Microstructure evolution and tribological behavior of laser cladded Al1.8CrCuFeNi₂/WC composite coatings on Ti-6Al-4 V

Abstract

Al1.8CrCuFeNi2/WC composite coatings – prepared on Ti-6Al-4 V alloy by laser cladding of a high entropy alloy (HEA) Al1.8CrCuFeNi2 powder with the addition of either 0, 10, 20, 30, 50, or 70 wt% WC – were studied in detail for their structure, morphology, phase composition, mechanical and tribological properties. The WC-free Al1.8CrCuFeNi2 coating is composed of a dendritic-shaped bcc matrix phase with ∼14.6 vol% fcc phases between these dendrites. With increasing WC addition, the fcc phase-fraction decreases and several carbide phases are formed leading to the formation of a more complex microstructure. For example, the HEA/WC composite coating prepared with the addition of 30 wt% WC to the HEA powder is composed of an Al-Ti-Ni-rich bcc phase, eutectic, equiaxed Ti-rich carbides, W-rich carbides, and fishbone-like Ti-rich carbides. This coating exhibits a very high hardness of 1372.6 HV0.2 across the outermost 1.1 mm of the 1.5 mm coating thickness and allows for the highest hardness values among the coatings studied within the initial 0.4 mm directly at the interface to the substrate. This coating further provides the lowest mean-coefficient of friction of 0.49 and lowest wear rate, which is with 6.52·10−7 mm3/Nm only 7% of that provided by the WC-free HEA coating. Thus, by the addition of WC to the HEA powder and the thereby initiated formation of various carbides during the laser cladding process of the Ti-6Al-4 V alloy, composite coatings are accessible, which easily outperform those prepared without WC.