Relationship between Microstructure and Notch Tensile Strength in Ti–15V–3Cr–3Sn–3Al Alloy at Elevated Temperatures

Abstract

The notch tensile strength (NTS) of Ti–15V–3Cr–3Sn–3Al (Ti-15-3) aged at temperatures ranging from 426 to 600°C was determined at elevated temperatures, and correlated to microstructure. Notch tensile tests were conducted in laboratory air at the room temperature, 150, 300 and 450°C. The base metal specimen aged at 426°C formed elongated α precipitates interlocked in a basket-weave like structure and then had peak hardness but inferior notch tensile strength at room temperature due to the trans-granular quasi-cleavage fracture seperated along the α/β interface in the aged specimen. As the aging and test temperature increased, the coarse Widmanstätten α in the specimen aged at 540°C was facilitated to perform high NTS owing to crack deflection or microcrack formation in Ti-15-3 alloy under 300°C, while the improved ductility and notch blunting of the specimen aged at 426°C reduced the notch brittleness and resulted in a remarkably improved NTS tested at 450°C. The NTS of the specimen aged at 426°C was much higher than that of the other aged specimen tested at 450°C. This result suggested that the basket-weave-like structure was more resistant to the softening of substance than the coarse Widmansttäten structure at 450°C.