Effects of Nd and B contents on property evaluation of (CoCrNi)100--B Nd medium entropy alloy films

To modify the microstructures and enhance the mechanical properties of CoCrNi medium-entropy alloys films (MEAFs), multiple strengthening will be multiple strengthening methods will be introduced in this study. We will add rare-earth, neodymium, and metalloid, boron, elements into the MEAFs system to introduce precipitation and solid solution strengthening. (CoCrNi)100-x-yBxNdy MEAFs will be deposited onto silicon wafers using magnetron three-target co-sputtering of CoCrNi, B and Nd targets. Nd and B concentrations in CoCrNi-based films were controlled by various sputtering powers. The influences of Nd and B contents on the microstructure of MEAFs were studied by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Meanwhile, mechanical properties were examined by a nanoindentation. The (CoCrNi)100-xBxNdy MEAFs showed an increase in Nd content, rising from 1.37 to 9.70 at.% as the Nd target power increased from 25 to 100 W. The B content began at 0.94 at.%, increasing slightly to 1.59 at.% as the Nd content reached 4.25 at.%. The maximum hardness of 13.28 GPa is exhibited by MEAFs with minor B doping and no Nd, due to interstitial solid solution strengthening. The presence of an amorphous structure initially caused a decreased hardness of 9.81 GPa in MEAFs with 1.50 at.% B and 1.37 at.% Nd. The presence of a small-radius boron atom as interstitial atoms and a large atom of Nd could be the main mechanisms for strengthening, resulting in both solid solution strengthening effects and grain refinement.