Surface strengthening in confined spaces: A novel deflecting abrasive waterjet peening for improving the surface integrity of nickel-based superalloys GH4169

Abstract

Abrasive waterjet peening (AWJP) has become an essential surface treatment technique to improve the surface integrity and mechanical properties of metallic parts due to its high controllability and small thermal influence. However, since existing AWJP processes are based on straight nozzles, they are difficult for complex geometrical profiles and confined spaces treatment, such as dovetail slots. In the present work, a novel deflecting AWJP (DAWJP) process with a designed deflecting nozzle was proposed and verified by experiments on the nickel-based superalloy GH4169. First, the DAWJP's deflecting nozzle was designed based on the AWJP's straight nozzle and deflecting pin with deflection angle. Second, the internal and external flow field distribution and abrasive movement state of deflecting nozzles with different deflection angles (R = 0, 1, 1.5, 2 mm) were studied by using the FLUENT CFD software. Finally, the surface integrity of the GH4169 specimen treated by the proposed DAWJP with an optimized deflecting nozzle was investigated, including microstructure, height difference, surface roughness and microscopic morphology, surface and subsurface microhardness and compressive residual stress (CRS). The results of this study highlighted that the deflecting nozzle with a deflection angle of 1.5 mm could obtain relatively optimized jet flow velocities of the water and abrasive mixed phases. The GH4169 specimen treated by the DAWJP with different processing parameters using the optimized deflection angle formed a plastic deformation depth of 22–51 μm, a height difference between the as-received and DAWJP treated surface of 4–48 μm, and the surface roughness Ra and Sa of 0.199–0.503 μm and 0.535–0.953 μm. The surface microhardness and CRS of the DAWJP treated specimen were approximately 522–573 HV and 773–991 MPa, which is 7.6 %–18.1 % and 209 %–296 % times higher than the as-received specimen, respectively. The work-hardened layer and CRS depth of the near surface of the specimen induced by the DAWJP treatment were approximately 120–180 μm and 112–203 μm. This work presents a novel DAWJP method and investigates its effect on the surface integrity of the GH4169 material, which is expected to have applications in improving the surface integrity and mechanical properties of metallic parts with confined spaces.