Influence of cryogenic treatment applied prior to aging treatment on fatigue crack propagation behavior of Ti-15V-3Al-3Sn-3Cr metastable beta titanium alloy

Purpose: There have been a few studies about the effect of the cryogenic treatment on titanium alloys' microstructural and mechanical properties in the literature. However, studies in which cryogenic treatment is applied to metastable P. titanium alloys are quite limited. Therefore, in this study, cryogenic treatment with or without single-step and duplex aging treatment was applied to the alloy. In addition, tensile, microhardness, and fatigue crack propagation tests were applied to heat-treated sample groups. Thus, fatigue crack propagation behavior of the samples that were aged after the cryogenic treatment for the first time in the literature was examined. Theory and Methods: Cryogenic treatment was applied at-196 degrees C for 24 hours. Single-step and duplex aging treatments were applied after the cryogenic treatment. Aging treatments were applied at both high (85-195 degrees C below P. transition temperature) and low (200-450 degrees C) aging temperatures. The tensile, microhardness and fatigue crack propagation tests were applied to heat-treated sample groups. Results: alpha phases were precipitated at a finer size in the duplex aged samples, and precipitation-free zones were not observed in the microstructure. In addition, significant increases in strength values were obtained without a decrease in the elongation of the alloy in the aged samples after the cryogenic treatment. Compared to singlestep aged samples, crack propagation rate was obtained lower due to uniform precipitation of finer alpha phases in the duplex aged samples. Conclusion: Maximum strength versus maximum elongation was obtained in Kry+300/10-450/8 specimens subjected to duplex aging after cryogenic treatment. Also, fatigue crack propagation resistance of the duplex aged samples was found higher than the single-step aged samples.