Effect of Heat Treatment on Structure and Oxidation Resistance of Flame-Sprayed Ni-20 wt.% Al on Carbon Steel

摘要

In this study, the effects of time and temperature of heat treatment on Ni-20 wt.% Al flame spraying coatings were studied. The objectives are to find the optimal sample in terms of microstructure and compare its oxidation resistance with the as-sprayed coating. The coatings were deposited by flame spraying on low carbon (St 37) steel substrate. The specimens were heat-treated in vacuum at 850 degrees C and 950 degrees C for 1 h and at 1050 degrees C for 1, 3, and 6 h. Microstructural characterization and phase analysis were performed by scanning electron microscopy, energy-dispersive spectrometry, and x-ray diffraction, respectively. The results showed that the lowest porosity (0.43 %) and the highest NiAl content were achieved for the sample heat-treated at 1050 degrees C for 1 h. Optimized heat-treated, as-sprayed, and bare steel specimens were exposed to ambient air at 800 degrees C in order to evaluate their durability and oxidation resistance. The results showed that their oxidation rate constants were 24.66, 65.06, and 269.42, respectively. Most of the NiAl content in the coating was responsible for covering the coating surface by a protective gamma-Al2O3 layer during the high-temperature oxidation process.