Microstructure and wear resistance of Al 2 O 3 –TiB 2 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.