Quality Assurance Assessment of Thin Films

Abstract

Thin films produced by a number of deposition technologies have found many applications over the past few years in a range of sectors of engineering. As the use of such coatings becomes widespread, the need to assess the quality and reliability of these films becomes more important, for both coating suppliers as a means of process monitoring and end users as a means of identifying if the properties of the coating are suitable for the intended application. There are a number of coatings evaluation tests which are used at present by both suppliers and end users as ranking tools and it would be an advantage if such tests could be extended to be used for quality assurance (QA) assessment. An ideal QA test would be nondestructive, rely on readily available equipment, be quick and easy to perform and interpret, nonsubjective, amenable to automation, and of relevance to the intended application. Unfortunately such tests do not exist and it is essential to make the best use of the tests that are available if QA assessment is to be attempted on test coupons which can be coated alongside real components. In tribological applications it is often the hardness of the coating which dictates component performance, provided that the adhesion of the coating to the substrate is sufficient. Thus it would appear that hardness testing and scratch adhesion testing might be useful bases for QA tests. A methodology by which both tests can be used for QA assessment, given a ‘standard’ coating for comparison which shows the required performance in the intended application, is discussed. The inferences which may be drawn about the reasons for deviations from the standard behaviour are discussed and illustrated for PVD titanium nitride films. This has highlighted the fact that suitable QA of the components before coating is essential if the coating quality is to be reliably assessed.