Microstructure and tribological properties of laser clad γ/Cr{sub}7C{sub}3/TiC composite coatings on γ-TiAl intermetallic alloy

摘要

In order to improve the wear resistance of the γ-TiAl intermetallic alloy, microstructure, room- and high-temperature (600℃) wear behaviors of laser clad γ/Cr{sub}7C{sub}3/TiC composite coatings with different constitution of NiCr-Cr{sub}3C{sub}2 precursor-mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS), block-on-ring (room-temperature) and pin-on-disk (high-temperature) wear tests. The responding wear mechanisms are discussed in detail. Results show that microstructures of the laser clad composite coatings have non-equilibrium solidified microstructures consisting of primary hard Cr{sub}7C{sub}3 and TiC carbides and the inter-primary γ/Cr{sub}7C{sub}3 eutectic matrix, about three to five times higher average microhardness compared with the TiAl alloy substrate. Higher wear resistance than the original TiAl alloy is achieved in the clad composite coatings under dry sliding wear conditions, which is closely related to the formation of non-equihbrium solidified reinforced Cr{sub}7C{sub}3 and TiC carbides and the positive contribution of the relatively ductile and tough γ/Cr{sub}7C{sub}3 eutectics matrix and their stability under high-temperature exposure.