2019 年 60 巻 9 号 p. 1733-1739
In this study, the microstructure, tensile strength, elongation, and reduction of area of near-β Ti alloys (Ti-17) were investigated after being subjected to solution and aging treatments. Ti-17 was forged at temperatures between 700 and 850°C followed by air cooling. Then, the forged Ti-17 was subjected to solution treatment at 800°C for 4 h followed by water quenching and aging treatment at 620°C for 8 h followed by air cooling. Tensile tests were performed at room temperature, 450°C, and 600°C. The change in microstructure at different forging temperatures was exhibited by only the volume fraction and morphology of the grain boundary (GB) α phase. That is, a granular GB α phase was formed in the samples forged at 700 and 750°C. Moreover, a film-like GB α phase was formed in the samples forged at 800 and 850°C. The tensile strength was the same for all the tested samples, indicating that the microstructure has little effect on the tensile strength. The elongation and reduction of area increased with decreasing volume fraction in the GB α phase. It is considered that the film-like morphology slightly improves ductility.
