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C. Fuger, B Schwartz, T. Wojcik, V. Moraes, M. Weiss, A. Limbeck, C Macauley, O Hunold, P. Polcik, D. Primetzhofer, P. Felfer, P.H. Mayrhofer, H. Riedl:
"Influence of Ta on the oxidation resistance of WB2-z coatings";
Journal of Alloys and Compounds, 864 (2021), 158121; 1 - 9.

Ternary W1-xTaxB2-z is a promising protective coating material possessing enhanced ductile character and phase stability compared to closely related binaries. Here, the oxidation resistance of W1-xTaxB2-z thin films was experimentally investigated at temperatures up to 700 °C. Ta alloying in sputter deposited WB2-z coatings led to decelerated oxide scale growth and a changed growth mode from paralinear to a more linear (but retarded) behavior with increasing Ta content. The corresponding rate constants decrease from kp⁎ = 6.3 ∙ 10-4 µm2/s for WB2-z, to kp⁎ = 1.1 ∙ 10-4 µm2/s for W0.66Ta0.34B2-z as well as kl = 2.6 ∙ 10-5µm/s for TaB2-z, underlined by decreasing scale thicknesses ranging from 1170nm (WB2-z), over 610nm (W0.66Ta0.34B2-z) to 320nm (TaB2-z) after 10min at 700 °C. Dense and adherent scales exhibit an increased tantalum content (columnar oxides), which suppresses the volatile character of tungsten-rich as well as boron oxides, hence being a key-factor for enhanced oxidation resistance. Thus, adding Ta (in the range of x = 0.2 to 0.3) to α-structured WB2-z does not only positively influence the ductile character and thermal stability but also drastically increases the oxidation resistance.

Oxidation Resistance; Transition Metal Diborides; Scale Growth; Diborides

http://dx.doi.org/10.1016/j.jallcom.2020.158121

https://publik.tuwien.ac.at/files/publik_292352.pdf

Project Head Helmut Riedl:
CDL-SEC