Effect of microstructure on creep and creep-fatigue behavior in Ti-6Al-4V alloy at elevated temperature
Nishino Seiichi; Shiozawa Kazuaki; Aikawa Yasunori
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 a structure, lenticular a structure and bimodal (mixed of equiaxed a and lenticular a ) structure. Creep test was carried out under constant load condition at 773 K in air. Creep-fatigue test was carried out under total strain controlled condition using trapezoidal wave form with the hold time of 2 min and 10 min at 773 K in air. The following conclusions were obtained. (1) The creep rupture strength of equiaxed a structure was similar to that of lenticular a structure and was larger than that of bimodal structure. (2) The number of cycles to failure under creep-fatigue condition of lenticular a 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 a and bimodal structures was transgranular fracture under creep-fatigue condition. On the other hand, crack of lenticular a structure was initiated and propagated at the interface between a layer precipitated at grain boundary and lenticular a structure. Key Words:Ti-6Al-4V alloy, creep, low-cycle fatigue, creep-fatigue, high temperature, heat treatment, microstructure