Adhesion characterization of hard ceramic coatings by the scratch test

The development of reproducible test methods for the adhesion and wear of high performance surface coatings is an important industrial requirement. Although no international standard exists to provide guidelines for adhesion testing of coatings, scratch testing has been accepted as the most likely candidate for such an application. An industrial grade scratch tester has been designed and built at Queen's as a part of the mandate of the Industrial Consortium on Hard Coatings. This tool has been used to assess commercial TiN coatings on M2 tool steel using effective coefficient of function measurements as the primary test parameter. The system is more robust than conventional scratch testers but the calculation of a theoretical value for the work of adhesion for PVD TiN on M2 steel shows that it has not suffered a loss in sensitivity as a result. The TiN on M2 system has been assessed for various processing conditions, including variations in the coating technique, thickness and surface roughness. A baseline for the properties of TiN on M2 tool steel has thus been set and can be used for comparative assessment of future productions. A draft test protocol has been written and submitted to the International Standards Organization (ISO). This document describes the test method, evaluates the testing variables, determines an optimum set of test parameters using the TiN on M2 steel system and describes how to interpret the test results. Special attention is given to test parameters which can cause shifts in experimental results such as the state of wear of critical components. This Standard Proposal satisfies one of the goals of the Consortium which is to develop an industrially acceptable, consistent set of characterization methods for the members benefit which will contribute to a Canadian Standard and potentially lead to application as an International Standard.