The behavior of recovery of o) and transition from u to a was investigated by means of hardnesss testing, tensile testing and microstruclural examinations in a Ti-13mass%Cr alloy produced by powder metallurgy. Sintered materials were subjected to the solution treatment of 1273K-1.8ks followed by water quenching, in advance. Age-hardening by iu precipitation is most significant in the aging at around 623K, and hardness reaches the maximum after 3ks aging at 623K. Age-hardened specimens undergo softening during secondary aging at temperatures above 623K (step aging) due to recovery of ui. When the secondary aging temperature is higher than 823K, hardness of pre-aged specimens drops to that of as solution-treated materials, because all of u can completely recover. In the intercritical temperatures between 623K and 823K, however, a part of CD retains and provides the nuclei for a precipitation. This results in a fine dispersion of a and a great increase in tensile strength of the alloy with step aging.
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