Method of making metal composite materials

Abstract: According to the method of the present invention one or more organic or inorganic metal salts or compounds of at least one of the groups IV, V and VI of the periodic system particularly, V, Cr, Mo and W optionally together with one or more organic iron group metal salts are dissolved in at least one polar solvent with at least one complex former comprising functional groups in the form of OH or NR 3 , (R=H or alkyl) and complex bound with at least one complex former. Hard constituent powder and optionally soluble carbon source are 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 and optionally with other coated hard constituent powders and/or carbon to obtain the desired composition can be compacted and sintered according to standard practice.

Description: The present invention relates to a method of producing metal composite materials such as cemented carbide. US 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 in at least one polar solvent such as ethanol, methanol, water and complex bound with at least one complex former comprising functional groups in the form of OH or NR 3 , (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 atmosphere. As a result, hard constituent powder coated with at least one iron group metal 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. When making submicron cemented carbide i.e. with a WC grain size of <1 µm grain growth inhibitors have to be added in order to avoid WC grain growth during sintering. Examples of such grain growth inhibitors are VC, Cr 3 C 2 The above mentioned patent discloses a method of depositing a layer of binder metal onto the surfaces of the hard constituent grains. It is, however, desirable to be able to precipitate at the same time also the elements inhibiting grain growth. It is thus an object of the present invention to provide a method of precipitating also the metals of groups IV, V and VI of the periodic system particularly V, Cr, Mo and W. It has now surprisingly been found that the method disclosed in the above mentioned patent can be extended also to the precipitation of the metals of groups IV, V and VI of the periodic system particularly V, Cr, Mo and W. Fig 1 shows at 10000X the microstructure of the coated hard constituent powder according to the invention. According to the method of the present invention one or more organic or inorganic metal salts or compounds of at least one of the groups IV, V and VI of the periodic system particularly V, Cr, Mo and W optionally together with one or more organic iron group metal salt are dissolved in at least one polar solvent such as ethanol, methanol and water and complex bound with at least one complex former comprising functional groups in the form of OH or NR 3 , (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 atmosphere. As a result coated hard constituent powder is obtained which after addition of pressing agent alone or optionally with other coated hard constituent powders and/or binder phase metals can be compacted and sintered according to standard practice. The process according to the invention comprises the following steps where Me= Metals of groups IV, V and VI of the periodic system, preferably V, Cr, Mo and W, most preferably V and Cr: 1. At least one Me-salt or compound containing organic or, preferably, inorganic groups, optionally combined with an addition of one or more organic iron group metal salt, is dissolved in at least one polar solvent such as ethanol, methanol, water, acetonitrile, dimetylformamide or dimetylsulfoxide and combinations of solvents such as methanol-ethanol and water-glycol, preferably methanol and/or water. Triethanolamine or other complex former especially molecules containing more than two functional groups, i. e. OH or NR 3 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. Optionally, sugar (C 12 H 22 O 11 ) or other soluble carbon source such as other types of carbohydrates and/or organic compounds which decompose under formation of carbon in the temperature interval 100-500°C in non-oxidizing atmosphere can be added (<2.0 mole C/mole metal, preferably about 0.5 mole C/mole metal), and the solution heated to 40°C in order to improve the solubility of the carbon source. The carbon is used to reduce the MeO formed in connection with heat treatment and to regulate the C-content in the final produce. 3. Hard constituent powder such as WC, (Ti,W)C, (Ta,Nb)C, (Ti,Ta,Nb)C, (Ti,W)(C,N), 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). 4. The loosened powder lump obtained in the preceding step is heat treated in nitrogen and/or hydrogen at about 400-1100°C, preferably 400-800°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. A holding time for reduction of a 5 kg powder batch in a pure hydrogen atmosphere at 650°C of 60-120 minutes has been found suitable. Nitrogen and/or hydrogen is normally used but Ar, NH 3 , CO and CO 2 (or mixtures thereof) can be used whereby the composition and microstructure of the coating can be modulated. 5. After the heat treatment the coated powder is mixed with a pressing agent in ethanol to form a slurry either alone or with other coated hard constituent powders and/or binder phase metals and/or carbon to obtain the desired composition. The slurry is then dried, compacted and sintered in the usual way to obtain a sintered 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 production. Alternatively the pressing agent can be added together with the hard constituent powder according to paragraph 3, directly dried, pressed and sintered. The following examples are given to illustrate various aspects of the invention. Example 1 A WC-10 %Co-0.4 %Cr 3 C 2 -0.3 %VC cemented carbide was made in the following way according to the invention: 23 g chromium (III)nitrate-9-hydrate (Cr(NO 3 ) 3 x 9H 2 0) and 3.6 g ammonium vanadate (NH 4 VO 3 ) was dissolved in 1700 ml methanol (CH 3 OH). 297.5 g cobalt acetate tetrahydrate (Co(C 2 H 3 O 2 ) 2 ·4H 2 O) was added to the solution. To this solution, 105 g triethanolamine ((C 2 H 5 O) 3 N was added during stirring. After that 686 g WC (d WC = 0.6 µm) 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 nitrogen atmosphere in a closed vessel, heating rate 10°C/min to 550°C, completed with reduction in hydrogen for 90 minutes, finally followed by cooling in nitrogen atmosphere at 10°C/min. No cooling step between burning off and reduction step was used. Fig 1 shows the microstructure of the coated hard constituent powder at 10000X. The powder obtained was mixed with pressing agent in ethanol with adjustment of carbon content (carbon black), dried, compacted and sintered according standard practice for WC-Co alloys. A dense cemented carbide structure was obtained with porosity A00 and hardness HV3=1730. Example 2 A WC-10 %Co-0.4 %Cr 3 C 2 -0.3 %VC cemented carbide was made in the following way according to the invention: 13.4 g chromium (III)nitrate-9-hydrate (Cr(NO 3 ) 3 x 9H 2 0) and 2.1 g ammonium vanadate (NH 4 VO 3 ) was dissolved in 700 ml methanol (CH 3 OH). To this solution, 12.2 g triethanolamine ((C 2 H 5 O) 3 N was added during stirring. After that 400 g WC (d WC = 0.6 µm) 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 nitrogen atmosphere in a closed vessel, heating rate 10°C/min to 600°C, completed with reduction in hydrogen for 90 minutes, finally followed by cooling in nitrogen atmosphere at 10°C/min. No cooling step between burning off and reduction step was used. The powder obtained was mixed with pressing agent and Cobinder (Co-powder extra fine) in ethanol and adjustment of carbon content (carbon black), dried, compacted and sintered according standard practice for WC-Co alloys. A dense cemented carbide structure was obtained with porosity A00 and hardness HV3=1700.

Claims: Method of making a metal composite material characterised in comprising the following steps dissolving at least one organic or inorganic metal salt or compound of at least one of the groups IV, V, and VI of the periodic system particularly V, Cr, Mo and W optionally together with one or more organic iron group metal salt in at least one polar solvent and complex binding said metal salt or compound with at least one complex former comprising functional groups in the form of OH or NR 3 , (R=H or alkyl) adding hard constituent powder and optionally a soluble carbon source to the solution evaporating the solvent heat treating the remaining powder in inert and/or reducing atmosphere to obtain said hard constituent powder coated with said at least one of the groups IV, V, and VI of the periodic system metals adding pressing agent alone or with other coated hard constituent powders and/or carbon to obtain the desired composition to said coated hard constituent powder, compacting and sintering according to standard practice. Method of making a metal composite material according to the preceding claim characterised in that pressing agent is added together with said hard constituent powder and said soluble carbon source to said solution, drying, pressing and sintering according to standard practice considering the heat treatment conditions.

Inventors: SVENSSON ROLF, WALDENSTROEM MATS, SVENSSON, ROLF, WALDENSTROEM, MATS, Waldenström, Mats
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1998
Main classification: C22C1
IPC codes: B22F1, B22F3, C22C1