Abstract The 304 stainless steel coating was prepared successfully in water environment directly through an in-situ underwater laser cladding technique utilizing an underwater gas-shielding laser cladded nozzle, and the interaction mechanism of water on cladding coating formation, grain morphology and size, microstructure and corrosion performance was investigated. For underwater laser cladding, the high-density aerosol particles decreased the laser power density and reduced the stability of cladding process, causing the conduction mode of molten pool and decreasing the wettability of molten metal. In underwater laser cladding coating, columnar dendrites nucleated near the fusion line and track band and grew up along the opposite direction of maximum temperature gradient whilst equiaxed grains formed in the center region; besides, the grain size decreased overall and the number of equiaxed grain dropped owing to the water cooling effect compared with in-air coating. For in-air and underwater cladding coatings, the solidification mode of molten metal was ferrite-austenite mode and the ferrite mainly distributed in the austenite matrix with skeleton shape. Attributed to the higher cooling rate, a small amount of lathy ferrite was observed in underwater cladding coating, and the ferrite content increased within the overlap region of tracks, causing the corrosion resistance of coating reduced.

中文翻译：

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水环境中304不锈钢原位激光熔覆涂层的研究

摘要 采用水下气体保护激光熔覆喷嘴原位水下激光熔覆技术，直接在水环境中成功制备了 304 不锈钢涂层，并研究了水对熔覆涂层形成、晶粒形貌和尺寸、微观结构和显微组织的相互作用机制。腐蚀性能进行了研究。对于水下激光熔覆，高密度气溶胶颗粒降低了激光功率密度，降低了熔覆过程的稳定性，造成熔池传导模式，降低了熔融金属的润湿性。在水下激光熔覆涂层中，柱状枝晶在熔合线和轨道带附近成核，并沿与最大温度梯度相反的方向生长，而等轴晶在中心区域形成；除了，与空气涂层相比，由于水冷效应，晶粒尺寸整体减小，等轴晶粒数量减少。对于空气中和水下熔覆涂层，熔融金属的凝固模式为铁素体-奥氏体模式，铁素体主要分布在具有骨架形状的奥氏体基体中。由于较高的冷却速度，水下熔覆涂层中观察到少量板条状铁素体，并且在轨道重叠区域铁素体含量增加，导致涂层的耐腐蚀性能下降。熔融金属的凝固方式为铁素体-奥氏体方式，铁素体主要分布在具有骨架形状的奥氏体基体中。由于较高的冷却速度，水下熔覆涂层中观察到少量板条状铁素体，并且在轨道重叠区域铁素体含量增加，导致涂层的耐腐蚀性能下降。熔融金属的凝固方式为铁素体-奥氏体方式，铁素体主要分布在具有骨架形状的奥氏体基体中。由于较高的冷却速度，水下熔覆涂层中观察到少量板条状铁素体，并且在轨道重叠区域铁素体含量增加，导致涂层的耐腐蚀性能下降。