Effects of Nb content on the microstructure and properties of CoCrFeMnNiNbx high-entropy alloy coatings by laser cladding

CoCrFeMnNiNbx (x = 0, 0.25, 0.5, 0.75, and 1.0) high-entropy alloy coatings were prepared on the AISI 1045 steel substrate surface by laser cladding to explore the effects of different Nb content on the microstructure, microhardness, wear resistance, and corrosion resistance of high entropy alloy coatings. The microstructure of CoCrFeMnNi was composed of single face-centered cubic (FCC) solid-solution phases without Nb addition. The high-entropy alloy coating was mainly composed of a dual-phase structure of the FCC and Laves phases after Nb addition. Nb addition transformed the microstructure of coatings from hypoeutectic to eutectic and hypereutectic compositions. The microhardness of CoCrFeMnNiNbx high-entropy alloy coatings increased gradually with the increase of Nb content. When Nb content x was 1, the average microhardness of coatings was optimal (416.54 HV0.5), which was 2.21 times that of Nb0. The wear resistance of CoCrFeMnNiNbx high-entropy alloy coatings increased gradually with the increase of Nb content, and the wear volume decreased from 0.0739 to 0.0145 mm3. The primary mechanisms responsible for friction and wear were identified as adhesive wear and abrasive wear. The corrosion resistance of coatings first increased and then decreased with the increase of Nb content. When Nb content was 0.75, the passivation film on the coating surface was the stablest and densest, with the optimal corrosion resistance. The results in the work provide a theoretical reference for preparing high-entropy alloy coatings with Nb content.