Laser surface alloying of brass with NiCrSiB for improving cavitation erosion resistance and corrosion resistance

Brass (Cu-38Zn-1.5Pb) specimens were laser surface alloyed with NiCrSiB (Ni-16.5Cr-3.5Si-3.8B-15.5Fe-<1C) using a 2 kW continuous wave Nd-YAG laser for improving the cavitation erosion resistance and corrosion resistance. Surface alloyed layers were achieved by a two-step process, with thermal spraying of NiCrSiB powder onto the substrate followed by laser irradiation. Using a laser power density of 141 W/mm2 and a scanning speed 5 mm/s, alloyed layers with a dilution ratio DR of 22% [DR defined as (1-t/D), where t = thickness of thermal sprayed layer and D = thickness of alloyed layer] were obtained. The cavitation erosion resistance and anodic polarization characteristics of the laser surface alloyed specimens in 3.5% NaCl solution at 23 °C were studied. The cavitation erosion resistance of the alloyed surface with a DR of 22% was 7 times that of the brass substrate. The microhardness profile also indicated an increase from 110 Hv of the substrate to 378 Hv (average). Potentiodynamic test also recorded an increase in the pitting potential from -175 mV of the as-received brass to -112 mV of the laser modified specimen. XRD and EDX were used to identify the phases present and the compositional profile respectively, while SEM and optical microscopy were used for microstructural and morphological analysis and to identify the damage mechanism.