Corrosion behaviour of crystalline and amorphous forms of the glass forming alloy Fe43Cr16Mo16C15B10

The corrosion behaviour of both crystalline and largely amorphous forms of the Fe-based glass forming alloy, Fe43Cr16Mo16C15B10 alloy was investigated. Two different methods were used to induce transformation to the amorphous form of the alloy: laser melting and HVOF spraying. Both methods produced largely amorphous material, however the high brittleness of the alloy makes it susceptible to cracking during laser treatment, hence this technique is not suitable for largescale application. Potentiodynamic scanning showed that in 0.5M H2SO4 and 3.5% NaCl electrolytes both amorphous forms of the alloy had better corrosion resistance (lower current densities for -200 to +1000mV SCE) compared to the crystalline material. The laser treated material and HVOF coating performed similarly in 3.5% NaCl. In 0.5M H2SO4 the HVOF coating had a lower current density than the laser melted material for almost all of the potential range -300 to +1000mV SCE. The improved corrosion behaviour of the largely amorphous material is attributed to its homogeneity, and particularly to the elimination of the Mo-rich phase that underwent preferential corrosion in the crystalline form of the material

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