WEAR MECHANISM OF TIN-COATED HIGH-SPEED STEEL DURING SLIDING

The wear mechanism of high-speed steel coated with TiN by arc ion plat ing during sliding against alumina and AISI 52100 steel under lubricat ed conditions has been investigated experimentally. The results show t hat a transition in wear behaviour occurs after a defined period of sl iding time for both of the countermaterials. Examinations of wear samp les show that the wear transition mechanism differs, however, dependin g on the countermaterials. When slid against alumina, which is harder than the coating, the coating wears slowly by abrasion in the initial stage until the substrate is exposed, which leads to the onset of rapi d substrate abrasion in the following wear stage. The time required fo r this transition does not relate to substrate hardness but increases with increasing coating thickness and decreasing applied load. On the other hand, when slid against AISI 52100 steel, which is softer than t he coating, the coating does not wear significantly in the initial sta ge, but delaminates abruptly after a definite sliding time only under heavy loads. The time required for this delamination increases with in creasing substrate hardness and decreasing applied load, and there exi sts an optimal coating thickness for the delayed coating delamination. It is suggested that severe plastic flow in the form of twins observe d in the substrate at the vicinity of the interface could play an impo rtant role in this coating delamination.