The Nucleation and the Intrinsic Microstructure Evolution of Martensite from 332〈113〉β Twin Boundary in β Titanium: First-Principles Calculations.

A clear understanding on the inter-evolution behaviors between 332 〈 113 〉 β twinning and stress-induced martensite (SIM) α″ in β-Ti alloys is vital for improving its strength and ductility concurrently. As the preliminary step to better understand these complex behaviors, the nucleation and the intrinsic microstructure evolution of martensite α″ from 332 〈 113 〉 β twin boundary (TB) were investigated in pure β-Ti at atomic scale using first-principles calculations in this work. We found the α″ precipitation prefers to nucleate and grow at 332 〈 113 〉 β TB, with the transformation of 332 〈 113 〉 β TB→ 130 〈 3 ¯ 10 〉 α ″ TB. During this process, α″ precipitation firstly nucleates at 332 〈 113 〉 β TB and, subsequently, it grows inwards toward the grain interiors. This easy transition may stem from the strong crystallographic correspondence between 332 〈 113 〉 β and 130 〈 3 ¯ 10 〉 α ″ TBs, and the region close to the 332 〈 113 〉 β TB presents the characteristics of intermediate structure between β and α″ phases. Kinetics calculations indicate the α″ phase barrierlessly nucleates at 332 〈 113 〉 β TB rather than in grain interior, where there is higher critical driving energy. Our calculations provide a unique perspective on the "intrinsic" microstructure evolution of martensite α″ from 332 〈 113 〉 β TB, which may deepen our understanding on the precipitation of martensite α″ and the inter-evolution behaviors between 332 〈 113 〉 β twinning and martensite α″ in β-Ti alloys at atomic scale. [ABSTRACT FROM AUTHOR]