Microstructure and properties of in-situ nickel-aluminum bronze coating by underwater wire-feed laser cladding

The in-situ laser cladding layer on nickel-aluminum bronze was prepared in water environment directly by the underwater wire-feed laser cladding technology for the first time, in which the local dry cavity was generated by a self-designed underwater laser cladding nozzle to protect the cladding zone from water environment. After optimizing the processing parameters such as the protection gas flow rate, laser power and lap ratio, the underwater alloy coatings with good formability without internal defects were obtained, and the interaction mechanism of water environment on the microstructure evolution, mechanical properties and corrosion resistance behavior of cladding was investigated. The results showed that the large cooling rate during underwater laser cladding process inhibited the eutectoid transformation from the high-temperature β phase to the α phase, resulting in an increase in the proportion of the β' phase and finer α layer structure in the underwater laser cladding layer. Compared with the in-air cladding layer, the grains in the underwater cladding layer were smaller, and more low-angle grain boundaries were observed. The grain refinement and the increase of the β' phase ratio as well as grain boundaries gave rise to the higher microhardness of the underwater cladding metal. The electrochemical response of the cladding layer was primarily influenced by the presence of copper, resulting in similar corrosion resistance among the cladding layer samples.