Adhesion of hard coatings by RST 100 scratch tester
Adhesion of hard coatings plays a crucial role in development and production of high-quality cutting tools. To access this property, scratch test method is often the only solution. This application report demonstrates the use of a new simple scratch tester RST 100 for adhesion measurement of hard coatings for cutting tools.
Hard coatings with micrometer thickness have played a pivotal role in enhancing performance of cutting tools for several decades. They have enabled the processing of materials that were previously difficult to machine such as nickel alloys, dual steels and hardened steels. These hard surface coatings increase the lifetime of the the cutting inserts, drills and other tools. They also allow for better surface finishes, higher machining temperatures and faster machining, thereby improving overall efficiency. However, their development and production require careful monitoring of their properties, more specifically their adhesion: even the best coating will be useless if its adhesion is poor. While thorough cleaning of the substrate before deposition often improves adhesion of hard coatings, even the most efficient cleaning and surface activating procedures cannot replace adhesion testing. For many years, the well-established method for adhesion measurement of hard coatings has been the scratch test method. It is the only method that provides quantitative information about the adhesion of the coating – unlike the competitive Rockwell test, which offers only qualitative results based on observation of the coating’s damage near the imprint. Additionally, the Rockwell test has several restrictions regarding the ratio of elastic modulus and hardness of the coating and substrate which limits its use. Scratch test, on the other hand, can easily be used for a wide range of hard coatings and substrates.
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