KR20100085019A - Metal powder mixture and the use thereof - Google Patents

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 Mixtures and Uses of this Metal Powder Mixture {METAL POWDER MIXTURE AND THE USE THEREOF}

The present invention relates to metal powder mixtures and to the use of such metal powder mixtures which are particularly advantageous.

In order to make it possible to produce materials with specific alloy compositions, it is common to use such metal powder mixtures of metal powders and metal alloy powders.

In doing so, metal alloy powders comprising a selection of at least one metal and alloying element corresponding to the metal powders used are also used for such metal powder mixtures. This metal powder mixture is a dissimilar metal powder mixture consisting of at least two chemically and / or morphologically different components consisting solely of an intermediate phase, depending on the manner of preparation of the desired metal alloy, each of which meets the requirements to be produced during the heat treatment. .

The metal powder mixture consists of fine parts (eg 10% <10 μm) and the remaining large parts (eg 90% <45 μm and 10%> 10 μm) naturally occurring during manufacture. Such metal powder mixtures have the advantage of enabling an improved packing density based on the desired space utilization by the adjusted particle distribution.

Based on metallurgical causes, metal powders and metal alloy powders are usually characterized by different fusing and phase change behaviors. Thus, each of the temperature ranges in which the solid phase portion and the liquid phase (eutectic phase) are present at the same time, respectively, exists, for example a change / increase in mass transfer based on the increased diffusion coefficient of the element can be observed based on the phase transformation in the solid phase. have. However, since the metal powder mixtures are not typically used for metallurgical melt production of alloying materials, the foregoing plays a large role in the final material production.

Thus, during the heat treatment that must be carried out for the formation of the desired metal alloy or the desired metal, effective atomic and microtransfer properties (eg diffusion, relocation, grain growth) in the contact area of the powder particles are determined between the metal and the metal. It is the basis for the compaction and homogenization of the initial heterogeneous mixture consisting of alloy powder or metal powder. In this sense, the term “heterogeneous” also refers to particle size distributions that induce mass transfer based on high levels of activity of fine particle portions, as opposed to (almost) monomodal distributions of particle sizes. It includes the difference about (bold part, fine part). In this regard, the effects demonstrated by the caloric method for each powder or powder mixture, and the effects utilized through the chemical composition of the alloy chemically graded between adjacent powder particles, for example It plays a central role during metal formation and material relocation.

It is difficult from a technical and economic point of view to form the desired metal alloy in the form of fine powder (d ₅₀ <10 μm) for powder metallurgy manufacture of the corresponding material / component, and to treat such powder only on the basis of emerging problems. When it has low commercial significance. Due to the high temperatures required during the required heat treatment (sintering), essential components are lost on the basis of the high vapor pressure during the powder metallurgy treatment, which results in modifications to the target alloy composition and heat treatment based on the material accumulation Technical problems within the device are caused.

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

Such metal powder mixtures are made of at least two even three different powders. In this regard, each powder is formed of a different metal alloy and is characterized by a narrow particle size distribution.

However, in the case of some metal alloys, such as soft metal alloys, the metal mixtures described in the state of the art have to be produced in a very expensive manner in order to be able to reach the desired very small particle size.

Problems also arise that are based on the fact that a uniform distribution of each metal used to form the desired metal alloy can only be achieved to a very limited degree in the final manufactured material. Thus, it is almost impossible to form microstructures such as those required for porous materials, for example. Applying this concept, it remains difficult to achieve a uniform distribution of alloying components. This will therefore degrade the material's properties, in particular its tendency to corrosion and mechanical strength.

According to the state of the art, it is possible to produce metal fine powders (d ₅₀ <10 μm) from easily reduced metal compounds without any effort. Metal alloy powders configured to form part of the desired metal powder mixture are usually melted and crushed when aiming at spraying alloy melts (gas or water spray), or particle sizes with d ₅₀ <45 μm. Can be produced in a cost effective manner.

Accordingly, the object of the present invention is to provide a cost effective means for a material made of a metal alloy after the heat treatment is performed in which the material must be characterized by a more uniform distribution of the respective alloy forming component and the metal forming component (alloy and element powder). It is to provide a metal powder mixture that can be used to obtain in a manner. In a second aspect, it should be possible to reduce the maximum temperature required in the course of the heat treatment to produce the material.

According to the invention, this problem can be solved by a metal powder mixture characterized by the features of claim 1. Suitable applications for such metal powder mixtures can be found in claim 16.

 Advantageous embodiments and other aspects of the invention may be obtained by the features mentioned in the dependent claims.

Here, the metal powder mixture according to the invention consists of at least two different powder parts. For the first powder part, a metal powder consisting of a metal alloy containing the first metal is used, with the other alloying components of the first powder part contained in the metal alloy relative to the first metal, the start of phase transformation The heat treatment takes place at a temperature of at least 200 K below the temperature at which melting of the material formed of the metal powder mixture begins.

The first powder part has an average particle size of d ₅₀ <45 μm.

The second powder part contained in the metal powder mixture according to the invention preferably consists of a second single metal which is the metal alloy part of the first powder part. However, the second powder part may also consist of a mixture of at least two metals. This powder part has an average particle size of d ₅₀ <10 μm. Here, in the case of the second powder part, the term "single metal" means a metal which consists almost entirely of a single metal or mixture and only very small amounts, up to 3% by weight of alloying additives or contaminants are acceptable. do. In the case of a second powder part consisting of a mixture of at least two metals, one of the metals must be present in a significantly higher share than the other metals contained in the mixture. In this regard, the share should be at least 75% by weight relative to the metal. Hereinafter, this metal is called a second metal.

The average particle size of the first powder portion should be at least three times the average particle size of the second powder portion. The second powder fraction should be contained in at least 1% by weight.

For the first powder part, a two-component metal alloy, ie a metal alloy consisting of two components, can be used. However, it is more cost effective to use a metal alloy composed of at least three different metals for the first powder part.

Here, the first powder part in the corresponding metal alloy contains at least one metal in a quotient corresponding to twice the quotient contained in the material formed of the metal powder mixture when the heat treatment is performed. 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.

The metals which are subjected to phase transformation at low temperatures already mentioned above can be used in the metal alloy of the first powder part, which metal is selected from aluminum, magnesium, zinc, tin and copper. Together with the other alloy components of the first powder part, these metals have the property to lower the melting temperature of the metal alloy or to reach partial volume phase conversion, including melting conditions.

Powdered iron, nickel, cobalt and copper can be used as the metal for the second powder part. At this time, one of these metals may be contained alone in the second powder part. However, the second powder part may also consist of at least two of these metals which are powder mixtures.

One option for producing a metal powder mixture according to the invention is to use a metal alloy for the first powder part, characterized by the general composition M1M2CrR. In this composition, M 1 is selected from aluminum, magnesium, tin, zinc and copper. Metal M2 is selected from iron, nickel and cobalt. R is selected from yttrium, molybdenum, tungsten, vanadium, manganese, rare earth metals, lanthanide elements, rhenium, hafnium, tantalum, niobium, carbon, boron, phosphorus and silicon.

In such metal alloys, the metal M1 may be contained in a quotient of 1 to 70% by weight, the metal M2 may be contained in a share of 1 to 60% by weight, and the Cr may be contained in a quotient of 0 to 80% by weight. And R may be contained in an amount of from 0 to 70% by weight.

It is also advantageous to construct aluminum in at least 15% by weight of the metal alloy for the first powder part. In this way, at least 3% by weight, preferably at least 15% by weight, of aluminum may be contained in the material obtained after the heat treatment is performed in which the material is produced from the metal powder mixture according to the invention.

If the powder is used in the metal powder mixture according to the invention together with the second powder part made of powdered iron, for example the first powder part formed of an alloy containing iron, chromium and aluminum, the iron is subjected to heat treatment. Materials can be prepared which are based on chromium with a proportion of 15 to 30% by weight and aluminum to 5 to 20% by weight.

In the metal powder mixture according to the invention, the second powder part should comprise at least 10% by weight, preferably at least 30% by weight and particularly preferably at least 50% by weight of the total mass.

The powder constituting the first powder portion contains, in combination with other alloying components, at least 10% by weight of metal which achieves a phase change temperature of at least 200 K lower than the temperature (transition temperature) at which melting of the material to be produced begins. Should be.

Using the metal powder mixture according to the invention, it is possible to produce materials in which all of the metal components exhibit a much more uniform distribution in the material volume than in the case of conventionally used metal powder mixtures. At this time, the heat treatment may be carried out at a temperature of at least 10 K lower than the temperature required according to the state of the art.

Here, a much finer powder is used for the combination of the two powder parts correspondingly selected according to the invention and also for the second powder part having a substantially smaller particle size than for the first powder part described above. It is advantageous to.

During the heat treatment, it is possible to use the present invention to achieve significantly increased mass transfer based on diffusion, relocation and particle growth. In this way, it is also possible to achieve the reduced maximum temperature required for the heat treatment during the production of the material from the metal powder mixture, with a uniform distribution of the respective metal alloy components.

The heat treatment can be carried out by using a known sintering technique. However, the sintering technique should be suitable for the desired sintering atmosphere and temperature.

By using the metal powder mixture according to the invention, an improved sintering behavior of the molded body is obtained based on the slurry or by pressing.

Based on the improved shrinkage behavior, the metal powder mixtures according to the invention can be used to improve the properties of the components of the metal powder mixtures produced or of the corresponding protective layers applied to the components. In addition, the corrosion resistance can be improved. In this way, the corrosion resistance can be improved on the basis of the formation of the target corresponding oxide layer on the surface, where the oxide layer typically has a layer thickness of 0.1 to 0.1 when the metal powder mixture according to the invention contains aluminum. It is characterized by a 10 μm.

The materials produced by using the metal powder mixtures according to the invention can be characterized by improved pitting corrosion possibilities when compared to corrosion resistant high alloy steels.

In a construction of another variant of the invention, the metal powder mixture may also contain further portions consisting of metals. This additional portion may preferably be iron, wherein the metal powder mixture should contain less than 3% by weight of contaminants and trace elements, if it contains all of iron, contaminants and trace elements. do. Here, the additional part may also be a powder, which may be of much coarser particle size than the two powder parts described above. In this way, the average particle size may be larger than 150 μm and may well exceed the above values. However, the additional portion may also consist only of fibers and may contain fibers together with the particles.

The fibers can be characterized by a diameter in the range of about 1 mm and a length value of several millimeters.

If the metal powder mixture according to the invention contains additional parts, the share of the second powder parts may be very low, ie less than 5% by weight.

It may be practiced by techniques known per se, such as thermal injection or deposition welding, which apply a layer on the surface of the component.

The components or parts of the metal powder mixture can also be prepared using so-called rapid prototyping. At this time, in order to be able to achieve even higher density and uniformity, it may be advisable to further perform heat treatment upon completion of the production.

For materials made by using a metal powder mixture according to the invention, which consists of a metal alloy NiCrAl, chromium evaporation may be prevented, in contrast to known solutions according to the state of the art, and at least significantly reduced chromium evaporation. It may be because the temperature during the heat treatment is lower. This is particularly applicable to comparisons of metal powder mixtures characterized by the corresponding alloying components of the material produced before the heat treatment is carried out.

In the following, the invention is explained in more detail in an exemplary manner.

According to the invention, a material consisting of a metal alloy is obtained in a cost-effective manner after the implementation of heat treatment in which the material must be characterized by a more uniform distribution of the respective alloy forming component and the metal forming component (alloy and elemental powder). There is provided a metal powder mixture that can be used to reduce the maximum temperature required in the course of the heat treatment to produce the material.

1 shows a part of a shell of a hollow ball made of FeCrAl alloy, in which chemical analysis on elements Fe, Cr and Al has been carried out at five positions,
2 is a view showing a part of a hollow ball made of a FeCrAl alloy having a low porosity of the shell,
Figure 3 shows a graph demonstrating the increase in mass after oxidation of the FeCrAl hollow ball,
4 shows a cross-sectional sample in chemical point analysis of FeCrAl fibers.

Example 1

In this example, the first powder part having an average particle size (d ₅₀ ) of 25 μm and having a Ni-50Cr-25Al-0.025Hf alloy composition during the production of the hollow metal ball made of Ni-20Cr-10Al-0.05Hf material; A second powder part is used, which has an average particle size (d ₅₀ ) of 5 μm and consists mainly of nickel (99.9 wt%).

The share of the first powder portion is 40 wt% and the share of the second powder portion is 60 wt%.

To obtain a uniform particle distribution in the suspension, 100 g of metal by 100 g of water, 3 g of polyvinyl alcohol, and 0.5 g of Dolapix in a disperser at a rate of 3000 RPM for an hour period The powder mixture is dispersed. The suspension obtained as described above does not precipitate when vigorously stirred.

The low viscosity metal powder suspension obtained is applied as a coating to spherical particles made of polystyrene and dried. After the coating on the polystyrene particles reaches a layer thickness of 100 μm, heat treatment can be performed.

In this example, the process is carried out in an atmosphere in which hydrogen flows (30 L / min). Initially, the organic component is thermally decomposed, wherein the heating process takes place at a heating rate of 1 K / min until reaching a temperature of 600 ° C. Thereafter, the temperature is increased to 1280 ° C., where a heating rate of 5 K / min is maintained. After the 2-hour hold time at the maximum temperature had expired, a cooling to room temperature was performed at 5 K / min.

The hollow metal balls produced as described above were characterized by having an outer diameter of approximately 2 mm and a wall thickness of approximately 70 μm. The volume density is 450 g / L. The shell material of the hollow metal balls produced by this example of the metal powder mixture according to the invention consists of 20% by weight of chromium, 10% by weight of aluminum and 0.05% by weight of hafnium.

In the course of the parallel test example, an alloy consisting of Ni-20Cr-10Al-0.05Hf is processed into a fine alloy powder having a particle size (d ₅₀ ) of 10 μm by an inert gas spraying the metal alloy. In a method analogous to the example according to the invention, the powder is subjected to the steps of suspension preparation, coating, drying of polystyrene particles and heat treatment. The hollow metal balls produced as described above had higher final strength values measured based on the strain to fracture than those made with the metal powder mixture according to the invention.

Example 2

Metal powder mixtures containing a first powder portion characterized by an average particle size (d ₅₀ ) of 15 μm and a second powder portion characterized by an average particle size (d ₅₀ ) of 3 μm were used. For the first powder part, the Fe-49Cr-23Al alloy was chosen and the second powder part consisted mainly of iron (99.5 wt.%).

Similar to Example 1, 43.5% of the first powder portion and 56.5% of the second powder portion were processed. 1 and 2, the uniformity of the shell material is evident from the cross section through the shell of the hollow ball manufactured as described above. The shell material made of the metal powder mixture according to this example was a Fe-23Cr-10Al alloy.

Sintering was carried out in a hydrogen atmosphere at 1240 ℃ for 2 hours.

Upon completion of the sintering process, an apparent density (FD) according to ASTM D212 / 417 of about 0.4 g / cm 3, a carbon content of 70 ppm and an oxygen share of 0.24% can be achieved for the hollow balls prepared as described above. there was. By using Table 1 shown in FIG. 3, the above-described method is based on the mass increase of the material after 700 hours have elapsed at a holding temperature of 900 ° C. to 1000 ° C. when the air is previously removed at 1100 ° C. for 2 hours. It is possible to demonstrate the oxidative properties of the material obtained by making one.

Example 3

A first powder portion of 2 kg in weight having an average particle size (d ₅₀ ) of 8 μm and consisting of a Fe-49Cr-23Al alloy and a second powder part of 0.1 kg in weight of an average particle size (d ₅₀ ) of 3 μm and consisting of pure iron And a metal powder mixture consisting of a Fe-20Cr-9Al component with a metal powder mixture containing 3 kg of an additional portion consisting of metal fibers and having an average outer diameter of 150 μm and an average length of 5 mm.

In this example, the metal fiber prepared by milling a block of the highest purity iron (99.9% iron) was circulated at a speed of 20 RPM in a 5 liter Eurich mixer. The temperature of the mixing vessel was maintained at 50 ° C ± 10 K by sending hot air to the mixing vessel.

Dispersants were prepared from 2 kg of acetone and 0.2 kg of polyvinyl alcohol (PVA) as well as 2 kg of the first powder part and 0.1 kg of the second powder part. During the cycling process, this dispersant was sprayed into the mixer in a centralized manner until all of the powder mass was applied to the surface of the fiber. In doing so, the required safety regulations based on organic combustible components were followed.

As described above, the coated fibers were placed in a pan made of Al ₂ O ₃ and heat treated at 1240 ° C. for 2 hours in a hydrogen atmosphere. In this example, PVA was discharged as described in Example 1.

Figure 4 shows a cross-sectional sample through the fiber prepared as described above. Based on the chemical point analysis, it was possible to determine that the fiber material component at the completion of the heat treatment was a uniform Fe-19Cr-9Al alloy.

Example 4

In this example, a metal powder mixture containing a first powder portion characterized by an average particle size (d ₅₀ ) of 4.4 μm and a second powder portion characterized by an average particle size (d ₅₀ ) of 3.0 μm Used. The Fe-49Cr-23Al alloy was chosen for the first powder part, and the second powder part consisted mainly of iron (99.5 wt.%).

To obtain a uniform distribution of the particles in the suspension, 100 g (45 g) of this metal powder mixture with 100 g of water, 3 g of polyvinyl alcohol and 0.5 g of Dolafix for a 2 hour period at a speed of 3000 RPM in a disperser First powder part and 55 g of second powder part) were dispersed.

For example, according to the so-called Schwartzwalder procedure, as described in particular in US Pat. No. 3,090,094, open cell porous metal foams were prepared. In this example, a reticulated polyurethane foam cut into each piece with dimensions 40 * 40 * 10 mm and a porosity of 80 ppi was coated with a metal powder binder suspension. In this example, the polymer foam structure is coated with the suspension as completely as possible. Thereafter, the coated fragments were dried for a period of 2 hours at a temperature of 60 ° C.

Thereafter, heat treatment was performed in a hydrogen atmosphere. In this example, the temperature was increased to 600 ° C. using a heating rate of 1 K / min to remove organic components. The temperature was then further increased to 1280 ° C. while maintaining the heating rate at 5 K / min, at which time the temperature was maintained for 2 hours. Even during the cooling process to room temperature, a heating rate of 5 K / min was maintained.

When the heat treatment and cooling were completed, an open cell foam structure having a physical density of 0.8 g / cm 3 was obtained, wherein the porous web of heat treatment was made of a Fe 23 Cr 10 Al alloy.

Claims (16)

A metal powder mixture consisting of at least two different powder parts,
The first powder part consists of a metal alloy containing the first metal, and with the other alloy components of the first powder part contained in the metal alloy with respect to the first metal, the start of phase transformation is carried out by heat treatment of the metal powder mixture At least 200 K below the temperature at which melting of the material to be formed begins, the first powder portion is characterized by an average particle size of less than 45 μm, and the second powder portion is the second metal or at least two metals. A mixture of and characterized by an average particle size of less than 10 μm, wherein the mixture of the second metal and the at least two metals is contained in the second powder portion by at least 97% by weight. The metal powder mixture of claim 1 wherein a metal alloy is used for the first powder portion consisting of at least three metals. The metal alloy of claim 1, wherein the metal alloy of the first powder portion contains at least one metal in a share corresponding to at least 1.5 times the share contained in the material formed of the metal powder mixture upon completion of the heat treatment. Metal powder mixture, characterized in that. 4. The metal powder mixture as claimed in claim 1, wherein for the second powder part one or several metal (s) selected from iron, nickel and cobalt are used. 5. The metal powder mixture as claimed in claim 1, wherein for the first powder part a first metal selected from aluminum, magnesium, zinc, tin and copper is used. 6. 6. The metal powder mixture as claimed in claim 1, wherein the first powder part contains an additional element selected from boron, silicon and carbon. 7. The method of claim 1, wherein the first powder portion is formed of a bicomponent alloy consisting of a first metal and a second metal, the first metal being aluminum, magnesium, zinc, tin and copper. Metal powder mixture, wherein the second metal is selected from iron, nickel and cobalt. 8. The element of claim 1, wherein the first powder portion contains at least one other element as an additional alloying element, the further alloying element being chromium, yttrium, rare earth metal, lanthanide element. , Metal molybdenum, tungsten, rhenium, hafnium, tantalum, niobium, vanadium, manganese, carbon, boron, phosphorus and silicon. The metal powder mixture according to claim 7 or 8, wherein the first metal is contained in an amount of 1 to 70% by weight, and the second metal is contained in an amount of 1 to 60% by weight. 10. The metal powder mixture according to claim 9, wherein chromium is contained in an amount of 0 to 80% by weight and additional alloying elements are contained in an amount of 0 to 70% by weight. The metal powder mixture according to claim 1, wherein the metal alloy forming the first powder part contains at least 15% by weight of aluminum as the first metal. 12. The metal powder mixture according to any one of the preceding claims, wherein the average particle size of the first powder portion is three times the average particle size of the second powder portion. The metal powder mixture according to claim 1, wherein the second powder part is contained in at least 1% by weight. The metal powder mixture according to any one of claims 1 to 13, further comprising an additional portion consisting of particles and / or metal fibers having an average particle size of greater than 150 μm. 15. The metal powder mixture of claim 14, wherein the additional portion consists of iron, which is a metal. Use of the metal powder mixture according to any one of claims 1 to 15 as a material to be applied to the surface or open cell porous structure of the component for the production of sintered components.

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