Influence of Heat Treatment on Microstructure and Mechanical Properties of HVOF Sprayed Cr3C2-NiCr Coating

Deposition of the Cr3C2-NiCr cermet by the HVOF process results in the dissolution of Cr3C2 in the NiCr metal phase and decreasing the hardness and the elastic modulus of the resulting coating. In this study, Cr3C2-25wt% (Ni-20Cr) powder was applied to Hastelloy X super alloy substrates by high velocity oxy-fuel (HVOF) process. Influence of heat treatment on Cr3C2 phase recovery and improvement of hardness and elastic modulus of coatings was investigated. For this purpose, microstructural examination performed by field emission scanning electron microscopy and phase composition analysis by X-ray diffraction (XRD) analysis on the coating before and after heat treatment. Analysis of back scattered electron microscopy images showed that up to 11% of the dissolved carbide phases in the NiCr alloy recovered during heat treatment. In the XRD patterns of the heat-treated coatings, the amorphous regions disappeared and the NiCr peaks pronounced more in the background phase pattern. Also, the hardness and elastic modulus of coating after heat treatment increased by 156 HV0.3 and 98 GPa, respectively.