Laser surface alloying of Mn-Ni-Al bronze for cavitation erosion resistance

Cavitation erosion of a metal surface is caused by the repeated nucleation, growth and collapse of cavities in vibratory and high-speed flowing liquid. It occurs on surfaces including propellers, pipelines, valves, pump impellers and casings, many of which are made of copper alloys. In order to improve the cavitation erosion resistance of Mn-Ni-Al bronze (MAB), alloyed layers of Cr, Ni, Nb and Mo with MAB substrate were achieved by laser surface alloying (LSA) using a 2.5-kW continuous wave Nd:YAG laser. The laser-alloyed layers have a thickness of about 400 to 450 μm and exhibit very fine microstructure. The microstructure, hardness, corrosion, cavitation erosion resistance of the laser-alloyed specimens were studied and compared with the asreceived MAB substrate. The micro-hardness of the alloyed layers was significantly increased. The cavitation erosion and corrosion behavior of the LSA coatings in 3.5% NaCl solution at 25°C was studied with a vibratory cavitation tester and a potentiostat. The cavitation erosion resistance of the alloyed layers was improved by at most 7.5 times that of the as-received MAB. In addition, the corrosion resistance of the alloyed layers was also enhanced as reflected by the shift in the corrosion potential and reduction in current density.