Effect of microstructure on creep and creep-fatigue behavior in Ti-6A1-4V alloy at elevated temperature

Abstract

The effect of microstructure on creep and creep-fatigue behavior at 773K was studied in the Ti-6A1-4V alloy having three different microstructures. The three types of microstructures prepared using different heat treatment conditions included the equiaxed α structure, lenticular α structure and bimodal (composed of equiaxed α and lenticular α) structure. Creep tests were carried out under constant load conditions at 773K in air. Creep-fatigue tests were carried out under total strain controlled conditions using a trapezoidal waveform with hold times of 2min and 10min at 773K in air. Creep rupture strength of the alloy with equiaxed α structure was similar to that of the alloy with lenticular α structure and was higher than that of the alloy with bimodal structure. The number of cycles to failure under creep-fatigue condition of the alloy with lenticular α structure was lower than that of the other two structures. The effect of microstructure on crack propagation life was small as compared with crack initiation life under creep-fatigue conditions. The fracture mode of the alloy with equiaxed α and the bimodal structures was transgranular under creep-fatigue condition. On the other hand, the crack of the alloy with lenticular α structure was initiated and propagated at the interface between the α layer precipitated at the grain boundary and the lenticular α structure.