Evaluation of hard coatings obtained on AISI D2 steel by thermo-reactive deposition treatment

Niobium carbide, vanadium carbide and iron boride layers were obtained on AISI D2 steel by thermo-reactive treatments in different borax baths, containing ferroniobium, ferrovanadium or ferrotitanium, and aluminum. Vickers microhardness and micro-abrasive (ball crater) wear tests were used to evaluate the tribologic properties of the layers. Hardness values of the niobium carbide layer and the vanadium carbide layer, having depths of 15.6 ± 1.2 and 14.2 ± 1.0 μm were 2372 ± 93 and 2461 ± 112 HV, respectively. Both niobium and vanadium carbide layers presented a smooth interface with the substrate. The iron boride layer (essentially Fe2B) presented a lenticular morphology with a depth varying from 35 to 60 μm. Its hardness was 1537 ± 57 HV. All of the obtained layers presented excellent adhesion with the substrate. Wear resistance of the coated samples was far superior to the hardened uncoated AISI D2 steel. The niobium and vanadium carbide layers were more wear resistant than the boride layer.