Effect of heat treatment at the temperature above β-transus on the microstructures and fatigue properties of pure Ti

Commercially pure Ti (CP-Ti) was heat treated at 1273 K (1000°C), which was higher than β-transus temperature, followed by water quenching. The dwell time at 1000°C was changed from 1 to 240 h. The heat treatment at 1000°C resulted in α grain coarsening, whereas martensitic transformation occurred due to the rapid cooling from β phase. The hardness increased by the martensitic transformation, where higher hardness was achieved by longer dwell time at 1000°C. However, the fatigue strengths of the heat-treated CP-Ti were lower than that of the as-received one. The fatigue strength of the specimen with the shortest dwell time of 1 h was the lowest among the heat-treated samples with different dwell times. Untransformed coarse α grains were seen in the heat-treated specimens, which resulted in the lower fatigue crack initiation resistance and fatigue strength than the as-received specimen.