Thermal evolutions of residual stress and strain hardening of GH4169 Ni-based superalloy treated by laser shock peening

Residual stresses and strain hardening in GH4169 Ni-based superalloy treated by four different laser shock peening (LSP) configurations and their thermal evolution behaviors under two vacuum annealing conditions were investigated with X-ray diffraction (XRD) and two uniaxial progressive loading tests with two loading rates. Results showed that the thermal relaxations of residual stress under the two vacuum annealing conditions are quite limited, which can be attributed to the fairly low strain hardening levels (<3 %) produced by the current LSP configurations. Besides, an abnormal elevation of strain hardening under vacuum annealing condition VA2 (650 °C, 12 h) was observed, which is caused by the precipitation and growth of plate-like δ-phase particles at the grain boundaries (GBs) and the twin boundaries (TBs). Last but not least, the characteristic relationship between strain hardening and XRD peak width calibrated in this study can also be used to quantitatively study strain hardening of GH4169 Ni-based superalloy in the same heat treatment state treated by other cold working processes below 650 °C.