In-service performance of components treated with plasma nitriding and arc ion plating duplex coatings

Abstract

In previous work by the authors, substrate softening was identified as one of the most influential factors on the performance of nitride/hard coating duplex treatments. In the present work, high carbon and low alloy steels, which are both known to be prone to substrate softening, are nitrided at various temperatures. The subsequent hard coating deposition is carried out at the relatively low temperature of 300 °C by arc ion plating (AIP). Through standard laboratory tests and in-service field trials of the components made of these high carbon (JIS SK5) and low alloy (63CRM) steels, it is highlighted again that the avoidance of substrate softening is of prime importance to the performance of this type of duplex system. For the JIS SK5 shear blades used to cut optical fiber cable, it is found that the optimum performance is obtained with the mid-nitriding temperature of 350 °C. This is deemed to be a result of sufficient nitrogen diffusion for hard coating load support coupled with tolerable substrate softening. Metal sheet snip blades, made from 63CRM, are however found to perform best at the highest nitriding temperature of 400 °C. This is attributed to the enhanced nitriding and the relative insensitivity to substrate softening of this steel at this temperature. The difference in the nitride layer depth profile of these two steels is discussed.