Effects of Y Additions on the Microstructure and Mechanical Properties of CoCr1.7Ni Medium-Entropy Alloys

In order to improve the room temperature yield strength of X and enhance its engineering applicability, a series of CoCr1.7NiYx (x = 0, 0.01, 0.02, 0.03, 0.04, and 0.1 at.%) medium-entropy alloys were synthesized to investigate the effect of Y addition on the microstructures and mechanical properties of the CoCr1.7Ni-based alloy. The X-ray diffraction results show that the alloys exhibit face-centered cubic (FCC) + body-centered cubic (BCC) + hexagonal close packing (HCP) triphasic structure when the Y is adopted, whereas the CoCr1.7Ni-based alloy has a FCC+BCC biphasic structure. The volume fraction of BCC and HCP phase increased with increasing Y content, which led to alloy grain refinement. As a result, the microhardness and strength of alloys were both enhanced. The addition of Y resulted in dispersion strengthening and solid solution strengthening of CoCr1.7Ni alloy, the appearance of HCP, and an increase in BCC, which improved the room temperature yield strength and hardness of CoCr1.7Ni alloy. In particular, for CoCr1.7NiY0.1 alloy, its microhardness and yield strength, respectively, increased by 98.18% and 260.59% as compared with those of CoCr1.7Ni alloy.