Studying the anisotropic behaviour of TiB2±z by synchrotron nano-diffraction and micro-mechanical testing

Abstract

Transition metal diborides are a favourable class of materials for the use as protective coatings based on their excellent mix of thermal and mechanical properties. Particularly TiB2±z is of great interest in research and development for wear-resistant applications, as its hardness and elastic modulus are exceptionally high. The super-hardness (> 40 GPa) of direct current magnetron sputtered TiB2±z thin films was reported to be direction-dependent: a preferred crystal growth in 0001-direction is mainly responsible for reaching values above 40 GPa [1,2]. The anisotropic behaviour of hexagonal AlB2-structured diborides was not only reported for TiB2±z but also for ZrB2 and WB2-z [1,3,4]. The growth orientation of TiB2±z is highly dependent on the process parameters, especially the deposition pressure and angular distribution during sputtering [1]. By varying the deposition pressure throughout the film cross-section, the orientation and mechanical properties have been adapted. To study the progression of the relations between crystal orientation and mechanical properties through the film cross-section, X-ray nano-diffraction synchrotron experiments (beamline P03 at PETRA III) have been performed. Additionally, the structure-mechanical properties were described by a broad set of characterization techniques such as SEM, TEM, and micro-mechanical testing experiments.