X-ray evaluation of pulse-plated crack-free Cr layer

Several crack-free Cr plating processes using pulse-current electrolysis have been proposed for improving corrosion resistance. However, industrial applications of crack-free Cr platings are very few since these Cr layers are subjected to tensile residual stress and easily form macrocracks after plating operations, particularly at temperatures higher than 373K. The residual stress of crack-free Cr layers deposited by pulse-current electrolysis was evaluated by the X-ray diffraction method. With changing pulse conditions, various residual stresses were measured. The specimen in which initial compressive residual stress of the Cr layer exceeded -150MPa did not form macrocracks after holding at 473K for 2h, and showed a high corrosion resistance without rusting even after a 700h neutral salt spray test (NSST). The amount of change in the residual stress as a result of heat treatment correlated with the integral breadth of the diffraction profile, and became smaller and more stable with heat treatment as the integral breadth became narrower.