Development of thermal spray nanocrystalline coatings by devitrification of amorphous phase

In this paper thermal spray nanocrystalline coatings were developed by devitrification of Fe-based amorphous phase. In this approach a new composition of Fe-Cr-Mo-P-B-C-Si amorphous powder was produced in solid state by mechanical alloying of elemental powder mixture. After optimizing the powder morphologies as well as the size distributions, some coatings were produced by high velocity oxy fuel (HVOF) on carbon steel substrates. The phase transformations of coatings during devitrification were investigated by x-ray diffractometry (XRD), and transmission electron microscopy (TEM). It was found that by carefully controlling the HVOF parameters and the rate of cooling, the amorphous phase could be crystallized in the controlled manner and the microstructures with fully amorphous and nanocrystalline phases in the range of 10-20 nm were obtained. Therefore, these coatings will have the modified mechanical and tribological properties.