Microstructure and tribological property of novel Nb, Mo containing Fe-Cr-B based metamorphic coating layers manufactured by thermal spray process

Fe-Cr-B based metamorphic alloy can be partially transformed from crystalline to amorphous under friction, and has excellent wear and corrosion resistance. For modifying the chemical composition suitably for thermal spraying, the novel Fe-Cr-B-Nb-Mo metamorphic alloy (M2) was designed, initial powders were prepared by gas atomization, and manufactured using a high velocity oxygen fuel spray (HVOF) process. The microstructure and wear properties of the fabricated coating layers were investigated, compared to the conventional Fe-Cr-B-based metamorphic coating layer (M). In the XRD analysis results, all the coating layers consisted of α-Fe, (Cr, Fe)₂B and metallic glass phases. Initial microstructures observations indicated a combination of fine crystalline and metallic glass in the splat region. On the other hand, unmelted regions were composed of crystalline and a little metallic glass. The average Vickers hardness of each coating layer was 725.7 Hv (M) and 760.4 Hv (M2), respectively. Wear test results revealed that the M2 had lower wear loss compared to M. It is noteworthy that HVOF-sprayed M2 had about 3 times better wear resistance than the HVOF-sprayed metallic glass coating layer. Based on the above results, the wear mechanism of the novel Fe-based metamorphic coating layers manufactured by the HVOF spray was also discussed.