Effects of Y on Microstructure and Friction and Wear Properties of CoCrNi-Based Medium-Entropy Alloys AITranslate

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Chinese Library Classification Number:TG115.58[金属学及工艺]

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Given the low room-temperature hardness and poor wear resistance of CoCrNi alloys,and that rare earth elements possess large atomic size and high chemical reactivity(even trace addition significantly enhances alloy properties),this study designed and prepared(CoCrNi)_100-xY_x(x=0,1,2,4,6,8,mass fraction,%)medium-entropy alloys via non-consumable vacuum arc melting.The influence of rare earth Y content on the microstructure and hardness of CoCrNi-based medium-entropy alloys was investigated,and their friction and wear properties and mechanisms in an ambient dry environment and a simulated seawater with 3.5%NaCl were analyzed.The results indicate that after Y addition,the morphology of CoCrNi alloy transforms from columnar grains to dendritic grains,accompanied by significant phase structural changes.On the basis of the FCC single phase,Ni-and Y-rich HCP phases(x=1,2,4,6,8)and Cr-rich BCC phases(x=4,6,8)precipitate,and the grains of the alloy are obviously refined.The hardness of the alloy increases from 154 HV without Y addition to 351 HV with 6%Y addition,due to the combined effects of secondphase strengthening and grain refinement strengthening.In an ambient dry environment,the wear mechanism of(CoCrNi)_100-xY_x transforms from oxidative/adhesive wear to abrasive/adhesive wear with increasing Y content.The(CoCrNi)₉₄Y₆ alloy demonstrates the optimal wear resistance,with an average friction coefficient as low as 0.36 and a volume wear rate of 1.42×10^-4mm³/(N·m).In a simulated seawater with 3.5%NaCl,the wear mechanism of(CoCrNi)_100-xY_x involves the synergistic effects of abrasive wear,oxidative wear and corrosive wear.The(CoCrNi)₉₄Y₆ alloy exhibits superior wear resistance,with an average friction coefficient of 0.33 and a volume wear rate of 1.65×10^-5 mm³/(N·m).The lubricating effect of the corrosive medium(3.5%NaCl solution)results in a reduction of the alloy's volume wear rate in the 3.5%NaCl simulated seawater by an order of magnitude compared to the ambient dry environment.