Wear-resistant amorphous and nanocomposite steel coatings

In this article, amorphous and nanocomposite thermally deposited steel coat ings have been formed by using both plasma and high-velocity oxy-fuel (HVOF ) spraying techniques. This was accomplished by developing a specialized ir on-based composition with a low critical cooling rate (approximate to 10(4) K/s) for metallic glass formation, processing the alloy by inert gas atomi zation to form micron-sized amorphous spherical powders, and then spraying the classified powder to form coatings. A primarily amorphous structure was formed in the as-sprayed coatings, independent of coating thickness. After a heat treatment above the crystallization temperature (568 degreesC), the structure of the coatings self-assembled (i.e., devitrified) into a multip hase nanocomposite micro structure with 75 to 125 nm grains containing a di stribution of 20 nm second-phase grain-boundary precipitates. Vickers micro hardness testing revealed that the amorphous coatings were very hard (10.2 to 10.7 GPa), with further increases in hardness after devitrification (11. 4 to 12.8 GPa). The wear characteristics of the amorphous and nanocomposite coatings were determined using both two-body pin-on-disk and three-body ru bber wheel wet-slurry sand tests. The results indicate that the amorphous a nd nanocomposite steel coatings are candidates for a wide variety of wear-r esistant applications.