Modelling and experimental study of surface treatment in abrasive waterjet peening of Nickel-based superalloy: Inverse problem

Abrasive waterjet peening (AWJP) is a promising method of surface treatment for modifying mechanical properties of components by introducing compressive residual stress (CRS) to a workpiece surface. Many efforts have been paid so far to modelling and optimisation of the AWJP process, however, most of these studies focus on the forward problems, i.e. estimating the CRS of workpiece surface according to processing parameters. There are still significant challenges in implanting different CRS at target areas in workpiece surface, which is the foundation of implanting uniform distribution of CRS on free-form surface or workpiece with uneven initial stress state. In this paper, a novel temporally and spatially controlled method for AWJP has been proposed, where the distribution of CRS can be adjusted by the optimisation of the abrasive waterjet parameters. That is, to achieve the AWJP system configuration for specific CRS on a target area, an inverse problem of CRS distribution has been modelled and solved, where the pump pressure, traverse speed and centre distance were optimised together to reach a prescribed CRS distribution. The proposed method was validated through experiments of implanting uniform distribution and non-uniform distribution of CRS at target areas. The results revealed that the maximum error between target and experimental CRS was only 14.25% in 18 sets of experiments. In addition, microstructure analysis of the AWJP surface suggested that a relatively low pump pressure and traverse speed can be selected to induce grain refinement and strain hardening layer on the workpiece surface without cracks and heavy surface topography fluctuations.