Influence of cBN on the microstructure and tribology properties of (CoCrNi)94Al3Ti3 medium-entropy alloy coating prepared by high-speed laser cladding: The evolution and strengthening mechanism of cBN

Ceramic particle reinforced medium entropy alloys (MEAs) coatings have attracted considerable attention because of their excellent hardness and wear resistance. In this study, (CoCrNi)94Al3Ti3 MEA coating and (CoCrNi)94Al3Ti3-cBN MEA composite coating were prepared by high-speed laser cladding. The phase constituents, microstructure,hardness and wear mechanisms of the two coatings were investigated using XRD, Raman spectra, SEM, EDS, and TEM. Results show that (CoCrNi)94Al3Ti3 comprises only simple FCC phase because of the high -entropy effect. However, the addition of cBN transforms the phase from FCC to FCC + BCC, but also generates micron -scale TiN and CoCr, as well as nanoscale TiN and CrB. In addition, part of the cBN is converted to hBN with lubricating effect under high energy laser. As for the properties, compared with (CoCrNi)94Al3Ti3 coating, (CoCrNi)94Al3Ti3-cBN coating exhibits increased hardness by 2.2 times, increased wear resistance by 5.6 times, and decreased friction coefficient from 0.58 to 0.47. It is expected that this research will provide research ideas for the preparation coating of friction reduction and wear resistance performances on titanium alloy surfaces.