METHOD FOR THE MANUFACTURE OF A METAL MATRIX COMPOSITE, AND A METAL MATRIX COMPOSITE

Abstract: A method for the manufacture of a metal matrix composite by the SHS technique comprises a reaction between titanium and carbon or between titanium and borium, forming titanium carbide or titanium diboride. Tantalum and molybdenum or chromium are blended to the raw materials of the metal matrix composite to improve the resistance of the metal matrix composite to high temperatures and/or corrosion. The invention also relates to a metal matrix composite which contains elements at whose presence a protective oxide layer is formed on the surface of the metal matrix composite during the use.

Description: Method for the manufacture of a metal matrix composite, and a metal matrix composite The present invention relates to a method for the manufacture of a metal matrix composite by the SHS technique, in which method titanium carbide and titanium diboride are formed in a reaction between titanium and carbon or between titanium and borium, respectively, and which metal matrix composite comprises a metallic binder or an inter- metallic binder material. The invention also relates to a metal matrix composite made by the SHS technique and comprising titanium carbide or titanium diboride, and a metal binder or a binder between metals. Known sintered hard metals, such as the mixture of tungsten carbide and cobalt (WC-Co) and the mixture of tungsten carbide and nickel (WC-Ni), are applied in uses requiring a particularly wear-resistant material. However, these materials have the problem of poor resistance to high temperatures. Under conditions of a high temperature, the surface of a hard metal is oxidized, and as it is often subjected to mechanical stresses as well, the material will begin to wear fast. Problems are caused at a temperature as low as about 500°C. The SHS technique (self-propagating high-temperature synthesis) refers to a manufacturing method, in which a reaction of strong produc- tion of heat is caused between powderized starting materials by heating the raw materials locally to a light-off temperature. As a result of the reaction, a new compound is obtained. By the SHS technique it is possible to produce, in a fast and inexpensive way, metal matrix composites with a very good wear resistance, such as metal matrix composites based on titanium carbide or titanium diboride. The problem is, however, their resistance to corrosion and resistance at high temperatures. As an example, it can be mentioned that a metal matrix composite based on titanium carbide is destroyed and becomes useless at a temperature exceeding 1000°C. By the method according to the invention, it is possible to produce mixtures whose resistance to high temperatures and/or corrosion is substantially better than that of materials of prior art. The method according to the invention is characterized in that tantalum and molybdenum or chromium are blended into the raw materials of the metal matrix composite to improve the temperature resistance and/or corro- sion resistance of the metal matrix composite. The metal matrix composite according to the invention is characterized in that the metal matrix composite contains elements at whose presence a protecting oxide layer is formed on the surface of the metal matrix composite during the use. By the method according to the invention, it is possible to manufacture metal matrix composites which are resistant at temperatures of 1200°C; in other words, they can be used to cover the range from 500 to 1200°C. They also have a good corrosion resistance at tempera- tures lower than those mentioned above. The metal matrix composite materials made by the SHS technique can be utilized in all components which are subjected to wear at high temperatures. The SHS hard metals are considerably tougher than ceramic materials. The materials are fit for use at oxidizing conditions up to a temperature of at least 1200°C. They can be used, for example, in components of burners at power plants, such as in burner indents or nozzles. A large variety of uses for materials with such a combination of properties can also be found in the processing industry, for example in oil refining or other chemical industry, particularly at uses subjected to corrosion. By the SHS manufacturing technique, it is possible to produce solid pieces or powderized substances of the metal matrix composite mate- rial, to be used for example in thermal spraying or laser coating. The solid pieces are made by compressing a mass, which is warm and plastic after the exothermic reaction, to a dense component in a mould; in other words, the SHS technique can be used to make a form piece directly from powderized raw materials. The powders are made by allowing the mass to cool down without compression, wherein a porous material is formed, which is ground by methods known as such. The metal matrix composite is made by the SHS technique by allowing titanium and chromium, or titanium, tantalum and molybdenum, in doses suitable for the reaction, to react with carbon or borium. Normally, when titanium is compounded with chromium, 0.6 to 1.0 atoms of titanium and 0.1 to 0.4 atoms of chromium are used per 0.9 to 1.1 carbon atoms. When titanium is compounded with tantalum and molybdenum, 0.6 to 1.0 atoms of tantalum and 0.1 to 0.3 atoms of molybdenum are used per 0.9 to 1.1 carbon atoms. Before the reaction is started, other substances, such as metallic binders or binders between metals in powder form are normally added into the mixture. Metallic binders or binders between metals act as substances giving strength and toughness to the ready metal matrix composite, and they have good oxidation stability. Metallic binders or bind- ers between metals normally constitute 10 to 70 weight percent of the total mass of the raw materials of the metal matrix composite. Advantageous binders include mixtures containing iron, chromium and aluminum (FeCrAI mixtures) or mixtures containing nickel and chromium (NiCr mixtures) or mixtures containing nickel and aluminum (Ni-AI mix- tures) or mixtures containing nickel, chromium and aluminum (NiCrAI). An FeCrAI based binder normally contains 4 to 20 wt-% of aluminum, 10 to 30 wt-% of chromium and the rest of iron in the binder. In addition, the binder may contain 0.001 to 2 weight percent of reactive ele- ments or their oxides, such as zirconium (Zr) or zirconium oxide (Zr0 2 ), yttrium (Y) or yttrium oxide (Y 2 0 3 ), lanthanum (La), cerium (Ce), thorium (Th), rhenium (Re), rhodium (Rh), or titanium (Ti). Furthermore, the binder may contain silicon carbide (SiC) or molybdenum suicide (MoSi 2 ). As an FeCrAI based binder, it is possible to use, for example, a superalloy marketed under the trade name APM (Kanthal AB, Sweden). An FeCrAI based binder is normally used in high temperature applications of the metal matrix composite. As a NiCr based binder, it is possible to use, for example, a superalloy marketed under the trade name Inconel 625 (High Performance Alloys, Inc., USA). NiCr based binders are normally used in such applications of the metal matrix composite, in which the corrosion resistance is important. Advantageous metal compounds include nickel aluminides (NiAI or Ni 3 AI). Cobalt (Co) may be added in any of the above-mentioned metallic binders or binders between metals. Advantageous raw material compositions include the following: Titanium and chromium are allowed to react with carbon, and the binder is a mixture of nickel and chromium (NiCr). Titanium and chromium are allowed to react with carbon, and the binder is a mixture of iron, chromium and aluminum (FeCrAI), with a possible addition of zirconium oxide (Zr0 2 ). Titanium and chromium are allowed to react with carbon, and the binder is a mixture of iron, chromium and aluminum (FeCrAI), with an addition of silicon carbide (SiC) or zirconium oxide (Zr0 2 ) or both. Titanium, tantalum and molybdenum are allowed to react with carbon, and the binder is a mixture of nickel and chromium, with an addition of silicon carbide (SiC) or molybdenum suicide (MoSi 2 ). The hardness of the above-mentioned materials is typically 800 to 1500 HV, but hardness values up to 1800 HV can be achieved with these materials. The content of the carbide phase in the metal matrix composite according to the invention is 40 to 90 volume percent, typically 60 to 80 volume percent. At the best, the increase in the weight of the above-mentioned materials in oxidation tests at 1200°C has been similar to that of the best metal high-temperature superalloys. In a corresponding test, the commercial Inconel 625 material is destroyed and becomes useless. Considering the very high hardness of high-temperature SHS mixtures in comparison with metal superalloys (for example, 150 HV of APM mixture), the metal matrix composite according to the invention provides a new type of materials to be used, for example, in components of power plants which are exposed to hot erosion. When the corresponding material is used in powder form, it can be used to form a very dense coating on another material. The resistance of the metal matrix composite according to the invention at high temperatures or in uses subjected to corrosion is based on the fact that during the use, a protective oxide coating is formed on the surface of the metal matrix composite, which coating can be detected on the surface of the material by microscopy. A requirement for the formation of the protective layer is that there are elements present in the surface of the metal matrix composite which affect the formation of the layer. The surface must contain an element which is capable of forming an oxide layer. Such elements include, for example, aluminum, chromium and silicon. These elements are advantageously blended both in the carbide phase and in the metallic binder or the binder between metals, so that a uniform oxide layer is formed on the surface. Silicon oxide (Si0 2 ), which is formed as a result of silicon present, is capable of forming a very dense oxide layer as a protection from oxi- dation and corrosion and which also has an advantageous effect on the stability of other oxides forming an oxide layer, such as aluminum and chromium oxides, under the conditions of use. If tantalum and molybdenum or chromium are blended in the raw materials of the metal matrix composite, normally in its carbide phase, the protective oxide layer is formed as a layer with an even thickness of typically 1 to 50 μm, with a very good protecting effect. Metal matrix components resistant to high temperatures were achieved by the SHS technique by using the following raw materials and raw material ratios: Example 1. 0.8 atoms of titanium and 0.2 atoms of chromium were used per one carbon atom. In addition, 40 % of the mass of the mixture consisted of a binder containing 63.5 wt-% of iron (Fe), 21 wt-% of chromium (Cr), 15 wt-% of aluminum (Al), and 0.5 wt-% of zirconium (Zr). Example 2. 0.8 atoms of titanium and 0.2 atoms of chromium were used per one carbon atom. In addition, 40 % of the mass of the mixture consisted of a binder. The binder contained 63.5 wt-% of iron (Fe), 21 wt-% of chromium (Cr), 15 wt-% of aluminum (Al), and 0.5 wt-% of zirconium (Zr). Five weight percent of the mass of the mixture consisted of silicon carbide (SiC). Example 3. 0.8 atoms of titanium and 0.2 atoms of chromium were used per one carbon atom. In addition, 30 % of the mass of the mixture consisted of a binder containing 63.5 wt-% of iron (Fe), 21 wt-% of chromium (Cr), 15 wt-% of aluminum (Al), and 0.5 wt-% of zirconium (Zr). Example 4. 0.75 atoms of titanium and 0.25 atoms of chromium were used per one carbon atom. In addition, 40 % of the mass of the mixture consisted of a binder containing 63.5 wt-% of iron (Fe), 21 wt-% of chromium (Cr), 15 wt-% of aluminum (Al), and 0.5 wt-% of zirconium (Zr). Example 5. 0.75 atoms of titanium and 0.25 atoms of chromium were used per one carbon atom. In addition, 40 % of the mass of the mixture consisted of a binder which was Inconel 601 (a commercial NiCr based mixture, High Performance Alloys, Inc., USA). Example 6. 0.8 atoms of titanium, 0.1 atoms of tantalum and 0.1 atoms of molyb- denum were used per one carbon atom. In addition, 40 % of the mass of the mixture consisted of a binder containing 63.5 wt-% of iron (Fe), 21 wt-% of chromium (Cr), 15 wt-% of aluminum (Al), and 0.5 wt-% of zirconium (Zr). Example 7. 0.8 atoms of titanium, 0.1 atoms of tantalum and 0.1 atoms of molybdenum were used per one carbon atom. In addition, 40 % of the mass of the mixture consisted of a binder which was Inconel 601 (a commer- cial NiCr based mixture, High Performance Alloys, Inc., USA).

Claims: Claims: 1. A method for the manufacture of a metal matrix composite by the SHS technique, in which method titanium carbide and titanium diboride are formed in a reaction between titanium and carbon or between titanium and borium, respectively, and which metal matrix composite comprises a metallic binder or a binder between metals, characterized in that tantalum and molybdenum or chromium are blended into the raw materials of the metal matrix composite to improve the temperature resistance and/or corrosion resistance of the metal matrix composite. 2. The method according to claim 1 , characterized in that the metallic binder or the binder between metals contains a high-temperature mixture of aluminum oxide and/or chromium oxide. 3. The method according to claim 1 or 2, characterized in that the metallic binder is a mixture containing iron (Fe), chromium (Cr) and aluminum (Al). 4. The method according to claim 1 or 2, characterized in that the metallic binder is a mixture containing nickel (Ni) and chromium (Cr). 5. The method according to claim 1 or 2, characterized in that the metallic binder is a mixture containing nickel (Ni) and aluminum (Al). 6. The method according to claim 1 or 2, characterized in that the metallic binder is a mixture containing nickel (Ni), aluminum (Al) and chromium (Cr). 7. The method according to claim 1 or 2, characterized in that the metallic binder is a mixture containing nickel (Ni), iron (Fe) and chromium (Cr). 8. The method according to claim 1 or 2, characterized in that the intermetallic binder material is a mixture containing a nickel aluminide (N. 3 AI. NiAI). 9. The method according to any of the preceding claims, characterized in that at least one of the following substances is blended in the raw materials of the metal matrix composite: zirconium (Zr), zirconium oxide (Zr0 2 ), yttrium (Y), yttriym oxide (Y 2 0 3 ), lanthanum (La), cerium (Ce), thorium (Th), rhenium (Re), rhodium (Rh), titanium (Ti), silicon carbide (SiC), or molybdenum suicide (MoSi 2 ). 10. A metal matrix composite made by the SHS technique and comprising titanium carbide or titanium diboride, and a metallic binder or a binder between metals, characterized in that the metal matrix composite contains elements at whose presence a protective oxide layer is formed on the surface of the metal matrix composite during the use. 11. The metal matrix composite according to claim 10, characterized in that the raw materials of the metal matrix composite contain silicon, chromium and/or aluminum, which form a protective oxide layer on the surface of the metal matrix composite during the use. 12. The metal matrix composite according to claim 10 or 11 , charac- terized in that the raw materials of the metal matrix composite contain tantalum and molybdenum or chromium. 13. The metal matrix composite according to any of the preceding claims 10 to 12, characterized in that the thickness of the oxide layer is 1 to 50 μm. 14. The metal matrix composite according to any of the preceding claims 10 to 13, characterized in that the metal matrix composite is in the form of a solid piece or a powder.

Inventors: HANNULA SIMO-PEKKA, JANSSON ANSSI, LINDROOS TOMI, LINTULA PEKKA, LINTUNEN PERTTI, HANNULA, SIMO-PEKKA, JANSSON, ANSSI, LINDROOS, TOMI, LINTULA, PEKKA, LINTUNEN, PERTTI
Applicants: HANNULA SIMO-PEKKA, JANSSON ANSSI, LINDROOS TOMI, LINTULA PEKKA, LINTUNEN PERTTI, VALTION TEKNILLINEN, HANNULA, SIMO-PEKKA, JANSSON, ANSSI, LINDROOS, TOMI, LINTULA, PEKKA, LINTUNEN, PERTTI, VALTION TEKNILLINEN TUTKIMUSKESKUS
Application year: 2001
Main classification: B22F3
IPC codes: B22F3, C22C1, C22C29