Microstructure and properties of laser-cladded CoCrMoNb(TiC)x high entropy alloy coatings with various TiC contents

Abstract

In this work, CoCrMoNb(TiC)_x high entropy alloy coatings with various TiC contents were fabricated by using the laser cladding technology. The effect of TiC content on the microstructure and mechanical properties of the coatings was investigated. The tribological properties of the CoCrMoNb(TiC)_7.5% coatings were investigated in the temperature range from room temperature (RT) to 800 °C. The results showed that the CoCrMoNb(TiC)_x coatings were mainly composed of BCC, FCC phases, and a small amount of Laves phases. The addition of TiC introduced new compounds such as Cr₃C₂ and NbC into the coatings. As the TiC content increased, the skeletal-like structure progressively bonded and fused in the coating, resulted in a denser structure. The CoCrMoNb(TiC) 7.5 % coating exhibited the largest microhardness of 938HV_0.3 and best wear resistance (1.6 × 10⁻⁵ mm³/Nm) at RT, which was mainly attributed to the synergistic effect of solid solution strengthening, fine grain strengthening, and dispersion strengthening by hard phases such as TiC, Cr₃C₂ and NbC. The CoCrMoNb(TiC)_7.5% coating demonstrated the best tribological property at 800 °C, primarily due to the formation of a dense enamel layer composed of Cr₂O₃, Co₃O₄, Nb₂O₅, and other oxides on the worn surface, which effectively reduced the friction and enhanced the anti-wear resistant of the coating.