Modified high hardness steel coating for biomass corrosion protection

Abstract Biomass is a renewable and CO 2 -neutral energy source. However, the efficiency of biomass combustion plants remains lower than that of current fossil fuel-based systems. To minimize corrosion from aggressive species found in biomass combustion, these plants currently operate at a maximum temperature of 550 °C. The European project BELENUS explored new materials and coatings to raise the operating temperature to 600 °C, thereby improving plant efficiency. Among the coatings under investigation, a super high-hardness steel (SHS) modified with Al, applied by high velocity oxy-fuel (HVOF) thermal spray on ferritic steel SVM12, has demonstrated an improved performance in the laboratory, exposed to a model biomass environment containing KCl deposits for 8000 h at 600 °C. Microstructural analysis by field emission scanning electron microscopy (FESEM) and X-ray diffraction was conducted on the tested samples to examine the coating’s evolution in these environments, as well as the associated protection and degradation mechanisms. The presence of Al within the coating significantly enhanced its resistance to biomass corrosion when compared to uncoated SVM12 and the Al-free SHS coating. Possible reasons for the improved behaviour of the Al-modified coating are the reduction of porosity as well as the blocking effect of either intermetallic FeAl or Al oxide which forms at the splat boundaries prior to exposure to the corrosive atmosphere.