Oxidation Behavior and Mechanism of Slurry Fused NiCr/HfB2 Cermet Coating at Different Temperatures

Abstract

The behavior and mechanism of NiCr–HfB2 cermet coating oxidation at 1,000, 1,100 and 1,200 °C in pure oxygen were investigated using thermogravimetric equipment, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Analyses of the oxidation kinetics confirmed that the parabolic rate law was followed at each temperature and the activation energy of oxidation was 284 kJ/mol−1. The oxidation layers were detected to be composed of NiO, NiCr2O4, Cr2O3. The cross-sectional morphologies indicated that the oxidation layer consisted of three parts: Ni-rich oxide layer, spinel NiCr2O4 layer and a thin layer of Cr2O3. The oxidation process was controlled by the outward diffusion of the oxide-forming elements Ni, Cr and inward penetration of oxygen, by which the interaction mechanisms between the microstructures was clarified. On the basis of the experimental results and fundamental analyses, the NiO/NiCr2O4/Cr2O3 multi-layer oxidation mechanism was accordingly established to illustrate the oxidation behaviors.