The Cyclic Stress-Strain Response of Age-Hardenable Beta Titanium Alloys.

摘要

The cyclic stress-strain response of the three age-hardenable beta-phase (bcc) titanium alloys,Beta C,Ti-8823,and Ti-38V-1Si,has been investigated as a function of heat treatment. Cyclic softening occurs initially (up to approximately 100cycles) in all alloys and conditions tested. Such softening is interpreted in terms of dislocation dynamics in which the combination of an increasing mobile dislocation density,high flow (friction) stress,and low work hardening capacity causes softening. After approximately 100cycles,cyclic stability (i.e.,the saturation of the peak stress to a constant value) occurs in all conditions of the Beta C and Ti-8823alloys and in the overaged and a thermomechanically treated condition of the Ti-V-Si alloy. However,the Ti-V-Si alloy shows cyclic instability when tested in the solution-treated or peak hardness conditions. Bauschinger strain data and other observations indicate that the mobile dislocations predominantly shear the second phase particles in all but the overaged Ti-V-Si alloy. Thus the combination of particle shearing and the degradation of the particle strength as a result of repeated shearing is interpreted to be the cause of cyclic instabilities and continued softening. (Author)