Comparison of three kinds of MC-type carbide modified thick W coatings fabricated by plasma transferred arc surfacing

Three kinds of W-based composite powders containing NbC, TiC and VC were prefabricated on a carbon steel substrate, respectively. Prefabricated powders were then processed by plasma transferred arc (PTA) surfacing to form thick W-NbC, W-TiC and W-VC coatings, respectively. Microstructures and nano-indentation properties of the three kinds of coatings were investigated and compared. It was observed that, in addition to W and MC-type carbide phases, Fe7W6 phase was formed in the three kinds of coatings because of the dilution effect of Fe from the substrates. The relative contents of Fe7W6 phase in the W-NbC, W-TiC and W-VC coating were 48.1 wt.%, 52.2 wt.% and 36.3 wt.%, respectively. Tungsten grain size in the W-NbC coating was about 2.8 μm, which was smaller than that in the W-TiC coating (about 3.4 μm) and that in the W-VC coating (about 4.7 μm). There was no simple relation between the mechanical response and the nano-indentation hardness H or the effective Young's modulus E* alone; however, this response was strongly dependent on the ratio H/E*. For coatings with high H/E* value, the elastic recovery was also be larger. The best ability to resist elastic strain-to-failure and the highest toughness were obtained in the W-VC coating when compared with that in the W-NbC and W-TiC coatings.