Abstract
Three Ni-based alloys (Ni60, Ni65, Ni60W) were selected to be coated on the surface of 40Cr and 20 steel. The microstructure, phase composition and elemental distribution of the coatings were characterised respectively to discuss the effects of different substrates, cladding materials, and processes. The corrosion and thermal fatigue behaviour of the coatings were investigated. The results show that the coatings prepared by plasma cladding have a dense microstructure with few defects and a white bright band of a certain thickness was formed between the coating and the substrate. The white bright band between the coating prepared by flame spraying and the substrate was not obvious. The main phase compositions of the coatings are Cr23C6, Cr7C3, Ni2.9Cr0.7Fe0.36 and FeNi3 phases, with the W2C phase also present in the Ni60W coating. The heat-affected zone (HAZ) of the coating is influenced by the coating preparing processes, substrate material and process state of substrates: the size of the HAZ of the plasma cladded coating is smaller than that of the flame sprayed coating, the HAZ of the 40Cr substrate is smaller than that of the 20 steel, and the HAZ of the tempered 40Cr substrate is smaller than that of the annealed 40Cr substrate. The Ni-based alloy coating can effectively improve the surface hardness of the substrate. The Ni65 alloy powder is the most effective (HV0.5992), followed by the Ni60W alloy powder (HV0.5798) and finally the Ni60 alloy powder (HV0.5712). The Ni65 alloy coating has the relatively best thermal fatigue properties, followed by the Ni60W alloy coating and the Ni60 alloy coating is the relatively worst. At the same time, the corrosion resistance of different Ni-based alloy coatings is consistent with the thermal fatigue properties of the coatings.
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