Regulating wear and corrosion performance of laser-cladded CoCrMo coating on 304 stainless steel via subsequent laser polishing and shock peening

In the present research, the CoCrMo coatings were fabricated on 304 stainless steel via laser cladding (LC), followed by laser polishing (LP) or laser shock peening (LSP) to enhance their wear and corrosion performance. Their microstructure, wear and corrosion performance were systematically characterized. The results reveal that CoCrMo powders could be well remelted on the 304 stainless steel surface by LC, but the relative rapid solidification results in massive unmelted powders on surface and increases surface roughness. The LC coating exhibit typical columnar grain structure with 29.9% ε-Co phase, which appears as lamellar structures containing some micro-twins. The relative rough surface and coarse grains lead to relative poor wear and corrosion resistance. The subsequent LP effectively remelts the surface layer of coating, reducing surface roughness to approximately 1.2 μm and promoting ultrafine columnar grains oriented perpendicular to the surface. The ε-Co phase fraction increases to 40.6%, accompanied by a higher density of low-angle grain boundaries (LAGBs) and refined lamellar structures. These microstructural improvements significantly enhance wear and corrosion resistance, reducing wear rate to 8.56 × 10 -5 mm 3 /(Nm) and corrosion rate to 0.011 mm/yr-representing reductions of 48.57% and 95%, respectively, compared to the LC coating. The LSP applied on the polished LC coating induces severe deformation in surface layer, refining grain size but reducing the ε-Co phase fraction to 11.5% due to strain-induced phase transformation. Despite this, the LC/LSP coating also exhibited improved performance, with wear and corrosion rates of 1.17 × 10 -4 mm 3 /(N·m) and 0.019 mm/yr, respectively.