Fabrication, microstructure, and wear properties of novel Fe-Cr-B-Nb-Mo metamorphic alloy coatings manufactured by the HVOF thermal spray process

Novel Fe-Cr-B based metamorphic alloy coating layers were manufactured using newly designed Fe-Cr-B-C-Mo-Nb metamorphic alloy powders (M1 (Nb:3.50 wt%), M2 (Nb: 1.75 wt%)) and an HVOF (highvelocity oxygen fuel) thermal spray process. The microstructures and wear properties of the coating layers were investigated and compared with those of a conventional Fe-Cr-B based metamorphic alloy (M) coating layer. The investigation of the microstructure revealed that the (Cr, Fe)2B phase is densely distributed in the & alpha;-Fe matrix and metallic glass phases in the M and M2 coating layers. The M1 coating layer was mainly composed of the & alpha;-Fe phase, some metallic glass, and nano-sized Nb boride particles. The results of measuring the oxide fraction indicated that the M2 layer showed 10 times better in-flight oxidation resistance than the M layers. A wear test resulted in the wear rates of M, M1, and M2 being 1.68 x 10-6 mm3/Nm, 7.65 x 10-6 mm3/Nm, and 8.16 x 10-7 mm3/Nm respectively, indicating that the wear resistance of the M2 coating layer was 2.06 times higher than that of the M coating layer. Based on the above results, the dependence of the wear mechanism of the HVOF Fe-Cr-B based metamorphic alloy coating layers on the additive element content is also discussed.