The effect of deformation-induced transformation of metastable β phase on the ductility and toughness of four commercial titanium alloys was investigated. Tensile tests, Charpy impact tests, and both static and dynamic fracture toughness tests were carried out at temperatures between 77 and 473 K on four titanium alloys containing metastable β phase. Deformation-induced α″ (orthorhombic martensite) was observed in an (α + β)-type Ti-6Al-2Sn-4Zr-6Mo alloy. The dynamic fracture toughness of this alloy increased considerably at 223 K compared to those at other temperatures. In another (α + β)-type Ti-6A1-4V alloy, the static fracture toughness at 123 K and the dynamic fracture toughness at 223 K were increased considerably by the presence of deformation-induced martensite compared to those at other temperatures. The strength increased as the temperature decreased in this alloy. An abnormal elongation of a β-type alloy, Ti-15V-3Al-3Sn-3Cr, at 123 K was attributed to the mechanical twinning of the β phase. However, the effect of deformation-induced transformation on the fracture toughness of Ti-3Al-8V-6Cr-4Mo-4Zr alloy was not observed.
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