Modifying crystallinity and mechanical properties of (CoCrNi)95.8Ce4.2 medium entropy alloy films by post-annealing treatment

Abstract

In this work, (CoCrNi)95.8Ce4.2 medium entropy alloy films with amorphous and nanocrystalline phases were deposited on 304 steel substrates via radio frequency magnetron co-sputtering. The post-annealing treatment was conducted to investigate the effects of different annealing temperatures (250, 350, 450 and 500 °C) on the microstructures and mechanical properties of the films. The crystallinity increased with the increasing annealing temperature. When the films were annealed at 250 and 350 °C, some nanocrystals were formed in the amorphous matrix. Interestingly, plenty of stacking faults were observed in 450 and 500 °C annealed films because of the low stacking fault energy and annealing process. The hardness and Young's modulus were measured by nanoindentation. Both hardness and Young's modulus increased and then decreased with the increasing annealing temperature. The hardness and Young's modulus reached the maxima of 12.60 and 231.24 GPa, respectively, due to the increasing crystallinity and the formation of stacking faults at 450 °C annealing. However, in the annealing temperature range from 450 to 500 °C, hardness and Young's modulus decreased because of the grain growth. Therefore, the results of this work suggested that the moderate post-annealing treatment was beneficial to promote the formation of stacking faults and strengthen the mechanical properties.