Abstract
Oxidation behaviors of FeB and Fe2B layers formed on pure iron by gas boronizing were studied in air at high temperatures by the measurements of weight gain, X-ray diffraction, infrared spectroscopic analysis and microscopic examinations.
Main results obtained are as follows.
The results of infrared spectroscopic analysis showed that the B2O3 phase was produced principally on the surface due to preferential oxidation of boron in the boronized layer in the temperatures range between 650 and 850°C. X-ray diffraction lines similar to the α-Fe were detected from the inner layer formed at the same temperatures.
At temperatures higher than 850°C the layer structures were not found, but Fe(BO2)2, Fe2O3, and Fe3O4 were observed as the oxide scale simultaneously with the formation of B2O3 and α-Fe.
It was observed from the determination of weight changes that the oxidation rate of boronized iron decreased in comparison with that of pure iron and an intermittent weight loss was caused by imperceptible effervescence of B2O3 formed on the surface. These data show that the oxidation resistance of the boride layer at high temperatures should not be persistent.
