The effect of silicon as a reactive element for NiCrAl coating performance on hastelloy substrate

Abstract

The isothermal oxidation behavior, microstructure, phase formation and microhardness of NiCrAl coatings with and without silicon addition were investigated. Characterization of heat treated and oxidized samples were carried out by X-ray diffractometer (XRD), scanning electron microscope (SEM) and vicker hardness tester. The NiCrAl and NiCrAlSi coatings were deposited with high velocity oxygen fuel (HVOF) on the surface of hastelloy substrate. Oxide scales consists of Al2O3 and NiCr2O4 phases were formed on the surface of coating sample after isothermal oxidation at temperature of 1000 °C for 100 hours. The addition of silicon increases the oxidation resistance of NiCrAl coating through the formation of Al2O3 phase, whereas on NiCrAl coating without silicon addition, mass loss was observed, which indicated scale spallation. The addition of silicon at 0.4wt% can prevent outward diffusion of refractory elements such as Mo from the hastelloy substrate. The measured hardness of NiCrAl and NiCrAlSi coatings were 317.53 and 330.9 Hv, respectively. The experimental results showed that NiCrAl with silicon addition improved the resistance of high temperature oxidation and hardness.