Laser surface alloying of AISI 1050 mild steel for cavitation erosion resistance using NiCrSiB

Specimens of AISI 1050 mild steel were surfaced alloyed with NiCrSiB using a two-step process. NiCrSiB powder was flamed sprayed onto the substrate and the as-sprayed layer was remelted by a 2 kW continuous wave Nd:YAG laser to achieve surface alloying. The cavitation erosion resistance of the surface alloyed specimens in 3.5% NaCl solution at 23°C was determined by means of a 20kHz ultrasonic vibrator at a peak-to-peak amplitude of 30 m. The corrosion characteristics were studied using potentiodynamic polarisation technique. At a dilution ratio of 12% (corresponding to a laser scanning speed of 25 mm/s), the cavitation erosion resistance of the alloyed surface was 8.9 times that of the as-received AISI 1050 specimen, while at a higher dilution ratio of 48% (corresponding to a scanning speed of 15 mm/s), the erosion resistance dropped to 7.7 times. The corrosion resistance was also improved as reflected by a noble shift of the corrosion potential of about 150 mV, and a reduction in the current density of least one order of magnitude as compared with the as-received specimen at the same potential. The improvement in cavitation erosion resistance could be attributed to the formation of carbides and carbo-borides which increased the hardness, and the improvement in corrosion resistance was due to the increase in the Cr content in the alloyed layer.