Laser-cladding and robotic hammer peening of stainless steel 431 on low alloy steel 4140 for surface enhancement and corrosion protections

Surface enhancement and coating are distinct methods that have long been developed for protecting metallic components from corrosion, erosion, and wear in aggressive working environments. The former is to engineer the surface and near-surface of the base material towards desired performance improvements. In comparison, a coating is to deposit extrinsic materials with better-desired performance direct on the surface of the base material. Recent developments in additive manufacturing rendered increased interest in the hybrid process of surface enhancement and coating. Here, we report laser-cladding (LC) and robotic hammer peening (RHP) of stainless steel (SS431) layers on 4140 alloy steel substrates for corrosion protection. Materials and structural studies reveal that the LC-SS431 layers are dominated by crack-free equiaxed dendrites. Their hardness and compressive residual stress have been apparently improved by the RHP process without introducing any interface degradations. Corrosion test in an aqueous NaCl (3.5 wt.%) electrolyte shows that proper RHP processes can enhance the corrosion resistance of the SS431 coatings, and the enhancement is more than that of the substrate.