2상 Ti-6Al-4V 합금, 준단상 Ti-6.85Al-1.6V 및 단상 Ti-7.0Al-1.5V 합금의 고온 변형거동에 관한 연구

Abstract

The high-temperature deformation mechanisms of a <TEX>${\alpha}+{\beta}$</TEX> titanium alloy (Ti-6Al-4V), near-a titanium alloy (Ti-6.85Al-1.6V) and a single-phase a titanium alloy (Ti-7.0Al-1.5V) were deduced within the framework of inelastic-deformation theory. For this purpose, load relaxation tests were conducted on three alloys at temperatures ranging from 750 to <TEX>$950^{\circ}C$</TEX>. The stress-versus-strain rate curves of both alloys were well fitted with inelastic-deformation equations based on grain matrix deformation and grain-boundary sliding. The constitutive analysis revealed that the grain-boundary sliding resistance is higher in the near-<TEX>${\alpha}$</TEX> alloy than in the two-phase <TEX>${\alpha}+{\beta}$</TEX> alloy due to the difficulties in relaxing stress concentrations at the triple-junction region in the near-<TEX>${\alpha}$</TEX> alloy. In addition, the internal-strength parameter (<TEX>${\sigma}^*$</TEX>) of the near-<TEX>${\alpha}$</TEX> alloy was much higher than that of the <TEX>${\alpha}+{\beta}$</TEX> alloy, thus implying that dislocation emission/ slip transfer at <TEX>${\alpha}/{\alpha}$</TEX> boundaries is more difficult than at <TEX>${\alpha}/{\beta}$</TEX> boundaries.