A comparison of the dry sliding wear behavior of NiCoCr medium entropy alloy with 316 stainless steel

The aim of this work was to determine the wear behavior of the f.c.c. medium entropy alloy NiCoCr, which has been shown by others to possess both a very good strength-ductility balance and an especially high fracture toughness. Pins of NiCoCr were tested in dry sliding wear against disks of yttria-stabilized zirconia at a sliding velocity of 0.1 m/s both in air and in argon. Identical wear tests on 316 stainless steel were performed for comparison. It was found that the wear rates of the NiCoCr pins were lower than those of the 316 stainless steel in air, but that the wear rates of the two materials were almost identical in dry argon. Scanning electron microscopy analysis of both the worn pins' surfaces and cross sections indicated that the worn surface of NiCoCr pins were flatter and showed less fracture due to the better toughness compared to the 316 stainless steel pins. Wear tests in air resulted in the formation of oxides. X-ray photoelectron spectroscopy of the NiCoCr pin showed that the oxides in the debris were Cr2O3 and Co2O3. The oxides play an important role in the development of a mechanically mixed layer, which formed on the NiCoCr pin's tip to protect the contacting material during wear tests in air.