Abstract
A nickel based amorphous alloy powder has been plasma sprayed under ambient and low pressure conditions onto mild steel substrates. These alloys previously have been considered for possible applications as wear and corrosion resistant coatings. However, the significance of the microstructure on the relevant properties has not been investigated. In this study the microstructural characteristics of the sprayed coatings are examined. X-ray diffraction results indicated that the air plasma sprayed coatings consist of a mixture of amorphous and crystalline phases, while the vacuum plasma sprayed coatings show a predominantly crystalline structure. The crystalline phase in both coatings consists of a supersaturated nickel solid solution. On annealing, this metastable phase precipitates into equilibrium boride phases. Transmission electron microscopy has been used to determine the morphology of the product phases and the microstructure. In addition, extended X-ray absorption fine structure (EXAFS) analysis has been used to determine the extent of disorder. The effect of microstructural changes within the coating on the hardness, cavitation-erosion resistance and corrosion properties are reported.
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