α″ martensite and amorphous phase transformation mechanism in TiNbTaZr alloy incorporated with TiO2 particles during friction stir processing

This work studied the formation of the α″ martensite and amorphous phases of TiNbTaZr alloy incorporated with TiO2particles during friction stir processing. Formation of the amorphous phase in the top surface mainly results from the dissolution of oxygen, rearrangement of the lattice structure, and dislocations. High-stress stemming caused by dislocations and high-stress concentrations at crystal–amorphous interfaces promote the formation of α″ martensite. Meanwhile, an α″ martensitic transformation is hindered by oxygen diffusion from TiO2to the matrix, thereby increasing resistance to shear.