Mo20Nb20Co20Cr20(Ti8Al8Si4) refractory high-entropy alloy coatings fabricated by electron beam cladding: Microstructure and wear resistance

Abstract

The refractory high-entropy alloys (RHEAs) possess excellent mechanical properties and electron beam cladding (EBC) has the advantages of vacuum protection and higher energy utilization. In this study, the Mo20Nb20Co20Cr20(Ti8Al8Si4) RHEA coatings under different cladding currents (16, 17, 18,19 mA) are fabricated by EBC to improve the surface wear resistance of the Ti600 substrate. The microstructure and phase structure of RHEA coatings are investigated by OM, SEM, XRD, TEM. The mechanical properties of tcoatings and substrate are studied by microhardness, nanoindentation and dry wear test. The results show that the HEA coatings involve four main phases: BCC1(Mo,Nb,Al-rich-A2/B2), BCC2(Co,Cr,Ti-rich-B2), IMC1(Laves phase-CoTi) and IMC2((Ti,Nb,Zr)5Si3), respectively. With the cladding current increasing, the dilution rate of the substrate increases to cause the Ti content within coatings to rise. The size of BCC1(DR regions), IMC1 and IMC2 becomes larger and the microhardness, nanoindentation hardness, elastic modulus and room-temperature creep resistance decrease. The properties improvement of the coating is attributed to the solid solution, second phase and precipitation strengthening caused by the solid solution structures and intermetallic compounds. The maximum microhardness of the coatings at current 16 mA is 1150 HV0.2, more than 3 times that of the substrate and the friction coefficient of Ti600 is 2.16 times that of current 16 mA, which suggests that the Mo20Nb20Co20Cr20(Ti8Al8Si4) RHEAs can be used as an excellent wear-resistant coating with broad application prospect.