Tribological behaviors of two distinct classes of white etching layers on rail surface

The presence of hard, brittle, thin White Etching Layers (WELs) on rail surfaces plays a critical role in varying the tribology behaviours at the wheel and rail interface. The reciprocating sliding tests were carried out on the rail samples covered with two types of WELs, including thermomechanically-induced WEL (TP-WEL) and mechanically-induced WEL (SD-WEL) at room temperature and 600 degrees C. A WEL-free rail sample was also employed for the comparison. The wear mechanism of WEL-free rail shifts from severe abrasive wear at room temperature to adhesive dominant wear at 600 degrees C. Under the pressurized sliding conditions of 1.2 GPa at 600 degrees C, the WEL-free rail was observed to form WEL and BEL. The pre-existed SD-WEL and TP-WEL on the rail samples could transform into worn WEL at the topmost contact rail surface with Brown Ething Layer (BEL) formation beneath it. The formation of BEL is attributed to the tempered effect on pre-existed WEL. Due to their high hardness, both SD-WEL and TP-WEL-covered rails exhibit minimal abrasive behaviours at room temperature while displaying adhesive dominant wear mechanisms at 600 degrees C. Of the two types of WELs, TP-WEL has lower wear resistance, whereas SD-WEL promotes high friction and reduces wear loss.