Abstract
Actual alloy and process development for high temperature turbine applications in the aerospace sector is strongly aimed at reaching the high demands on reduction of CO2 emissions responsible for the green house effect. Based on weight reduction the main objective resides in improving engine performance and efficiency. Last generation intermetallic titanium aluminides (γ TiAl) have a big potential to reach this goals. γ TiAl is nevertheless a very demanding material requiring very sophisticated processing routes. Access has developed a casting route for production of high quality γ TiAl components based on skull induction melting (SIM) and centrifugal investment casting. Although the feasibility of the technology has been already proven in earlier projects, it is still necessary to improve the process for series production of parts with the high quality standards required by the aerospace industry. With aid of a new developed centrifugal casting facility Access and its partners are conducting a comprehensive qualification process for the production of aerospace components, e.g. low pressure turbine blades. Basic issues comprising casting cluster design based on numerical simulation, process control and quality management are being addressed.
Highlights
Actual alloy developments for high temperature applications in the aerospace industry are mainly aimed on reducing CO2 emissions by means of weight reduction and improvement of high temperature capabilities of engine components
Access has being developing and qualifying in pilot scale a complete production route for high quality TiAl components based on centrifugal investment casting
Single phase γ-(TiAl) intermetallics exist in binary TiAl alloys with more than 48 at.-% Al and provide very low solubility for interstitial impurities [1]
Summary
Actual alloy developments for high temperature applications in the aerospace industry are mainly aimed on reducing CO2 emissions by means of weight reduction and improvement of high temperature capabilities of engine components. Single phase γ-(TiAl) intermetallics exist in binary TiAl alloys with more than 48 at.-% Al and provide very low solubility for interstitial impurities [1] For this reason relative small traces of H, C, N and O lead to dramatic embrittlement. Called 2nd generation alloys posses wider process windows, better corrosion resistance and creep properties which allow their application beyond 760°C These qualities were already attractive enough to introduce them for industrial applications and first attemps to improve casting properties were conducted. The addition of high Niobium contents on alloys of the 3rd generation resulted in acceptable RT ductility which allows for easier machining of cast components. Investment casting of TiAl Most TiAl cast parts are produced in investment casting Some reasons for this are e.g. high temperature brittle-ductile transition, narrow solidification range, reactivity of solidifying melt with mould materials and cost and time intensive machining. The main steps of the process as described for qualifying the process for production of TiAl components are shown in figure 3
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