Effect of α′ Martensite on Microstructure Refinement After α + β Isothermal Treatment in a Near-α Titanium Alloy Ti60

The effect of the α′ martensite on microstructure refinement after α + β isothermal treatment in a near-α titanium alloy Ti60 was investigated. A high density of the refined acicular α plates nucleate and grow inside α′ martensite during the isothermal treatment. The refinement mechanism of the α′ martensite was determined by comparing the direct β to α and α′ to α phase transformations. The α phase prefers to nucleate along the grain boundaries during the β → α transformation. However, in the α′ martensite, the refinement of the α phase is attributed to the precipitation of a small amount of β phase in between the adjacent α phase, and the stacking faults inside the α′ martensite. In addition, the yield strength and elongation of the alloy both increase due to the refinement of the α phase.