Research on Microstructures and Properties of CoNiCr and CoNiCu Medium-entropy Alloys

Abstract

CoNiCr and CoNiCu medium-entropy alloys (MEAs) were prepared by powder metallurgy with Co, Ni, Cr, Cu powders milled for 5h and 30h, and the effects of different milling time and different elements on the microstructures and properties of MEAs were studied. Through microstructures characterization (by scanning electron microscope and energy dispersive spectrum analysis, X-ray diffraction analysis) and mechanical properties (compressive performance, hardness, wear resistance) testing, the following conclusions are drawn: First, with the increase of the milling time, the density of the sintered samples is increased. Second, the microstructure of CoNiCr MEA is composed of Ni-rich FCC solid solution, Cr-rich BCC solid solution and CoNiCr intermetallic compound, while the microstructure of CoNiCu MEA is mainly composed of FCC solid solution with uniform Co, Ni, and Cu, and Co-rich FCC solid solution. Third, as the agglomeration of powder is weakened and the density of sintered sample is increased, the hardness of CoNiX (X=Cr/Cu)-30h is higher (about 20HV) than that of CoNiX (X=Cr/Cu)-5h, and long-term ball milling effectively improves the wear resistance, moldability and compressive strength of CoNiCr MEA, while the moldability and compressive strength of CoNiCu MEA are reduced, and the wear resistance of CoNiCu MEA is slightly improved. Finally, the hardness and wear resistance of CoNiCr MEA are better than that of CoNiCu MEA, the hardness is increased by about 70HV, and the wear resistance is increased by about 20-40 times, but the compressive performance of CoNiCu MEA is better than that of CoNiCr MEA.