LASER-SURFACE MODIFICATION OF UNS S31603 STAINLESS-STEEL USING NICRSIB ALLOY FOR ENHANCING CAVITATION EROSION RESISTANCE

Laser surface modification using NiCrSiB alloy(Ni - 16.5Cr - 15.5Fe -3 .5Si -3.8B -0.1C) on austenitic stainless steel UNS S31603 (Fe -17.6Cr - 11.2Ni -2.5Mo -1.4Mn -1.4Cu -0.4Si -0.03C) was achieved by using a 2 kW continuous wave Nd-YAG laser. The cavitation erosion and pitting corrosion characteristics of the laser surface modified UNS S31603 in 3.5% NaCl solution at 23 degrees C were studied by means of a 20 kHz u ltrasonic vibrator at a peak-to-peak amplitude of 30 pm and a potentio stat, respectively. The NiCrSiB alloy layer was flame sprayed on the s urface of UNS S31603 stainless steel. The surface was then scanned wit h the laser beam. The melt depth and dilution of the sprayed layer wit h the substrate material increased with the decrease of scanning speed . At low dilution ratio of sprayed layer thickness to melt depth, less secondary phases such as CrB, CrB2, Fe2B and M-7(CB)(3) and low hardn ess were observed in the laser-modified layer. The cavitation erosion resistance R-e (reciprocal of the mean depth of penetration) of the la ser-modified specimen with a dilution ratio of 0.65 was improved by 2. 7 times as compared with that,of the as-received UNS S31603 specimen. In addition, the pitting potential was close to that of the as-receive d UNS S31603 and the protection potential shifted in the noble directi on by a substantial amount(from -3 to 121 mV). The R-e of the laser su rface modified specimen with dilution ratio of 0.88 was improved by fo ur times as compared with that of the as-received UNS S31603 and very close to that of super duplex stainless steel UNS S32760 (Fe -25.6Cr - 7.2Ni -4Mo -0.6Mn -0.7Cu -0.8W -0.3Si -0.2N -0.03C). However, its pitt ing potential was lowered from 359 to 50 mV and its protection potenti al shifted in the active direction from -3 to -238 mV. On the other ha nd, the degree of pitting damage as judged from the pitting morphology was less severe in the laser surface modified specimens. The R-e of l aser surface modified UNS S31603 was found to be linearly related to h ardness. The deformation mechanism by cavitation erosion of the laser- modified specimens was also investigated. (C) 1998 Elsevier Science S. A. All rights reserved.