HK1095111A - Method for the production of fine metal powder, alloy powder and composite powder - Google Patents

Description

Method for producing fine metal powder, alloy powder and composite material powder

The invention relates to a method for producing metal, alloy or composite powders having an average particle diameter D50 of at most 25 [ mu ] m, wherein the starting powder is first formed into plate-shaped particles, which are then comminuted in the presence of an abrasive, and to the metal, alloy or composite powders obtained thereby.

Many metallurgical or chemical processes for producing metal and alloy powders are known. To produce fine powders, known processes often start from a melt of a metal or alloy.

If the melt is dispersed by spraying, powder particles are directly formed by solidification from the formed melt droplets. Depending on the cooling (treatment with air, inert gas, water), the process parameters used, such as nozzle geometry, gas velocity, gas temperature or nozzle material, the material parameters of the melt, such as melting and freezing point, solidification behavior, viscosity, chemical composition and reactivity with the treatment medium, lead to a number of possibilities, but at the same time also to limitations of the process (W.Schat, K. -P.Wieters, "Powder Metallurgy-Processing and materials", EPMA European Powder Metallurgy Association, 1997, pages 10-23).

Since the manufacture of powders by spraying is of particular industrial and economic interest, various spraying processes have been established. The particular process chosen depends on the desired powder properties such as particle size, particle size distribution, particle morphology, impurities, the characteristics of the melt to be sprayed, such as melting point or reactivity, and the affordable cost. Nevertheless, there are often limitations from economic and industrial points of view to obtain a specific property profile of the Powder (particle size distribution, impurity content, "defined particle size" yield, morphological sintering activity, etc.) at reasonable cost (W.Schatt, K. -P.Wieters "Powder Metallurgy-Processing and Materials", EPMA European Powder Metallurgy Association, 1997, pages 10-23).

The main disadvantage of making powders by spraying is that a large amount of energy and spraying gas has to be used, which makes the process very expensive. In particular, the production of fine powders from high-melting alloys with melting points > 1400 ℃ is not very economical, since, on the one hand, the high melting point makes it necessary to provide very high amounts of energy for the melt to be produced, and, on the other hand, the gas consumption increases considerably when the desired particle size is reduced. Furthermore, difficulties also tend to arise if at least one of the alloying elements has a very high affinity for oxygen. Some cost advantages can be achieved by using specially developed nozzles when manufacturing, in particular, fine alloy powders.

In addition to the production of particles by spraying, other single-stage melt metallurgical processes such as so-called "melt spinning" in which molten material is poured onto cooled rolls to produce thin, usually easily comminuted strips, or so-called "crucible melt extraction" in which cooled grooved rolls rotating at high speed are immersed in molten metal to obtain particles or fibres are often used.

Another important variant of powder manufacture is the chemical process by means of reduction of metal oxides or metal salts. However, alloy powders cannot be obtained by this method (W.Schatt, K. -P.Wietters in "Powder Metallurgy-Processing and Materials", EPMAEurope Powder Metallurgy Association, 1997, pp. 23-30).

Ultrafine particles with a particle size of less than 1 μm can also be produced by combining the evaporation and condensation processes of metals and alloys and by means of gas phase reactions (W.Schatt, K. -P.Wieters "Powder Metallurgy-Processing and Materials", EPMA European Powder Metallurgy Association, 1997, pp.39-41). However, these methods are very expensive industrially.

If cooling of the melt occurs in relatively large volumes/lumps, it is necessary to carry out coarse, fine and extra-fine comminution of the mechanical process steps to produce metal or alloy powders that can be processed by powder metallurgy processes. An overview of mechanical manufacturing powders is given in "Powder Metallurgy-Processing and Materials", EPMA European Powder Metallurgy Association, 1997, pages 5-47, by Schatt, K.

Mechanical comminution, especially in mills, is highly advantageous from an industrial point of view as the oldest particle size adjustment method, because it is low cost and applicable to a large number of materials. However, it imposes certain requirements on the material being processed, such as the size of the platelets and the brittleness of the material. In addition, the pulverization cannot be carried out at will. In fact, a grinding equilibrium is formed, which may also be self-regulating if the grinding process starts with relatively fine powder. If the physical limit of the grinding capacity is reached for various abrasives, it is necessary to improve the conventional grinding process, while certain phenomena such as embrittlement at low temperatures or the action of grinding aids improve the grinding properties or the grinding capacity.

A method for finely grinding relatively brittle pre-ground materials, which is very suitable in many cases, is based on the concept of gas back-jet mills (there are many industrial suppliers, for example Hosokawa-Alpine or Netzsch-Condux). This method is very widespread and, in particular in the case of brittle materials, has considerable advantages from an industrial (low impurity content, automatic grinding) and economic point of view compared with conventional mills using purely mechanical comminution, such as ball mills or stirred ball mills. Jet mills reach their industrial and thus economic limits when comminuting tough raw material powders, in other words materials which are difficult to pulverize, and with low defined particle diameters. This can be explained by the reduced kinetic energy of the powder particles being pulverized in the gas jet. Since the kinetic energy of the powder particles will be supplied only by the carrier gas, the specific energy consumption increases to an economically unreasonable extent in the case of ultrafine comminution, and is therefore practically inapplicable in the case of high-toughness powders. In addition, the sintering activity of these powders thus pulverized cannot be compared with that of powder particles produced by ordinary grinding.

Very fine particles can be obtained, for example, by combining the milling step with hydrogenation and dehydrogenation reactions, including combining the reaction products to form the desired powder phase composition (i.r. harris, c.noble, t.bailey, Journal of the Less-Common Metals, 106(1985), L1-L4). However, this method is limited to only those alloys that contain elements that can form stable hydrides. The mechanical influence on the comminution in the form of lattice defects or other defects can thus be eliminated as far as possible. This is especially important when the functional properties of the powder particles, such as crystallites, seriously affect the properties of the powder product, as in NdFeB permanent magnets.

These methods always reach their limitations if they are very fine powders that produce tough metals or alloys that have both high reactivity to oxygen and high sintering activity.

Cold-flow comminution processes have been developed for the production of such products, in which intensively cooled metal particles are centrifuged at very high velocities up to mach 1 through a venturi nozzle onto a cooled plate. It is said that products having a particle size of 5 to 10 μm can be produced therefrom (W.Schatt, K. -P.Wieters, "Powder metals-Processing and Materials", EPMAEuropean Powder metals Association, 1997, pages 9 to 10). The operation of accelerating the raw powder to sonic velocity makes it necessary to provide extremely high energy in this process. In addition, wear problems may occur, dangerous impurities being introduced into the abrasive due to the interaction between the particles and the opposite plate.

Another method of making fine powders from ductile materials is the mechanical alloying method. In this process, agglomerates are obtained by intensive comminution, which are composed of crystallites of a size of about 10 to 0.01. mu.m. The metal ductile material changes in such a way that fine individual particles may be formed due to high mechanical stress. These particles comprise typical alloy compositions. However, this method has the disadvantage that sometimes, mainly by abrasion, very large amounts of impurities are introduced. However, uncontrolled wear is often just an obstacle for industrial applications. Furthermore, only after very long grinding times can dispersed ultrafine particles be produced. Fine metal and alloy powders cannot be economically produced by mechanical alloying alone.

It is therefore an object of the present invention to provide a method for producing fine, in particular ductile, metal, alloy or composite powders which is particularly suitable for producing alloys, i.e. multi-substance systems, and which permits targeted adjustment or influencing of basic properties such as particle size, particle size distribution, sintering activity, impurity content or particle morphology.

According to the invention, this object is achieved by a two-stage process in which the starting powder is first shaped into plate-like particles, which are then comminuted in the presence of a grinding aid.

The subject of the invention is therefore a process for producing metal, alloy or composite powders having an average particle diameter D50 of at most 25 μm from starting material powders having a larger average particle diameter D50 using a particle measuring instrument Microtrac^®X100 is measured according to ASTM C1070-01, wherein,

a) the particles of the raw material powder are processed into flaky particles in the molding step, the ratio of the particle diameter to the thickness of the particles is between 10: 1 and 10000: 1,

b) the flaky particles are subjected to crushing grinding in the presence of a grinding aid.

Microtrac of particle measuring instrument^®X100 is commercially available from Honeywell u.s.a.

To determine the ratio of particle size to particle thickness, the particle size and particle thickness were measured using an optical microscope. For this purpose, the flake particles are first mixed with a viscous transparent epoxy resin in a ratio of 2 parts by volume of resin and 1 part by volume of flakes. The bubbles introduced during mixing are then expelled by evacuating the mixture. The bubble-free mixture was poured onto a flat substrate and then rolled flat with a roller. Preferably, the plate-like particles are thereby oriented in the flow field between the roller and the substrate. The preferred position is where the face normal orientation of the chips is on average parallel to the face normal of a planar substrate, in other words the chips are on average lying flat on the substrate in layers. After curing, samples of appropriate size were processed from the epoxy boards on the substrate. The samples were examined microscopically both perpendicular and parallel to the substrate. Using a microscope with a graduated lens and taking into account the appropriate particle orientation, at least 50 particles are measured and the average is calculated from the measured values. This average represents the particle size of the plate-like particles. After vertically cutting the substrate and the sample to be measured, the particle thickness was measured using a microscope having a graduated lens, which was also used for measuring the particle diameter. Care should be taken to measure only those particles that are positioned as parallel as possible to the substrate. Since the particles are completely surrounded by the transparent resin, there is no difficulty in selecting appropriately oriented particles and reliably specifying the boundaries of the particles to be evaluated. At least 50 particles were also measured and an average value was calculated from the measured values. This average value represents the particle thickness of the plate-like particles. From these determined values, the particle size to particle thickness ratio was calculated.

Using the method according to the invention, it is possible to produce, in particular, fine, ductile metal, alloy or composite powders. As used herein, malleable metal, alloy or composite powders are those powders that undergo plastic stretching or deformation before significant material failure (material embrittlement, material fracture) occurs when subjected to mechanical stress until the yield point is reached. Such plastic material variations depend on the material and range from 0.1% to a few 100% based on the starting length.

The degree of ductility, i.e., the ability of a material to undergo plastic, i.e., permanent, deformation under mechanical stress, can be determined or described by mechanical tensile or pressure testing.

In order to determine the degree of ductility by means of mechanical tensile testing, so-called tensile test specimens are produced from the material to be evaluated. It may be, for example, a cylindrical sample having an internal diameter reduced by about 30-50% over a length of about 30-50% of the total sample length at half the length. The tensile specimen is fixed to a clamping device of an electromechanical or electrohydraulic tensile testing machine. The length sensor was mounted on a measured length of about 10% of the entire sample length in the middle of the sample before the actual mechanical test. These sensors make it possible to track the increase in length during the application of mechanical tensile stress within a selected measuring length. The stress was increased until the sample broke and the tensile strain recording was used to evaluate the plastic part of the length change. In such tests, those materials that are capable of achieving plastic length deformation in the range of at least 0.1% are considered to be malleable within the context of this specification.

Similarly, a cylindrical sample of material having a diameter to thickness ratio of about 3: 1 can also be subjected to mechanical compressive stress on a commercially available compression tester. In this case, the cylindrical test piece is also permanently deformed after the application of sufficient mechanical compressive stress. Once the pressure is removed and the sample removed, the increase in the diameter to thickness ratio can be measured. In such tests, materials that are capable of plastic deformation in the range of at least 0.1% are considered to be malleable within the context of this specification.

A fine ductile alloy powder having a degree of ductility of at least 5% is preferably produced by the method according to the present invention.

According to the invention, the grinding aid added purposefully or produced during the grinding process and acting mechanically, mechanochemical and/or chemically is used to improve the grinding ability of alloys or metal powders which cannot be ground further. An essential aspect of this method is that the chemical "desired composition" of the powder produced therefrom is not altered in general, or the effect thereof is even such that the process properties, such as sintering behavior or flowability, are improved.

The process according to the invention is suitable for the production of various fine metal, alloy or composite powders having an average particle diameter D50 of at most 25 μm.

For example, metal, alloy or composite powders of the composition of formula I can be obtained

hA-iB-jC-kD (I)

Wherein

A represents one or more elements selected from Fe, Co and Ni,

b represents one or more elements selected from V, Nb, Ta, Cr, Mo, W, Mn, Re, Ti, Si, Ge, Be, Au, Ag, Ru, Rh, Pd, Os, Ir, Pt,

c represents one or more elements selected from Mg, Al, Sn, Cu, Zn,

d represents one or more elements selected from Zr, Hf, rare earth metals,

and h, i, j and k represent the weight contents, wherein

H, i, j and k in each case independently of one another represent from 0 to 100% by weight, with the proviso that the sum of h, i, j and k is 100% by weight.

In formula I, it is preferred

A represents one or more elements selected from Fe, Co and Ni,

b represents one or more elements selected from V, Cr, Mo, W, Ti,

c represents one or more elements selected from Mg, Al,

d represents one or more elements selected from Zr, Hf, Y and La.

h preferably represents from 50 to 80% by weight, particularly preferably from 60 to 80% by weight. i preferably represents 15 to 40% by weight, particularly preferably 18 to 40% by weight. j preferably represents 0 to 15% by weight, particularly preferably 5 to 10% by weight. k preferably represents 0 to 5% by weight, particularly preferably 0 to 2% by weight.

The metal, alloy or composite powder produced according to the invention is characterized by its small average particle size D50. The average particle diameter D50 is preferably at most 15 μm, measured according to ASTM C1070-01 (measuring instrument: Microtrac)^®X 100)。

For example, a powder that already has the desired composition of the metal, alloy or composite powder may be used as the raw material powder. However, in the process according to the invention it is also possible to use mixtures of several starting powders which only after a suitable choice of the mixing ratio lead to the desired composition. In addition, the choice of grinding aid can also be used to influence the composition of the metal, alloy or composite powder produced if it remains in the product.

Preferably, spherical or irregularly shaped particles having an average particle diameter D50 of more than 25 μm, preferably from 30 to 2000 μm, particularly preferably from 30 to 1000 μm, determined according to ASTM C1070-01, are used as starting powder.

The desired starting powder can be obtained, for example, by spraying the molten metal and, if desired, subsequently screening or sifting.

According to the invention, the raw material powder is first subjected to a deformation step. The deformation step may be carried out in known equipment such as roll mills, vortex mills, high energy mills or attritors or stirred ball mills. By suitably selecting the process parameters, in particular as a result of mechanical stresses sufficient to achieve plastic deformation of the material or powder particles, the individual particles are deformed so that they finally have a chip-like shape, the thickness of the chips preferably being 1-20 μm. This can be done, for example, by pressing once in a roller mill or hammer mill, or repeatedly in several "small" deformation steps, for example, by pressing in a vortex mill or a Simoloyer^®Internal impact milling, or by a combination of impact milling and friction milling, for example in an attritor or ball mill. The high material stresses during this deformation may lead to structural failure and/or material embrittlement, which can be used to crush the material in a subsequent step.

Known melt metallurgy rapid solidification methods can also be used to make the bars or "slices". These are then suitable for attrition milling as described below, as are mechanically manufactured chips.

The equipment, milling media and other milling conditions for performing the deformation step are preferably selected so that the impurities due to abrasion and/or reaction with oxygen or nitrogen are as small as possible and below the critical values for the product application or within the specifications of the material.

This can be achieved, for example, by appropriate selection of the milling container and milling media materials and/or use of gases that prevent oxidation and nitridation during the deformation step and/or addition of protective solvents.

In a particular embodiment of the process according to the invention, the flake-like particles are produced in a rapid solidification step, for example by so-called "melt spinning" directly from the melt by cooling on or between one or more preferably cooled rolls, thereby directly forming flake-like flakes.

According to the present invention, the flake-like particles obtained in the deforming step are subjected to crushing grinding. In this process, on the one hand, the ratio of particle size to particle thickness is varied, and primary particles having a ratio of particle size to particle thickness of from 1: 1 to 10: 1 are generally obtained. And to a desired average particle size of at most 25 μm without generating agglomerates of particles which are difficult to pulverize.

Comminution grinding can be carried out, for example, in mills such as eccentric mills, but also in Gutbett mills, extruders or similar devices which can lead to comminution of the material as a result of different movements and stress ratios in the chips.

According to the invention, the comminution and grinding are carried out with a grinding aid. For example, liquid grinding aids, waxes and/or friable powders may be used as grinding aids. In this case, the grinding aid may act mechanically, chemically or mechanochemical.

For example, the grinding aid can be paraffin oil, paraffin wax, metal powder, alloy powder, metal sulfide, metal salt, organic acid salt, and/or hard material powder.

The brittle powder or phase can act as a mechanical grinding aid and can be used, for example, in the form of alloy powders, elemental powders, hard material powders, carbide powders, silicide powders, oxide powders, boride powders, nitride powders, or salt powders. For example, pre-milled elemental and/or alloy powders may be used which, together with the hard-to-pulverize raw powders used, may result in the desired composition of the product powder.

The brittle powder used is preferably a powder comprising A, B, C of the element in the starting alloy used and/or a binary, ternary and/or higher composition of D, wherein A, B, C and D have the same meaning as above.

Liquid and/or easily deformable grinding aids, such as waxes, may also be used. Mention may be made, by way of example, of hydrocarbons, such as hexane, alcohols, amines or aqueous media. These are preferably compounds which are required for subsequent further processing steps and/or are easily removed after attrition milling.

It is also possible to use the known special organic compounds which are used in pigment production to stabilize the individual fragments against sticking in a liquid environment.

In one embodiment, a grinding aid is used that will participate in the targeted chemical reaction with the feedstock powder to effect the grinding process and/or to adjust certain chemical constituents of the product. They may be, for example, decomposable compounds in which only one or more components need to be adjusted to achieve the desired composition, and it is possible to remove as much as possible at least one component or composition by heat treatment.

Examples of reducible and/or decomposable compounds which are at least partially removed from the abrasive material in subsequent processing steps and/or powder metallurgical treatment of the product powder include hydrides, oxides, sulphide salts and sugars, the residual residue chemically supplementing the powder composition in the desired manner.

Grinding aids may also be added not separately but generated in situ during the attrition milling process. In this case, grinding aids can be produced, for example, by adding a reaction gas which reacts with the starting powder under the conditions of attrition milling and simultaneously forms a brittle phase. Preferably hydrogen is used as the reaction gas.

The brittle phases produced during the treatment with the reaction gases, for example by forming hydrides and/or oxides, can be removed again by suitable process steps, generally after attrition milling or during the processing of the fine metal, alloy or composite powders obtained.

If the grinding aids used are not removed or only partially removed from the metal, alloy or composite powders produced according to the invention, they are preferably selected such that the residual components influence the properties of the material in the desired manner, such as, for example, improved mechanical properties, reduced corrosiveness, increased hardness and improved wear characteristics or friction and sliding properties. Here, for example, a hard material may be used, the content of which in a subsequent step is increased to such an extent that the hard material can be further treated with alloy components to form a cemented carbide or a hard material-alloy composite.

After the deformation step and the attrition milling, the primary particles of the metal, alloy or composite powder produced have an average particle diameter D50 of at most 25 μm according to the invention, passing ASTM C1070-01 (Microtrac)^®X100) is measured.

Despite the use of grinding aids, in addition to the formation of the desired fine primary particles, the known interactions between ultrafine particles lead to the formation of relatively coarse secondary particles (agglomerates) whose particle size is significantly greater than the desired average particle size of up to 25 μm.

It is therefore preferred to carry out a deagglomeration step after the attrition milling, during which the agglomerates are broken down and primary particles are released. Deagglomeration can be carried out, for example, by applying shear forces in the form of mechanical and/or thermal stress and/or by removing the separating layer which is introduced between the primary particles during processing. The de-agglomeration method employed depends on the degree of agglomeration, the intended application of the micropowder, as well as the oxidation sensitivity of the micropowder and the allowable impurities in the finished product.

Deagglomeration can be carried out, for example, by mechanical methods, such as by treatment in gas back-jet mills, screening, sieving or treatment in pulverizers, kneaders or rotor-stator dispersers. It is also possible to use stress fields as generated in the ultrasound treatment, thermal treatments, e.g. dissolution or transformation of previously introduced separation layers between primary particles by low-or high-temperature treatment, or chemical transformations of introduced or intentionally generated phases.

The deagglomeration is preferably carried out in the presence of one or more liquids, dispersion aids and/or binders. A slurry, kneaded mass or suspension having a solids content of 1 to 95% by weight can be obtained. Solids contents of 30-95% by weight can be processed directly by known powder processing procedures such as injection molding, film injection molding, coating and hot molding, and then reacted to form the final product in appropriate drying, releasing and sintering processes.

Gas back-jet mills, preferably operated under an inert gas such as argon or nitrogen, are used for deagglomeration of powders which are sensitive in particular to oxygen.

The metal, alloy or composite powder produced according to the invention has advantages in many specific properties over conventional powders having the same average particle size and the same chemical composition, for example produced by spraying.

The invention therefore also provides metal, alloy or composite powders having an average particle diameter D50 of at most 25 [ mu ] m, which can be obtained by the process according to the invention, wherein the average particle diameter D50 is determined using the particle measuring instrument Microtrac^®X100 is determined according to ASTM C1070-01.

The metal, alloy and composite powders according to the invention exhibit, for example, excellent sintering properties. At low sintering temperatures the same sintered density as for powders produced, for example, by spraying can be achieved. Starting from powder compacts of defined compression density, higher sintering densities can be achieved at the same sintering temperature. This increased sintering activity is also manifested, for example, in that, up to the maximum shrinkage reached, the shrinkage during sintering is greater than in conventionally produced powders.

The invention therefore also provides metal, alloy or composite powders having an average particle diameter D50 of at most 25 [ mu ] m, in whichA maximum shrinkage is reached, which is at least 1.05 times that of a metal, alloy or composite powder having the same chemical composition and the same average particle size D50, wherein the average particle size D50 is Microtrac using a particle measuring device^®X100 is measured according to ASTM C1070-01, the shrinkage is measured using an dilatometer according to DIN 51045-1, and the powder to be investigated is compressed to a compressed density of 50% of the theoretical density before shrinkage is measured.

The powder to be investigated can be compacted by applying a common compaction promoter, such as paraffin wax or other waxes or salts of organic acids, e.g. zinc stearate.

Metal, alloy or composite powders which are produced by spraying and to which the powder according to the invention has improved sintering properties are to be compared with those produced by the usual spraying methods known to the person skilled in the art.

The advantageous sintering properties of the metal, alloy or composite powder according to the invention can also be seen, for example, in the course of the sintering curve and the shrinkage curve as shown in fig. 7.

FIG. 7 shows the shrinkage S or shrinkage rate AS (both in relative units) of a comparative powder (V) and a powder according to the invention (PZD) AS normalized to the respective sintering temperatures T_STemperature T of_NThe process of the function of (a).

The comparative powder (V) is a product produced by spraying under inert conditions, having the same composition as the material described in example 1 and the same morphology as this powder. The particle size distribution (D50 is about 8.4 μm) corresponds to the distribution shown in fig. 5. The powder according to the invention (PZD) was the powder produced according to example 1 having the morphology shown in figure 6 and an oxygen content of 0.4 wt.%.

After mixing with 3 wt.% microcrystalline wax as compression promoting additive, a powder compact was produced from the two powders by applying a uniaxial pressure of 400-600MPa in a press mold. In both cases the green density was about 40% of the theoretical density. These compacts are respectively in dilatometerDIN 51045-1 was sintered under protective gas conditions using argon as working gas. In this process, the heating rate was about 1K/mm (corresponding to about 6 x 10)^-4*T_SMin, wherein T_S: about 1600K). The push rod of the dilatometer (Fahlstempel) does not exert any pressure on the sample, which is the temperature range considered for sintering (about 0.5T)_S-about 0.95T_S) The internal sintering shrinkage provides a measurable value.

At up to about 0.45 × T_SThe organic compression aid is discharged at the temperature of (2). Thereafter by heating at the same rate from about 0.5T_STo about 0.99T_SFurther heating to produce actual sintering process to obtain compact body.

The advantages of PZD powder lead to the following observations and general rules illustrated with the aid of figure 7. For this reason, the required terminology should first be introduced to give an overview of the sintering process.

^VT₉₀And^PZDT₉₀: at about 6 x10^-4*T_SAt a heating rate at which the shrinkage of the two sintered bodies reaches 90% of the same final shrinkage (100) reached (in terms of T)_N＝T/T_SNormalized unit of).

^VT₁₀And^PZDT₁₀: at about 6 x10^-4*T_SAt a heating rate at which the shrinkage of the two sintered bodies reaches 10% based on the same final shrinkage (100) reached (in terms of T)_N＝T/T_SNormalized unit of).

^VT₁And^PZDT₁: at about 6 x10^-4*T_SAt a heating rate of (a), a temperature at which the shrinkage of the two sintered bodies reaches 1% based on the same final shrinkage (100) reached (in terms of T)_N＝T/T_SNormalized unit of). Shrinkage is initiated at these temperatures.

^VT_maxAnd^PZDT_max: temperature at which maximum shrinkage rate is reached (in T)_N＝T/T_SNormalized unit of).

^VS(T_N)，^PZDS(T_N): shrinkage as normalized temperature T_NAs a function of (c).

^VAS(T_N)，^PZDAS(T_N): shrinkage rate d (S (T) as a function of temperature_N))/dT_NFrom the shrinkage curves to be compared^VS(T_N) And^PZDS(T_N) And (6) determining.

^VS_maxAnd^PZDS_max: maximum rate of contraction, according to temperature^VS(T_N) And^PZDS(T_N) The derived shrinkage curve.

The following general product properties were obtained with the powder according to the invention compared to conventionally produced spray powders:

(^PZDT_max-^PZDT₁₀)/^PZDT_max ＞ (^VT_max-^VT₁₀)/^VT_max (I)

^PZDT_max ＜ ^VT_max (II)

^PZDT₁₀ ＜ ^VT₁₀ (III)

^PZDT₁ ＜ ^VT₁ (IV)

^PZDS_max ＜ ^VS_max (V)

(^PZDT_max-^PZDT₁₀) ＞ (^VT_max-^VT₁₀) (VI)

(^PZDT_max-^PZDT₁) ＞ (^VT_max-^VT₁) (VII)

(^PZDT_max-^PZDT₁₀) ＞ (^VT₉₀-^VT₁₀) (VIII)

(^PZDT_max-^PZDT₁) ＞ (^VT₉₀-^VT₁) (IX)

from these inequalities, the following conclusions can be drawn about the different properties of the powder produced according to the invention (P2D-powder) and of a comparative powder produced by the conventional spraying method:

the sintering temperature range of PZD powder is wider.

The temperature at which shrinkage starts, reaches 10% of this final shrinkage on the basis of the same final shrinkage and reaches its maximum value is lower for the PZD powder.

The peak of the shrinkage rate obtained from the normalized graph of fig. 7 means that the PZD powder is in^PZDT_maxHas a specific comparison powder in^VT_maxLower shrinkage rate.

The initial temperature range up to the peak of shrinkage is wider for PZD powders.

The temperature range from the onset of shrinkage up to the maximum shrinkage is greater for PZD powders.

The temperature range between the temperature at which 10% shrinkage is reached and the temperature at which 90% shrinkage is reached is greater for PZD powders.

The temperature range from the start of the shrinkage until a temperature of 90% of the final shrinkage is reached is greater for PZD powders.

These conclusions are related to the single-phase starting state of the powder. Not all inequalities (I) to (IX) must always be satisfied simultaneously if other phases are present, in particular very high shrinkage rates may occur at local positions of the PZD powder compact due to the particular sintering activity of the liquid phase, which shrinkage rates constitute a further advantage with respect to processing capacity. However, the effectiveness of the inequalities (III), (IV), (VIII) and (IX) is also unaffected in this case.

The metal, alloy and composite powders according to the invention are also characterized by outstanding compression properties due to the particular particle morphology with rough particle surfaces, and by a high compression density due to a relatively broad particle size distribution. This can also be illustrated by the fact that the compacts produced with the spray powder have a lower flexural strength than the compacts produced with the powder according to the invention having the same chemical composition and the same average particle size D50, under otherwise identical production conditions. The compression properties can be further improved if a powder mixture is used which contains 1 to 95% by weight of the metal, alloy or composite powder according to the invention and 99 to 5% by weight of the spray powder.

The sintering behavior of the powders produced according to the invention can also be influenced in a targeted manner by the choice of grinding aids. One or more alloys can thus be used as grinding aids, wherein the one or more alloys, due to their lower melting point than the starting alloy, form liquid phases during heating, which improve particle rearrangement and material diffusion and thus sintering and shrinkage characteristics and thus make it possible to achieve a higher sintering density at the same sintering temperature or the same sintering density at a lower sintering temperature than with the comparative powder. It is also possible to use chemically decomposable compounds whose decomposition products with the starting material produce a liquid phase or a phase with an increased diffusion coefficient which promotes compression.

X-ray analysis of the metal, alloy or composite powder according to the invention shows a broadening of the X-ray reflection compared to the X-ray reflection of a powder with the same average particle size and the same chemical composition obtained by spraying. The broadening is manifested by a half-value width broadening. The X-ray reflection half-width is typically broadened by a factor of > 1.05. This is caused by the mechanically stressed state of the particles, the presence of a higher dislocation density, i.e. disturbances in the atomic range to the solid, and the crystallite size within the particles. In the case of composite powders, in addition to the broadening of the X-ray reflection of the main phase, there are also alloy-and/or process-induced phases in the diffraction diagram, which are very important with respect to shrinkage behavior.

The method according to the invention makes it possible to produce metal, alloy and composite powders in which the oxygen, nitrogen, carbon, boron and silicon contents are purposefully adjusted. In the case of oxygen or nitrogen incorporation, oxide and/or nitride phases may be formed due to the high energy applied. Such may be desirable for certain specific applications as they may lead to strengthening of the material. This effect is referred to as the "particle dispersion strengthening" effect (PDS effect). However, the introduction of these phases is often associated with a deterioration of the processing properties (e.g. compressibility, sintering activity). The latter may thus have a sintering-inhibiting effect due to the property of the dispersion being generally inert to the alloy constituents.

As a result of the attrition milling carried out according to the invention, the phase is immediately distributed superficially in the powder produced. The phases formed (e.g. oxides, nitrides, carbides, borides) are therefore more finely and homogeneously distributed in the metal, alloy and composite powders according to the invention than in the powders usually produced. This again leads to an increased sintering activity compared to the same phase introduced separately.

The processing properties, such as the compression and sintering properties, and the ability to be processed by metal powder injection molding (MIM), slurry-based processes or doctor blade forming, of the metal, alloy and composite powders according to the invention can often be further improved by adding metal, alloy or composite powders which are usually produced and in particular by spraying.

The invention therefore also provides mixtures which contain 1 to 95% by weight of the metal, alloy or composite powder according to the invention and 99 to 5% by weight of the metal, alloy or composite powder usually produced.

The mixture according to the invention preferably contains 10 to 70% by weight of the metal, alloy or composite powder according to the invention and 90 to 30% by weight of the conventionally manufactured metal, alloy or composite powder.

According to the invention, the conventionally manufactured metal, alloy or composite powder is preferably a powder manufactured by spraying.

The metal, alloy or composite powder generally manufactured may have the same chemical composition as the PZD powder contained in the mixture. Such mixtures differ from pure PZD powders in particular by a further improvement of the compression properties.

However, it is also possible that the PZD powder and the powder usually produced have different chemical compositions in the mixture. In this case, the composition can be varied in a targeted manner and thus the specific powder properties and thus the properties of the material can be set in a targeted manner.

The following examples are presented to illustrate the invention in greater detail, wherein these examples are presented to facilitate an understanding of the principles of the invention and are not to be construed as limiting thereof.

Examples

The average particle diameter D50 given in the examples is UmeMicrotrac of China Honeywell corporation^®X100 is determined according to ASTM C1070-01.

Example 1

Using Nimonic of composition Ni20Cr1692.5Ti1.5Al atomized with the aid of argon^®The 90 type alloy melt is used as raw material powder. The obtained alloy powder was sieved to 53-25 μm. The density is about 8.2g/cm³. The starting powder has largely spherical particles, which is evident from fig. 1 (scanning electron microscope image (SEM image) magnified 300 times).

The raw material powder was deformation-milled in a vertical stirred ball mill (Netzsch Feinmahltechnik Corp.; model PR 15) so that the initially spherical particles became flake-like. Among these, in particular the following parameters are used:

volume of grinding vessel: 5l

Rotation speed: 400 rpm

Circumferential velocity: 2.5m/s

Ball filling: 80 vol.% (bulk of pinus ball)

Grinding vessel material: 100Cr6(DIN 1.3505: about 1.5 wt% Cr, about 1 wt% C, about 0.3 wt% Si, about 0.4 wt% Mn, < 0.3 wt% Ni, < 0.3 wt% Cu, balance Fe)

Ball material: cemented carbide (WC-10Co)

Diameter of the ball: about 6mm (total mass: 25kg)

Initial weight of powder: 500g

Treatment duration: 2h

Solvent: ethanol (about 2l)

Fig. 2 is a scanning electron microscope image in which the chips manufactured in the deforming step are magnified 300 times. The high degree of deformation of the material caused by the specified grinding process can be seen compared to the starting powder. Damage to the material structure (crack formation) is also evident.

Then, the mixture is pulverized and ground. A so-called eccentric vibration mill (SiebtechnikGmbH, ESM 324) was used, in which the following process parameters were used:

volume of grinding vessel: 5l operating with a planetary mill (diameter 20cm, length about 15cm)

Ball filling: 80 vol.% (bulk of pinus ball)

Grinding vessel material: 100Cr6(DIN 1.3505: about 1.5 wt% Cr, about 1 wt% C, about 0.3 wt% Si, about 0.4 wt% Mn, < 0.3 wt% Ni, < 0.3 wt% Cu, balance Fe)

Ball material: 100Cr6

Diameter of the ball: 10mm

Initial weight of powder: 150g

Grinding aid: 2g Paraffin wax

Amplitude: 12mm

Abrasive environment: argon (99.998%).

After a milling duration of 2 hours, ultrafine particle agglomerates were obtained. Fig. 3 is a scanning electron microscope image of the product obtained at 1000 times magnification. The cauliflower-like structure of the agglomerates (secondary particles) can be seen, the particle size of the primary particles being much smaller than 25 μm.

In the third process step of deagglomeration, a sample of the primary particles or ultrafine particle agglomerates is sonicated in isopropanol in an ultrasonic apparatus TG400(sonic ultraschalllanlavanlagenbau GmbH) for 10 minutes at 50% of the maximum power to obtain separated primary particles.

Using a Microtrac^®X100 (manufacturer: Honeywell, US) the particle size distribution of the deagglomerated sample was determined according to ASTM C1070-01. Fig. 4 shows the particle size distribution thus obtained. The D50 value of the starting powder was 40 μm, and was prepared according to the inventionThe treatment was reduced to about 15 μm.

The residual amount of primary particles from the comminution grinding is carried out in an alternative third process step of deagglomeration by treatment in a gas back-jet mill and subsequent sonication in an ultrasonic apparatus TG400(Sonic ultrashallalanlangagenbau GmbH), wherein the sonication is carried out in isopropanol at 50% of the maximum power. Reuse of Microtrac^®X100 particle size. Fig. 5 shows the particle size distribution obtained. The D50 value was only 8.4. mu.m. This demonstrates the possibility of further increasing the fine particle fraction in the powder produced according to the invention by means of a high-energy aftertreatment.

Fig. 6 shows an SEM image (600 x magnification) of the powder after treatment in a gas back-jet mill. By using a suitable screening method it is accordingly possible to obtain alloy powders with a narrower particle size distribution. In this way D50 values of less than about 8 μm can be achieved industrially and economically.

The grinding aid paraffin wax introduced can be removed by thermal decomposition and/or evaporation in the powder metallurgical further processing of the alloy powder and can be used as a pressing aid.

Example 2: production of ultrafine powders of Fe24Cr10Al1Y using mechanical grinding aids without changing the composition of the raw powders

500g of a spherical Fe24Cr10Al1Y alloy raw powder with an average particle size D50 of 40 μm was processed in a deformation stage to form chips, wherein the conditions were similar to those described in example 1.

The comminution grinding is then carried out in an eccentric vibration mill as described in example 1. A mixture of pulverized brittle Fe70Cr, Fe60Al, and Fe16Y powders having an average particle size of about 40 μm and a fine Fe powder having an average particle size D50 of 10 μm was added as a grinding aid.

Grinding aid 15g was used for the attrition grinding. About 10 vol.% of the mechanical acting grinding aid addition is typical for this step. Smaller amounts of grinding aid may also be used depending on the intended purpose. The composition of the grinding aid used is summarized in table 1. A mixture comprising 65 wt% Fe, 24 wt% Cr, 10 wt% Al and 1 wt% Y was obtained. The chemical composition of the starting powder is therefore not changed by selecting a given alloy content. The composite powder obtained by the production according to the invention has a specific distribution of the components used (raw powder, grinding aid) so that the composite powder undergoes a metallurgical change during further processing, for example by sintering or another heat treatment.

TABLE 1 composition of mechanical grinding aid

Components	Dosage [ g ]]	Fe[g]	Cr[g]	Al[g]	Y[g]
						Fe16Y	0.93	0.78	0	0	0.15
Fe60Al	2.50	1.0	0	1.5	0
						Fe70Cr	5.14	1.54	3.6	0	0
Fe	6.43	6.43	0	0	0
						Total amount of	15	9.75	3.6	1.5	0.15

After attrition milling and deagglomeration in an ultrasonic field, a composite powder with an average particle diameter D50 of 15 μm was obtained. An alloy can be obtained from such composite powders metallurgically by means of a thermodynamic after-treatment.

Example 3

Production of ultrafine powders of Fe24Cr10Al1Y using mechanical grinding aids and varying the composition compared to the starting powder

Unlike example 2, a change in chemical composition is desired or allowed during the grinding operation. A spray alloy having an average particle size D50 of 40 μm and a composition of Fe25, 6Cr10, 67Al was subjected to a deformation step under the conditions described in example 1. Flaky particles having an average particle diameter D50 of 70 μm were obtained, the appearance of which was not significantly different from that in example 1.

Then, the mixture is pulverized and ground. The procedure was as in example 1, but 10g of Fe16Y powder having an average particle diameter D50 of 40 μm were used as grinding aid and grinding was continued for 2 hours.

Table 2 shows the composition and amount of flake-form starting alloy and grinding aid added for attrition grinding.

TABLE 2 composition of flake-like starting alloy and of mechanical grinding aid used

Components	Dosage [ g ]]	Fe[g]	Cr[g]	Al[g]	Y[g]
						Fe25，6Cr10，67Al	150	95.6	38.4	16.0	0
Fe16Y	10	8.4	0	0	1.6
						Total amount of	160	104	38.4	16.0	1.6

As can be seen from table 2, the composition of the obtained composite powder was Fe24Cr10Al 1Y. The composite powder was subjected to ultrasonic treatment to obtain a composite powder having an average particle diameter D50 of 13 μm after the treatment.

Example 4

The procedure is as in example 3, but a mixture of a number of brittle materials and pure iron powder is used as grinding aid.

Table 3 includes the composition and weighing of the raw material powder and grinding aid. Brittle grinding aids Fe60Al, Fe70Cr and Y2, 2H were treated in a separate grinding step to an average particle size D50 of 40 μm prior to use. The average particle diameter D50 of the Fe powder used was 10 μm.

TABLE 3 composition of flake-shaped starting alloy and of mechanical grinding aid used

Components	Dosage [ g ]]	Fe[g]	Cr[g]	Al[g]	Y[g]
						Fe25，6Cr10，67Al	150.00	95.60	38.40	16.00	0.00
Fe60Al	1.19	0.48	0.00	0.71	0.00
						Fe70Cr	2.35	0.71	1.64	0.00	0.00
Y2，2H	1.66	0.00	0.00	0.00	1.66
						Fe	10.00	10.00	0.00	0.00	0.00
Total amount of	165.20	106.79	40.04	16.71	1.66

As can be seen from table 3, the composition of the obtained composite powder was Fe24Cr10Al 1Y. The composite powder was subjected to ultrasonic treatment, and after the treatment, a composite powder having an average particle diameter D50 of 15 μm was obtained.

Example 5 production of ultrafine powders of Fe24Cr10Al1Y from two FeCrAl master alloys using Fe16Y as a separate brittle mechanical grinding aid

In a separate deformation step similar to example 1, chips with an average particle size D50 of 70 μm were produced from two spray alloys of composition Fe19, 9Cr24, 8Al and Fe27, 9Cr5Al with an average particle size D50 of 40 μm, the appearance of which was not significantly different from the powder shown in fig. 2.

In the subsequent comminution grinding, a particularly brittle Fe16Y alloy, which had been comminuted beforehand to an average particle diameter D50 of about 40 μm, was used as the sole grinding aid. The procedure is as in example 1, grinding is continued for 2.5 hours.

Table 4 includes the composition and weighing of two flake-like FeCrAl starting alloys and a brittle grinding aid (Fe 16Y).

TABLE 4 flake-shaped starting alloy and mechanical grinding aid usedComposition of the agent

Components	Dosage [ g ]]	Fe[g]	Cr[g]	Al[g]	Y[g]
						Fe19，9Cr24，8Al	43	23.8	8.6	10.5	0
Fe27，9Cr5Al	107	71.8	29.8	5.5	0
						Fe16Y	10	8.4	0	0	1.6
Total amount of	160	104	38.4	16	1.6

As can be seen from table 3, the composition of the obtained composite powder was Fe24Cr10Al 1Y. The composite powder was subjected to ultrasonic treatment, and after the treatment, a composite powder having an average particle diameter D50 of 12 μm was obtained.

Example 6 in situ grinding aid Generation

To an atomized Ni15Co10Cr5, 5Al4, 8Ti3Mo1V alloy (commercially available under the trade name IN 100)^®) The deformation step was carried out under an inert atmosphere as described in example 1.

No brittle grinding aid was added during the subsequent attrition grinding process, rather it was formed in situ during grinding. For this purpose, the eccentric vibration mill was filled with a gas mixture consisting of 94 vol.% argon and 6 vol.% hydrogen. The milling vessel is thermally insulated so that the process temperature is adjusted to about 300 ℃ during milling due to the application of energy. The remaining milling conditions corresponded to the procedure described in example 1. The increased temperature and increased hydrogen content in the process gas lead to the formation of brittle Ti-H and V-H compounds which act in the same manner as the grinding aids introduced in examples 1-5 and thus lead to comminution. After milling in a hydrogen-containing atmosphere for 3 hours, an alloy powder having an average particle diameter D50 of 13 μm was obtained.

The chemical composition of the resulting ultra-fine powder is only slightly different from that of the raw material powder. The hydrogen content rises to < 1000 ppm. During the further processing of the alloy powder produced according to the invention, the hydrogen content is again reduced to below about 50ppm by sintering under vacuum.

Example 7Si powder as mechanical grinding aid

The deformation step was carried out as described in example 1 on spherically atomized Ni38Cr8, 7Al1, 09Hf with an average particle size D50 of 40 μm.

150g of the flakes produced in the pulverizer were subjected to pulverization and grinding in an eccentric vibration mill as described in example 1, to which 13g of Si powder having an average particle diameter D50 of 40 μm was added as a grinding aid. After grinding for 2 hours, an alloy powder having an average particle diameter D50 of 10.5 μm and a desired composition Ni35Cr8Al8Si1Hf was obtained. The silicon used is desirable or necessary from an alloy process handling point of view. Among the brittle grinding aids possible, Si is particularly suitable due to its properties. After treatment, the oxygen content was about 0.4 wt%.

Example 8

Ni38Cr8, 7Al1, 09Hf were spherically sprayed with an average particle diameter D50 of 40 μm, and a deformation step was performed by using an attritor (stirred ball mill) as described in example 7.

Subsequently, the comminution grinding was carried out in the presence of Si powder (13g) as grinding aid, also in a stirred ball mill, using the following process parameters:

volume of grinding vessel: 5l

Ball filling: 80vol. -%)

Grinding vessel material: 100Cr6

Ball material: 100Cr6

Diameter of the ball: 3.5mm

Powder weighing: 150g of Ni38Cr8, 7Al1, 09Hf

Circumferential velocity: 4.2m/s

The grinding liquid: ethanol

Duration of grinding: 1.5h

Grinding aid: 13g of Si powder (D50: about 40 μm)

After grinding for 1.5 hours and subsequent ultrasonic deagglomeration, an alloy powder with an average particle diameter D50 of 13 μm was obtained, from Microtrac^®X100 is measured. Silicon used herein is desirable or necessary both from the standpoint of alloying process to adjust the final composition to Ni35Cr8Al8Si1Hf and from the standpoint of processing to obtain the desired grinding effect. Among the elements that can be considered, silicon is most suitable as a grinding aid due to its brittleness. This milling treatment results in an increase in the oxygen content of the powder. The oxygen content at the end of the grinding treatment was 0.4% by weight.

Example 9

A spherically atomized Ni17Mo15Cr6Fe5W1Co alloy (commercially available under the trade name Hastelloy) having an average particle size D50 of 40 μm^®) Subjected to a deformation step as described in example 1.

The resulting flakes were ground in an eccentric vibratory mill with tungsten carbide as grinding aid under the following conditions:

volume of grinding vessel: 5l

Ball filling: 80vol. -%)

Grinding vessel material: 100Cr6

Ball material: WC-10Co hard alloy material

Diameter of the ball: 6.3mm

Powder weighing: 150g

Amplitude: 12mm

Abrasive environment: argon (99.998%)

Duration of grinding: 90 minutes

Grinding aid: 3.5g WC powder (D501.8 μm)

As a result of the pulverization grinding, an alloy-hard material composite powder was formed in which the alloy component had been pulverized to an average particle diameter D50 of about 5 μm and the hard material component had been pulverized to an average particle diameter D50 of about 1 μm. The hard material particles are distributed as uniformly as possible in the volume of the alloy powder.

The alloy-hard material composite powder may be processed by conventional processing steps to form a spray powder. To this end 797g of WC having an average particle diameter D50 of 1 μm, measured according to ASTM B330 (FSSS), ethanol, PVA (polyvinyl alcohol) and a suspension stabilizer were added to 163g of the alloy-hard material composite powder produced according to the invention for dispersing and producing a suspension. A suspension consisting of 25 vol.% of the metallic binder phase and 75 vol.% of the WC hard material phase was produced. This suspension was further processed by spray granulation and classification to form an initial spray powder with a particle size of 20-63 μm. The organic additives were first removed from this initial spray powder by degassing at 100-400 ℃ and then sintering occurred at about 1300 ℃ under an inert atmosphere. In the process, a tight connection is produced in the spray particles and a less tight connection is formed between the individual small particles. Finally deagglomeration is carried out and classified into the desired particle fractions (for example 15-45 μm). The powder thus obtained may be further processed by thermal spraying in a known manner to form parts coated with cemented carbide or an alloy-hard material composite.

Example 10

According to the invention, a titanium powder with an average particle size D50 of 100 μm was treated in analogy to example 1 to form chips.

The splits were then further processed in a comminution step similar to example 1, with 10g of TiH being added to the Ti splits used (weighing: 150g)₂Used as a grinding agent. After the pulverization and grinding, a fine titanium powder having an average particle diameter D50 of about 15 μm was obtained.

The titanium powder produced according to the invention can be further processed by customary process steps to form moulded bodies. To prevent oxidation, the titanium powder produced according to the present invention is stored in an organic solvent such as n-hexane. Long-chain hydrocarbons, such as paraffins or amines, are added before the powder metallurgy further processing. For this purpose, the paraffin is dissolved in, for example, n-hexane and added to the powder, which is then evaporated by continuously recycling the powder. A surface seal against uncontrolled oxygen absorption and an improvement in compressibility are thereby obtained. This step makes it possible to treat the titanium powder in air.

After the powder process treatment to form a molded body by uniaxial compression, removal of organic components, thermal decomposition of grinding aids and sintering were carried out in a heat treatment to form a molded body as dense as possible.

Example 11

Will be similar to example 1 from alloys 17-4PH^®The chips produced (fe17cr12ni4cu2.5mo0.3nb) were treated in a reverse jet mill. The chips had a particle size to particle thickness ratio of about 1000: 1 and an average particle size D50 of 150 μm. The reverse jet mill was operated under inert gas. An unpretreated sprayed spherical material of the same alloy with a particle size of 100-63 μm was used as a grinding aid. The grinding chamber (volume: about 51) was filled with a total volume of 2.5l (67% by weight of grinding aid and 33% by weight of chips) of powder and the grinding process was started. The produced fine fraction of 10 μm was separated by corresponding adjustment of the screen connected downstream of the mill.

By means of said steps, in contrast to the preceding examples, the comminution grinding and the usually required deagglomeration are carried out in one step. This step is characterized by the use of special or alloy-like powders which cannot or hardly be ground, which results in greater energy application during grinding and thus in an improved grinding effect.

Example 12

Atomized Ni17Mo15Cr6Fe5W1Co alloy (commercially available under the trade name Hastelloy) having an average particle size of 100-63 μm was milled in a high-energy mill (eccentric vibration mill)^®) The mechanical treatment was carried out under the following conditions:

volume of grinding vessel: 5l (diameter 20cm, length about 15cm)

Ball filling: 80vol. -%)

Grinding vessel material: 100Cr6

Ball material: WC-Co hard alloy

Diameter of the ball: 10mm

Powder weighing: 300g

Amplitude: 12mm

Abrasive environment: argon (99.998%)

Duration of grinding: 2h

The chips were produced with a 1: 2 ratio of diameter to thickness and a chip thickness of about 20 μm.

Then the grinding is carried out in a gas back-jet mill. During the comminution, particles with a particle size of < 20 μm are removed by suitable adjustment of the downstream-connected sieve. Thus, after the ultrasonic treatment, a fine alloy powder having an average particle diameter D50 of 12 μm and a D90 value of 20 μm was produced, and Microtrac was used as the average particle diameter value^®X100.

Claims (17)

1. Method for producing metal, alloy and composite powders having an average particle diameter D50 of at most 25 [ mu ] m from starting powders having a larger average particle diameter D50 using a particle size measuring instrument Microtrac^®X100 is measured according to ASTM C1070-01, said method being characterized in that:

a) the particles of the raw material powder are processed in a deformation step into flake-like particles having a ratio of particle size to particle thickness of between 10: 1 and 10000: 1, and

b) the flake-like particles are subjected to crushing grinding in the presence of a grinding aid.

2. The process according to claim 1, characterized in that the deagglomeration step is carried out after the attrition milling.

3. The method according to claim 1 or 2, characterized in that the metal powder, alloy powder or composite powder has the composition of formula (I)

hA-iB-jC-kD (I)

Wherein

A represents one or more elements selected from Fe, Co and Ni,

b represents one or more elements selected from V, Nb, Ta, Cr, Mo, W, Mn, Re, Ti, Si, Ge, Be, Au, Ag, Ru, Rh, Pd, Os, Ir, Pt,

c represents one or more elements selected from Mg, Al, Sn, Cu, Zn, and

d represents one or more elements selected from Zr, Hf, rare earth metals,

and h, i, j and k represent the weight contents, wherein

In each case h, i, j and k represent, independently of one another, from 0 to 100% by weight, with the proviso that the sum of h, i, j and k is 100% by weight.

4. The method of claim 3, characterized in that

A represents one or more elements selected from Fe, Co and Ni,

b represents one or more elements selected from V, Cr, Mo, W, Ti,

c represents one or more elements selected from Mg, Al, and

d represents one or more elements selected from Zr, Hf, Y and La.

5. A process as claimed in claim 3 or 4, characterized in that

h represents 50 to 80% by weight,

i represents 15 to 40% by weight,

j represents 0 to 15% by weight,

k represents 0 to 5% by weight,

provided that the sum of h, i, j and k is 100 wt%.

6. The method according to any of claims 1 to 5, characterized in that the metal powder, alloy powder or composite powder produced has an average particle size D50 of at most 15 μm, said average particle size D50 using Microtrac^®X100 is determined according to ASTM C1070-01.

7. The method according to any one of claims 1 to 6, characterized in that the starting powder is a spherical or irregularly shaped powder having an average particle size D50 of more than 25 μm, the average particle size D50 using Microtrac^®X100 is determined according to ASTM C1070-01.

8. The method of any of claims 1-7, characterized in that the deforming step is performed in a roll mill, a vortex mill, a high energy mill, or an attritor.

9. A method according to any one of claims 1 to 8, characterized in that a liquid grinding aid, waxes and/or brittle powders are added as grinding aid during the comminution grinding.

10. The method according to claim 9, characterized in that the grinding aid is paraffin oil, paraffin wax, metal powder, alloy powder, metal sulfide, salt and/or hard material powder.

11. A process according to any one of claims 1 to 10 characterised in that the grinding aid is formed in situ during the attrition milling process.

12. The method of claim 11 characterized in that the grinding aid is formed by adding a reactive gas which reacts with the feedstock powder under attrition milling conditions and simultaneously forms a brittle phase.

13. The process according to any of claims 2 to 12, characterized in that the deagglomeration is carried out in a gas back-jet mill, an ultrasonic bath, a kneader or a rotor-stator system.

14. A process according to any one of claims 2 to 13, characterised in that the deagglomeration is carried out in the presence of one or more liquids, dispersion aids and/or binders.

15. Metal powders, alloy powders and composite powders having an average particle size D50 of at most 25 μm, obtained by the method of any one of claims 1 to 14, wherein the average particle size D50 is measured using a particle gauge Microtrac^®X100 is determined according to ASTM C1070-01.

16. A metal powder, alloy powder or composite powder having an average particle size D50 of at most 25 μm, wherein the average particle size D50 is measured using a particle gauge Microtrac^®X100 is measured according to ASTM C1070-01, characterised in that, until the maximum shrinkage is reached, which is at least 1.05 times that of a metal powder, alloy powder or composite powder prepared by spraying, having the same chemical composition and the same mean particle diameter D50, the shrinkage being measured using an dilatometer according to DIN 51045-1, the powder to be investigated being compressed to a compressed density of 50% of the theoretical density before the shrinkage is measured.

17. A mixture comprising 1 to 95% by weight of a metal powder, alloy powder or composite powder according to claim 15 or 16 and 99 to 5% by weight of a metal powder, alloy powder or composite powder produced by spraying.