Improved hardness and wear resistance of plasma sprayed nanostructured NiCrBSi coating via short-time heat treatment
Surface and Coatings Technology
School of Engineering
NiCrBSi alloy coatings deposited by atmospheric plasma spray technology were heated at 440 °C, 460 °C, and 480 °C for a short-time respectively to achieve a better understanding of the relationship between their microstructures and properties. Optical microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy and tribological tests were conducted to evaluate the microstructures and wear performance of the coatings. Both the hardness and wear resistance of the coatings increase at the initial stage of short-time heat treatment followed by decreasing. The heat-treated coatings show 15.4% higher maximum hardness and 60% lower minimum wear volume than the as-sprayed one. The as-sprayed NiCrBSi coating possesses a mixed microstructure mainly composed of the crystalline phases and the amorphous phase (about 10 vol%). After 3-min heat treatment at 480 °C, the volume fraction of the amorphous phase decreases to 1.6 vol%, while the fractions of compounds (such as Ni3B and Cr3B4) and γ-Ni increase correspondingly. The precipitates of Ni3B and Cr3B4 are responsible for the hardening of the coatings. As heat treatment proceeds, the γ-Ni grains coarsen, leading to a deceasing tendency in the hardness and wear resistance of the coatings. As the abrasive modes of the coatings are not varied after short-time heat treatment, the hardness of the coatings plays a dominant role in the wear resistance of the coatings.