Microstructure and Properties of Chromium Boride–Chromium Carbide–Alumina Composite Coatings Prepared by Reactive Plasma Spraying

Abstract

A chromium boride–chromium carbide–alumina composite coating was prepared in situ on a Ti-6Al-4V titanium alloy substrate by plasma spraying of Cr₂O₃-Al-B₄C composite powder. The results show that, in the process of plasma spraying the Cr₂O₃-Al-B₄C composite powder, a chemical reaction occurred among Cr₂O₃, Al, and B₄C, and CrB₂, Cr₃C₂, and γ-Al₂O₃ phases with nanosize were formed in situ in the composite coating. Compared with the coating prepared by plasma spraying CrB₂-Cr₃C₂-Al₂O₃ composite powder, the coating prepared by the Cr₂O₃-Al-B₄C composite powder has a more uniform and refined microstructure, lower porosity, higher microhardness, better toughness, excellent scratch resistance, and sliding wear resistance. This is attributed to the densification effect and to the fine grain strengthening and toughening effect of nanocrystals produced by the participation of the in situ chemical reactions in the plasma spraying process of the Cr₂O₃-Al-B₄C composite powder.