High-temperature corrosion studies of HVOF-sprayed Cr 3C 2-NiCr coating on SAE-347h boiler steel

Abstract

Cr3C2-NiCr coating was deposited on SAE-347H boiler steel by high velocity oxy fuel (HVOF) spray process. Subsequently, high-temperature corrosion behavior of the bare and coated boiler steel was investigated at 700 C for 50 cycles in Na2SO4-82Fe2(SO4)3 molten salt, as well as air environments. Weight-change measurements after each cycle were made to establish the kinetics of corrosion. X-ray diffraction, field emission-scanning electron microscopy/energy dispersive spectroscopy, and x-ray mapping analyses were performed on the exposed samples to analyze the oxidation products. The bare 347H steel suffered accelerated oxidation during exposure at 700 C in the air as well as the molten salt environment in comparison with its respective coated counterparts. The HVOF-spray Cr3C2-NiCr coating was found to be successful in maintaining its adherence in both the environments. The surface oxide scales were also found to be intact. The formation of chromium rich oxide scale might have contributed for the better hot corrosion/oxidation resistance in the coated steel.