Void Formation and Spatial Distribution in Plasma Sprayed Nd-Fe-B Coatings

Neodymium iron boron (Nd-Fe-B) is a type of rare-earth transition-metal alloy that exhibits strong magnetic properties and demonstrate potential applications in minute components such as micro motors and micro generators. Nd-Fe-B coatings with average thickness of 200 μm were deposited on stainless steel substrate via the atmospheric plasma spray process. Microstructure of the coatings was studied in detail as a function of standoff distance. Two distinct phases, i.e. the light Nd-rich and the dark Fe-rich phases, were observed in the coatings indicating the occurrence of phase separation during plasma spray process. Porosity and phase percentage within the coatings were analysed using the image analysis technique. The size and spatial distribution of pores within the coatings were evaluated, and related to the micro hardness and surface roughness of the coatings. Spatial distribution of the two phases within the coatings is also presented where the average distances to the nearest neighbour between the same phase and different phases were determined.