Investigation of oxidation behavior and Thermal spray of mechanically milled CoNiCrAlY–YSZ powders

In this study, the effects of mechanical milling and YSZ reinforcing on oxidation behavior of CoNiCrAlY coatings were investigated. Various amounts of YSZ particles (۰%, ۵%, ۱۰% and ۱۵ wt.%) were mixed with commercial CoNiCrAlY powder and milled for ۲۴ hrs. Then, the mechanically milled and commercial powders were deposited on Inconel ۶۱۷ substrate using High Velocity Oxygen-Fuel (HVOF) process. Freestanding bodies of nanostructured and conventional HVOF CoNiCrAlY coatings were oxidized at ۱۰۰۰ °C for different times to form the thermally grown oxide layer. X-ray diffraction analysis, scanning electron microscopy and X-ray mapping were used to analyze the scales formed on the surface of the oxidized samples. The results showed that nanostructured coatings exhibited higher porosity due to undesirable morphology of feedstock powders. This factor accelerated diffusion rate of oxygen into coating body. On the other hand, undesireable oxidation of nanostructured particles during spraying leads to increase in the oxidation rate of coatings.

Keywords:

CoNiCrAlY , Oxidation behavior , YSZ , High velocity oxy-fuel