Influence of silicon containing phases on the high-temperature fracture behavior of Ti-based diborides

Ti-TM-Si-B 2±z (TM = Ta, Mo) coatings are a new class of materials known for their excellent oxidation resistance and mechanical stability. This study explores their fracture characteristics, particularly at room and elevated temperatures. We synthesized hexagonal structured coatings including TiB 3.06 , Ti 0.26 Si 0.15 B 0.59 , Ti 0.23 Mo 0.07 Si 0.16 B 0.54 , and Ti 0.28 Ta 0.07 Si 0.12 B 0.53 using non-reactive DC magnetron sputtering. Conducting in-situ cantilever bending tests from room temperature to 850 °C revealed interesting insights into their plastic deformation capabilities. Specifically, Ti 0.26 Si 0.15 B 0.59 and Ti 0.23 Mo 0.07 Si 0.16 B 0.54 exhibited an onset of plastic deformation at approximately 600 °C, with a pronounced plastic response at 850 °C, which is attributed to Si-rich grain boundaries and Si nanoclusters identified by atom probe tomography. In contrast, the binary TiB 3.06 and quaternary Ti 0.28 Ta 0.07 Si 0.12 B 0.53 coatings exhibited fully linear-elastic behavior across all tested temperatures, despite silicide segregation in the quaternary coating. Notably, the Mo-containing coating exhibited the highest ductility, with strain to failure increasing from 1.7 % at room temperature to 3.3 % at 850 °C. Our findings indicate that the high-temperature fracture behavior of Ti-TM-Si-B 2±z coatings is mainly governed by Si distribution and the underlying segregation pathways: The formation of pure Si-nanoclusters is found to promote enhanced ductility, whilst (mixed) silicide formation stabilises a less compliant grain-boundary network.