Surface smoothening and strengthening combined effect of mechanical hammer peening on inconel 718 superalloy

Abstract

ABSTRACT In this study, the surface strengthening and smoothening combined effect of the mechanical hammer peening (MHP) treatment is demonstrated. On a IN718 nickel-based superalloy workpiece surface, the MHP treatment introduced a subsurface residual stress field featured with a maximum stress around −1.4 GPa and a penetration depth exceeding 1 mm, and an increase of the micro-hardness from 286.43 HV to 426.27 HV. Simultaneously, it produced a significantly smoothened surface (Ra 27 nm) compared with the untreated sample (Ra 555 nm). Moreover, applying an electric pulse of 100 A would further reduce the surface roughness, without deteriorating the surface strengthening effect. The surface strengthening effect of MHP treatment mainly originates from the increase of dislocation density, grain misorientation and refinement, which are caused by impacts of the punching head; while the surface smoothening effect is the result of precisely controlled and regularly aligned punching indents. Utilizing MHP in the manufacturing process chain of aircraft parts could combine the surface strengthening and smoothening processes into one single process, which substantially improves both the production efficiency and enhances the surface finish. Especially, the working principle of MHP makes it suitable for arbitrary or complicated surfaces, that is, aeroengine blades.