Micro-abrasive wear test of niobium carbide layers produced on AISI H13 and M2 steels

Very hard and wear resistant layers were produced on AISI H13 and M2 steels by TRD (thermoreactive deposition and diffusion) treatment in molten borax added with ferroniobium and aluminum, at 1000 °C for 4 h. Optical microscopy, X-ray diffraction and Vickers microhardness were used to analyze the samples. The wear resistances of the layers were evaluated by the micro-abrasive (ball-cratering) wear method. The wear behavior of the uncoated and ionitrided AISI H13 steel was also analyzed for comparison. Well-defined layers formed on both AISI H13 and M2 steels, with excellent thickness regularity. These layers consisted of niobium carbide (NbC) according to X-ray analyses. The AISI H13 steel presented a layer with thickness of 6 μm and hardness of 2333 HV0.050 while the layer on AISI M2 steel measured 9 μm thickness and had a hardness of 2345 HV0.050. The micro-abrasive wear resistance of NbC coated AISI H13 was considerably higher than uncoated AISI H13. In comparison with ionitrided H13 sample, the NbC layer also was more wear resistant. The niobium carbide layers deposited on AISI H13 and M2 presented similar micro-abrasive wear behavior. Worn surfaces showed that the wear mechanism in these layers was abrasive wear: grooving abrasion and rolling abrasion.