Experimental investigation on surface integrity and fatigue of nickel-based single-crystal superalloy DD6 during grinding-shot peening composite manufacturing

Surface integrity is an important factor affecting service performance of parts. Favorable machined surface state can greatly improve fatigue life of parts. Multi-process composite manufacturing is a common processing method in high-end manufacturing. In this study, the surface integrity and fatigue properties of nickel-based single-crystal superalloy DD6 after grinding-shot peening composite manufacturing were investigated. The influence of grinding and shot peening process parameters on the surface integrity of DD6 was introduced in detail and mainly analyzed the changes of surface topography and roughness, microstructure, microhardness, residual stress, fatigue life, and fracture morphology. The results show that compared with grinding, grinding-shot peening composite manufacturing increases the surface roughness with the increase of process strength. Grinding-shot peening composite processing will aggravate the shear fracture degree of γ phase and γ′ phase, forming a deeper surface plastic deformation layer; the surface microhardness reaches 645 HV; the hardened layer depth reaches 110 μm; and the residual compressive stress introduced on the surface improves with the increase of process strength. The fatigue life of composite manufacturing at 760 °C is 2.06 times longer than that of grinding. The fatigue fracture surface cracks along the {111} crystal plane. The grinding-shot peening composite manufacturing can slow down the crack propagation to the surface and prolong the fatigue life.