DE102007052198B3 - Metal powder mixture for sintering, comprises first fraction containing metal alloy and components initiating phase conversion well below melting point - Google Patents

Abstract

The first powder fraction is formed by a metal alloy. This contains a first metal, which, in conjunction with other alloying components, initiates phase conversion at a temperature at least 200 K lower than incipient melting of the material to be formed from the metal powder mixture, during a thermal treatment. The first powder fraction mean particle size is less than 45 mu m. The second powder fraction is a second metal or mixture of metals. Its mean particle size is less than 10 mu m. 97 wt% of the second metal (or mixture) is contained in the second powder fraction. Three or more metals are contained in the first powder fraction. The proportion of at least one metal in the alloy of the first powder fraction is at least 1.5 times that proportion which should be contained in the material formed from the metal powder mixture, on conclusion of thermal treatment. For the second powder fraction, one or more of the following metals is selected from: iron, nickel and cobalt. The metal of the first powder fraction is Al, Mg, Zn, Sn or Cu. The first powder fraction contains an additional element selected from boron, silicon and carbon. The first powder fraction is a binary alloy of first and second metals; the first is: Al, Mg, Sn, Zn, or Cu; the second is iron, nickel or cobalt. One or more additional alloying elements in the first powder fraction are selected from Cr, Yb, a rare earth metal, a lanthanide, Mb, T, Re, Hf, Ta, Ni, V, Mn, C, B, P, and Si. 1-80 wt% of the first metal and 1-70 wt% of the second metal are contained. 0-80 wt% Cr is included, with 0-70 wt% of a further alloying element. The first powder fraction contains Al at a proportion of 15 wt%. The mean particle size of the first powder fraction is at least three times greater than that of the second powder fraction. The second powder fraction forms a proportion of 1 wt% or more. In a further fraction, the mean particle size exceeds 150 mu m and/or metal fibers are contained. In this fraction, the metal is iron.

Description

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

It is common, To use metal powder mixtures of metal-metal alloy powders, to produce materials with a specific alloy composition to be able to.

there be for such metal powder mixtures also used metal alloy powder, the contain a selection of alloying elements and at least one metal, which corresponds to the metal powder used. These are to heterogeneous metal powder mixtures consisting of at least two chemical and / or morphologically different components that only an intermediate stage on the way to training a desired Metal alloy or a requirement to be produced Material in a heat treatment represent.

It Mixtures of metal powders are also used in succession one in the production in natural Manner of occurring fine fraction (eg 10% <10 μm) and a remaining coarse fraction (eg 90% <45 μm and 10%> 10 μm). Such mixtures have the advantage that an improved bulk density due to the favorable space filling achievable with adapted particle size distribution is.

there show metal powder and metal alloy powder metallurgical establish usually a different melting and phase transformation behavior. Therefore, there are temperatures or temperature ranges where fixed and liquid (eg, eutectic) phase components are present simultaneously or by phase transformations in the solid phase, a change / increase in the Mass transport, z. B. as a result of an increased diffusion coefficient of an element, can be observed. Since those in question Metal powder blends usually not for the melt metallurgical Production of alloyed materials used plays but this for the final material production a significant role.

at the heat treatment, the for the training of the desired Metal alloy or a desired one To perform metal is, therefore, form in the contact area of the powder particles acting atomic and microscopic transport properties (eg. As diffusion, rearrangement, grain growth) the basis for the compression and homogenization of the original heterogeneous mixture of metal and Metalllegie tion powder or a Metal powder. Under heterogeneous in this sense, the difference in the particle size distribution (Coarse, fine fraction), which in contrast to a (broad) monomodal distribution of particle size, mass transport as a result of high activity causes the fine particle fraction. They play over caloric Methods to be detected on the individual powders or the powder mixture Effects (phase transformations, melting and solidification areas) and accordingly over the chemical composition of the alloy to be used, z. B. chemically graded between adjacent powder particles one central role in the alloy or metal formation and representation of the Material.

The Formation of the desired Metal alloy in the form of a fine powder (d50 <10 μm) for powder metallurgy Production of appropriate materials / components is technical and economically difficult and has due to the problems encountered in the processing of such powders only a small commercial Importance. While the powder metallurgical processing occur in the required heat treatment (Sintering) as a result of high required temperatures losses of elemental constituents due to their high vapor pressure on, that's about a change lead to the desired alloy composition and due to material deposition cause technical problems in the thermal processing plants.

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

These Metal powder blends will consist of at least two or even three produced different powders. Here are the individual Powder may be formed from different metal alloys and a narrow particle size distribution exhibit.

The Metal powder blends described in this prior art have to but very expensive in particular to achieve the desired very small particle size to be able to what with some metal alloys, eg. B. ductile is difficult.

Problems also arise from the fact that in the material ultimately produced only to a very limited extent 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 finely divided structures, as required for example 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, especially the tendency to corrosion and the mechanical strength deteriorate.

The Production of metallic fine powders (d50 <10 μm) from easy-to-reduce metal compounds is according to the state the technology easily possible. Metal alloy powder, which is part of a desired Metal powder mixture are provided, can be by atomization (gas or water atomization) an alloy melt or by conventional means by melting and then mincing cost-effectively produced when particle sizes d50 <45 microns should be. The production of coarser metal powder by atomization is also possible.

It It is therefore an object of the invention to provide a metal powder mixture available put, with the cost-effective following a heat treatment a material formed from a metal alloy can be obtained can by removing the individual alloying or metal-forming components (Alloy and element powders) are distributed more homogeneously. In one second aspect is intended for the preparation of the material in the heat treatment required maximum temperature can be reduced.

According to the invention this Task with a metal powder mixture, which has the characteristics of the claim 1, solved become. Suitable uses of such a metal powder mixture are mentioned in claim 16.

advantageous Embodiments and developments of the invention can with in subordinate claims designated characteristics can be achieved.

The Inventive metal powder mixture is composed of at least two different powder fractions educated. For The first powder fraction is a metal powder used that a metal alloy is formed in which contain a first metal is where in conjunction with the others in the metal alloy contained alloy components of the first powder fraction of Beginning of a phase transformation takes place at a temperature, the at least 200K lower than the beginning of melting one from the metal powder mixture to be formed by a heat treatment Material is.

The first powder fraction has an average 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 a constituent 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 ₅₀ <10 μm. It should be understood for the second powder fraction 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 larger than the mean particle size of the second Be powder fraction. The second powder fraction should be with a Be contained at least 1% by mass.

For the first Powder fraction may be a binary metal alloy, So a metal alloy formed from two components used become. better it is, however, for the first powder fraction to use a metal alloy, the at least three different metals is formed.

there should in the first powder fraction at least one metal in the corresponding Metal alloy containing a proportion of twice that the proportion corresponds, as in one with the metal powder mixture following a heat treatment should be included formed material. The share 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 may be a metal whose Phase transformation at the lower temperature already mentioned be used, which is selected from aluminum, magnesium, Zinc, tin and copper. These metals have in conjunction with others Alloy components of the first powder fraction, the property Lower melting temperatures of the metal alloy or in partial volumes Phase transformations, including molten conditions to reach.

When Metal for the second powder fraction may be powdered iron, nickel, cobalt and copper are used. It can be one of these metals in the second powder fraction alone: the second powder fraction but can also with at least two of these metals, as a powder mixture be formed.

A possibility for the Production of a Metal Powder Mixture According to the Invention is in, for the first powder fraction to use a metal alloy, the one general composition has M1M2CrR. Here is the metal M1 selected made of aluminum, magnesium, tin, zinc and copper. The metal M2 is selected made of iron, nickel and cobalt. R is selected from yttrium, molybdenum, tungsten, Vanadium, manganese, a rare earth element, a lanthanide, rhenium, Hafnium, tantalum, niobium, carbon, boron, phosphorus and silicon.

In of such a metal alloy, metal M1 may contain 1-70% by weight, Metal M2 with a share of 1-60 Wt .-%, Cr in a proportion of 0-80 wt .-% and R with a Proportion of 0-70% by weight be included.

Advantageous it is also in the metal alloy for the first powder fraction aluminum with a share of at least 15% by weight. So can be done in one after one heat treatment obtained material which has been produced from the metal powder mixture according to the invention is a proportion of aluminum of at least 3 wt .-%, preferably be maintained at least 15 wt .-%.

Becomes with a metal powder mixture according to the invention in a first powder fraction, a powder containing an alloy formed, which contains iron, chromium and aluminum, with a second powder fraction formed from powdered iron, used, for example, a material after a heat treatment produced in addition to predominantly Iron, chromium in a proportion of 15 to 30 wt .-% and a proportion of aluminum from 5 to 20% by weight.

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

in the Powder, from which the first powder fraction is formed, should that Metal in combination with the other alloy components a at least 200 K lower phase transition temperature reached, as the temperature at the beginning of the melting of the to be produced material (transition temperature), should a minimum proportion of 10 wt .-% may be included.

With the metal powder mixture according to the invention can after a heat treatment Materials are produced in which all metal components clearly distributed more homogeneously in the volume of material than in conventionally used the case is. This can be the heat treatment performed at temperatures which are at least 10K below that of the prior art required.

in this connection affects the combination of the invention the selected one two powder fractions and also the use of a much finer powder for a second powder fraction, with the much smaller particle sizes in question than this for The first powder fraction of the case is advantageous.

at the heat treatment can with the invention a significantly increased mass transfer in a row Diffusion, rearrangement and grain growth can be achieved. Thereby In addition to the homogeneous distribution of the individual metal alloy components in the material volume also a reduced maximum temperature, the for one Heat treatment in the production of the material from the metal powder mixture is required to be achieved.

The heat treatment can be done using known sintering technologies. they should however for the desired sintering atmospheres and temperatures are suitable.

With a metal powder mixture according to the invention can an improved sintering behavior of a slip-based or obtained by pressing molded body can be achieved.

An improved shrinkage behavior can be used to achieve an improvement in the properties of a component produced therefrom or a corresponding protective layer applied to a component with the metal powder mixture according to the invention. It can also be an improved ^Cor rosionsbeständigkeit be achieved. Thus, for example, if aluminum is present in the metal powder mixture according to the invention, an improved corrosion protection can be achieved by the targeted formation of a corresponding oxide layer on the surface, which usually achieves a layer thickness of 0.1-10 μm.

One with the metal powder mixture according to the invention produced material can have an improved pitting potential compared to high-alloyed corrosion-resistant steels.

In a further alternative embodiment of the invention, the metal powder mixture may also contain a further fraction which is formed from a metal. This may preferably be pure iron in which impurities and trace elements, if any, should be present at less than 3% by weight. The further fraction can likewise be pulverulent and clearly coarse more granular than the already described two powder fractions. Thus, the mean particle size can be larger than 150 μm and also considerably higher. The further fraction can also be formed alone with fibers or contain fibers in addition to particles.

The Fibers can Diameter in the range of 1 mm and lengths of several millimeters exhibit.

in the Case that in the metal powder mixture according to the invention another fraction is included, the proportion of second Powder fraction be kept very small and below 5% by mass lie.

A Formation of layers on surfaces of components can be done with known technologies, such. B. thermal spraying or Cladding respectively.

It can also components or parts thereof in so-called rapid prototyping getting produced. It makes sense, following the Manufacturing, in addition a heat treatment perform, an even greater density and achieve homogeneity to be able to.

at one with a metal powder mixture according to the invention produced material, which is formed with a metal alloy NiCrAl is, in contrast to those known in the art solutions also avoids evaporation of chrome, but at least clearly can be reduced, since the temperatures during the heat treatment are lower. This concerns in particular the comparison with metal powder mixtures, the before the heat treatment already the respective alloy composition of the product to be produced Material have.

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

there demonstrate:

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 Al was carried out;

2 Part of a hollow sphere of a FeCrAl alloy with lower porosity of the shell;

3 a diagram illustrating the mass increase in the outsourcing of FeCrAl hollow spheres and

4 a cross-section with chemical point analyzes of a FeCrAl fiber.

example 1

there should for the production of metallic hollow spheres from a material Ni-20Cr-10Al-0.05Hf a first powder fraction with a mean particle size d50 of 25 μm and a composition of the alloy Ni-50Cr-25Al-0,125Hf and a second powder fraction with a mean particle size d50 of 5 μm predominantly Nickel (99.9 wt .-%) can be used.

Of the Proportion of the first powder fraction is 40 wt .-% and the proportion of the second powder fraction is at 60% by weight.

100 g of this metal powder mixture are mixed with 100 g of water, 3 g of polyvinyl alcohol and 0.5 g of Dolapix with a disperser over a period of 1 h dispersed at a speed of 3000 rpm to give a homogeneous To achieve distribution of the particles in a suspension. The way suspension obtained does not sediment during intensive stirring.

The obtained low-viscosity metal powder suspension is used as a coating on spherical Particles of polystyrene applied and dried. After reaching a layer thickness of 100 μm, The coating on the polystyrene particles can be the heat treatment carried out become.

in this connection will be in an atmosphere with pouring Hydrogen (30 l / min) worked. First, the organic Thermally decomposed components, wherein at a heating rate of 1 k / min is heated to a temperature of 600 ° C. Thereafter, the temperature up to 1280 ° C elevated while maintaining a heating rate of 5 K / min in the hydrogen atmosphere. After a holding time of 2 h at the maximum temperature took place a cool down to room temperature with 5 K / min.

The thus produced metallic hollow balls had an outer diameter of about 2 mm and a wall thickness of about 70 microns. The bulk density is at 450 g / l. The shell material of the metallic hollow spheres, the with this example of a metal powder mixture according to the invention is nickel with 20 wt .-% chromium, 10 wt .-% aluminum and 0.05 wt .-% hafnium formed.

In a parallel experimental example, a 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 are in an analogous procedure, as in the example of the Invention, the steps of suspension preparation, coating, drying of polystyrene particles and heat treatment performed. The metallic hollow spheres produced in this way achieved significantly lower breaking strengths, measured on the basis of the deformation until breakage, than those produced with the metal powder mixture according to the invention.

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 powder fraction, an Fe-49Cr-23Al alloy was selected and the second powder fraction was formed of 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 1 and 2 is with cut through the shell of a hollow ball thus produced, the homogeneity of the shell material 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 ° C over a Period of 2 hours.

After sintering, a filling density (FD) 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 spheres produced in this way. With the in 3 Table 1, the oxidation properties of the thus prepared material can be illustrated by the mass increase after 700 hours at holding temperatures in the range 900 ° C to 1000 ° C without and with prior outsourcing for 2 hours in air at 1100 ° C.

Example 3

From a metal 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 an average 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 outer diameter was 150 μm and whose mean length was 5 mm were produced metallic fibers of composition Fe-20-Cr-9Al.

there The metallic fibers were made by milling from a block of purest Iron (99.9% iron) has been provided in a 5 liter Eirich mixer at a speed of 20 rev / min circulated. Of the mixing tank was heated by blowing with Air from the outside at a temperature of 50 ° C ± 10 K. held.

Out the 2 kg of the first and the 0.1 kg of the second powder fraction as well 2 kg acetone and 0.2 kg polyvinyl alcohol (PVA) prepared a dispersion. These Dispersion was during of the circulation the fibers are sprayed centrally into the mixer until the entire powder mass on the surfaces the fibers has been applied. Here were the required Safety regulations due to the organic combustible components respected.

The thus-coated fibers were placed in a crucible made of Al ₂ O ₃ and subjected to a heat treatment at 1240 ° C in a hydrogen atmosphere over a period of 2 hours. PVA was expelled, as explained in Example 1.

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

Claims (16)

Metal powder mixture which is 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 constituent alloying constituents of the first powder fraction, the beginning of a phase transformation at a temperature 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 the first powder fraction has an average particle size less than 45 microns and the second powder fraction with a second metal or a mixture of at least two Metals is formed and has an average particle size smaller than 10 microns; wherein the second metal or mixture in the second powder fraction is contained at least 97% by mass. Metal powder mixture according to claim 1, characterized in that that for the first powder fraction is a metal alloy used, the is formed of at least three metals. Metal powder mixture according to claim 1 or 2, characterized in that in the Metalllegie tion of the first powder fraction is at least one metal in a proportion corresponding to at least 1.5 times the proportion, as it should be included in a formed with the metal powder mixture following a heat treatment material. Metal powder mixture according to one of the preceding Claims, characterized in that for the second powder fraction used one or more metal (s) are, the selected is / are made of iron, nickel and cobalt. Metal powder mixture according to one of the preceding Claims, characterized in that for the first powder fraction is a first metal that is selected made of aluminum, magnesium, zinc, tin and copper. Metal powder mixture according to one of the preceding Claims, characterized in that in the first powder fraction an additional Element selected is made of boron, silicon and carbon is included. Metal powder mixture according to one of the preceding Claims, characterized in that the first powder fraction with a binary Alloy is formed of first and second metal; the first metal selected is made of aluminum, magnesium, tin, zinc, and copper and the second metal selected is made of iron, nickel and cobalt. Metal powder mixture according to one of the preceding Claims, characterized in that in the first powder fraction additionally as additional alloying element (s) at least one further element, that selected is made of chromium, yttrium, a rare earth metal, a lanthanide, Molybdenum, tungsten, Rhenium, hafnium, tantalum, niobium, vanadium, manganese, carbon, boron, Phosphorus and silicon, is included. Metal powder mixture according to claim 7 or 8, characterized characterized in that the first metal in a proportion of 1 to 70 Mass% and the second metal in a proportion of 1 to 60% by mass are included. Metal powder mixture according to claim 9, characterized in that that chromium in a proportion of 0 to 80% by mass and another alloying element are contained in a proportion of 0 to 70% by mass. Metal powder mixture according to one of the preceding Claims, characterized in that in which the first powder fraction forming Metal alloy, as the first metal aluminum with a share of at least 15% by mass is included. Metal powder mixture according to one of the preceding Claims, characterized in that the mean particle size of the first Powder fraction at least three times larger than the average particle size of the second Powder fraction is. Metal powder mixture according to one of the preceding Claims, characterized in that the second powder fraction with a Content of at least 1% by mass is included. Metal powder mixture according to one of the preceding Claims, characterized in that a further fraction is contained, with particles whose average particle size is greater than 150 microns and / or with fibers of a Metal is formed, is included. Metal powder mixture according to claim 14, characterized in that that the further fraction of iron is formed as metal. Use of a metal powder mixture according to one the claims 1 to 15, for the production of sintered components or as a material for the order on component surfaces.