Ti–4.5Al–3V–2Fe–2Mo合金の形状記憶特性に及ぼす熱処理温度の影響

抄録

In this study, effects of heat-treatment temperature on microstructure, lattice parameters of martensite phase, and shape memory properties of Ti–4.5Al–3V–2Fe–2Mo alloy (SP-700) were investigated. The volume fraction of α phase decreased and therefore martensitic transformation temperatures increased with increasing heat-treatment temperature. Increasing heat-treatment temperature also changed the lattice parameters of α″ martensite phase but did not form α′ phase. The maximum calculated transformation strain was estimated in the specimen without α phase precipitation. Shape memory effect and superelasticity were confirmed at room temperature and subsequent heating in the heat-treated specimens. Comparing to the specimens in which stress-induced martensitic transformation occurred during loading, a smaller shape recovery strain was observed in a specimen deformed by the reorientation of martensite variants during heating. It was suggested that dislocations were easily introduced during the twinning deformation in the reorientation process because of large magnitudes of twinning shear of SP-700.