Process parameter influences on 17‐4PH martensitic stainless-steel coatings produced by extreme high-speed laser cladding (EHLA)

Extreme high-speed laser cladding (EHLA) is a promising route for the efficient fabrication of high-performance surface coatings owing to its low dilution and rapid solidification characteristics. Achieving a fully martensitic microstructure in the as-built state, however, remains challenging for 17‐4PH stainless steel because of its high Cr content and relatively low martensite-start (Ms) temperature which narrow the processing window. In this work, 17‐4PH coatings were successfully fabricated by EHLA. By optimizing the laser processing parameters, fully martensitic coatings were obtained in the as-built state, exhibiting a dense and defect-free microstructure and sound metallurgical bonding to the substrate. Microstructural characterization revealed two distinct dilution mechanisms, namely diffusion-controlled bonding at the coating-substrate interface and convection-induced Cr dilution within the coating interior, with the latter playing a key role in the corrosion resistance of the coating. In addition, phase transformation kinetics were analyzed using thermal histories derived from process simulations. The results show that thermal cycles with peak temperatures within the austenite stability range critically govern the final phase constitution. These findings provide new insights into EHLA processing of martensitic stainless steel and demonstrate the feasibility of designing high-performance stainless-steel coatings.