Effect of shot peening on the microstructure, residual stress, and mechanical properties of Inconel 690 alloy

Inconel 690 alloy is a key structural material for heat transfer tubes in pressurized water reactor nuclear power plants, where it endures harsh service conditions. Shot peening (SP) is a widely adopted surface treatment technique to enhance the durability and extend the service life of such components. This study systematically examines the effects of SP process parameters, including shot material, peening intensity, and peening coverage, on the microstructure, residual stress, and mechanical properties of Inconel 690 alloy. The results reveal that SP produces a pronounced gradient microstructure comprising a nanocrystalline surface layer, a plastically deformed sub-surface region, and a deep compressive residual stress field extending to about 240 μm. Moreover, SP induces a gradient compressive residual stress field in Inconel 690 alloy, with the magnitude and penetration depth strongly influenced by shot material, peening intensity, and coverage. The surface modifications significantly improve the mechanical performance: the yield strength increases by up to 62.4 % (from 311 MPa to 505 MPa for the SP-300 % sample), and surface hardness rises by approximately 68.5 % (from 2.990 GPa to 5.038 GPa), albeit with a slight reduction in ductility. Additionally, all SP-treated samples exhibit enhanced wear resistance, as evidenced by reduced specific wear rates due to surface hardening. This work delivers fundamental mechanism understanding of the effects of shot peening on microstructure and mechanical properties, and guides the systematic screening and optimization of SP parameters such as shot material, peening intensity, and coverage.