Micro-scale impact testing - A new approach to studying fatigue resistance in hard carbon coatings. (September 2020) - Beake, Ben D.
Abstract: Improving the fatigue resistance of DLC coatings under highly loaded repetitive contact is an important step to increasing their performance in demanding applications. The nano-impact test has been shown to be effective at highlighting differences in resistance to contact damage in thin hard carbon coatings deposited on hardened steel. A novel micro-scale rapid impact test capability capable of producing repetitive impacts at significantly higher strain rate and energy than in the nano-impact test has been developed recently enabling the study of coating fatigue with less sharp spherical indenters than in the nano-impact test. Results with the new micro-impact technique on two commercial hard carbon coatings (Graphit-iC and Dymon-iC from Teer Coatings) on tool steel are presented. The role of coating mechanical properties on the fatigue resistance and the load-sensitivity of the impact failure mechanism is discussed. The harder coating with higher sp 3 /sp 2 bonded C (Dymon-iC) was found to be significantly less durable under fatigue loading than the softer Graphit-iC. Reasons for the observed differences are discussed. Highlights: Novel micro-scale repetitive impact test developed to assess the fracture resistance of carbon coatings. Fills a gap between nano- and macro-impact tests. Harder coating with higher sp 3 /sp 2 bonded C was less durable.