Abstract
The effect of microstructure on creep and creep-fatigue behavior at elevated temperature was studied in Ti-6Al-4V alloy having three different microstructures. The three types of microstructure were prepared with different heat treatment conditions; that is, equiaxed α structure, lenticular α structure and bimodal (mixed of equiaxed α and lenticular α) structure. Creep test was carried out under constant load condition at 773K in air. Creep-fatigue test was carried out under total strain controlled condition using trapezoidal wave form with the hold time of 2min and 10min at 773K in air. The following conclusions were obtained. (1) The creep rupture strength of equiaxed α structure was similar to that of lenticular α structure and was larger than that of bimodal structure. (2) The number of cycles to failure under creep-fatigue condition of lenticular α structure was smaller than those of other structures. (3) The effect of microstructure on crack propagation life was small as compared with crack initiation life under creep-fatigue condition. (4) The fracture mode of equiaxed α and bimodal structures was transgranular fracture under creep-fatigue condition. On the other hand, crack of lenticular α structure was initiated and propagated at the interface between α layer precipitated at grain boundary and lenticular α structure.
