HVOF and Laser-Cladded Fe–Cr–B Coating in Simulated Biomass Combustion: Microstructure and Fireside Corrosion

Biomass is often considered as a low carbon alternative to fossil fuels in the power industry. However, the heat exchangers in biomass plants can suffer from chloride-based aggressive fireside corrosion. A commercially available amorphous Fe–Cr–B alloy was deposited onto a stainless steel substrate by HVOF thermal spray and laser cladding. The controlled environment corrosion tests were conducted in a HCl-rich environment at 700 °C for 250 h with and without KCl deposits. The samples were examined with XRD, SEM and EDX mapping to understand the corrosion mechanisms. In the absence of any deposits, the amorphous HVOF coating performed very well with a thin oxide growth, whereas the crystalline laser cladding suffered from ~350 µm metal loss. The scales were composed of MnWO4, Fe2O3, Fe3O4 and Cr2O3. When a KCl deposit was present, the HVOF-sprayed coating delaminated from the substrate and MnCl2 was found in the scale.