Titanium alloys can experience a cooling-induced phase transformation from a body-centred cubic phase into a hexagonal close-packed phase which occurs in 12 crystallographically equivalent variants. Among them

variant selection II

60°/12¯10

is very close to the orientation of {101¯1}12¯10 twins (57.42°/12¯10). We propose that the cyclic thermal loading during additive manufacturing introduces large thermal stresses at high temperature

enabling grain reorientation that transforms the 60°/12¯10 variant boundaries into the more energetically stable 57.42°/12¯10 twin boundaries. This transformation twinning phenomenon follows a strain accommodation mechanism and the resulting boundary structure benefits the mechanical properties and thermal stability of titanium alloys.