A new method of controlled alloying of intermetallic γ-TiAl with carbon

Intermetallic γ-TiAl alloys belong to very promising materials for the production of components working in extreme conditions, mainly due to their low density, high creep resistance and good corrosion resistance. The biggest problem for the wider use of these alloys in practice is the problematic production of components, their high price and low strength at temperatures above 800 °C. Precision casting is the most cost-effective method of manufacturing components from γ-TiAl alloy. Usually, vacuum induction furnaces equipped with either a ceramic crucible or a cold crucible (ISM - induction scull melting) are used for melting and casting of γ-TIAI alloys. The ISM process is a very costly technology, especially for the high purchase price of the melting furnace and its uneconomical operation, as a substantial part of the energy required for melting is converted into waste heat into cooling water. In addition, the cooled walls of the cold crucibles are thermally inefficient and prevent achieving the required superheating temperature of the melt which is necessary for perfect filling of complex moulds. Due to the low superheating of the melt, the rejection rate increases, which significantly contributes to the increase in the price of components from γ-TiAl alloys. The melting and casting in oxide crucibles (Al2O3, Y2O3, ZrO2, CaO) leads to an increase in oxygen content of the alloys, which has an adverse effect on the mechanical properties. From the point of view of the thermodynamic stability, Y2O3 appears to be the most suitable oxide ceramic. However, this ceramic is expensive, increases the total cost of casting production and moreover, it is not completely resistant to γ-TiAl melts. Graphite crucibles, which are relatively cheap, are not recommended for melting of γ-TiAl alloys due to the high alloy contamination by carbon and the formation of large primary carbide particles that cause a significant drop in mechanical properties. To increase the high-temperature strength of γ-TiAl alloys, alloying with carbon is currently used, which leads to the formation of fine carbide precipitates. Carbon is added to the alloys during their metallurgical preparation. The melting of these alloys is then carried out either by the ISM method or by induction melting in ceramic crucibles, followed usually by casting in ceramic or permanent molds A team of inventors from an established Slovak research institute and a well-known Czech university has managed to eliminate the above-mentioned shortcomings by the new method of controlled alloying of intermetallic γ-TiAl alloys with carbon during vacuum induction melting in graphite crucibles. The new method consists in that the alloy is melted in a crucible from isostatically pressed graphite (with defined density, open porosity and average graphite grain size), wherein the melting of the alloy is carried out in a vacuum induction furnace by means of a medium-frequency induction heating with a medium-frequency inductor (with defined power and frequency) in a protective atmosphere of argon at a defined vacuum in the vacuum chamber of the induction furnace. The proposed technology of induction melting combined with centrifugal casting can be used to produce precise castings, e.g. turbocharger wheels for combustion engines, turbine blades or exhaust valves for combustion engines. The institute and the university are looking for a partner (licensee) for licensing the technology in this or related fields. The preferred cooperation type is license agreement.