Size Effects of Fracture Toughness and Dependence of Microstructure in Ti-Alloys
Seiji KANAMORI, Eiji ABE, Tetsuya TAGAWA and Takashi MIYATA
Abstract:The effects of microstructure and constraint on the process of micro-void coalescence type of fracture and toughness of a/b titanium alloys with equiaxed a phase were investigated. Materials tested were 3 types of titanium alloys (Ti-6Al-4V, Ti-4.5Al-3V-2Fe-2Mo, and Ti-10V-2Fe-3Al alloy) and two or three different heat treatments were conducted for these three alloys in order to obtain different a grain size. Fracture toughness testing was performed and JIC and Tmat values were evaluated. Correlation between the toughness and the ductility under the high triaxial stress state was investigated to clarify the dominant factors constructing the fracture toughness. It was shown that the refinement of microstructure leads to the reduction of ductility and fracture toughenss because the most of micro-voids in a/b titanium alloys were nucleated at a/b interface. However, near-b titanium alloys with ultra-fine particle of a (< 1mm) have exceptionally a different tendency from other a/b titanium alloys. About the size effects, the difference of specimen thickness hardly affects on JIC value but Tmat in paricular material was significantly influenced by the specimen thickness, corresponding to the dependence of triaxiality on the ductility. Key Words:a/b titanium alloy, Fracture toughness,Tearing modulus, Microstructural parameter, Dimple size, Size effects, Stress triaxiality