Investigations on the behavior of laser cladding Ni-Cr-Mo alloy coating on TP347H stainless steel tube in HCl rich environment

Combustion of biomass with a high content of alkali and chlorine can result in operational problems including deposition and rapid corrosion of critical components such as superheater tubes. Alloy modification is an effective way to reduce corrosion problems. Considering the excellent corrosion resistance but high cost of Ni-Cr-Mo alloy bar, the microstructure and high-temperature corrosion behaviors of the laser cladding Ni-Cr-Mo alloy coating were investigated and compared with the Ni-Cr-Mo alloy bar and the biomass boiler superheater tube material TP347H stainless steel in this study. Corrosion exposures were carried out in a tube furnace under simulated combustion gases containing 12%CO2-5%O2-0.05%HCl-N2 for 168 h at 650 °C and 700 °C. The performance of three materials was evaluated by means of several analysis methods including: kinetic analysis (corrosion rate), SEM (microcosmic morphology of surface and cross-section),EDS (distribution of elements of cross-section) and XRD (phases formed on the surface layer). Compared to the other two materials, the overall performance was better for the laser cladding Ni-Cr-Mo alloy coating which on one hand had optimal ratio of corrosion resistance elements and on the other hand had grain strengthening effect by laser cladding technique.