Microstructure and wear resistance of Al2O3–TiB2 composite coating deposited by axial plasma spraying

Abstract

Two Al2O3–TiB2 composite coatings were deposited by axial plasma spray using two types of feedstocks. One of the feedstocks was a conventional micrometre sized Al2O3–30 wt-%TiB2 composite powder from a self-propagating high temperature synthesis (SHS) process. The second was fabricated by spray drying SHSed Al2O3–30 wt-%TiB2 composite powder doped with 10 mass-% nanosized Al2O3 powder. The microstructure of the feedstocks and as sprayed coatings were comparatively investigated by scanning electron microscope and X-ray diffraction. Wear resistance of as sprayed coatings were assessed using block on ring wear test at room temperature. Results showed that Al2O3–TiB2 composite coatings were composed of α-Al2O3, γ-Al2O3, TiB2 and a small amount of TiO2. TiB2 that mostly remained in the shape of undeformed particle were dispersedly distributed in the matrix of the composite coatings. The coating from spray dried powder exhibited finer and denser microstructure and demonstrated better wear resistance than the coating from the SHSed powder under the same sliding conditions.