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E. Aschauer, H. Riedl, H. Bolvardi, P. Polcik, P.H. Mayrhofer:
"Influence of Ti on the Phase Stability of Magnetron Sputtered Mo-Si-B Thin Films";
Poster: 45th International Conference on Metallurgical Coatings and Thin Films (ICMCTF) 2018, San Diego, CA; 2018-04-23 - 2018-04-27; in: "45th ICMCTF", (2018), 93 - 94.

In terms of fuel and cost efficiency, the replacement of high-density Ni-based super alloys in aerospace industries came into the focus of research. A promising candidate are Mo-Si-B alloys, since they offer a high creep resistance, phase stability in a very broad range as well as excellent oxidation resistant. This broad field of mechanical and chemical properties is achieved by taking advantage of different phase combinations within the ternary phase diagram, leading to a multicomponent material. As it is well known in literature, molybdenum offers a poor oxidation resistance due to the formation of volatile oxides already above 400 °C - so called pesting phenomena. Alloying silicon and boron to refractory metals like molybdenum promotes the formation of glassy-like borosilicate oxide scales and inhibits the volatilisation of MoO3. Nevertheless, retarded oxidation kinetics in a wide temperature field is strongly linked to the proper Si to B ratio. The molybdenum rich corner, known as Berczik triangle, offers a phase combination of Mo (A2), c-Mo3Si (A15), and T2 Mo5SiB2 (D8l), next to the so-called Akinc triangle including c-Mo3Si (A15), T2 Mo5SiB2 (D8l), as well as T1-Mo5Si3 (D8m). Especially, the T1 and T2 phases provide the ideal ratio of boron and silica to form either B-rich SiO2 or even pure SiO2 at low and high temperatures, respectively.
In order to access this highly interesting material characteristics, physical vapour deposition (PVD) can be used to make this promising material system accessible to many other applications and extend the field of operation. However, the most common deposition temperatures of about 500 °C do not lead to the desired phase combination, but rather to homogeneous, X-ray amorphous thin films. Alloying titanium to the ternary system is known to stabilise the T2 phase, by substituting the Mo atoms within the tetragonal crystal structure up to concentrations of 40 % - also reducing the density significantly.
Therefore, the focus of the provided study is on the fundamental understanding of the phase evolution of magnetron sputtered Mo Ti-Si B thin films varying deposition parameters such as total pressure, bias voltage, and deposition temperature. Furthermore, the phase stability after thermal treatments in different atmospheres (vacuum, inert gas, and oxygen) is investigated up to temperatures of
1500 °C by using X-ray diffraction analysis as well as various (high-resolution) electron microscopy techniques and differential scanning calorimetry (DSC). The mechanical properties were investigated by nano-indentation of the as deposited and annealed state.