Investigation of High-Temperature Recovery and Recrystallization Behavior in a Single Crystal Ni-Based Superalloy Treated with Shot Peening and Laser Peening

In this study, the effects of shot peening (SP) and laser peening (LP) on the high-temperature microstructural evolutions of a CMSX-4 single crystal Ni-based superalloy were scrutinized, with an emphasis on understanding the phenomena of recovery, recrystallization (RX), and oxide layer formation. CMSX-4 specimens were subjected to SP and LP, followed by thermal exposure at 1100 °C for 100 h to accelerate dislocation mobility and RX. Quantitative assessments revealed that SP induced significant microstructural changes, including a stark increase in surface hardness by 53% over the untreated specimens, and generated maximum residual stresses of − 1250 MPa. This intense mechanical impact and thermal input facilitated the formation of new grains characterized by high-energy angles of 50–60 degrees with an average diameter of 55 µm. Furthermore, SP followed by heat treatment was found to promote the growth of a 2.5 µm thick, continuous Al₂O₃ oxide layer, providing substantial coverage that could potentially enhance the alloy’s resistance to corrosion. In contrast, LP imparted less intense surface modifications, with an increase in hardness of only 26% and lower magnitude residual stresses peaking at − 750 MPa. However, LP preserved the alloy’s original crystal structure, exhibiting no evidence of RX.