WO2009053156A2

WO2009053156A2 - Metal powder mixture and the use thereof

Info

Publication number: WO2009053156A2
Application number: PCT/EP2008/062060
Authority: WO
Inventors: Roland Scholl; Ulf Waag
Original assignee: H.C. Starck Gmbh
Priority date: 2007-10-26
Filing date: 2008-09-11
Publication date: 2009-04-30
Also published as: WO2009053156A3; EP2205381A2; AU2008315429A1; KR20100085019A; JP2011501783A; CA2695764A1; RU2010120780A

Abstract

The invention relates to a metal powder mixture and particularly advantageous uses of such a metal powder mixture. It is common to use such metal powder mixtures made of metal and metal alloy powders in order to be able to produce active agents with a certain alloy composition. The aim of the invention is to provide a metal powder mixture, by means of which a material may be obtained that is formed from a metal alloy subsequent to a heat treatment in a cost-effective manner, in that the individual alloy- or metal-forming components (alloy and element powders) are distributed in a more homogenous manner. In a second aspect the invention seeks to reduce the maximum temperature required for the production of the material during heat treatment. The metal powder mixture is formed from at least two different powder fractions. A first metal is contained in the first powder fraction, wherein the beginning of a phase conversion takes place in conjunction with the further alloy components contained therein at a temperature that is at least 200 K lower than the beginning of the melting of a material to be formed from the metal powder mixture by means of heat treatment. The first powder fraction has a mean particle size of less than 45 μm. A second powder fraction is formed with a second metal, and has a mean particle size of less than 10 μm.

Description

Metal powder mixture and its use

The invention relates to a metal powder mixture and particularly advantageous uses of such a metal powder mixture.

It is customary to use metal powder mixtures of metal-metal alloy powders in order to be able to produce materials with a specific alloy composition.

For such metal powder mixtures, meta-alloying powders are also used which contain a selection of alloying elements and at least one metal which corresponds to the metal powder used. These are heterogeneous metal powder mixtures which consist of at least two chemically and / or morphologically different components, which represent only an intermediate stage on the way to a formation of a desired metal alloy or of a requirement-oriented material to be produced during a heat treatment.

Mixtures of metal powders are also used, which are formed as a result of a fines fraction naturally occurring during manufacture (e.g., 10% <

10 μm) and a remaining coarse fraction (for example 90% <45 μm and 10%> 10 μm). Such mixtures have the advantage that an improved filling density can be achieved due to the favorable space filling with adapted particle size distribution.

Metallic powders and metal alloy powders generally exhibit different melting and phase transformation behavior for metallurgical reasons. Therefore, there are temperatures in which solid and liquid (e.g., eutectic) phase components are coexistent, or phase changes in the solid phase

Change / increase of mass transfer, for example, as a result of an increased diffusion coefficients of an element, can be observed. Since the metal powder mixtures in question are generally not used for the production of alloyed materials by melt metallurgy, however, this plays a significant role in the final material production. Accordingly, in the heat treatment to be performed for the formation of the desired metal alloy or metal, the atomic and microscopic transport properties (eg, diffusion, rearrangement, grain growth) in the contact area of the powder particles form the basis for the densification and homogenization of the originally heterogeneous mixture Metal and metal alloy powder or a talcum powder. Heterogeneous in this sense, the difference in the particle size distribution (coarse, fine fraction) is understood, which causes in contrast to a (far) monomodal distribution of the particle size, the mass transport due to the high activity of the fine particle fraction.

The effects to be detected by caloric methods on the individual powders or of the powder mixture (phase transformations, melting and solidification ranges) and effects to be used correspondingly via the chemical composition of the alloy, e.g. chemically gra- ded between adjacent powder particles a central role in the alloying or metal formation and representation of the material.

The formation of the desired metal alloy in the form of a fine powder (d 50 <10 microns) for the powder metallurgy production of corresponding materials / components, it is technically and economically difficult and has little commercial importance due to the problems encountered in the processing of such powders. During powder metallurgical processing, due to the high temperatures required, the required heat treatment (sintering) results in losses of elemental components due to their high vapor pressure, which results in a change in the desired alloy composition and causes technical problems in the thermal processing plants due to material deposition.

Corresponding powder mixtures are known from DE 10331785 A1 and DE 10 2005 001198 A1.

These metal powder blends are made from at least two or even three different powders. The individual powders should be formed from different metal alloys and have a narrow particle size distribution. However, the metal-powder blends described in this prior art must be prepared in a very complex manner in order in particular to be able to achieve the desired very small particle size, which is difficult with some metal alloys, eg ductile.

Problems also arise from the fact that only a very limited extent in the ultimately produced material a homogeneous distribution of the individual metals with which the desired metal alloy is to be formed, can be achieved. This makes it difficult to form feinteiüge structures, such as those required for cellular materials. With the application of this concept, it is still difficult to achieve a homogeneous distribution of the alloy components. This in turn means that the material properties, in particular the tendency to corrosion and the mechanical strength worsen.

The production of metallic ultrafine powder (d50 <10 microns) from easy to reduce metal compounds is easily possible according to the prior art. Metal alloying powders, which are provided as part of a desired metal powder mixture, can be produced inexpensively by atomization (gas or water atomization) of an alloy melt or by conventional means by melting and comminuting, if particle sizes d 50 <45 μm are to be obtained. The production of coarser metal powder by Verdusung is also possible.

It is therefore the object of the invention to provide a metal powder mixture with which a material formed from a metal alloy can be obtained cost-effectively following a heat treatment by homogeneously distributing the individual alloying or metal-forming constituents (alloy and element powders). In a second aspect, the required for the production of the material during the heat treatment maximum temperature can be reduced.

According to the invention this object can be achieved with a metal powder mixture having the features of claim 1. Suitable uses of such a metal powder mixture are mentioned in claim 16. Advantageous embodiments and further developments of the invention can be achieved with features described in the subordinate claims.

The metal powder mixture according to the invention is formed from at least two different powder fractions. For the first powder fraction, a metal powder is used, which is formed of a metal alloy containing a first metal in which, in conjunction with the other alloying constituents of the first powder fraction contained in the metal alloy, the beginning of a phase transformation takes place at a temperature which is min - At least 200 K lower than the beginning of the melting of a material to be formed from the metal powder mixture by a heat treatment.

The first powder fraction has a mean particle size of d ₅₀ <45 μm.

The second powder fraction contained in the metal powder mixture according to the invention is preferably formed from a single second metal which is part of the metal alloy of the first powder fraction. However, it can also be formed from a mixture of at least two metals. This powder fraction has an average particle size d _so <10 microns. It should be understood for the second Puiverfraktion under a single metal such that at least almost entirely consists of the single metal or the mixture and in which only very small alloying additions or impurities, up to a maximum of 3 wt .-% are allowed. In a second powder fraction formed with a mixture of at least two metals, one of the metals should be present in a significantly higher proportion than another metal contained therein. For a metal, the proportion should be at least 75% by weight. This metal will be referred to below as the second metal.

The mean particle size of the first powder fraction should be at least three times greater than the mean particle size of the second powder fraction. The second powder fraction should be present at a level of at least 1% by weight.

For the first powder fraction, a binary metal alloy, ie a metal alloy formed from two components, can be used. Cheaper is However, it is to use for the first Puiverfraktion a metal alloy formed of at least three different metals.

In this case, at least one metal in the corresponding metal alloy should be present in the first powder fraction in a proportion which corresponds to twice the proportion as it should be contained in a material formed with the metal powder mixture subsequent to a heat treatment. The proportion of the second metal in the metal alloy of the material produced after the heat treatment should be at least 10% by weight.

In the metal alloy of the first powder fraction, there may be used a metal whose phase transformation occurs at the lower temperature already mentioned, which is selected from among aluminum, magnesium, zinc, tin and copper. These metals, in conjunction with other alloying constituents of the first powder fraction, have the property of lowering the melting temperatures of the metal alloy or of achieving partial phase transformations, including molten states, in partial volumes.

The metal used for the second powder fraction may be powdered iron, nickel, cobalt and copper. In this case, one of these metals may be contained in the second Puiverfraktion alone: The second powder fraction may also be formed with at least two of these metals, as a powder mixture.

One possibility for the production of a metal compound mixture according to the invention consists in using for the first powder fraction a metal alloy which has a general composition M1 M2CrR. In this case, the metal M1 is selected from aluminum, magnesium, tin, zinc and copper. The metal M2 is selected from iron, Nicke! and cobalt. R is selected from yttrium, molybdenum, tungsten, vanadium, manganese, a rare earth metafl, a lanthanide, rhenium, hafnium, tantalum, niobium, carbon, boron, phosphorus and silicon.

In such a metal alloy, Metail M1 can be used in a proportion of 1-70% by weight, metal M2 in a proportion of 1-60% by weight, Cr in a proportion of 0-80

Wt .-% and R in a proportion of 0 - 70 wt .-% be contained. It is also advantageous to provide aluminum in the metal alloy for the first powder fraction with a proportion of at least 15% by weight. Thus, in a material obtained after a heat treatment to be carried out, which has been produced from the metal powder mixture according to the invention, a proportion of aluminum of at least 3 wt.%, Preferably at least 15 wt.

If a powder, which is formed with an alloy containing iron, chromium and aluminum, with a second powder fraction, which is formed from powdered iron, is used with a metal powder mixture according to the invention in a first powder fraction, for example, a material can be used a heat treatment are prepared, which in addition to predominantly iron, chromium in a proportion of 15 to 30 wt.% and an aluminum content of 5 to 20 wt .-%, are produced.

In a metal powder mixture according to the invention, a second powder fraction should have at least 10% by weight, preferably at least 30% by weight and more preferably at least 50% by weight of the total mass.

In the powder from which the first powder fraction is formed, the metal which, in combination with the other alloying constituents, should reach a phase transition temperature at least 200 K lower than the temperature at which the start of the melting of the material to be produced occurs (transition temperature), should be at least 10% by weight.

With the metal powder mixture according to the invention, after a heat treatment, it is possible to produce materials in which all the metal components are distributed significantly more homogeneously in the material than is the case with conventionally used ones. In this case, the heat treatment can be carried out at temperatures which are at least 10 K below that required by the prior art.

Here, the inventive combination of the two selected powder fractions selected and also the use of a clear affects finer powder for a second powder fraction, with the in question smaller particle sizes, as this is the case for the first powder fraction, advantageous.

In the heat treatment can be significantly enhanced with the invention

Mass transport in consequence of diffusion, rearrangement and grain growth can be achieved. As a result, in addition to the homogeneous distribution of the individual metal alloy components in the material volume, it is also possible to achieve a reduced maximum temperature required for a heat treatment during the production of the material from the metal powder mixture.

The heat treatment can be carried out using known sintering technologies. However, they should be suitable for the desired sintering atmospheres and temperatures.

With a metal powder mixture according to the invention, an improved sintering behavior of a slip-based or press-formed shaped body can be achieved.

By an improved shrinkage behavior can with the inventive

Metalipulvermischung be achieved an improvement in properties of a component made therefrom or a corresponding protective layer applied to a component. It can also be achieved an improved corrosion resistance. Thus, for example, if aluminum is present in the metal powder mixture according to the invention, improved corrosion protection can be achieved by the targeted formation of a corresponding oxide layer on the surface, which usually reaches a layer thickness of 0.1-10 μm.

A material produced with the metal powder mixture according to the invention may have an improved pitting potential in comparison to high-alloyed corrosion-resistant steels.

In a further alternative embodiment of the invention may be contained in the metal powder mixture, a further fraction which is formed of a metal. This may preferably be pure iron, in which contaminants and trace elements, if any, should be present at less than 3% by mass. The further fraction may also be pulverulent and significantly coarse-grained than the two powder fractions already described. Thus, the mean particle size can be larger than 150 μm and also considerably higher. The other faction can also be alone with

Fibers be formed or contain fibers in addition to particles.

The fibers may have diameters in the range of 1 mm and lengths of several millimeters.

In the event that a further fraction is contained in the metal powder mixture according to the invention, the proportion of second powder fraction may be kept very small and less than 5% by mass.

Formation of layers on surfaces of devices may be accomplished by techniques known in the art, such as those disclosed in U.S. Pat. thermal spraying or build-up welding done.

It is also possible to produce components or parts thereof in the so-called rapid prototyping. It is advisable, after the production, additionally to carry out a heat treatment in order to achieve an even greater density and homogeneity.

In a material produced with a Metallpuivermischung invention according to the invention, with a metal alloy NiCrA! is formed, in contrast to the solutions known in the prior art, a vaporization of chromium can be avoided, or at least significantly reduced, since the temperatures during the heat treatment are lower. This applies in particular to the comparison with metal-powder mixtures which already have the respective alloy composition of the material to be produced before the heat-treatment.

The invention will be explained in more detail by way of example in the following.

Showing: FIG. 1 part of a shell of a hollow sphere made of an FeCrAl alloy, with five points on which a chemical analysis of the elements Fe, Cr and At was carried out;

Figure 2 Part of a hollow ball! FeCrAI alloy with lower shell porosity;

FIG. 3 shows a diagram which illustrates the mass increase during the removal of FeC-rAI hollow spheres and FIG

FIG. 4 shows a cross section with chemical point analyzes of an FeCrAl

Fiber.

example 1

In this case, for the production of metallic hollow spheres of a material Ni-20Cr-1 OAl-O ₁ OSHf a first powder fraction having a mean particle size d50 of 25 microns and a composition of the alloy Nt-SOCr-25AI-0.125Hf and a second powder fraction with a mean particle size d50 of 5 μm predominantly pitch! (99.9 wt .-%) can be used.

The proportion of the first Pulverfraktϊon is 40 wt .-% and the proportion of the second powder fraction is 60 wt .-%.

100 g of this Metaüpulvermischung are dispersed with 100 g of water, 3 g of polyvinyl alcohol and 0.5 g Dolapix with a disperser over a period of 1 h at a speed of 3000 rev / min to a homogeneous distribution of the particles in a suspension to reach. The suspension thus obtained does not sediment during intensive stirring.

The resulting low-viscosity metal powder suspension is applied as a coating on spherical particles of polystyrene and dried. After reaching a layer thickness of 100 microns, the coating on the polystyrene particles, the heat treatment can be performed. In this case, working in an atmosphere with flowing hydrogen (30 i / min). First, the organic components are thermally decomposed, being heated at a heating rate of 1 k / min up to a temperature of 600 ⁰ C. Thereafter, the temperature is increased to 1280 ⁰ C while maintaining a heating rate of 5 K / min in the hydrogen atmosphere. After a holding time of 2 h at the maximum temperature, the mixture was cooled to room temperature at 5 K / min.

The metallic hollow spheres produced in this way had an outer diameter of about 2 mm and a wall thickness of about 70 μm. The bulk density is included

450 g / l. The shell material of the metallic hollow spheres, which was produced with this Betspiel a metal powder mixture according to the invention, is formed in addition to nickel with 20 wt .-% chromium, 10 wt .-% aluminum and 0.05 wt .-% hafnium.

In a parallel experimental example, an Ni-20Cr-10-Al-0.05Hf alloy is processed by inert gas atomization of a metal alloy into a fine alloy powder having a particle size d ₅₀ of 10 μm. From this powder, in an analogous procedure, as in the example according to the invention, the steps of suspension production, coating, drying of polystyrene particles and heat treatment are carried out. The metallic hollow spheres produced in this way achieved significantly lower fracture strengths, measured on the basis of the deformation up to breakage, than those produced with the metal powder mixture according to the invention.

Step Example! 2

A metal powder mixture with a first powder fraction, which had a mean particle size d ₅₀ of 15 μm, and a second powder fraction, which had a mean particle size d ₅₀ of 3 μm, was used. For the first

The powder fraction was selected to be an Fe-49Cr-23Al alloy and the second powder fraction was formed from predominantly iron (99.5 mass%).

As in Example 1, 43.5% of the first and 56.5% and the second powder fraction were processed. In FIGS. 1 and 2, with a section through the shell of a hollow sphere produced in this way, the homogeneity of the shell material is shown. recognizable. The shell material made with the metal powder mixture of this example was an Fe-23Cr-10Al alloy.

The sintering in a hydrogen atmosphere was carried out at 1240 ⁰ C over a period of 2 hours,

After sintering, a fill density (FD) according to ASTM B212 / 417 of about 0.4 g / cm ³ , a carbon content of 70 ppm and an oxygen content of 0.24% could be achieved in the hollow beads produced in this way. With the table 1 shown in Figure 3, the oxidation properties of the material thus prepared by mass increase after 700 hours at holding temperatures in the range 900 ⁰ C to 1000 ⁰ C without and with prior outsourcing for 2 hours in air at 1100 ° C are illustrated.

Example 3

From a powdered powder mixture in which a first powder fraction having an average particle size d ₅₀ of 8 μm of an Fe-49Cr-23Al alloy having a mass of 2 kg, a second powder fraction having a mean particle size d ₅₀ of 3 μm and a mass of 0, 1 kg of pure iron and 3 kg of another fraction consisting of metallic fibers whose average outside diameter was 150 μm and whose mean length was 5 mm were produced metallic fibers of composition Fe-20-Cr-9AI.

In this case, the metallic fibers, which were provided by milling of a block of pure iron {99.9% iron), circulated in a 5 liter Eiche mixer at a speed of 20 rev / min. The mixing vessel was by blowing with heated air from the outside at a temperature of 50 ⁰ C ± 10 K.

From the 2 kg of the first and the 0.1 kg of the second powder fraction and 2 kg of acetone and 0.2 kg Polyvenylalkoho! (PVA) prepared a dispersion. This dispersion was sprayed centrally into the mixer while circulating the fibers until all of the powder had been applied to the surfaces of the fibers. Here, the required safety regulations were met because of the organic combustible components. The thus-coated fibers were placed in a crucible consisting of Al ₂ O ₃ and subjected to a heat treatment at 1,240 ^° C. in a hydrogen atmosphere over a period of 2 hours. PVA was expelled 5, as explained in Example 1.

FIG. 4 shows a transverse section through a fiber produced in this way. By means of chemical point analyzes, the composition of the fiber material after the heat treatment could be determined to be a homogeneous Fe-19Cr-9Al alloy.

Example 4

In this case, a metal powder mixture having a first powder fraction, the 15. an average particle size d ₅₀ of 4.4 microns and a second powder fraction having an average particle size d _5Q of 3.0 microns, was used. For the first powder fraction was a _. Fe-49Cr-23AI alloy selected and the second powder fraction formed with predominantly iron (99.5 mass%).

20 There were 100 g of this metal powder mixture (45 g first powder fraction and

55 g second powder fraction) with 100 g water, 3 g polyvinyl alcohol and 0.5 g Dolapix with a disperser over a period of 2 h at a speed of 3000 rev / min dispersed to achieve a homogeneous distribution of the particles in the suspension.

25

After the so-called Schwartzwalder method, as it u.a. in US 3,090,094, an open-cell porous metal foam is produced. The result is a reticulated polyurethane foam cut into individual pieces with a porosity of 80 ppi and the dimensions

30 40 * 40 * 10 mm of the pieces coated with the metal powder binder suspension. The polymeric foam structure should be coated as completely as possible with the suspension. The coated pieces were then dried for a period of 2 hours at a temperature of 60 ⁰ C.

Subsequently, a heat treatment was performed in a hydrogen atmosphere. This was done with a heating rate of 1 K / min to a Tempe- temperature of 600 ° C heated to remove the organic components. Thereafter, while maintaining a heating rate of 5 K / min, heating was continued up to a temperature of 1280 ° C. and this temperature was maintained for a period of 2 h. When cooling down to room temperature, a rate of 5 K / min was also observed.

After the heat treatment and cooling were carried out, an open-cell foam structure having a physical density of 0.8 g / cm ^{3 was} obtained in which the ridges of the porous structure were formed after the heat treatment with a Fe23Cr1OAl alloy.

Claims

claims

1. A metal powder mixture formed with at least two different powder fractions, characterized in that a first powder fraction is formed with a metal alloy in which a first metal is contained, in which, in conjunction with the other contained alloy constituents of the first powder fraction, the beginning of a phase transformation at a temperature which is at least 200 K lower than the beginning of the melting of a material to be formed from the metal powder mixture by a heat treatment, and

while the first powder fraction has an average particle size less than 45 microns, and

the second powder fraction is formed with a second metal or a mixture of at least two metals and has an average particle size smaller than 10 μm; in which

the second metal or mixture is contained in the second powder fraction of at least 97% by mass.

2. Metal powder mixture according to claim 1, characterized in that a metal alloy is used for the first powder fraction, which is formed from at least three metals.

3. Metal powder mixture according to claim 1 or 2, characterized in that in the metal alloy of the first powder fraction at least one metal is contained in a proportion which corresponds to at least 1.5 times the proportion, as in one with the metal powder mixture in the Connection to a material formed by heat treatment should be included.

4. Metal powder mixture according to one of the preceding claims, characterized in that for the second powder fraction one or

, several metal (s) are used, which is / are selected. Iron, nickel and cobalt.

5. Metal powder mixture according to one of the preceding claims, characterized in that for the first powder fraction, a first metal which is selected from aluminum, magnesium, zinc, tin and

Copper, is used.

6. Metal powder mixture according to one of the preceding claims, characterized in that in the first powder fraction, an additional element which is selected from boron, silicon and carbon is contained.

7. Metal powder mixture according to one of the preceding claims, characterized in that the first powder fraction is formed with a binary alloy of first and second metal; being the first metai! is selected from aluminum, magnesium, tin, zinc, and copper and the second metal is selected from iron, Nicke! and Cobaite.

8. Metal powder mixture according to one of the preceding claims, characterized in that in the first powder fraction additionally as further (s) alloying element (s) at least one. another element selected from chromium, yttrium, a rare earth element, a

Lanthanide, molybdenum, tungsten, rhenium, hafnium, tantalum, niobium, vanadium, manganese, carbon, boron, phosphorus and silicon.

9. Metällpulvermischung according to claim 7 or 8, marked thereby, that the first metal in a proportion of 1 to 70% by mass and the second metal in a proportion of 1 to 60% by mass are included.

10. Metal powder mixture according to claim 9, characterized in that chromium are present in a proportion of 0 to 80% by mass and a further alloying element in a proportion of 0 to 70% by mass.

11. Metal powder mixture according to one of the preceding claims, characterized in that forming in the first powder fraction Metailiegierung, as the first metal aluminum with a share of at least 15 Wlasse-% is included.

12. Metalipulvermischung according to any one of the preceding claims, characterized in that the average particle size of the first powder fraction is at least three times greater than the average particle size of the second powder fraction.

13. Metal powder mixture according to one of the preceding claims, characterized in that the second powder fraction is contained in a proportion of at least 1% by mass.

14. MetaHpulvermischung according to any one of the preceding claims, characterized in that an additional fraction is contained, which is formed with particles whose average particle size is greater than 150 microns and / or which is formed with fibers of a metal.

15. Metal powder mixture according to claim 14, characterized in that the further fraction of iron is formed as metal.

16. Use of a metal powder mixture according to any one of claims 1 to 15, for the production of sintered components, as a material for the order on Bauteiioberflächen or open-celled porous structures.