Investigation on high temperature short-term creep and stress relaxation of titanium alloy

In this paper, the short-term creep and stress relaxation tests were performed on Ti-6Al-4V alloy at temperatures of 650-800 degrees C. Creep time of 60 min and stress relaxation time of 30 min were adopted, respectively. The obtained stress exponent of 1.62 from stress relaxation test falls within exponent range of 1.6-1.69 from creep tests at 700 degrees C while stress exponent of 1.82 obtained from stress relaxation is in the exponent range of 1.52-1.97 from creep tests at 750 degrees C. The thermal activation energy of 238.13 kJ is obtained from creep tests under initial stress of 45 MPa. The microstructures of the tested specimens were investigated by transmission electron microscope and electron back-scattered diffraction to study and compare the mechanisms of creep and stress relaxation. Microstructure analysis shows that the creep and stress relaxation behaviors are both governed by vacancy diffusion at 650 degrees C. Above 650 degrees C, the two behaviors are mainly controlled by dislocation climb. Nevertheless, the dislocations are generated from different sources for creep and stress relaxation. (C) 2014 Elsevier B.V. All rights reserved.