Microstructure characteristics and formation mechanism of TC17 titanium alloy induced by laser shock processing

•Gradient microstructure characterized by TEM.•Kinetics calculation of rotation dynamic recrystallization (RDR) mechanism.•Deformation twins become less prevalent at ultrahigh strain rates (107/s).•Grain refinement of top surface induced by laser shock processing.

As one of the surface strengthening technologies, laser shock processing (LSP) can form a gradient refined surface layer in metallic materials. The gradient microstructural characteristics of TC17 titanium alloy induced by ultrahigh strain rate deformation in LSP were systemically examined by transmission electron microscope (TEM). The microstructure near substrate consisted of dislocations and deformation twins with high density; The microstructures featured of dislocation tangles, dislocation cells and subgrains closer to the surface, and the deformation twins became less prevalent due to higher strains and strain rates where there were insufficient time for atoms to reposition to the twinned orientation to accomplish the twinning deformation; The original coarse grains with size of tens of micrometers (average grain size 43 μm) were refined instantly to hundreds of nanometers (average grain size 396 nm) in the top surface of TC17 titanium alloy after LSP, which was the result of rotation dynamic recrystallization (RDR) proved with quantitative calculation of recrystallization kinetics. There was a gradient distribution of hardness values of the LSPed surface layer.