高温構造材料としてのTiAlの特徴と乗用車ターボチャージャとしての実用化

Abstract

This report begins by indicating the position of TiAl as a high-temperature structural material in comparison with metallic materials and ceramics. The primary advantage of TiAl is that it exhibits excellent high-temperature strength for a lightweight material, while its chief disadvantage is brittleness. However, its endurance temperature is lower than for ceramics or for single crystal superalloys, and currently only small components can be readily fabricated. Accordingly, likely suitable applications for TiAl are those that presently employ conventionally cast or forged superalloys, and for which specific strength becomes applied stress. In cases where weight reduction directly improved equipment performance, the disadvantage of TiAl brittleness will be outweighed. Given the foregoing properties, research on practical applications for TiAl has centered on turbochargers for passenger vehicles, exhaust valves for passenger vehicle engines, turbine blades for jet engines, and structural component for aircraft. With respect to the former two applications that in which efforts at practical development have been most active, this report summarizes research results in terms of materials development, manufacturing technology development, and empirical testing. Finally, a development example undertaken by the authors with respect to passenger vehicle turbochargers is also presented. This project involved the development of high-performance TiAl alloy and the requisite manufacturing technology, and concluded in successful practical application following numerous empirical tests. The resulting high-response TiAl turbochargers are used in Mitsubishi Motors Corp. Lancer Evolution Series automobiles, marketed since January 1999.