WO2008031121A1

WO2008031121A1 - Method for production of w/mo composite powders and composite powder

Info

Publication number: WO2008031121A1
Application number: PCT/AT2007/000407
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: AT504302A1; JP2010503764A; AT504302B1; EP2061614A1; AT504302B8

Abstract

The invention relates to a method for production of a composite powder comprising Mo and W, where a powder starting material A, comprising Mo or W metal powder is mixed with a powder starting material B, which comprises, in the case of starting material A being Mo or a Mo/W alloy, oxidic compounds of W or a powder starting material B which comprises, in the case where starting material A is W, oxidic compounds of Mo, the weight ratio (V) in the mixture of Mo to W is in the range 1:99 to 99:1 and the powder mixture is subjected to an at least single stage reductive process, in the course of which the particles of the metal or metal alloy in starting material A are at least partly preferably completely covered over by a layer of the metal from starting material B.

Description

Process for the preparation of W-Mo 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 11.

Furthermore, the invention relates to a method according to the preamble of claim 18 and to a composite powder produced by this method according to the preamble of claim 24.

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 powders obtained by the process according to the invention are 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 should be readily usable for the production of hard metal powders, in particular for the sintering of nitrited or carburized hard materials.

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 10.

The composite powder produced by these process steps according to the invention is characterized in particular by the features of claim 11. 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 over 50%, by a cladding layer of tungsten or molybdenum.

Further advantageous features of such a composite powder are given in claims 12 to 17.

A method according to the preamble of claim 18 is inventively characterized by the features cited in the characterizing part of claim 18. The composite powder used to carry out this process can be nitrided and / or carburized in a particularly good, rapid and homogeneous manner, and produces exceptionally good material parameters.

The reaction with the corresponding elements carbon and / or nitrogen advantageously takes place in accordance with the features specified in claims 19 to 22, which ensure a targeted procedure. With this method, a composite powder is created, which is characterized by the features of the characterizing part of claim 23. This powder has good Sinterbzw. Further processing properties and is versatile.

Advantageous features of such composite powder can be found in claims 24 to 30.

The production of tungsten-molybdenum materials by alloying of W and Mo or sintering of intimate metal powder mixtures.

The present invention is based primarily on the fact that the dispersibility and thus uniformity of the distribution of tungsten or molybdenum, especially by the precursors and pre-distribution and the proportions of the starting materials can be controlled.

The composite powders obtained with the invention thus contain a core of W or Mo or a W-Mo alloy which is at least partially coated with a sheath layer of Mo or W or a sheath layer of Mo or W containing carbides and / or nitrides of the metals Mo and / or W is surrounded. The core can also be carburized and / or nitrided.

The intermediate composite powder which is also self-contained for certain uses, e.g. For sintering purposes, comprises particles with a cladding layer of tungsten or molybdenum, which surround a core of Mo or W or a Mo-W alloy at least partially, advantageously entirely.

Furthermore, the grain size of the core particles and the cladding layer can be easily controlled by varying the proportions, the particle size and the reaction temperatures and adjusted within certain limits with great accuracy. According to the invention, a composite powder is thus produced which comprises core particles of W or Mo or of a Mo-W alloy and a cladding layer of W or Mo, wherein in a further embodiment the cladding layer and optionally also the respective core particles in the form of carbides and / or Nitrides may be present or contain. After mixing the metal powder of the starting material A with the

Starting material B in the predetermined ratio, for example by mixing in a tumble mixer and / or wet or dry grinding, for example in a ball mill, an attritor, a planetary ball mill and / or dispersing and / or spraying is carried out 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 100 hours. The reduction process is carried out at a temperature of 400 to 1200 ⁰ C. It is envisaged that the particle size of the starting material A and B 0.1 to

50 microns.

It is also possible to dope the metals of the starting materials or the compounds used. It is advantageous if the metals or metal alloys present in the starting material A or B 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 ) in the starting material A or in the starting material B provided metal (e) to dope. It is understood that in the case that a starting material contains Mo, doping with Mo is eliminated.

The reduction process can be carried out in different ways. Advantageously, one-stage or two-stage reduction operations are feasible. In this regard, the features of claims 7 and 8 are advantageous.

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

Gas phase transport, eg of WO2 (OH) ₂ or WO ₃ (g). The Mo acts as a nucleation aid for tungsten and leads to a very uniform composite powder. The macroscopic morphology of the W-Mo composite powder corresponds to the macroscopic morphology of the powder of the core component used. In Figure 1, the attachment 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. 1 denotes WO ₂ (or MoO ₂ ) with 2 W (or Mo), with 3 WO ₂ (OH) ₂ (or a volatile Mo compound) with 4 W (or Mo). Figure 2 shows a mathematical model concerning the structure of the

Composite powder shown.

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 Mo metal.

V ₁ = (-πRi --πR ³ ₂ ) (shell volume V1) V ₂ = -πR _j (core volume V2)

If we now put the volumes of the substances used W and Mo in relation, we obtain a logical radius relationship, with the knowledge of the radius of the core component or the core particle and the W: Mo or WC: Mo

Amount ratio, the layer thickness of the shell and the particle size of the

Estimate composite powder particle:

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

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

in which

R1 mean radius of the particles of the composite powder

V _A Volume of the metal of the starting material A (core)

V ₆ volume of the metal of the starting material B (sheath) R2 mean radius of the particles of the starting material A or of the core particles. In the procedure according to the invention can be controlled by the choice of the grain size of the starting material A (= core component), the grain size of the resulting composite powder, since the thickness of the cladding layer of the resulting composite powder of the difference of the radii R ₁ - R ₂ corresponds.

FIG. 3 shows a schematic representation of the metal composite powders, where 1 W or Mo and 2 Mo or W are used. The occurring Mo-W or W-Mo composite powder particles are shown schematically. Depending on the weight ratio W: Mo used and the distribution of the W and Mo phases, holistic (a) and partially (b) overgrown structures are possible. In (c) and (d) possible overgrowths of non-spherical particles and agglomerates are illustrated.

FIGS. 4 and 5 show the X-ray diffractograms of W-Mo (FIG. 4) and Mo-W (FIG. 5) with phases W (bcc) and Mo (bcc).

Fig. 6 shows SEM images of Mo-W powder; on the right is an EDS spectrum of the composite powder, on the left is a tungsten crystal with a not completely overgrown molybdenum core to see. On the right side, the corresponding spectrum of the EDS analysis is shown. Based on this SEM image, it can be seen that tungsten epitaxially grows on molybdenum, which is possible due to the very similar lattice parameters (both cubic-centered). Fig. 7 shows electron micrographs of Mo-W; left: Mo-W

(Unetched); right: Mo-W (etched).

Fig. 8 shows SEM images of Mo-W composite powder (etched). The copper-ground sections of the MoW powders of FIGS. 7 and 8 clearly show the core-shell structure. The layer thickness of tungsten around the molybdenum appears to be largely uniform. The reverse overgrowth of tungsten with molybdenum shows comparable results (Figure 9) with a clear core-shell structure. Fig. 9 shows pictures of the W-Mo composite powder, above: REM and below: light microscope.

The resulting composite powders generally exhibit a thickness of the cladding layer of 12 nm to 15 μm, which depends on the ratio of the starting materials and the size of the starting particles.

The results of X-ray diffractometry show tungsten and Mo in bcc form. The oxygen content of the composite powder is <5000 ppm. The Teilcheng rosse of the composite powder is about 50 nm to 50 microns determined by scanning electron microscopy. It should also be noted that the starting materials or

Compounds should have a high degree of purity or impurities should be present only in a customary in the sintering technology extent. 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 in the Mantefschicht of the particles and optionally also in the core particles of the 5 composite powder carbon and / or nitrogen are 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 2200 ⁰ C, so that the metals in the cladding layer and0 optionally also in the core particles in the corresponding compounds with carbon and / or nitrogen, in particular nitrides and / or carbides are reacted , Preferably in tungsten mono- and / or Molybdändicarbid, and / or proceed appropriate storage reactions.

The mixing of the already existing composite powder with carbon black or graphite 5 can be carried out in conventional mixing or milling units, such as, for example, 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, 0 optionally a heating rate and / or a cooling rate of 2 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 W or Mo or a Mo-W alloy which are overgrown with a cladding layer of 5 Mo or W, the core layer and optionally the cladding layer being carburized and / or nitrided available. With appropriate process control, the core particles can thus also contain C and / or N inclusions or carbides and / or nitrides.

FIG. 10 schematically illustrates a Mo ₂ C-WC / WC-Mo ₂ C 30 composite powder, consisting of a Mo ₂ C or WC core and a WC or Mo ₂ C shell, with 3 Mo ₂ C or WC and 4 WC or Mo ₂ C is designated.

Figure 11 shows the X-ray diffractogram of the Mo ₂ C-WC composite powder with the occurring phases WC and Mo ₂ C.

Fig. 12 shows SEM images of a composite powder with 90WC / 1 OMo ₂ C (under 35th Cu cut, etched).

The composite powders of the invention obtained by the reaction show that at least 50% of the particles are wholly in contact with the carbides and / or nitrides overgrown coat layer are overgrown. The composite powder has a particle size of 50 nm to 15 microns, wherein the thickness of the cladding layer is 8 nm to 50 microns.

In the case of 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 Mo and / or Nb in an amount of from 50 ppm to 2 Wt .-% of each doped metal is doped.

Example 1: WO ₂ (0.5-2 μm) is intimately mixed with Mo metal powder (3-4 μm) in a ratio W: Mo of 90:10 (w%) by means of a tumble mixer for 40-60 minutes. This mixture is then reduced with hydrogen at temperatures of 800-950 ⁰ C. The result is a Mo-W composite powder with a clear core-shell structure in which the molybdenum particles is overgrown by> 90% of tungsten. The particle size is in the range of 5 - 7 microns with a W-layer thickness of 1 - 2 microns.

By carburizing this composite powder with carbon (soot), a Mo ₂ C-WC composite powder is formed, wherein the molybdenum carbide is> 90% surrounded by tungsten monocarbide and has a distinct core-shell structure.

Example 2:

MoO ₂ (0.5-2 μm) is intimately mixed with W metal powder (2-4 μm) in a ratio Mo: W 1: 1 (w%) by means of a tumble mixer for 40-60 minutes. This mixture is then reduced with hydrogen at temperatures of 900 - 1000 ⁰ C. The result is a W-Mo composite powder with a clear core-shell structure in which the tungsten particles are over> 90% of molybdenum overgrown. The particle size is in the range of 3 - 5 microns with a Mo layer thickness of about 0, 5 microns.

From the present explanations, it turns out that Mo and W are equivalent or largely interchangeable, since the reaction kinetics are comparable.

Only the structures of the W oxides and the Mo oxides used differ.

Claims

claims:

A process for producing a composite powder containing Mo and W, wherein a powdery starting material A comprising Mo or W metal powder or a

5 alloy powder of these two metals,

- with a powdery raw material B, which in case is present as starting material A Mo or a Mo-W alloy, at least one of the following substances comprises oxidic compounds of W, in particular WO _3, WO _29, W ₂ o0 _50, WO ₂ .7 _2> W ₁₈ O ₄₇ 10 or other W oxides, H ₂ WO ₄ ,

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

or with a powdery starting material B which, in the case of the starting material A W or a W-Mo alloy, comprises at least one of the following substances:

15 oxidic compounds of Mo, in particular, MoO ₃ , MOO ₂ . ₉₂ , Mo ₁₃ O ₃₈ , Mo ₄ O ₁ - _I 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 , 20, in particular homogeneously, in that a weight ratio (V) is mixed in the mixture. from Mo to W in the size of 1:99 to 99: 1, preferably from 1:20 to 20: 1, and that the powder mixture is subjected to at least a one-step reduction process, during which the particles of (r) in the starting material a contained ^■ 25 metal or metal alloy, at least partially, preferably completely, with a layer of the metal of the starting material B used are overgrown.

2. The method according to claim 1, characterized in that the reduction process in a hydrogen atmosphere or in an atmosphere of

30 mixtures of a reducing gas (hydrogen, carbon monoxide, methane) and at least one inert gas takes place.

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 400 to 1200 ⁰ C.

4. The method according to any one of claims 1 to 4, characterized in that the particle size of the starting material A 0.1 to 500 microns and the particle size of the starting material B 0.1 to 50 microns.

5. The method according to any one of claims 1 to 4, characterized in that the starting material A and / or the starting material B 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 A or B metals (s) are doped.

6. The method according to any one of claims 1 to 5, 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.

7. The method according to any one of claims 1 to 6, characterized in that in a one-stage reduction process one, in particular constant, temperature of 500 to 1200 ⁰ C, preferably 700 to 1200 ⁰ C, with a residence time of 10 min to 100 h, adjusted becomes.

8. The method according to any one of claims 1 to 7, characterized in that in a two-stage reduction process for the first reduction stage one, in particular constant, temperature is set between 400 and 70O ⁰ C for a residence time of 10 min to 100 h, and that in the second reduction stage one, in particular constant, temperature between 650 and 1200 ⁰ C for a residence time of 10 minutes to 100 h is set.

9. The method according to any one of claims 1 to 8, characterized in that a heating rate and / or a cooling rate between 1 to 500 K / min is set.

10. The method according to any one of claims 1 to 9, 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.

11. Composite powder, prepared by a process according to claims 1 to 9.

A composite powder, in particular produced by a process of claims 1 to 10, comprising core particles of Mo or W or a Mo-W alloy, which core particles at least partially with a cladding layer of the other metal, i. W or Mo, or in a core particle of a Mo-W alloy with Mo or W at least partially, advantageously completely, overgrown.

13. Composite powder according to claim 11 or 12, characterized in that at least 50% of the particles of the composite powder are overgrown with the cladding layer.

14. Composite powder according to one of claims 11 to 13, characterized in that the particles of the composite powder have a size of 50 nm to 50 microns.

15. Composite powder according to one of claims 11 to 14, characterized in that for the mean radius R1 of the particles of the composite powder is 0, 6 X <RK1, 2X

wherein V _A the volume of the metal or the metal alloy of the starting material A, V _B the volume of the metal of the starting material B and

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

16. Composite powder according to one of claims 11 to 15, characterized in that the thickness of the cladding layer is 8 nm to 15 microns.

17. Composite powder according to one of claims 11 to 16, characterized in that present in the composite powder W and Mo in cubic body-centered form.

18. A process for producing a doped with C and / or N or these elements containing composite powder, wherein the carbides and / or nitrides at least in one a core particle at least partially enclosing cladding layer are included, characterized in that subsequent to the process steps according to one of claims 1 to 10, the composite powder thus obtained is subjected to an intercalation reaction, in particular carburization and / or nitration, in which the cladding layer of Particles of the resulting composite powder and optionally also in the core particles C and / or N are stored.

19. The method according to claim 18, characterized in that the resulting composite powder with carbon, in particular carbon black and / or graphite is mixed

10 and / or the resulting composite powder is exposed to an atmosphere of H ₂ and / or N ₂ and / or H ₂ / CH ₄ and / or CO and / or CO ₂ and / or N ₂ and that at a temperature of 800 to 2200 ⁰ C, the metal in the cladding layer and optionally also the metal or the metal alloy of the core particle in the corresponding compounds with carbon and / or nitrogen, in particular in carbides and / or

15 nitrides, reacted and / or subjected to the incorporation reaction.

20. The method according to any one of claims 18 or 19, characterized in that the carburization and / or nitration is carried out at a, in particular constant, temperature of 800 to 2200 ⁰ C for 10 min to 50 h.

20th

21. The method according to any one of claims 18 to 20, characterized in that a heating rate and optionally a cooling rate of 2 to 500 K / min is set.

25 22. The method according to any one of claims 18 to 21, characterized in that in the carburization and / or nitration, a powder bed height of 200 mm is not exceeded.

23. Composite powder, in particular produced by a process according to any one of claims 30 to 22, in particular using a starting composite powder according to one of claims 11 to 17.

24. Composite powder, in particular produced by a process according to any one of claims 18 to 22, comprising core particles of Mo or W or a Mo-W

35 alloy, which core particles are at least partially overgrown with a cladding layer of the respective other metal, ie W or Mo, or in the case of core particles of a Mo-W alloy with Mo or W, in which cladding layer C. and / or N are incorporated and / or in particular in the form of carbides, nitrides, optionally also incorporated in the core particles C and / or N or in particular in the form of carbides and / or nitrides.

25. A composite powder according to claim 23 or 24, characterized in that at least 50% of the particles are overgrown with the carbide and / or nitride-containing cladding layer.

26. Composite powder according to one of claims 23 to 25, characterized in that the WC contained in the shell layer in hexagonal form or in the

Sheath layer Mo ₂ C present in hexagonal form.

27. Composite powder according to one of claims 23 to 26, characterized in that for the mean radius R _{1 of} the particles of the composite powder is 0, 6 X <RK1, 2X

where X = R

where V _{A is} the volume of the metal or the metal alloy of the starting material AV _B the volume of the metal 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.

28. Composite powder according to one of claims 23 to 27, characterized in that the composite powder has a particle size of 50 nm to 50 microns.

29. Composite powder according to one of claims 23 to 28, characterized in that the thickness of the cladding layer is 8 nm to 50 microns.

30. Composite powder according to one of claims 23 to 29, characterized in that at least one of the carbides of Mo and / or W contained in the composite powder with Cr and / or V and / or Mo and / or Ta and / or Nb to an extent of 50 ppm to 20 wt .-% of the respective metal is doped.