Microstructure, mechanical properties, thermal decomposition and oxidation sequences of crystalline AlB2 thin films

Materials & Design, vol. 250, pp. 113584

Abstract

Despite AlB 2 is the most typical structure prototype of transition metal diborides (TMB 2 ), studies on AlB 2 thin films are scarce. Furthermore, although Al is the primary alloying element for TMB 2 to improve their oxidation resistance , no such data are available for AlB 2 thin films. Here, we develop AlB x thin films through non-reactive magnetron sputtering of an AlB 2 compound target and investigate their microstructure, mechanical properties, thermal stability and oxidation resistance. Keeping the substrate temperature at 700 °C and increasing the Ar pressure during deposition from p Ar = 0.4 to 0.8 to 1.2, Pa, the films‘ chemistry slightly varies between x = 1.99, 1.97, and to 2.27, respectively. Detailed transmission electron microscopy shows that the highly (0001)-oriented AlB 2.27 thin film exhibits small platelet-like amorphous B regions next to the large columnar α-structured AlB 2 crystals. In the as deposited state, this film exhibits an indentation hardness and elastic modulus of 19.2 ± 1.2 GPa and 331.8 ± 14.4 GPa, respectively. Between 850 and 900 °C, the AlB 2.27 thin film starts to decompose into tetragonal (t-) AlB 12 , but still maintains dominant α structure up to 950 °C. At 1000 °C, the thin film is completely decomposed into t-AlB 12 and hexagonal AlB 10 . The AlB 2.27 thin film also shows exceptional oxidation-resistance with an onset temperature for the formation of oxides (α-Al 2 O 3 and o-Al 18 B 4 O 33 ) between 950 and 1000 °C when exposed to lab-air.

Authors 9

1. Chun Hu corresponding

   TU Wien

   Affiliation as printed

   Institute of Materials Science and Technology, TU Wien, Getreidemarkt 9, Vienna A-1060, Austria

2. Stanislav Mráz Aachen Materials Chemistry

   RWTH Aachen University

   Affiliation as printed

   Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, D-52074 Aachen, Germany

3. Tomasz Wójcik

   TU Wien

   Affiliation as printed

   Institute of Materials Science and Technology, TU Wien, Getreidemarkt 9, Vienna A-1060, Austria

4. Maximilian Podsednik

   TU Wien · Österreichisches Forschungsinstitut für Chemie und Technik

   Affiliation as printed

   Institute of Chemical Technologies and Analytics, TU Wien, A-1060 Wien, Austria

   KAI Kompetenzzentrum Automobil- und Industrieelektronik GmbH, Technologiepark Villach Europastraße 8, A-9524 Villach, Austria

5. Balint Istvan Hajas

   TU Wien

   Affiliation as printed

   Institute of Materials Science and Technology, TU Wien, Getreidemarkt 9, Vienna A-1060, Austria

6. Andreas Limbeck

   TU Wien

   Affiliation as printed

   Institute of Chemical Technologies and Analytics, TU Wien, A-1060 Wien, Austria

7. Nikola Koutná

   Linköping University · TU Wien

   Affiliation as printed

   Department of Physics, Chemistry, and Biology (IFM), Linköping University, Linköping SE-58183, Sweden

   Institute of Materials Science and Technology, TU Wien, Getreidemarkt 9, Vienna A-1060, Austria

8. Jochen M. Schneider Aachen Materials Chemistry

   RWTH Aachen University

   Affiliation as printed

   Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, D-52074 Aachen, Germany

9. P.H. Mayrhofer

   TU Wien

   Affiliation as printed

   Institute of Materials Science and Technology, TU Wien, Getreidemarkt 9, Vienna A-1060, Austria