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

Abstract

Ambient (room) temperature studies have been carried out on an ␣-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 m. 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 m 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 ␣-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.

A Review of Metastable Beta Titanium Alloys

“…If the beta phase stabilizing element is included only in a limited quantity that is less than the critical concentration listed in Table 1, then the Ti alloy microstructure will consist of only the hcp α-phase after quenching from above the quantity T β , such as in the binary Ti-1.6 wt. % V alloy [39,40]. Although the beta phase stabilizing element V is included in the binary alloy, the concentration is significantly less than the critical concentration of 15 wt.…”

“…% V alloy [39,40]. Although the beta phase stabilizing element V is included in the binary alloy, the concentration is significantly less than the critical concentration of 15 wt.…”

Intragranular Deformation Mechanisms during Ambient-Temperature Creep in Hexagonal Close-Packed Metals

“…However, their creep strains were much less than that of CP-Ti 2 and the tensile creep test of Mg, respectively. Ankem et al 23) found that the time-dependent deformation twins were the dominant deformation mechanism in Ti-0.4Mn with d ¼ 500 mm. Although the deformation twins are introduced during the ambient-temperature creep of coarse-grained Ti, the present results for CP-Ti 1A and Mg reveal that the activation of deformation twins reduce the creep behavior.…”

“…23) Although those results suggest that the deformation twins are yielded in ambient-temperature creep in coarse-grained materials, the role of the deformation twins in a finer-grained sample has not been clear.…”

Time Dependent Twinning and the Role of Oxygen in the Low Temperature (<0.25 Tm) Creep Behavior of Alpha Titanium Alloys

“…Twinning contributes to structural performance in many Ti alloys by accommodating deformation in concert with slip. Although unimpeded twin growth is observed to occur at significant fractions of the speed of sound in a metal (for example [1]), slow twin growth is also observed in some cases [2,3]. The slow growth of deformation twins, or "time-dependent twinning", acts as a creep deformation mechanism and significantly affects alloy performance.…”