The effects of stress level and grain size on the ambient temperature creep deformation behavior of an alpha Ti-1.6 wt pct V alloy

Ambient (room) temperature studies have been carried out on an α-Ti-1.6 wt pct V alloy to determine the effects of stress level and grain size on ambient temperature creep behavior. Creep tests were performed at five different stress levels ranging from 75 to 95 pct of the yield stress value on specimens with an average grain size of 226 μm. It has been found that the alloy exhibits appreciable creep at stress levels far below the yield stress, with creep occurring at values as low as 75 pct of the yield stress. The extent of creep strain was found to decrease with a decrease in stress level. Creep tests were also performed on this alloy with different grain sizes ranging from 38 to 226 μm at a stress level of 90 pct of the yield stress. It was seen that the extent of creep strain decreased with a decrease in grain size. Fine slip and time-dependent twinning were found to be the creep deformation mechanisms. Based on the results of this investigation and earlier studies, it is suggested that time-dependent twinning is a major creep deformation mechanism in α-titanium alloys that contain small amounts of alloying elements. The time-dependent twinning phenomenon has been attributed to the diffusion of oxygen away from the twin-matrix interface, permitting the growth of twins.