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

Austenitic stainless steel UNS S31603 was laser surface alloyed with variou s 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 t he corrosion characteristics of the alloyed specimens. In Part II, the cavi tation erosion characteristics of the alloyed specimens in 3.5% NaCl soluti on at 23 degrees C were studied by means of a 20 kHz ultrasonic vibrator at a peak-to-peak amplitude of 30 mu m. The hardness profile and the composit ional profile of the alloyed layers were investigated by a Vickers hardness tester and by EDX respectively. The cavitation erosion resistance of speci mens alloyed with AlSiFe, C and NiCrSiB were highest, reaching 11.1, 10.5 a nd 7.9 times that of the substrate respectively. The damage mode was identi fied to be ductile fracture for specimens containing austenite as the major phase, and brittle fracture when the major phase was ferrite or intermetal lic. Cavitation erosion was initiated at the phase boundaries where there w as an abrupt change in mechanical properties (e.g. hardness) and then propa gated into the weaker phase. II was also noted that large improvement in ca vitation erosion resistance and corrosion resistance could not be simultane ously achieved in the present study. (C) 2000 Elsevier Science S.A. All rig hts reserved.