Oxidation behaviour and mechanical properties of sputter-deposited TMSi2 coatings (TM = Mo, Ta, Nb)

Transition-metal disilicides (TMSi2) based thin films are suggested as promising, novel protective coating materials used in various high-temperature applications. In this study, we investigate the phase formation, microstructure, and mechanical properties (i.e. H, E, and KIC) of sputter-deposited TMSix films (TM = Mo, Ta, Nb) in correlation with the varied bias potential. The as-deposited TaSix and MoSix coatings show Si substoichiometries with Si/Me (x) < 2, while all the NbSix coatings are overstoichiometric in Si. All TaSix and NbSix coatings are stabilized in their preferred hexagonal structure, whereas the MoSix coatings exhibit small fractions of T1-Mo5Si3 next to the dominant metastable hexagonal beta-phase. The oxidation behaviour of the coatings was examined up to 1400 degrees C. MoSix based films are distinguished by an outstanding oxidation resistance, forming dense and protective silica scales of only 650 nm after 100 h at 1200 degrees C - also obtaining an extremely high interfacial stability. In contrast, TaSix suffers accelerated oxidation at 1200 degrees C due to the formation of mixed, non-protective scales consisting of Ta2O5 and SiO2. Moreover, NbSix coatings show retarded oxidation kinetics up to 60 h at 1200 degrees C, forming a dense and uniform SiO2 scale of only 533 +/- 131 nm. Micro-cantilever bending experiments reveal that TaSi1.7 coating exhibit the highest fracture toughness, KIC, of 2.7 +/- 0.2 MPa center dot m1/2 compared to 2.3 +/- 0.1 and 1.7 +/- 0.1 MPa center dot m1/2 for NbSi24 and MoSi1.9, respectively. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).