Influences of Machine Hammer Peening on Inconel 718 Workpieces Manufactured by Wire-based Laser Metal Deposition

Abstract

Additive manufacturing techniques, such as laser metal deposition (LMD), have been used to produce complex-shaped workpieces with high accuracy and material utilization. However, the as-built workpieces often suffer from typical defects such as porosity, surface roughness, and tensile residual stresses that may limit their mechanical properties and service life. To overcome these limitations, post-processing steps such as mechanical forming are recommended to improve the material properties. Surface treatment, such as machine hammer peening (MHP), can significantly improve wear resistance and fatigue strength of the additively manufactured workpiece. MHP is a deterministic, high-frequency forming process that can produce smooth surfaces with high compressive residual stresses. It also offers advantages in producing defined surface structures that exhibit friction-reducing properties. However, the influence of MHP process parameters, such as hammer frequency, step over distance, and stroke distance, on the surface integrity of additively manufactured workpieces is still unknown. In the present work, the influence of MHP on Inconel 718 workpieces manufactured by wire-based laser metal deposition (LMD-w) is analyzed. A Design of Experiments (DoE) of LMD-w parameters was employed to manufacture the workpieces. The workpieces with the least typical defects such as cracks and pores were then selected. In the next step, the selected workpieces were post-processed based on a DoE of MHP parameters. To investigate the influences of MHP on the microstructure of the workpieces, the resulting mechanical properties were measured. It was found that for Inconel 718 workpieces manufactured by LMD-w, MHP can significantly improve surface properties by reducing roughness and increasing hardness. Therefore, this study shows that MHP is a promising post-processing technique to enhance the surface integrity and mechanical properties of LMD-w manufactured workpieces.