Mechanical and dry sliding tribological properties of CoCrNiNb_x medium-entropy alloys at room temperature

The CoCrNiNb_x (x = 0, 0.1, 0.2, 0.3, 0.385, 0.4 and 0.5) medium-entropy alloys (MEAs) were successfully prepared by the arc-melting and casting injection technique. Laves phase and typical lamellar eutectic structure were formed in the Nb-alloyed CoCrNi MEAs. There are three categories of CoCrNiNb_x MEAs, i.e., hypo-eutectics (x < 0.385), eutectics (x = 0.385) and hyper-eutectics (x > 0.385). Specially, the eutectic CoCrNiNb_0.385 MEA attracts most owing to its full lamellar eutectic structure and brilliant combination of mechanical properties. In tribological properties, the CoCrNiNb_0.385 MEA without the highest hardness shows the lowest friction coefficient and wear rate. According to the theory of multilayer films, the most uniform co-deformation between the FCC and Laves phases results in the reduction of friction and wear in the eutectic MEA.