Morphology of sintered silicide coatings remelted by high frequency electron beam

Abstract

Silicide coatings were prepared on Nb-based alloy Nb-10W by a fused slurry method. Such sintered silicide coatings have defects such as pores, cracks, and uneven top surfaces, which have negative influence on the high temperature oxidation resistance of the coatings. Electron beam remelting is considered one of the most convenient processes to reduce these disadvantages and improve coating oxidation resistance. The effect of high frequency electron beam irradiation on surface remelting and microstructural modification of silicide coatings was investigated in this study. Scanning electron microscopy, X-ray diffraction, and atomic force microscopy were used to characterize phase and morphology before and after EB surface treatment. The surface roughness of the silicide coatings was reduced by two orders of magnitude and the average grain size was reduced by about one order of magnitude after treatment. This resulted in improvement of the high-temperature oxidation resistance of the EB treated silicide coatings, which offered about 50h protection under isothermal oxidation in air at 1700°C.