A NEW TECHNIQUE FOR TESTING THE IMPACT LOAD OF THIN-FILMS - THE COATING IMPACT TEST

Conventional, well-known tests used to characterize thin films fail to take into account the real load applied to a film, eg. a coating-substrate composite, under operating conditions. In particular, existing conventional laboratory tests fail to consider the dynamic forces caused by impact load during milling or discontinuous cutting operations. The paper presents a new device capable of simulating the dynamic loads impacting on a thin-film-substrate composite in the machining process. The new "coating impact test" permits variation of the impact force, the impact frequency and the number of impacts for a cemented carbide insert contacting a thin film on a substrate. The resulting behaviour of different composites is presented in graphs plotting impact force vs. number of impacts and allowing quantification of the number of load cycles which a coated component can withstand and definition of a critical fatigue force. Typical failure patterns encountered in the coating impact test are described; these will prove useful for quality assurance in physical vapour deposition thin-film production.