METHOD OF MAKING METAL COMPOSITE MATERIALS

Abstract: According to the method of the present invention, at least one of Men(NO3)m and Men(SO4)m and other similar Men-Xm compounds containing X-groups with low or no carbon content, preferably Me-nitrates, solely or together with one or more metal salts of at least one iron group metal containing organic groups are dissolved and complex bound in at least one polar solvent with at least one complex former comprising functional groups in the form of OH or NR3, (R=H or alkyl). Hard constituent powder is added to the solution. The solvent is evaporated and remaining powder is heat treated in inert and/or reducing atmosphere. As a result, coated hard constituent powder is obtained which after addition of pressing agent can be compacted and sintered according to standard practice.

Description: Method of making metal composite materials The present invention relates to a method of produc¬ ing metal composite materials such as cemented carbide. U.S. Patent 5,505,902 discloses a method in which one or more metal salts of at least one iron group metal containing organic groups are dissolved and complex bound in at least one polar solvent with at least one complex former comprising functional groups in the form of OH or NR3, (R=H or alkyl) . Hard constituent powder and, optionally, a soluble carbon source are added to the solution. The solvent is evaporated and remaining powder is heat treated in inert and/or reducing atmos¬ phere. As a result, coated hard constituent powder is obtained which after addition of pressing agent can be compacted and sintered according to standard practice to a body containing hard constituents in a binder phase. A problem with said method is that the heat treatment of the coated powder in larger quantities (>1 kg) has to be performed in pure hydrogen and/or with unnecessary high gas flows in order to obtain the desired carbon content which for cemented carbide has to be kept in a very narrow range. It is thus an object of the present invention to provide an alternative method to the above mentioned US- patent in which the hydrogen reduction is essentially eliminated. According to the method of the present invention the at least one organic salt of the above mentioned patent is replaced partly or completely by a salt containing no or little carbon. The process according to the invention comprises the following steps where Me= Co, Ni and/or Fe, preferably Co: 1. At least one of Me n ( θ3) m and e n (S04) m and other similar Me n -X m compounds containing X-groups with low, <5 wt-%, preferably <2 wt-%, most preferably no carbon content, preferably Me-nitrates, are dissolved solely or together with at least one Me-salt containing organic groups such as carbooxylates, acetylacetonates, nitrogen containing organic groups such as schiff bases, preferably Me-acetates, in at least one polar solvent such as ethanol, acetonitrile, dimetylformamide or dimetylsulfoxide and combinations of solvents such as methanol-ethanol and water-glycol, preferably methanol. The amount of Me-salts with low or no carbon content, shall be >10%, preferably >50% of the total amount of Me-salts. Triethanolamine or other complex former especially molecules containing more than two functional groups, i. e. OH or NR3 with R = H or alkyl (0.1-2.0 mole complex former/mole metal, preferably about 0.5 mole complex former/mole metal) is added under stirring. 2. Hard constituent powder such as WC, (Ti,W)C, (Ta,Nb)C, (Ti,Ta,Nb)C, (Ti,W) (C,N), TiC, TaC, NbC, VC and Cr3C2, preferably well-deagglomerated e.g. by jet milling, is added under moderate stirring and the temperature is increased to accelerate the evaporation of the solvent. When the mixture has become rather viscous, the dough-like mixture is kneaded and when almost dry smoothly crushed in order to facilitate the evaporation (avoiding inclusions of solvent) . 3. The loosened powder lump obtained in the preced¬ ing step is heat treated in inert and/or slightly reducing atmosphere at about 400-1100°C, preferably 500- 900°C. To achieve a fully reduced powder, a holding temperature might be needed. The time of heat treatment is influenced by process factors such as powder bed thickness, batch size, gas composition and heat treatment temperature and has to be determined by experiments. Nitrogen and/or hydrogen is normally used but argon, helium and ammonia (or mixtures thereof) can be used whereby the composition and microstructure of the coating can be modified. 4. After the heat treatment the coated powder is mixed with pressing agent in ethanol to a slurry either alone or with other coated hard constituent powders and/or uncoated hard constituent powders and/or binder- phase metals and, possibly, carbon or tungsten to obtain the desired composition. The slurry then is dried, com¬ pacted and sintered in the usual way to obtain a sin¬ tered body of hard constituents in a binder phase. Most of the solvent can be recovered which is of great importance when scaling up to industrial produc- tion. Altematively, the pressing agent can be added to¬ gether with the hard constituent powder according to step 2, directly dried, pressed and sintered considering the conditions according to step 3. Example 1 A WC-6 % Co cemented carbide powder mixture was made in the following way according to the invention: A mixture of 72.63 g cobaltnitratehexahydrate (Co( θ3) 2 • 6H2O) and 62.26 g cobaltacetatetetrahydrate (Co(C2H3θ2>2 ' H 2°) in he ratio nitrate/acetate 7 to 6 was dissolved in 800 ml methanol(CH3OH) . 36.1 ml triethanolamine ( (C2H5O) 3N (0.5 mole TEA/mole Co) was added during stirring. Subsequently, 500 g jet milled WC powder was added and the temperature was increased to about 70°C. Careful stirring took place continuously during the time the methanol was evaporating until the mixture had become viscous. The dough-like mixture was worked and crushed with a light pressure when it had become almost dry. The powder obtained was fired in a furnace in a porous bed about 1 cm thick in different batch sizes and in varying flowing gas atmospheres (gas flow: 2000 1/h) , heating rate 10°C/min to 700°C, holding time: 3h, cool- ing 10°C/min. The powder batches were analysed for cobalt and carbon and the results of heat treatment program carried out are summarised below: Batch Batch size, Gas Mixture Powder Analysis, wt-% No. kg (N2/H 2 ) Co C-tot : * 1 0.2 N 2 (100%) 5.4 6.64 2 0.2 N 2 (75%) /H 2 (25%) 5.4 5.79 3 3.0 N 2 (75%)/H 2 (25%) 5.4 5.79 *Stoichiometric carbon content: 5.79 weight% A reference batch was made and heat treated in identical way except of replacement of the nitrate/acetate mixture according to above with only 134,89 g cobaltacetatetetrahydrate (Co (C2H3O2)2 " 4H 2°) • The reference powder was analysed for cobalt and carbon and the results of heat treatment program carried out are summarised below: Batch Batch size, Gas Mixture Powder Analysis, wt-% * No. kg (N2 H2) Co C-tot 1 3 0.2 N (100%) 5.4 7.25 4 0.2 N 2 (75%) /H 2 (25%) 5.4 5.79 5 3.0 N 2 (75%)/H 2 (25%) 5.4 6.42 ♦ Stoichiometric carbon content: 5.79 weight-%

Claims: Claims 1. Method of making a hard constituent powder coated with at least on iron group metal, Me, c h a r a c t e r i s e d in comprising the following steps - forming a solution by dissolving and complex binding at least one of Me n ( θ3) m and Me n {Sθ4) m nc ^ other similar Me n -X m compounds containing X-groups with low or no carbon content, preferably Me-nitrates, solely or together with at least one Me-salt containing organic groups in at least one polar solvent with at least one complex former comprising functional groups in the form of OH or NR3, (R=H or alkyl), the amount of Me-salts with low or no carbon content being >10%, preferably >50% of the total amount of Me-salts - adding hard constituent powder to the solution - recovering the powder by evaporating the solvent - heat treating the powder in inert and/or slightly reducing atmosphere to obtain said hard constituent pow- der coated with said at least one iron group metal. 2. The method of claim 1, c h a r a c t e r i s e d in that the Me-salts with low or no carbon contain less than 5 wt-% C, preferably less than 2 wt-% C. 3. The method of claim 1, c h a r a c t e r i s e d in that the organic solvent comprises ethanol, acetonitrile, dimethylformamide, dimethylsulfoxide or combinations of these preferably methanol. 4. The method of claim 1, c h a r a c t e r i s e d in that the hard constituent powder comprises WC, (Ti,W)C, (Ta,Nb)C, (Ti,Ta,Nb)C, (Ti,W) (C,N), TiC, TaC, NbC, VC and Cr3C2 or combinations of these. 5. The method of claim 1, c h a r a c t e r i s e d in that the heat treatment is at a temperature of 400- 1100 °C, preferably 500-900 °C. 6. The method of claim 1, c h a r a c t e r i s e d in that the heat treating atmosphere comprises nitrogen, hydrogen, argon, helium, ammonia or mixtures of these. 7. The method of claim 1, c h a r a c t e r i s e d in that the coated powder is formed into a mixture by mixing the coated powder with coated and/or uncoated hard constituent powders and/or binder phase metals and, possibly, carbon or tungsten and the mixture is com¬ pacted and sintered to form a densified body.

Inventors: EKSTRAND AASA, NYGREN MATS, WESTIN GUNNAR, EKSTRAND, AASA, NYGREN, MATS, WESTIN, GUNNAR
Applicants: SANDVIK AB, SANDVIK AB (PUBL)
Application year: 1996
Main classification: B22F9
IPC codes: B22F1, B22F9, C22C1