Formation mechanism of stacking faults within α′′ martensite in Ti-7 wt%Mo alloy

Abstract

Stacking faults commonly exist within martensite plates in α + β titanium alloys. However, their structure and formation mechanism remain unclear. In this study, stacking faults within α′′ martensite plates were systematically investigated in an as-quenched Ti-7 wt% Mo alloy using aberration-corrected scanning transmission electron microscopy and first-principles calculations. Two kinds of stacking faults were detected, lying on (001)α′′ and (110)α′′ planes, respectively. Across each of the faults, the arrangement of atoms is 180° rotation symmetrical. The stacking faults are all produced by a specific (112)[111¯]β shear and two opposite shuffles on every other (110)β plane during martensitic transformation. First-principles calculated results indicate that the occurrence of the two opposite shuffles is attributed to the decreased stacking fault energies near the Mo solute. Our findings contribute to a deep understanding of structural transformation during bcc-β to orthorhombic-α′′ martensitic transformation.