Complete characterization of the structure and mechanical properties of AlTiN coatings

AlTiN hard coatings play a crucial role in elevating the cutting performance of challenging-to-machine metals. The wear resistance of these coatings is related to their crystalline structure and mechanical properties. This application report demonstrates the methods used to characterize the hardness, adhesion, friction, and crystal structure of various AlTiN coatings.

AlTiN coatings have played a pivotal role in enhancing machining performance for several decades, with many companies including the 'traditional' variant featuring a 50:50 ratio of Al to Ti in their production portfolios. Unfortunately, the performance of this coating is somewhat constrained in more demanding applications, primarily due to its insufficient wear resistance and hardness. Ongoing research is thus dedicated to refining the mechanical properties and improving the wear resistance of AlTiN.
The primary focus of these efforts is on increasing the Al content in AlTiN, aiming to reach the theoretical limit of Al solubility in the TiN fcc lattice (Al67:Ti33). This composition is expected to yield higher hardness together with improved wear resistance. However, in many instances, an elevated Al content results in decreased hardness and wear performance, attributed to the formation of the softer hexagonal (wurtzite) AlN phase. It is hypothesized that this phase's growth can be mitigated through a negative deposition bias.
In this project, AlTiN coatings were deposited with three different Al:Ti ratios and three substrate bias levels. The study delved into the effects of Al content and deposition bias on hardness, elastic modulus, adhesion, frictional properties, and the crystal structure. This application report aims to illustrate how various instruments from Anton Paar can comprehensively characterize the mechanical properties and crystalline structure of AlTiN hard coatings. Furthermore, the methods employed, such as nanoindentation, scratch tests, pin-on-disc tribology, and X-ray diffraction (XRD), can be readily applied to other hard coatings of similar thickness.

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