Friction and wear behaviors of bare and diamond-like carbon/chromium bi-layer coated SKH51 steel at low temperatures

The durability and reliability of mechanical systems operating under low-temperature conditions are subject to degradation caused by abrupt changes in the tribological characteristics of contact pairs. In this regard, the friction and wear behaviors of bare and diamond-like carbon (DLC)/Chromium (DLC/Cr bi-layer) coated SKH51 steel at low temperatures were assessed comprehensively. The bi-layer coating was deposited onto the SKH51 substrate using a combination of pulsed DC and radio frequency magnetron sputtering. Tribological tests were conducted using a custom-built reciprocating tribo-tester installed inside a cooling unit with temperature-control capabilities. The nano-structural properties of the coating and governing wear mechanisms were investigated using high-resolution transmission electron microscopy (HR-TEM), laser confocal microscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and ultra-nano indentation. The results revealed a significant increase in the wear rate of SKH51 due to changes in wear mechanism and the degradation of mechanical properties as the temperature decreased. The DLC/Cr bi-layer coating significantly reduced the wear of SKH51, particularly at low temperatures. The formation of a thin layer of frozen water at subzero temperatures played a major role in determining the wear behaviors of the specimens.