Yezhe Lyu

Open System Tribology and Influence of Weather Condition

The tribology of an open system at temperatures ranging between 3 °C and −35 °C, with and without snow, was investigated using a pin-on-disc tribometer mounted in a temperature-controlled environmental chamber. The relationship between the microstructure and ductility of the materials and the tribology at the contacting surfaces was investigated. The study shows that during continuous sliding, pressure causes snow particles to melt into a liquid-like layer, encouraging the generation of oxide flakes on the contact path. The friction coefficient and wear rate are dramatically reduced through an oxidative friction and wear mechanism. In the absence of snow, the tribological process is controlled by the low temperature brittleness of steel in the temperature range from 3 °C to −15 °C. At these temperatures, cracks are prone to form and extend on the worn surfaces, resulting in the spalling of bulk scraps, which are crushed into debris that increases the friction coefficient and wear rate due to strong abrasion. When the temperature falls to −25 °C, an ice layer condenses on the metal surfaces and relaxes the tribological process in the same way as the added snow particles, which significantly decreases the friction and wear.

Non-Vacuum Sintering Process of WC/W2C Reinforced Ni-Based Coating on Steel

Ni-based composite coatings containing varied contents of tungsten carbides on low carbon steel were fabricated. Effects of sintering temperature and tungsten carbides contents on the surface, interface, microstructure and wear resistance of the coatings were investigated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Vickers microhardness tester, bulk hardness tester and pin-on-disc tribometer. The results indicated that with appropriate sintering temperature (1230 °C), smooth coating surfaces can be achieved. Favorable interfaces about 200 μm can be got that both the chemical composition and property of the interfacial region showed gradual transitions from the substrates to the coatings. Microstructure of the coatings consists of tungsten carbides and M7C3/M23C6 in the matrix. With excessive sintering temperature, tungsten carbides tend to dissolve. Ni-based coatings containing tungsten carbides showed much higher level of bulk hardness and wear resistance than ISO Fe360A and ASTM 1566 steels. With increasing contents of tungsten carbides from 25% to 40%, bulk hardness of Ni-based coatings gradually increased. Ni-based coating with 35% tungsten carbides performed the best wear resistance.

Open System Tribology in the Wheel–Rail Contact—A Literature Review

The tiny contact zone (approximately 1 cm2) where steel wheel meets steel rail is fundamental to rail transport. This work is a comprehensive presentation of recent research in wheel-rail contact t ...