Microstructure characterization and tensile properties of processed TC17 via high energy shot peening

The microstructure and tensile properties of the processed TC17 via high energy shot peening (HESP) were investigated, in which special attention was paid to reveal the fracture behaviour of the HESP processed surface layer. The results indicated that the severe plastic deformation (SPD) zone with the nanograins appeared in the HESP processed surface layer of TC17, in which the SPD thickness increased with the increasing of air pressure while it increased firstly and then decreased with the prolonging of peening duration, and the finer nanograins could be obtained at the higher air pressure and longer peening duration. Due to the generation of the gradient structure layer, the HESP processed TC17 had ruptured in a hybrid fracture. The fracture features corresponding to nanograined structure, ultrafine-grained structure and coarse-grained structure were the brittle fracture, the mixed fracture and the ductile fracture respectively. Comparing with the properties of the annealed TC17, the HESP processed TC17 possessed a better strength-ductility balance owing to combined effects of grain refinement, high-density dislocations, work hardening and compressive residual stress (CRS), in which the yield strength (YS) and the ultimate tensile strength (UTS) were increased by 10.1% and 13.9%, respectively.