Improvement of high temperature oxidation resistance of additively manufactured TiC/Inconel 625 nanocomposites by laser shock peening treatment

Abstract

Additive manufacturing has seen large growth due to its numerous process advantages, yet some undesirable defects in additive manufactured (AM) products include pores and micro-cracks. These defects weaken the high temperature oxidation resistance of the final parts. In this work, laser shock peening (LSP) is used as a post-treatment method to change the surface characteristics of selective laser melted (SLM) nano-TiC particle-reinforced Inconel 625 nanocomposites (TiC/IN625). The effects of LSP on surface morphology, residual stress, microhardness, microstructure, and high temperature oxidation behavior of fabricated parts are studied. The results indicate pores in the as-built sample can be closed by the severe plastic deformation, which is induced by LSP. The maximum hardness is found to reach 462 ± 7 HV with a ∼ 460 μm hardened layer, and the surface stress state transforms from tensile to compressive after LSP. The full width at half maximum (FWHM) values of the (111) and (200) diffraction broaden, which can be attributed to grain refinement and an increase in lattice strain in the LSP samples. It is found that LSP causes a large number of columnar dendritic structures in the as-built sample to transform into cellular dendritic structures. Dislocation walls and dislocation tangles with high dislocation density form in the LSP sample. Compared with as-built sample, the LSP samples exhibit lower mass gain after oxidation at 900 °C for 100 h, indicating that LSP samples have greater oxidation resistance at high temperature. The underlying mechanism governing the high temperature oxidation resistance is proposed based on the experimental results. This study shows that LSP can be used as an effective method to modify the surface characteristics of SLM TiC/IN625.