EP1412113B1 - Sinter metal parts with homogeneous distribution of non-homogeneously melting components and method for the production thereof - Google Patents

Abstract

Production of components and semi-finished products comprises: preparing a powder material made from light metal and alloying components, especially wear-resistant carriers; isostatically pressing into a molded body; and extruding close to the sintering temperature of the light metal. Preferred Features: The light metal is aluminum. The alloying components comprise 10-30 wt.% silicon, 0-3 wt.% magnesium, 0-5 wt.% copper, 0-7 wt.% zinc, and 0-7 wt.% iron. The wear-resistant carriers are selected from silicon and/or hard material particle additives, especially oxides, carbides and silicates in an amount of 0-30 wt.%.

Description

The invention relates to sintered metal parts with a homogeneous distribution not homogeneous melting components, in the west. from non-homogeneous melting non-ferrum Metal pouf mixes and processes for their production.

Here the term non-ferrum also means metal mixtures, the iron in small amounts, up to about 8 wt .-% - less Amounts of iron as alloy additives should be possible.

The production of sintered parts from non-homogeneously melting metal powder mixtures is known. Hot isostatic pressing is usually used for this (HIP = Hot Isostatic Pressing), Isostatic Pressing (CIP = Cold Isostatic Pressing) or the warm sintem. All of these procedures avoid a complete one Melting of the metal powder mixture, otherwise segregation phenomena would occur. With HIP and CIP, the parts must be discontinuously individually Pressure chambers are sintered, what a series production only in exceptional cases is portable.

Pressureless warm sintering requires less effort. Doing so the powder, granulate, semolina or the like to be sintered together with pressing aids in The final shape, as a rule, is pressed uniaxially and the green body thus produced in a sintering furnace at temperatures at 2/3 to 4/5 of the melting or solidus temperature of the metal powder, if necessary under a protective atmosphere, sintered.

Another known technique for compacting metal powder is powder forging. It is also a batch process in which individual Parts are produced in dies.

DD-23 510 A discloses a method of making wire made of a silver sintered material, a powder mixture being sintered and the sintered product using boron nitride as a lubricant at a Temperature between 400 and 900 ° C in a hydrostatic Is extruded.

Multi-phase powders and powder mixtures are generally near the Melting or solidus temperature of the lowest melting component the mixture sintered. Sintering occurs due to slightly oxidizing materials the increased oxidation rate and the long-lasting holding time

Sintering temperature often takes place under a protective gas atmosphere. To this real one Densification of the green part was followed by a heat treatment that the so formed Microstructure improved. After that, post-processing often closes or calibration in which the sintered parts are brought into the final shape. These additional steps are for hot-sintered parts, which are when cooling tend to be delayed, cost-intensive and time-consuming in a production line integrate.

In general, the sintered parts produced by known processes were not homogeneous melting metal mixtures, especially if not homogeneous melting powder mixtures were sintered, often by the different Diffusion speed of the elements caused by porous or segregated areas, in which individual phases of the immiscible components are inhomogeneous crystallize. This disrupts the sintered structure and its mechanical-technological Properties sustainable. The properties of the powder sintered so produced Parts were therefore due to these interference areas, their occurrence was unpredictable, deteriorated and there were large differences in individually made Sintered parts on what, for example, results in an increased tendency to break materials along the inhomogeneous areas and a reduced elasticity showed. This is especially true when the sintered parts are in operation with changing Loads are used - e.g. as gear wheels, pump wheels etc. disadvantageous and the conventional procedures lead due to the high reject rate at high cost. After all, conventional hot sintering is too energy-intensive because of the high heating costs for the various heat treatment steps and the sintering itself occurs.

In contrast, it is an object of the invention to produce sintered parts which have a more homogeneous Have more uniform metal structure and less expensive to produce are.

The object is achieved by a sintered metal part according to patent claim 1. component of the metal powder starting mixture through a die under conditions, that avoid the appearance of a liquid phase in the powder, with training a sintered profile close to the final contour, solved.

durchgefürt,
wobei σ_y (T) die Fließspannung des Werkstoffs bei der vorgesehenen Drucksintertemperatur darstellt und D die relative Dichte des kaltisostatisch vorgepreßten Ausgangsproduktes angibt. Die relative Dichte ist der Quotient aus der absoluten Dichte des vorgepreßten Ausgangsproduktes ρ₀ und der Dichte des massiven Legierung ρ _B .Furthermore, the invention relates to a method for producing a near-net-shape sintered metal part as defined in claim 10. The continuous isostatic pressure sintering is carried out at a pressure according to the formula

durchgefürt,
where σ _y ( T ) represents the yield stress of the material at the intended pressure sintering temperature and D indicates the relative density of the cold isostatically pre-pressed starting product. The relative density is the quotient of the absolute density of the pre-pressed starting product ρ ₀ and the density of the solid alloy ρ _B.

The pressure sintering process is carried out by a die open on one side Sintered profile; if necessary, separating the sintered profile into sintered products, heat treating the Sintered products or the sintered profile and, if necessary, reworking them.

Advantageous further developments result from the dependent claims.

The typical continuous isostatic pressure sintering at temperatures up to about 70% of the melting point of the main constituent of the metal powder starting mixture is preferably carried out on a hydraulic extrusion press adapted to the process parameters - the usual extrusion which is carried out with homogeneously melting materials at temperatures near the melting point, due to excessive heating of the press strand leads to few dimensionally stable product strands, which then have to be further processed, for example by pressing, forging etc. The continuous isostatic pressure sinter used here at very high pressures according to the above formula additionally allows a temperature to be selected in which the Heating of the press strand due to friction is also taken into account. The actual preheating temperature T _{v of} the geCIPten starting material is determined according to the following formula: T v = T - Q B -Q A π 4 ρ 2 0 l ρ B c B

Therein T means the temperature for the selected material's yield strength, Q _B the amount of heat supplied to the starting material, Q _λ the amount of heat given off to the tool surface, I the active tool length and c _B the compression speed.

The process is characterized in that by the possible reduction of the Preheating temperature, the powder material is only slightly and briefly heated - in Contrary to the usual extrusion, in which a continuous and higher Heating of the pressed material is desired.

The fact that the invention is now relatively cold with the greatest avoidance the liquid phase is pressed at high pressures, surprisingly Metal powder to be sintered relatively cold continuously from a profile So far it was assumed that this was only possible with procedures that the Green bodies at temperatures in the order of 80-90% of the Sinter the melting point of the main ingredient for a long time. It was completely unexpected that this isostatic continuous pressure sintem at these relatively low Temperatures can take place, using fine starting powders with medium grain sizes from 50 to 150 µm additional from hot isostatic Press known compression mechanisms, such as the nabarro hening crawling can be used by transfers.

It was shown that this process has a superior sintered parts Grain structure, which is characterized by an extremely homogeneous distribution of the distinguish miscible components and therefore compared to sintered parts according to conventional processes and also the powder forging better elastic Have properties and ductility. This has been achieved as the strong temperature-dependent volume diffusion, which means coarsening and segregation individual phases, is almost completely suppressed.

According to the invention, a powder compact is preferred - by known pressing methods for powder compaction - without lubricants, lubricants or sintering aids - as Starting material used for continuous isostatic pressing. This Powder compact can already have an inhomogeneous material distribution - in particular if inhomogeneous sintered parts - i.e. composite parts - are to be produced.

Typical is e.g. an outer material layer made of another, chemically or physically more resistant material - if, for example, a certain corrosion behavior is required in an outer or inner layer - as with powder metallurgy Pipes or discs - have. Then in a press with a die Powder compact is isostatically pressed / sintered relatively cold and experiences through the shear forces a connection reaction at the grain boundaries of the Ingredients without a liquid phase that could cause segregation occurs. So a homogeneous sintered product with superior material properties be preserved.

In another embodiment variant, this can be formed continuously by the die created sintered product by controlled cooling, for example by spraying be cooled with water in such a way that a finely crystalline state Quenching is generated or that a defined heat treatment, e.g. at Aluminum alloys can undergo a T4 heat treatment. The cooled one The strand can be mechanically reworked. That's usually how it is continuously produced profile-like sintered product separated at product height - by sawing, water jet cutting, laser cutting or other, the Processes familiar to a person skilled in the art. These sections defined length of the continuously produced sintered product can then be used as such or after post-processing - such as surface coating or calibration - can be used. The sintered part cut to length in this way can also be subjected to heat treatment if required be subjected to change or the material structure remunerated. For this, the heat treatment must be designed so that no liquid Phases can arise.

A typical post-processing of the sintered product according to the invention Calibrate on a press to the dimensionally very tightly tolerated final form of the Product. Machining is "machining" usually not necessary.

In fact, at temperatures up to 70% of the melting point of the main ingredient sintered product already finished final contour - this means that the Post-treatment steps require little effort.

Because the process is allowed continuously, the manufacturing speed is the superior properties of the sintered parts are considerably higher, than previously with discontinuous uniaxial or isostatic pressing processes was possible to produce sintered parts. Because now isostatic Continuous pressure sintering can cause segregation phenomena that occur at higher sintering temperatures due to diffusion of the powder components in liquid Phases can occur can be avoided. It becomes a finer and more homogeneous Structure of the non-homogeneously melting mixtures obtained than in the classic hot isostatic pressing processes, in which considerable diffusion processes, especially volume diffusion in the final stage of compression lead to severe grain coarsening and crystallization phenomena Segregation can occur. The sintered parts produced according to the invention metal mixtures which do not melt homogeneously show better machinability and higher ductility and higher elongation than those with processes were manufactured according to the state of the art. This is shown in the following Manufacturing process in the better reworkability. For the application of such Components become the mechanical, technological characteristics of the sintered parts Elasticity, tensile strength, and elongation are influenced very favorably. For example, a pressureless sintered component made of an aluminum alloy with 13% by weight silicon an elongation at break of less than 0.5%, while a component made of the same Alloy produced by the method according to the invention, typical Has values in the elongation at break of 7 to 12%. That is through oppression the formation of the melting phase, so that the structure is not inhomogeneous can partially crystallize

In terms of process technology, it can be seen that the scattering of the material parameters according to the invention sintered parts produced is much less than that of hot sintered Parts of the same composition - that is, narrower material value limits than is the case with conventional HIP or warm sintering. By avoiding the occurrence of melting phases, immiscible Components, such as hard phases, are incorporated homogeneously distributed as well as materials that are very difficult or even impossible using classic sintering processes are not accessible. The material powder used is typically one Powder mixture of metals or their alloys and other materials, such as Hard parts, fibers, or wear carriers such as boron carbide, BN.

In this way, metal matrix composites can be produced (metal matrix composite), wherein the second component can be fibrous or particulate.

Short or long fibers or particles in proportions between 5- 30 vol% must be added. Short fibers or whiskers have a length that is west. smaller than 100 times the fiber diameter. Long, endless or continuous Fibers are those whose fiber length is greater than 100 times their diameter is. Fibers can serve to improve the strength of the sintered parts.

Particle reinforced materials can also do so getting produced. So those with SiC, boron carbide etc.

Due to the great homogeneity guaranteed by the process other, typically sintered alloys, such as. Ti alloys, in particular Ti / Nb alloys, TiAl, and TiAl Nb as well as Co-Ti-B Mg + SiC, boron carbide, Al2O3 or AlPb alloys with high heat storage capacity, the cannot be produced by melt metallurgy, are processed - i.e. sintered Composite materials are continuously manufactured or beryllium parts - Magnesium parts, etc. Typical compositions are, for example, aluminum with Si, Mg, Cu, Zn and possibly Fe e.g. with 10 - 40% Si, Mg 0-3%, Cu 0-5%, Zn and Fe 0-7% as well as other light metal alloys, such as those of magnesium, calcium, Beryllium etc. For aluminum sintered parts, AlSi, AlSiCu, Aluminum sintered materials: AlCuMg, with - Al Cu 3.8-4.4, Mg 0.5-1.0: AlMgSi with Al Si 0.4-0.8 Mg 0.5 - 1.0, AlZnMgCu 0.05 0.6 Cu 0.25-1.6 Mg 0.1 - 1.5 Zn 1.5 8.0, AlSi with more than about 7% Si, in particular, the invention relates Light metal sintered parts made of difficult to machine light metal alloys. There are It is also possible to produce hypereutectic alloys, the expert being able to further advantages are obvious from his specialist knowledge.

The advantages of the sintered parts produced according to the invention include: Finest and uniform grain sizes of wear carriers, clearly finer wear carrier distribution, no segregation and segregation, perfect homogeneous structure and extremely high dimensional accuracy - Warmsintem delays do not occur in the method according to the invention on and so very dimensionally accurate parts are produced. The former powder particles are no longer in the microscope according to the inventive method recognize, while the very fine grain structure of the structure also a elongated deformation, which shows the strength of the thus produced Sintered composite also improved mechanically. After all, they stand out sintered parts according to the invention by at least 150% higher elongation than those same material composition, by powder forging, sintering or cast are made.

The incorporation of wear carriers is typical. It can be the finest and most even Grain size of the wear carrier and a significantly finer distribution of the same compared to other methods. There are no segregations and Separations on and get it like a homogeneous structure. It is about an extremely simple process for the production of highly wear-resistant sintered metal components with extremely high dimensional accuracy. It can also be hypereutectic Alloys are made.

By the one-sint of fibers such as ceramic fibers, carbon fibers or Hard fiber fibers become: higher strengths - increase in tensile strength, increase of the yield point, increase in the elastic modulus, better heat resistance and creep resistance - a reduction in thermal Expansion coefficients obtained. As wear carriers or hard materials typical SiC particles, AIN, BN, TiB2, boron carbide, SiO2, WC: fibers, such as Carbon fibers, metal fibers, ceramic or glass fibers.

Suitable metal phases can be selected from aluminum, titanium, copper, Beryllium, magnesium, calcium, nickel, lithium, chromium, molybdenum, tungsten, bronzes, Niobium, lead, zinc and cobalt.

It is also possible to use continuous isostatic printing at temperatures up to about 70% of the melting point of the main component of the starting metal powder mixture under inert gas, such as an inert gas, nitrogen, carbon dioxide, to carry out if easily oxidizable materials, such as Mg, at temperatures up to 70% of the melting point of the main component are sintered.

The method can also be used to make a composition of several areas - So a sintered part with layers, rings, strips, etc. existing Composite (preferably powder compact) are sintered. This can be the case, for example be interesting if a hard layer is required as the outer material - e.g. for Cutting discs or the like - as an inner material but a cheaper, more ductile and more elastic material is desired. Until now, such parts had to be created separately and put together - the method according to the invention enables the production in one step by common continuous isostatic Pressing which then sinters several materials together. As well sintered parts with a hard cutting edge can be made from a different material composition than other areas.

Fig.1 eine schematische Darstellung der Verfahrensschritte im Vergleich mit herkömmlichern Sinterpressen von Aluminium-Siliziumlegierung;

Fig.2 eine mikroskopische Aufnahme von Festkörperschliffen aus der Legierung AlSi14% - hergestellt durch schmetzmetallurgischen Guß, nach dem erfindungsgemäßen Verfahren und nach dem herkömmlichen Sintern.

Fig. 3: Warmdruckversuch erfindungsgemäßer Teile

Fig. 4: Reibungszahlkurven von AlSi14% gegen 100 Cr6 - nach dem erfindungsgemäßen Verfahren und durch Sintern hergestellter Teile

Fig. 5: Sinterprodukte mit inhomogenen Abschnitten - schematisch dargesteltl.

Fig. 6: Schematischer Verfahrensablauf der Herstellung von Sinterprodukten mit inhomogenen Abschnitten

Further objectives, features and advantages result from the consideration of the following description and the claims together with the accompanying drawings. For a more complete understanding of the nature and objects of the invention, reference is made to the drawings in which:

1 shows a schematic representation of the process steps in comparison with conventional sintering presses of aluminum-silicon alloy;

2 shows a micrograph of solid-state sections made of the AlSi14% alloy - produced by metallurgical casting, according to the method according to the invention and after conventional sintering.

Fig. 3: Warm pressure test of parts according to the invention

Fig. 4: Friction coefficient curves of AlSi14% against 100 Cr6 - by the method according to the invention and parts produced by sintering

Fig. 5: Sintered products with inhomogeneous sections - shown schematically.

Fig. 6: Schematic process flow of the production of sintered products with inhomogeneous sections

Below is a preferred embodiment of the invention based on the manufacture of AlSi14% molded parts that were previously sintered warm, described - but this is by no means limited to this application - it can other sinterable metallic powder, such as Ti, Ta, Mg, Be, Cs, Cu can be processed.

In Fig. 1, the process flow according to the teaching of the invention is shown schematically. As shown, the process involves the preparation of a continuous sintered part by continuous isostatic pressing of a sinterable Material mixture without lubricant from a closed by a matrix Sinter form is created.

EXAMPLES Example 1: Production of AlSi14% sintered discs

The starting material - here a non-homogeneously melting mixture of aluminum powder with 13% by weight silicon powder (AlSi only melts in the range 5 - 7% homogeneous) is mixed intimately and then in a powder press for the production of Powder bolts not transferred to near-net shape. It gets cold there under high pressure pressed into a bolt-like green compact. The bolt-like green body turns into one Plant for continuous isostatic sintering - here an extrusion press - transferred and pressed through the die under sintering. The AlSi14 sintered part emerges the die at temperatures up to 70% of the melting point of the main component as a sintered continuous profile, the outer contour of which is close to the final shape. The continuously sintered profile is now mechanically according to the desired one Separate disc height and the material discs at 250 ° C for 30 min. heat treated. The sintered disks from the heat treatment are then calibrated in a calibration press at a force of 150 KN - i.e. the final, dimensionally very closely tolerated shape achieved. The sintered parts thus produced must be the same as conventional hot isostatically pressed parts Composition can no longer be decapsulated and have a calibration sufficient flow behavior. You can then do this without further post-processing are used as finished parts.

Example 2 (comparative test):

AlSi14% sintered parts were conventionally made by sintering by Aluminum powder with 14 wt .-% silicon Si a green body with pressing aid Hoechst Wax C pressed into a disc, this disc then in a heat treatment step .20 min at 410 ° C, then in the sintering furnace, 30 min with Sintered at 590 ° C and then heat treated again at 400 ° C for 240 min, manufactured as comparative products.

2 shows a comparison of the microstructures of the sintered aluminum disks AlSi14, produced with conventional warnsintering according to comparison test and produced by the isostatic pressing according to the invention, shown. Clear shows that the part produced according to the invention has a smaller grain size and has less segregated areas - that produced according to the invention Sintered part is more homogeneous in its properties.

3 shows the coefficient of friction curves of hot isostatically pressed AlSi14% Shaped bodies and continuously isostatically pressure-sintered according to the invention AlSi14% moldings shown against 100Cr6.

It can clearly be seen that the isostatic pressure-sintered material initially has a greater surface roughness, but this is rolled out quickly, so that the coefficient of friction in the later course of the friction test for the isostatically pressure-sintered material is lower than for the hot isostatically pressed product. This suggests a higher ductility of the isostatically pressure-sintered material. Material characteristic ranges for AISi14%
(at room temperature. unless otherwise stated) composition HIP AlSi14 erfindungsgem.AlSi14 Density g / cm3 2.65 2.7 Hardness HB 95-150 80-105 Tensile strength N / mm2 210-250 260-280 Yield point N / mm2 130-210 160-180 Strain % 0.5 3-12 E-module GPa <80 <80 Si grain size in µm 10-20 5-10 Si distribution in the structure rel. homogeneously voltst. homogeneously Surface pressure N / mm2 at 150 ° C 780 550

Table 1 clearly shows that the process according to the invention produced sintered bodies have less scatter - so more precisely are adjustable and therefore also deliver fewer missing parts. The sintered parts are more homogeneous and also more stretchy which improves elastic behavior like it in particular of mechanically stressed parts, such as sprockets against steel chains, Rotor and stator in a camshaft phasing system or oil pump parts, Bearing parts, pump wheels, etc. is required.

Finally, a hot pressure test with the isostatically pressure sintered part was carried out carried out - it was found that after aging the prepared AlSi14 samples over 500 and 1000h in air at 150 ° C practically no change in the Hot compressive strength, expansion or the yield strength occurs. (Table 1)

From Table 1 it can be seen that the strength of the isostatically continuously sintered AlSi14% part of the invention is significantly better than the hot isostatic pressed part.

5 shows the result of the production of sintered parts according to the invention with different ones Material areas shown - here in Fig. 5a a cut round Sintered part with a different outer layer - in FIG. 5b a two-layer angular sintered part; 5c shows a tubular sintered part with different layers; in Fig. 5d one strip-shaped distribution in sintered parts. Combining different sintered materials is thus possible simultaneously with the production of the sintered part - for example that Applying an outer layer reinforced with hard materials can be done by direct "Mitansinter" can be avoided as a separate process step - etc.

Example 3: Production of a sintered material disc with a hard outer material and easily machinable Lining

There is a powder mixture of alloyed AlMg1 powder and 2 wt .-% silicon powder for the mixture of the inner material and a powder mixture of aluminum powder with 40% SiC for the outer material intimately mixed and in a divided Mold that has a corresponding powder bolt with AlSi as the core and AlSiC as Coat made, pressed. This powder bolt is in a continuous isostatic Press inserted with a round die and under high pressure Temperatures up to 70% of the melting point of the main ingredient sintered round Sintered profile processed. The sintered profile thus produced is water jet cut into slices of 15 mm height. These discs are suitable as Pump wheels for oil and water pumps that have an easily machinable inner zone for have the drilling of holes, while the outer area with the SiC hard part phase is resistant to abrasion.

Claims (11)

1. Sinter metal part with a homogeneous distribution of non-homogeneously melting components, essentially comprising non-homogeneously melting non-ferrous metal powder mixtures, produceabel by:

   producing a non-sintered powder compact;

   continuous isostatic pressure sintering of the aforesaid powder compact to densities corresponding essentially to the density of a hot isostatically pressed solid of the same composition through a die with two open sides under conditions avoiding a fluid phase in the powder, at temperatures up to 70 % of the metal melting point preferably up to 60 % of the metal melting point to form a sinter profile having essentially a final contour.
2. Sinter metal part according to claim 1, further characterized by: mechanically working of the sinter profile, e.g. by cutting to product length or height when making sinter products.
3. Sinter metal part according to claim 1 or 2, characterized by heat treatment of the sinter raw product.
4. Sinter metal part according to claim 1 to 3, characterized by having at least about 150% higher elongation, preferably about 120% higher elongation than hot sintered sinter parts.
5. Sinter metal part according to claim 1, characterized therein, that the starting mixture of the metal powder to be sintered comprises essentially metal and metal alloys, further small amounts of alloying components, hard particles, wear resistant components, fibers.
6. Sinter metal part according to one of the preceding claims, characterized therein that at the at least one metal ist selected from Al, Ti, Cu, Mg, Be, Ni, Cr. Mo, W, Bronzes, Nb, Pb, Co. Zn.
7. Sinter metal part according to claim 6, characterized therein, that the continuos pressure sintering takes place under inert gas atmosphere, like a noble gas, nitrogen, carbon dioxide side.
8. Sinter metal part according to one of the preceding claims, characterized therein, that the compact serving as starting material of the continues cold isostatic pressing has areas of different material composition.
9. Sinter metal part according to claim 8, characterized by having defined areas of different composition, like layers, strips, round closed forms, polygons.
10. Process for the near net-shape manufacture of a sinter metal part according to one of the preceding claims, characterized by : making of a powder compact, continuous isostatic sintering thereof through a die having two open sides to obtain a sinter profile having densities corresponding essentially to the density of a solid part while avoiding the existence of a fluid phase, at a temperature up to 70 % of the metal melting point, optionally cutting the sinter profile into sinter products, optionally heat treatment of the sinter products or the sinter profile and optionally aftertreatment thereof.
11. Process according to claim 10, characterized therein that the aftertreatment comprises calibrating in a calibrating press.

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