Nanostructured high entropy alloy coatings for tooling applications

The demand for materials able to withstand high temperatures and mechanical loads is connected with new technological and industrial developments. As the industrial needs are pushing the boundaries of materials ever higher, such materials are the focus of basic and applied research. A relatively new class of materials, the high entropy alloys (HEA) have recently been adopted by the thin film and coatings research community. While the production of HEAs is expensive and time consuming the development of protective coatings has the advantage of low material input and a versatile variety in process conditions accessible by physical vapor deposition (PVD). Magnetron deposition process enables the deposition of a large variety of materials; it also facilitates adding small amounts of another material. The process enables HEA coatings to adopt promising coating structural changes taking the established technology of transition metal nitride coatings depositions. Using the rotation table in the deposition chamber with multiple magnetron targets the coating layers can easily be stacked forming multilayered or nanolayered coatings. For a specific application one can »sandwich« a coating with superb tribological properties with other superhard and stable coatings to produce the nanolayered coating structure that can cope with strict industrial and environmental demands of our industrial partner. Therefore, the main objectives are: (i)              To deposit nanolayered HEA nitride coating and investigate basic structural and mechanical properties at room and elevated temperatures. Magnetron sputtering seems to be ideal for deposition of HEA nitride coatings. Using elementary and multi-elementary targets, slight composition changes can be made in a given HEA nitride coating to better fit the high-temperature (HT) application. Our objective is to fine tune one HEA nitride coating for better tribological properties and one with increased hardness (strong nitride-forming elements). The best performing compositions will be deposited simultaneously to form a multilayer or nanolayer structure. Mechanical, tribological and structural properties at high temperatures will be the focus of this newly formed coating for high temperature applications.  (ii)          To measure the hardness and fracture toughness of HEA nitride coatings at high temperatures. High coating hardness and its resistance to fracture are two of the important parameters to evaluate the coating performance. These properties change significantly with temperature. Even though these properties determine the success of the coating in an industrial application, the existing data on mechanical properties at actual high temperature are scarce. Hardness and fracture toughness will be determined at elevated temperature using an in-situ HT mechanical tester in order to better understand the friction and wear behaviour of coatings at high temperatures. (iii)         To develop a new nl-HEA nitride coating for tooling application and transfer it to the industry. While the research on the laboratory scale is demanding there is still a long way to the implementation of the coating to the industrial user. With this project and with the industrial partner at our side we aim for transfer the newly developed coating from laboratory size deposition systems to industrial unit and test the coating on real tools at their real application.