Tailoring microstructural evolution in laser deposited nickel-aluminum bronze alloy by controlling water cooling condition

Inspired by the application requirements of underwater in-situ repair of nickel-aluminum bronze (NAB), the study proposes whether the water-cooling conditions are conducive to forming an appropriate cooling rate during the repair process to prevent the formation of coarse κ phases. The appropriate cooling rates of underwater repair has been preliminarily verified through numerical simulation. Then onshore laser direct metal deposition (DMD) and underwater laser direct metal deposition (UDMD) technologies are employed to the repair of the trapezoidal grooves on NAB substrates. The experimental results show that the rapid cooling rates during UDMD result in a unique microstructure. Compared to DMD repaired samples, the width of the interlayer heat-affected zone and the average size of nano κ_Ⅱ phase are reduced, no κ_Ⅳ precipitates were observed in any of the repaired samples. An interesting finding is that the κ_Ⅲ phases are dispersively precipitated in the matrix. Both the tensile specimens fail in the substrate zone rather than the repaired zone. However, the thermal exposure on the substrate during deposition causes slight growth of the κ_Ⅱ phase in the heat-affected zone. The tensile strength of the samples repaired by DMD and UDMD is reduced by approximately 7 % compared to the cast substrate. This study proves the feasibility of in-situ underwater repair for large copper alloy components and can also provide new process references for controlling the evolution of microstructures through external environmental conditions during alloy manufacturing.