WO2008031122A1

WO2008031122A1 - Method for production of composite powders and composite powder

Info

Publication number: WO2008031122A1
Application number: PCT/AT2007/000408
Authority: WO
Inventors: Andreas Bock; Annegret Bicherl; Andreas Schön; Burghard Zeiler; Wolf-Dieter Schubert
Original assignee: Wolfram Bergbau- Und Hütten-Gmbh Nfg. Kg
Priority date: 2006-09-15
Filing date: 2007-08-24
Publication date: 2008-03-20
Also published as: JP2010503765A; AT504319B1; AT504319A1; EP2061615A1

Abstract

The invention relates to a method for production of a composite powder, wherein a powder starting material A, comprising at least tungsten and/or molybdenum and/or alloys and/or compounds of said metals is mixed with a powder starting material B, comprising at least Co and/or Fe and/or Ni and/or alloys and/or compounds of said metals, in the mixture an element ratio of tungsten and/or molybdenum to Co and/or Ni and/or Fe is set to the range of 99 : 1 (A:B) to 50 :50 (A:B) wt. % and the powder mixture is subjected to a reduction process in the course of which the charged Co, Fe and/or Ni is covered over by a layer of W and/or Mo. The composite powder obtained thus can be partly carburised, nitrided or carbonitrided in a subsequent process step.

Description

Process for the production of composite powders and composite powder

The invention relates to a method according to the preamble of claim 1 and a composite powder produced by this method according to the preamble of claim 15.

Furthermore, the invention relates to a method according to the preamble of claim 23 and to a composite powder produced by this method according to the preamble of claim 18.

An essential object of the invention is the production of a composite powder in a simple and rapid manner in which the yield of composite powder is as large as possible.

The composite powder obtained by the process according to the invention is intended for further

Uses are well suited; in particular, sintering processes, e.g. for the sintering of semi-finished products, tools and similar objects, economically feasible and from the material parameters with good results. Furthermore, such powders for the production of hard metal powders, in particular for sintering and melting of nitirated or carburized hard materials, especially so-called hard metals and hard coatings, should be well usable.

These objects are achieved in a method of the type mentioned above with the features mentioned in the characterizing part of claim 1. Advantageous embodiments of the method are given in claims 2 to 13.

The composite powder produced by these process steps according to the invention is characterized in particular by the features of claim 15. It turns out that these powders are good sinterable or can be converted well into hard materials. The composite powders comprise metallic cores or core particles which are overgrown throughout, but at least at least 50%, with a cladding layer of tungsten and / or molybdenum or a compound of these metals, in stoichiometric form or in the form of a metallic phase.

Further advantageous features of such a composite powder can be found in claims 16 to 21.

A method according to the preamble of claim 22 is inventively characterized by the features cited in the characterizing part of claim 22. The composite powder used to carry out this process is nitrided and / or carburized in a particularly good, rapid and homogeneous manner and gives very good material parameters. The reaction with the corresponding elements carbon and / or nitrogen is advantageously carried out according to the features indicated in claims 23 to 26.

With this method, a composite powder is created, which is characterized by the features of claim 5 characterizing claim 28. This powder has good Sinterbzw. Further processing properties and is versatile.

Advantageous features of such composite powder can be found in claims 29 to 34.

Carbides require an optimal distribution of the binder and the

10. Hard material phase, in particular by the trend towards ever finer carbides. Likewise, a uniform carbide is required in terms of grain size for good mechanical properties. In conventional hard metal production, the hard material phase (e.g.

WC) with the binding metal (for example: Co) in ball mills or attritors for several hours. The biggest difficulty is the even distribution of

15 tungsten carbide (hard material) and cobalt (binder) to achieve what in long mixing or

Grinding times results.

In order to provide a good binder distribution already in the powder, various technological approaches for WC-Co composite powder were investigated, so that long grinding processes for hard metal approaches can be shortened. It is usually assumed that Co 20 tungsten or Co-W oxide mixtures, which are prepared by co-precipitation, spray drying or decomposition or thermal decomposition (calcination) of Co-W salts. The resulting Co-W composite oxide powders are usually in the nano range. According to the Nanodyne process for the production of WC-Co composite powder is based on Co-W solutions, which spray and then react in a fluidized bed to WC-Co powders. This results in an extremely fine product, consisting of hollow spheres, which remain up to WC-Co, but are difficult to grind and cause difficulties during pressing.

W-Co composite powders are made by single-stage reduction of the oxide composite powder

30 produced. Using X-ray diffractometry, the resulting intermetallic

Phases Co ₃ W and Co ₇ W _{6 are} detected. As part of technical

Studies of tungsten reduction could be the incorporation of impurities in the

Tungsten during the reduction by the Gäsphasenprozess W0 ₂ (s) → WO ₂ (OH) ₂ (Sf) →

W (s) are also shown on the basis of cobalt, among others.

35 A large number of technological processes are leading the way in direct reduction or carburization of Co-W composite oxide powders, resulting in a passable one Distribution of WC-Co by coating the WC particles with cobalt or intimate, nanocrystalline WC-Co mixtures.

The carburization of W-Co mixtures or composite powder offers the advantage of a low carburizing temperature, since cobalt catalyzes the carburization. The 5 carburizing of nanocrystalline W-Co powders occurs already below 900 ⁰ C.

The present invention relies predominantly on the fact that the

Dispersibility and thus uniformity of the distribution of cobalt and / or iron and / or nickel, especially by the precursors and pre-distribution and the

Volume ratios of the starting materials is controlled. For the present invention applies that tungsten and molybdenum and / or

Compounds of these metals considered equivalent and against each other in the

Starting material A can be exchanged. The same applies to the metals iron, cobalt and nickel and their compounds, which can also be exchanged with each other. The composite powders obtained with the invention thus contain a core of 5 Fe and / or Co and / or Ni and / or their alloys, which is at least partially coated with a cladding layer of carbides and / or nitrides of the metals W and / or Mo and / or

Compounds of these metals are surrounded.

The intermediate composite powder which is also self-contained for certain uses, e.g. For sintering purposes, comprises particles 0 with a cladding layer of tungsten and / or molybdenum and / or their compounds which at least partially surround a core of iron and / or cobalt and / or nickel and / or their alloys and / or their compounds ,

Such composite powders are particularly advantageous if the metal of the

Kerns cobalt is, as by a coating of molybdenum and / or tungsten and / or 5 molybdenum and / or tungsten carbide, the internal oxygen-sensitive metal before

Oxidation is protected. Furthermore, the grain size of the core particles and the

Sheath layer by varying the proportions, the particle size and the

Reaction temperatures easily controlled and within certain limits with large

Accuracy can be adjusted. 30 The hard metal made of the hard metal composite powder has a uniform structure, an optimal distribution of the elements used, no local

Carbide growth and a fine structure already without use of

Grain growth inhibitors.

Another advantage is the good dispersibility of iron and / or cobalt 35. and / or nickel and thus a uniform distribution of elements.

For the preparation of the composite powder is preceded by a starting material A with a

Starting material B mixed. The starting material A comprises

Oxidic compounds of tungsten and / or molybdenum and / or other compounds and / or alloys of these metals, in particular

WO ₃ , WO ₂₉ , W ₂₀ Os ₀ , WO ₂₇₂ , Wi ₈ O ₄₇ or other W oxides, H ₂ WO ₄ ,

Ammonium paratungstate (APW) ₁ ammonium metatungstate (AMW), WO ₂ ,

MoO 3, MOO ₂ .9 ₂ , Mo ₁₃ O ₃₈ , Mo ₄ Oi ₁ or other Mo oxides, H ₂ MoO ₄ (MoO 3 H ₂ O), (NH ₄ ) ₂ MoO ₄ , ammonium dimolybdate ADM ((NH ₄ J ₂ '2MoO ₃ ), (NH ₄ ) ₂ O ^• 6MoO ₃ ,

MoO ₂ - The starting material B comprises:

Co and / or Fe and / or Ni and / or alloys and / or compounds of these metals, in particular CoO, Co ₃ O ₄ , Co ₂ O ₃ , CoO ₂ , Co-hydroxides, Co (OH) ₂ , CoOOH, CoWO 4, Co7W6, Co ₃ W

FeW, Fe ₂ W, Fe ₃ W ₂ , Fe ₇ W ₆ , NiW, NiW ₂ , Ni ₄ W, oxides, hydroxides and / or tungstates of Co and / or Fe and / or Ni and / or salts, in particular acetates or Oxalates, of Co and / or Fe and / or Ni, and / or Metal Tungsten Oxiόbrons (Metal = Fe, Co, Ni)

After mixing the starting material A with the starting material B in the predetermined ratio, e.g. by mixing in a tumble mixer and / or wet or dry grinding, e.g. in a ball mill, an attritor, one

Planetary ball mill and / or dispersing and / or spraying, takes place after any required drying the reduction process.

Appropriately, it is provided that the starting materials A and B dry or wet over a period of 1 to 300 h, preferably 1 to 50 h, in particular homogeneously, are mixed.

The reduction process takes place in a hydrogen atmosphere, it being advantageously possible for the duration of the reduction process to be set to 10 minutes to 10 hours. The reduction process is carried out at a temperature of 200 to 1200 ⁰ C.

It is provided that the particle size of the starting material A is 50 nm to 200 μm, preferably 80 nm to 50 μm, and the particle size of the starting material B is 10 nm to 50 μm, preferably 30 nm to 5 μm.

It is also possible to use non-pure metals or compounds or alloys of the two starting materials A and B; It is also possible to dope the metals of the starting materials or of the compounds used. Advantageous it is when the metals present in the starting material A, W and / or Mo and / or alloys and / or compounds, in particular metal oxides, of these metals with Cr and / or V and / or Mo and / or Ta and / or Nb in one Extent of 50 ppm to 2 wt .-% of (r) used in the starting material A metal (s) s are doped or if provided in the starting material B metals Co, Fe and / or Ni and / or alloys and / or compounds of these Metals are doped with Cr and / or V and / or Mo and / or Ta and / or Nb in an amount of 50 ppm to 20 wt .-% of (r) used in the starting material B metals (s).

The starting materials used can be present in various forms; It is advantageous if the doped metals or the doped metal compounds in the form of pure metals oxides, nitrates, acetates, formates, oxalates, liquid salt solutions and / or solid powders or solid salts, in particular in the form of tungstates or molybdenum, tungsten oxide bronzes and / or molybdenum oxide bronzes, are present! The reduction process can be carried out in different ways.

Advantageously, one-stage, two-stage or three-stage reduction operations are feasible. In this regard, the features of claims 9, 10 and 11 are advantageous.

It is envisaged that a heating rate and / or a cooling rate between 1 and 500 K / min is set. The dumping height of the mixed starting materials present in powder form must be selected as a function of the raw materials and their pouring properties (in particular bulk density, porosity).

When using tungsten and molybdenum on the one hand and iron or cobalt or nickel on the other hand one obtains intermetallic phases of tungsten with iron, cobalt and / or nickel, but in the reduction by a gas phase transport process, at least 50% of the core particles of tungsten and / or molybdenum overgrown. When using tungsten-containing starting material A and Co as the starting material B, a composite powder is obtained in which the cobalt is present predominantly as intermetallic phase Co ₇ W _{6 in} addition to cobalt, depending on the quantitative ratio used and on the particle size of the starting material B. The resulting Co-W composite powder has a particle size in the range of 50 nm to 50 microns. If agglomerates are present in the starting powder of the core particles, ie the starting material B, a completely optimal dispersion of the core component at the crystallite level will no longer be present, nevertheless the agglomerate regions as such are overgrown by tungsten or molybdenum.

The procedure described gives a Co-W composite powder in which the cobalt predominantly as intermetallic phase Co ₇ W _{6 in} addition to Co (fcc) (depending of used quantity ratio and particle size) is present. When W or Mo is used in the starting material A and Co, Fe, Ni, intermetallic phases of W and Mo are obtained with Co, Fe and / or Ni, which in the reduction by a gas phase

Transport process are ≥ 50% of tungsten or molybdenum overgrown. The resulting Co-W composite powders have a particle size in the range of 50 nm -

50 .mu.m.

The process of overgrowth works through the gas phase transport of

WO2 (OH) ₂ or WO3 ₍ g) or a corresponding Mo compound. This works

Cobalt acts as a nucleation aid for tungsten metal (or Mo) and causes a redistribution of the tungsten (Mo) with well-distributed Co (Fe, Ni) and thus leads to a very uniform composite powder. The macroscopic morphology of Co-W

Composite powder corresponds to the macroscopic morphology of the powder of the core component used.

In Fig. 1, the addition of the starting material B is shown as a cladding layer on the core particle. By the corresponding addition results in a particle of the composite powder, which is shown in Fig. 1 right. With 1, WO ₂ , with 2 Co (resp.

Co ₇ W ₆ ), designated 3 WO ₂ (OH) ₂ and 4 W.

In Fig. 2 is a mathematical model concerning the structure of the

Composite powder explained. The mathematical model assumes that the powder particles are spherical and ideally uniform and complete as core-shell structures.

Likewise, the calculation is based on Co-metal, whereby the formation of an intermetallic phase is neglected here.

V ₂ = | πR ^

If we now put the volumes of the substances used W / WC and Co in relation, we obtain a logical radius relationship, with the knowledge of the

Radius of the core component or core particle and W: Co / WC: Co

Quantitative ratio of the layer thickness of the shell and the particle size of the composite powder particle can be estimated:

(R? :) _ V _A

R ³ ₂ V _B

It is thus advantageous if, for the mean radius of the particles of the

Composite ^powder is: 0.6 ^■ X <R ₁ <1, 2 X, where X = R ₂

in which

R1 mean radius of the particles of the composite powder V _A volume of the metals of the starting material A

V _B Volume of the metals of the starting material B

R ₂ mean radius of the particles of the starting material B or the Kemteilchen are.

In the procedure according to the invention can be selected by the choice of

Grain size of the starting material B control the grain size of the resulting composite powder, since the thickness of the cladding layer of the resulting composite powder corresponds to the difference of the radii Ri - R ₂ .

Figure 3 shows a schematic of the metal composite powders denoted by 4W, _5Co 7W ₆ and 6Co. The occurring Co-W or Co-WC composite powder particles are shown schematically. Depending on the weight ratio W: Co and the distribution of the W and Co phases, holistic (a) and partially overgrown structures are possible (c). Similarly, with a correspondingly high Co content and large particles, a 2-layer structure can be formed Co-metal core consists of a cladding of intermetallic phase surrounded by tungsten (b). In (d) and (e) possible overgrowths of non- spherical particles and agglomerates.

The cobalt powder for the overgrowth is shown in Figure 4 (Umicor ultrafine 0.9 μm). The mean SEM grain size of the spherical powder is intermediate

0.2-0.7 μm with agglomerates up to 1.5 μm. The comparison with the Co-W composite powder shows that the macroscopic morphology of the starting powder (Co) is maintained, indicating a uniform overgrowth (see also Figure 5).

Figure 4 shows SEM images of Umicor cobalt powder for overgrowth (left) and Co-W composite powder (right).

There are no crystals of W (typically faceted) in the powder, indicating that the whole W is grown on cobalt.

Figure 5 shows SEM images of the co-powder used (left) and the Co-W powder (right); the picture shows the distribution and macroscopic morphology of the powder.

Figure 6 shows an X-ray diffractogram of the Co-W powder. Figures 7 and 8 show light micrographs of the Co-W

Composite powder in Cu-cut. The distribution of W and Co is clearly visible. Figure 7 shows a powder etched with diluted Murakami, the etched raised phases indicate the Co ₇ W ₆ . It turns out, however, apart from preparative effects, that not all Co or Co ₇ W _{6 is} completely overgrown. This is partly due to the relatively non-uniform co-output powder (agglomerates, uneven particle size distribution) or powder beds are 3-dimensional body, in which the view is dependent on the polished section.

Figure 7 is a photomicrograph of Cu-W Co-W composite powder: etched raised phases (dark) - Co ₇ W ₆ Figure 8: Photomicrograph of Co-W composite powder in Cu

Cut; bright: Co ₇ W ₆ , dark: W

Figure 9: SEM images of the Co-W powder in copper ground (Co ₇ W ₆ -W) Figure 10: SEM images of the Co-W powder in copper ground (Co ₇ W ₆ -W) The SEM images according to Figure 9 to 10 with the back-scattered detector show the Co-W composite powder in Cu-cut. The areas of the intermetallic phase Co ₇ W ₆ and light tungsten (black = copper (embedding agent)) appear dark.

The resulting composite powders generally exhibit a thickness of the cladding layer of 8 nm to 15 μm.

The results of X-ray diffractometry show tungsten in bcc-form and Co ₇ W ₆ and Co in fcc-form. The oxygen content of the composite powder is <5000 ppm. The particle size of the composite powder is about 50 nm to 50 microns determined by scanning electron microscopy. Of great importance is that, despite the solubility of tungsten in the core component and the formation of intermetallic phases (eg: between cobalt and tungsten), a composite powder is produced which has core particles coated with a cladding layer of a certain thickness and the metals of the starting material A, which are now carburized and / or nitrated, of the metals of the starting material B separated by a phase boundary. Formed phases between cobalt and tungsten are redissolved during nitriding or carburizing.

It should also be noted that the starting materials or compounds used should have a high degree of purity or impurities should be present in a degree usual in the field of hard metals.

In order to prepare composite powders in whose shell layer carbides and / or nitrides are present, the process described so far is continued such that the composite powder obtained or already undergoes a reaction in which the cladding layer of the particles of the resulting composite powder carbon and / or Nitrogen be stored. For this purpose it can be provided that the resulting composite powder with carbon, preferably in the form of carbon black and / or graphite, is mixed and / or in an atmosphere of H ₂ and N ₂ and / or H ₂ / CH ₄ and / or CO and / and or CO _{2 is} heated to a temperature of 800 to 1500 ⁰ C, so that the metals in the cladding layer are converted into the corresponding compounds with carbon and / or nitrogen, in particular nitrides and / or carbides, preferably in tungsten monocarbide.

The mixing of the already existing composite powder with carbon black or graphite can be carried out in conventional mixing or milling units, such as e.g. Tumble mixers, ball mills, planetary ball mills, attritors or dispersers. After appropriate mixing and in particular homogenization of the composite powder used, it is provided that the carburization and / or nitration is carried out at a, in particular constant, temperature for 10 minutes to 50 hours, optionally with a heating rate and / or a cooling rate of 1 to 500 K. / min is set. The atmosphere for the reaction is chosen according to the desired compound; accordingly, the temperatures are set.

The composite powder obtained in the course of the reaction comprises cores or core particles of Co and / or Fe and / or Ni, which are overgrown with a cladding layer of W and / or Mo, which are carburized and / or nitrated.

Figure 11 illustrates schematically a Co-WC composite powder consisting of a Co core (a cobalt alloy) and a WC jacket, showing a Co-WC composite powder, designated 6 cobalt and 7 tungsten carbide.

Figure 12 shows the X-ray diffractogram of the Co-WC composite powder with the occurring phases WC and Co (fcc).

The SEM images (Figure 13) of the WC-Co composite powder show that the pseudomorphism to the co-output powder is maintained.

Figure 14 clearly shows the co-WC composite powder with a core-shell structure (inside cobalt outside WC).

The composite powders obtained by the reaction show that at least 50% of the particles are completely overgrown with the cladding layer containing carbides and / or nitrides. Further, in the composite powder Co in face-centered cubic form and the WC contained in the sheath layer are in hexagonal form. The composite powder has a particle size of 50 nm to 50 microns, wherein the thickness of the cladding layer is 8 nm to 50 microns.

With these powders, it may also be provided on the basis of the starting composite powder used that at least one of the metals used contains Cr and / or V and / or Mo and / or Ta and / or Nb in an amount of from 50 ppm to 20% by weight. doped of the doped metal.

In the following the invention will be explained in more detail by means of examples.

Example 1 :

WO ₂ (0.5-2 μm) is intimately mixed with Co metal powder (0.5-1 μm) in a ratio W: Co of 90:10 by means of a tumble mixer for 40-60 minutes. This mixture is then reduced with hydrogen at a temperature profile of 700-950 ⁰ C. The result is a Co-W composite powder in which Co is present predominantly as an intermetallic phase (Co ₇ W ₆ ) and is ≥ 80% of tungsten overgrown, the particle size is in the range of 1-2 microns with a W-layer thickness of 0, 2-0,4μm. By carburizing this composite powder with carbon (carbon black), a Co-WC composite powder is formed, wherein the cobalt is surrounded to> 80% by tungsten carbide, the composite powder Co-WC has an average particle size of 1-2 μm, whereby the WC layer has a thickness of 0.3 μm. 0.5μm. The co-WC composite powder was then treated in cyclohexane for 2 hours or 24 hours with the addition of pressing aid (paraffin) in the ball mill. The milling medium was then separated on a rotary evaporator, the powder with the aid of a metal sieve (200 .mu.m) granulated and pressed with 200MPa in a laboratory press (25OkN) to rectangular rods. The sintering was carried out under vacuum at 1400 ⁰ C for a period of 60 min. The carbide alloy is characterized by a uniform microstructure (WC gate size <1 μm) and a hardness of HV30 = 1510. Figure 15 shows SEM images of the WC / 9.4Co hard metal alloy from WC-Co composite powder. Example 2:

WO ₂ (0.5-2 μm) is intimately mixed with Ni metal powder (2-5 μm, small proportion 5-8 μm) in a ratio W: Ni of 80:20 by means of a tumble mixer for 60 minutes. This mixture is then reduced with hydrogen at temperatures of 700-950 ⁰ C. The result is a Ni-W composite powder, in which Ni is predominantly present as an intermetallic phase and is ≥ 80% of tungsten overgrown, the particle size is in the range of 5-7 microns with a W-layer thickness of about 0.8 microns. Figure 16 shows an SEM absorption of the Ni-W composite powder (80W-20Ni).

Claims

claims:

A process for producing a composite powder, wherein a powdery starting material A comprising at least one of the following substances: oxide compounds of tungsten and / or molybdenum and / or others

Compounds and / or alloys of these metals, in particular WO _3, WO ₂ .9, W ₂₀ O _50, WO ₂ J _2, W ₁₈ O ₄₇ or other W-oxides, H ₂ WO _4,

Ammonium paratungstate (APW), ammonium metatungstate (AMW), WO ₂ ,

MoO 3, MoO ₂ .9 ₂ , MO ₁ 3O38, Mo ₄ O ₁₁ or other Mo oxides, H ₂ MoO ₄ (MoO 3 H ₂ O),

(NH ₄ ) ₂ MoO ₄ , ammonium dimolybdate ADM ((NH ₄ J ₂ ^• 2MoO ₃ ), (NH ₄ ) ₂ O ^• 6MoO ₃ , MoO ₂ , with a powdery starting material B which comprises at least one of the following substances:

Co and / or Fe and / or Ni and / or alloys and / or compounds of these metals, in particular

CoO, Co ₃ O ₄ , Co ₂ O ₃ , CoO ₂ , Co-hydroxides, Co (OH) ₂ , CoOOH, CoWO ₄ , Co ₇ W ₆₁ Co ₃ W

FeW, Fe ₂ W, Fe ₃ W ₂ , Fe ₇ W ₆ , NiW, NiW ₂ , Ni ₄ W, oxides, hydroxides and / or tungstates of Co and / or Fe and / or Ni and / or salts, in particular acetates or Oxalates, of Co and / or Fe and / or Ni, and / or metal tungsten oxide bronzes (Me = Fe, Co, Ni) in particular homogeneously mixed, that in the mixture, an elemental ratio of the starting material A contained tungsten and / or molybdenum to the Co contained in the starting material B and / or Ni and / or Fe in a ratio of 99: 1 to 50:50 (A: B) preferably 99: 1 to 70:30 (A: B) is set and that the powder mixture undergoes at least one stage reduction process and in the course of which contained in the starting material B metals, namely Co and / or Fe and / or Ni, and / or, in particular stoichiometric, compounds and / or intermetallic phases of these metals at least partially with a layer of the metals Starting material A, namely W and / or Mo, and / or, in particular stoichiometric, Compounds and / or intermetallic phases of these metals, overgrown.

2. The method according to claim 1, characterized in that the reduction process takes place in a hydrogen atmosphere or in an atmosphere of mixtures of a reducing gas (v.a., hydrogen, carbon monoxide, methane) and at least one inert gas.

3. The method according to claim 1 or 2, characterized in that the duration of the reduction process is set to 10 min to 100 h and / or that the reduction process is carried out at a temperature of 200 to 1200 ⁰ C.

4. The method according to any one of claims 1 to 3, characterized in that the particle size of the starting material A 50 nm to 200 microns, preferably 80 nm to 50 microns, and the particle size of the starting material B 10 nm to 50 microns, preferably 30 nm to 5 μm.

5. The method according to any one of claims 1 to 4, characterized in that the metals present at the starting material A, W and / or Mo and / or alloys and / or compounds, in particular metal oxides, of these metals with Cr and / or V and / or Mo and / or Ta and / or Nb in an amount of 50 ppm to 20 wt .-% (in the powder) of the (r) used in the starting material A metals (s) are doped.

6. The method according to any one of claims 1 to 5, characterized in that provided in the materials of the starting material B metals Co, Fe and / or Ni and / or alloys and / or compounds of these metals with Cr and / or V and / or Mo and / or Ta and / or Nb in an amount of 50 ppm to 20 wt .-% (in the powder) of the (r) used in the starting material B metals (s) are doped.

7. The method according to any one of claims 1 to 6, characterized in that the doped metals or the doped metal compounds in the form of pure metals,

Oxides, nitrates, acetates, formates, oxalates, liquid salt solutions and / or solid powders or solid salts, in particular in the form of tungstates and / or Molybdaten, tungsten oxide bronzes and / or molybdenum oxide bronzes present.

8. The method according to any one of claims 1 to 7, characterized in that the starting materials A and B dry or wet over a period of 1 to 300 h, preferably 1 to 50 h, in particular homogeneously, are mixed.

9. The method according to any one of claims 1 to 8, characterized in that in a one-stage reduction process one, in particular constant, temperature of 500 to 1200 ⁰ C, preferably 650 to 1050 ° C, with a residence time of 10 min to 100 h, adjusted becomes.

10. The method according to any one of claims 1 to 9, characterized in that in a two-stage reduction process with a temperature profile for the first reduction stage one, in particular constant, temperature is set between 200 and 700 ⁰ C for a residence time of 10 min to 100 h, and that in the second reduction stage a, in particular constant, temperature is set between 600 and 1200 ⁰ C for a residence time of 10 minutes to 100 hours.

11. The method according to any one of claims 1 to 10, characterized in that in a three-stage reduction process in the first reduction stage one, in particular constant, temperature of 200 to 500 ⁰ C for a residence time of 10 min to 100 h is set that in the second reduction stage one, in particular constant, temperature of 450 to 700 ⁰ C for a residence time of 10 min to 100 h is set and that in the third reduction stage one, in particular constant, temperature between 650 to 1200 ⁰ C for a residence time of 10 min to 100 h is set.

12. The method according to any one of claims 1 to 11, characterized in that a heating rate and / or a cooling rate between 1 to 500 K / min is set.

13. The method according to any one of claims 1 to 12, characterized in that during the reduction process, a dumping height of the mixed, powdered starting materials of not more than 100 mm is not exceeded.

14. Composite powder produced by a process according to claims 1 to 13.

15. Composite powder, in particular produced according to a method of claims 1 to 13, comprising core particles of Co, Fe and / or Ni and / or compounds thereof, in particular stoichiometric compounds and / or intermetallic phases, which at least partially with a shell layer of W and / or Mo and / or compounds these metals, in particular stoichiometric compounds and / or intermetallic phases, overgrown.

16. A composite powder according to claim 14 or 15, characterized in that at least 50% of the particles of the composite powder are completely overgrown with the cladding layer.

17. Composite powder according to one of claims 14 to 16, characterized in that the particles of the composite powder have a size of 50 nm to 50 microns.

18. Composite powder according to one of claims 14 to 17, characterized in that applies for the mean radius R1 of the particles of the composite powder

0, 6 X <R1 <1.2X

where X = Ä, .3pL + 1

where V _{A is} the volume of the metals of the starting material A, V _B the volume of the metals of the starting material B and

R ₂ corresponds to the mean radius of the particles of the starting material B or of the core particles.

19. A composite powder according to any one of claims 14 to 18, characterized in that in a composite powder Co formed with W and Co as core particles or in the transition region from the core particle to the cladding layer, an intermetallic phase of Co with W, in particular in the form Co ₇ W ₆ , is present.

20. Composite powder according to one of claims 14 to 19, characterized in that the thickness of the cladding layer is 8 nm to 50 microns.

21. Composite powder according to one of claims 14 to 20, characterized in that in the metallic composite powder tungsten in cubic body-centered form and cobalt in face-centered cubic form or as an intermetallic phase (eg: Co ₇ W ₆ ) is present.

22. A method for producing a doped with C and / or N or these elements containing composite powder in which the carbides and / or nitrides are contained in a cladding surrounding a core particles, characterized in that subsequent to the method steps according to one of claims 1 to 13 that thus obtained composite powder is subjected to a reaction in which are embedded in the cladding layer of the particles of the resulting composite powder C and / or N.

23. The method according to claim 22, characterized in that the resulting composite powder with carbon, preferably in the form of carbon black and / or graphite, is mixed and / or the resulting composite powder of an atmosphere of H ₂ and H ₂ / CH ₄ and / or CO and / or CO ₂ and / or N _{2 is} exposed and that at a temperature of 800 to 1500 ⁰ C, the metals in the cladding layer in the corresponding compounds with carbon and / or nitrogen, in particular in carbides and / or nitrides and / or carbonitrides , be implemented.

24. The method according to any one of claims 22 or 23, characterized in that the carburization and / or nitration is carried out at a, in particular constant, temperature for 10 min to 50 h.

25. The method according to any one of claims 22 to 24, characterized in that a heating rate and optionally a cooling rate of 2 to 500 K / min is set.

26. The method according to any one of claims 22 to 25, characterized in that in the carburization and / or nitration, a powder dump height of 200 mm is not exceeded.

27. Composite powder, in particular produced by a process according to one of claims 22 to 26, in particular using a starting composite powder according to one of claims 14 to 21.

28. Composite powder, in particular produced by a process according to one of claims 22 to 26, comprising core particles of Co and / or Fe and / or Ni and / or compounds of these metals, which core particles with a shell layer of W and / or Mo and / or Contains compounds of these metals at least partially overgrown, in which cladding layer N and / or C incorporated or contained in the form of carbides and / or nitrides and / or carbonitrides. '

29. A composite powder according to claim 27 or 28, characterized in that at least 50% of the particles are completely overgrown with the cladding and / or nitride-containing cladding layer.

30. Composite powder according to one of claims 27 to 29, characterized in that in the composite powder cobalt in face-centered cubic form with dissolved proportions of C and W and the WC contained in the shell layer is in hexagonal form.

31. Composite powder according to one of claims 27 to 30, characterized in that for the mean radius R _{1 of} the particles of the composite powder is 0, 6 X <R1 <1, 2X

where V _A corresponds to the volume of the metals of the starting material A, V ₈ corresponds to the volume of the metals of the starting material B and R ₂ corresponds to the mean radius of the particles of the starting material B or of the core particles.

32. Composite powder according to one of claims 27 to 31, characterized in that the composite powder has a particle size of 50 nm to 50 microns.

33. Composite powder according to one of claims 27 to 32, characterized in that the thickness of the cladding layer is 8 nm to 50 μm.

34. Composite powder according to one of claims 27 to 33, characterized in that at least one of the metals contained in the composite powder or one of

Metal compounds with Cr and / or V and / or Mo and / or Ta and / or Nb doped in an amount of 50 ppm to 2 wt .-% of the metal used based on the composite powder.