Revealing dynamic-mechanical properties of precipitates in a nanostructured thin film using micromechanical spectroscopy

Abstract

Abstract Nanostructured materials with their remarkable properties are key enablers in many modern applications. For example, industrial dry-milling processes would not be as widely spread without the use of hard, wear-resistant metal nitride coatings to protect the cutting tools. However, improving these nanostructured thin films with regard to dynamical properties is demanding as probing respective parameters of (sub-)micron layers without any substrate influence is still challenging. To extend the scientific toolbox for such spatially confined systems, a novel methodological approach based on resonance peak measurements of a cantilever-transducer system termed micromechanical spectroscopy (µMS) is developed and applied to a Al0.8Cr0.2N model system. The mainly wurtzite type supersaturated Al0.8Cr0.2N system showed precipitation of cubic CrN at grain boundaries and local Cr variations upon annealing at 1050°C. This was accompanied by an increase in the previously unknown damping capability of 63 percent and an increase in Young’s modulus by 36 percent. Impact statement There is a wide variety of applications for nano- to micrometer-sized thin films in today’s engineering technology, from thermal barrier- and wear-resistant coatings in turbines and bearings, over diffusion barriers and heatsinks in microelectronic devices, to optically active layers in lasers or mirrors. The mechanical properties of such thin films are oftentimes governed by their thermal history, leading to either intentional or undesired changes in the microstructure (e.g., the formation of precipitates). While the investigation of such features is usually constricted to static analysis using high-resolution techniques, such as transmission electron microscopy, understanding their impact on dynamic properties of the film remains a challenge. However, these are highly relevant in many engineering applications where cyclic behavior is common, such as high-speed dry milling. In the present work, we investigate the change in mechanical damping capability upon annealing of a 6-µm thin AlCrN film, commonly used in demanding dry-milling applications, using micromechanical spectroscopy (µMS) of cantilever-shaped specimens. After a carefully adjusted heat treatment, the film exhibits the formation of cubic CrN precipitates in an otherwise wurtzite AlCrN matrix, which leads to a previously unknown beneficial increase in damping capability of the film. Graphical abstract