Role of Duplex Aging Treatment on the Fatigue Crack Propagation Behavior of Ti-15V-3Al-3Sn-3Cr Metastable β Titanium Alloy

Abstract In this study, the fatigue crack propagation behavior of Ti-15V-3Al-3Sn-3Cr alloy, in which aging treatments were applied, was investigated under constant and variable amplitude loading. Single-step and duplex (pre-aging + second-step aging) aging have been conducted on the alloy at low and high temperatures. Duplex aging was applied with two different pre-aging treatment temperatures and times (24 hours at 250°C and 10 hours at 300°C). During single-step aging, the precipitation-free zones reduced with the aging temperature increase; thus, the crack propagation rate of high-temperature-aged samples was lower than the low-temperature-aged samples. In the duplex-aging-treated samples, the second-step aging temperature increase negatively influenced the alloy's fatigue crack propagation rate. However, the prolonged second-step aging time caused a decrease in crack propagation rate, especially at low temperatures. After the application of overload, the crack propagation rate of the solution-treated sample increased because of the formation of secondary cracks along the crack propagation direction. On the other hand, in the aged specimen, the microcracks that formed between the α/β phases after the overload caused the sample to be fractured.