Effect of nano-crystallization of high velocity oxy-fuel-sprayed amorphous NiCrBSi alloy on properties of the coatings

Abstract

NiCrBSi self-fluxing alloy coatings were deposited by high velocity oxy-fuel (HVOF) spraying. Annealing treatment was applied to the as-sprayed coatings to develop the microstructure of the Ni-based coating. The microstructure of the coating was characterized using optical microscopy, x-ray diffraction and transmission electron microscopy. The crystallization behavior of the amorphous coating was also characterized by differential scanning calorimetry. The properties of the coating were characterized by microhardness and abrasive wear tests. The results showed that the as-sprayed HVOF coating deposited by well melted spray particles exhibited a dense microstructure of amorphous phase. It was revealed that the crystallization of the amorphous phase in HVOF NiCrBSi coating occurs at a temperature of about 502°C. Annealing at temperature a little higher than recrystallization temperature leads to the formation of the nano-crystalline microstructure. The subsequent nanostructured Ni-based coating presents higher microhardness and excellent wear performance. With the further increase in annealing temperature, the growth of the nano-crystalline grains occurs and, accordingly, the microhardness of the coating and the wear performance decrease. Thereafter, the microstructure and properties of the Ni-based self-fluxing alloy coating can be controlled through postannealing treatment.