SURFACE ENGINEERING: PROVING THE QUALITY

Abstract

Surface engineering is an enabling technology which can provide specialist surface properties while preserving the important structural features of the substrate. It can also save energy, reduce wear and corrosion, and, importantly, conserve rare materials by localising specialist properties at the surface rather than their needing to obtain throughout the bulk. Despite these advantages, the technology remains underutilised, with uncertainties regarding treatment consistency and quality causing potential users to hesitate. The ultimate solution lies in a proper understanding of the surface engineering processes and the key parameters which dictate the surface properties they produce. It will be this rigorous quality assurance of the treatment or coating procedure which will ensure good quality. In the meantime, it remains necessary to inspect many treated components (quality control) to assess key properties such as adhesion, thickness, porosity, and hardness. Industrial requirements for quality control of surface engineering are reviewed and the strengths and weaknesses of a range of measurement procedures are considered. Three techniques are discussed in detail: X-ray fluorescence for assessing thickness; ultralow load hardness testing for characterising thin surface films; and scanning acoustic microscopy for investigating adhesion, porosity, and thickness, predominantly of sprayed coatings.