Some aspects of laser surface cladding in the turbine industry

Water droplet erosion of leading edge of the blade in a steam turbine could impair its efficiency and lifetime. To overcome this problem, laser cladding of the leading edge with Co-based stellite powder is commonly used. This paper discusses microscopically the effect of power density and beam interaction time in such a cladding process. It is realized that the beam interaction time has a significant effect on solidification and microstructure development process. The results indicate that the dendrite structure shall be fine for short interaction time compared to the coarse structure for long interaction time. Macro- and micro- cross-section electron probe microanalysis (EPMA) and microhardness profile has been employed to characterize the cladding. The results are correlated with the clad quality. Microstructure, hardness and dilution are discussed as a function of the processing parameters. A few of the actual results of the laser cladding of stellite 6L on 12Cr–Ni turbine blades are presented. Since the dilution of the base material into the cladding is significantly low at short interaction times, the clad could retain significant strength after long-term exposure, a unique feature for the turbine industries. Such possible applications are illustrated as well.