Influence of feedstock powder characteristics and spray processes on microstructure and properties of WC–(W,Cr) 2C–Ni hardmetal coatings

Abstract

The composition WC–(W,Cr) 2C–Ni (commercial designations WC–‘CrC’–Ni, WC–Cr 3C 2–Ni and WC–NiCr) is unique among the WC-based materials used for the preparation of thermally sprayed hardmetal coatings. These coatings show a significantly higher oxidation resistance and high-temperature sliding wear resistance than WC–Co and WC–CoCr coatings do. Unlike WC–Co and Cr 3C 2–NiCr, WC–(W,Cr) 2C–Ni is not a simple binary hard phase–binder metal composite as it is composed of two hard phases: WC and (W,Cr) 2C. Surprisingly this composition has been poorly investigated in the past. In this paper coating microstructures and properties obtained from five commercial feedstock powders of different origins using two different liquid-fuelled high velocity oxy-fuel (HVOF) systems (K2 and JP-5000) were investigated. Additional experiments were performed with one powder using atmospheric and vacuum plasma spraying (APS and VPS, respectively). The microstructures and phase compositions of the powders and the coatings were studied. Focus was on the appearance, composition and distribution of the (W,Cr) 2C phase which might form or might change its Cr/W ratio during the spray process. The composition of the (W,Cr) 2C phase was estimated from the lattice parameters. Hardness HV0.3 was measured for all coatings. The density, Young's modulus and abrasion wear resistance of HVOF-sprayed coatings were studied.