during sintering, the part combination is rigid, with the original separation point healing due to the high pre-compression and the high sintering activity of the finely divided powders during sintering.
• PDI and porous molded body DI are not necessarily geometrically similar bodies that are only compressed in the z-axis. Since the ductile flow properties of the DI allow material to be moved transversely to the pressing direction, it is possible to produce geometrically complex shapes with flowing transitions (multi-height parts) in simply constructed pressing dies in that a porous molded body identical in basic geometry is shaped like a stem in the rear shaft is extended by the additional volume required for pressing. The additional volume must be designed so that it stores the material of the target geometry required for compression.
• the density achieved by transverse compression in the PDI does not naturally achieve the homogeneity that can be achieved by compressing a geometrically simple tablet, due to the excellent material properties, even in those areas that are not fully compressed during pressing after sintering good tensile strengths and notched bar impact values were observed.
• the comparatively low pre-compression to approx. 5 g / cm 3 is sufficient to achieve a density of 6.9 g in this area after the sintering of the FeNi8 material used in this example. After sintering, this leads to a tensile strength of approximately 500 N / mm 2 .
• the process offers a clear competitive advantage with comparable material properties compared to conventional metal powder injection molding.
• the low raw material costs and the significantly lower sintering shrinkage allow the production of highly cantilevered geometries that cannot be mastered when sintering classic MIM parts. So it is possible via a Relining with support geometries to stabilize these projecting partial structures during sintering and to subsequently mechanically remove these support structures. This concept is generally uneconomical in the classic MIM process due to the prohibitively high raw material costs.
• the porous moldings must be placed in a mold for pressing. To minimize the cost of this additional step, cycle times of a few seconds are required.
• the pressing process itself is generally in the range of less than 1 sec and does not require a holding time.
• the speed-determining step therefore lies in feeding the parts to the press mold, which should be automated to minimize costs. Due to the high stability of the porous molded bodies, this is possible without any problems, provided that they are manufactured within relatively narrow tolerances and can therefore be inserted into the specified press cavity without tolerance problems.
• break gaps heal when pressed, since material flows from the other parts of the part due to the ductile flow behavior. Due to the high sintering activity, the material is homogeneous after sintering and also has the same high tensile strength as the rest of the matrix at the healed fracture gate.
• the sintering activity can often be reduced here so that the thin-walled geometries mentioned do not shrink inadmissible, but this is generally accompanied by a deterioration in the material properties and an increase in the pressing pressure.
• the weight of the parts had been reduced to 7.1 g by reducing the oxide.
• SF 0.98 to 1.015.
• the 29 parts were flowed through in a second experiment instead of H2 / N2 with 0.6 Nm3 / h of a gas mixture of CO / H2 / CH4 (30/65/5 vol.%).
• the weight of the parts had been reduced to 7.2 to 7.4 g by reducing the oxide.
• the parts had a dark gray metallic appearance and had shrunk uniformly in X and Y by a factor of 0.985 to 1.015%.
• Carbon deposits were visible on the surface of some parts, particularly in the area of edges and thin-walled geometries, which can be attributed to a Bouduard decay of the CO on the freshly formed iron surface.
• these thin-walled geometries swelled from 25.42 mm to 26.4 mm.
• Example 10 The experiment from Example 10 was repeated to suppress Bouduard decay with the addition of 5% by volume of NH3, water being added to the system at the same time to increase the O: C content.
• the parts showed no carbon deposits at an SF value of 0.975 to 1.02
• the dimensions of the parts thus corresponded to those of the within a spread of + / 0.4 -0.2 mm originally used Braunlings.
• the parts could be fed to the press mold automatically. After sintering these parts at 1280 ° C in vacuo, an inadmissibly high C content was found in some parts, which led to partial melting.
• the porous parts were impregnated with a commercially available mineral oil and then pressed in a mold using a pressure of 28 tons.
• the compacts obtained had a macro density of 6.3 to 6.4 g / cm 3 with a micro density of 7.55 g / cm 3 .
• These parts were sintered at 1280 ° C under hydrogen (7.5 ° C / min; 1 hour holding time at maximum temperature). After sintering, the parts had a uniform weight of 6.98 g, a macro density of 7.5 g / cm 3 and were ductile deformable under the action of impact.
• the parts were produced analogously to Example 13, but after the conversion, the porous moldings were infiltrated with a concentrated ammoniacal Cu [(NH 3 )] 4 2 " solution and under hydrogen at 900 ° C. in a belt furnace (total residence time 1.5 ' h) reduced to Cu °.
• the parts showed a copper color on a metallic gray matrix, which continued homogeneously into the part.
• These parts were pressed, sintered, hardened and tempered as described in Example 13. In comparison, the tensile strength was about 10 % higher than that of the comparison parts from example 12 without Cu infiltration.

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