Laser surface modification of UNS S31603 stainless steel. Part II: Cavitation erosion characteristics

Austenitic stainless steel UNS S31603 was laser surface alloyed with various elements (Co, Ni, Mn, C, Cr, Mo, Si) and alloys/compounds (AlSiFe, Si3N4 and NiCrSiB) as presented in Part I together with the microstructures and the corrosion characteristics of the alloyed specimens. In Part II, the cavitation erosion characteristics of the alloyed specimens in 3.5% NaCl solution at 23°C were studied by means of a 20 kHz ultrasonic vibrator at a peak-to-peak amplitude of 30 μm. The hardness profile and the compositional profile of the alloyed layers were investigated by a Vickers hardness tester and by EDX respectively. The cavitation erosion resistance of specimens alloyed with AlSiFe, C and NiCrSiB were highest, reaching 11.1, 10.5 and 7.9 times that of the substrate respectively. The damage mode was identified to be ductile fracture for specimens containing austenite as the major phase, and brittle fracture when the major phase was ferrite or intermetallic. Cavitation erosion was initiated at the phase boundaries where there was an abrupt change in mechanical properties (e.g. hardness) and then propagated into the weaker phase. It was also noted that large improvement in cavitation erosion resistance and corrosion resistance could not be simultaneously achieved in the present study.