A mathematical modeling and experimental study of forming and relaxation of the residual stresses in plane samples made of EP742 alloy after the ultrasonic hardening under the high-temperature creep conditions

The authors carried out a complex (computational and experimental) research of residual stresses in prismatic samples made of EP742 alloy after ultrasonic hardening and he temperature of 650 °С for 100 hours unloaded. The laws of residual stresses distribution over the thickness of the surface-hardened layer were discovered. The experiments proved that the ultrasonic hardening of the sample caused compression residual stresses in the surface layer. The maximum stresses were observed in the subsurface layer and they decreased on reaching the surface. When the temperature was exposed, the induced compression residual stresses became relaxed, the level of residual stresses decreased by 1.4-1.6 times and its maximum was displaced deep into the sample, but the thickness of the compressed layer was kept to about 200 micron. We developed the mathematical model of residual stresses forming in prismatic samples after surface plastic deformation and relaxation under high-temperature creep conditions. We used the hardened half-space as a model object for the prismatic sample, because the hardened layer was rather thin. We introduced Cartesian coordinate system, where x 0 y plane coincided with the half-space hardened surface, and 0 z axis was directed into the depth of the hardened layer.