Formation mechanism of stacking faults within alpha '' martensite in Ti-7 wt% Mo alloy

Stacking faults commonly exist within martensite plates in alpha + beta titanium alloys. However, their structure and formation mechanism remain unclear. In this study, stacking faults within alpha '' 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 de-tected, lying on (001)alpha '' and (110)alpha '' planes, respectively. Across each of the faults, the arrangement of atoms is 180 degrees rotation symmetrical. The stacking faults are all produced by a specific (112)[111 over bar ]beta shear and two opposite shuffles on every other (110)beta 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-beta to orthorhombic-alpha '' martensitic transformation. (c) 2022 Elsevier B.V. All rights reserved.