Influence of Ta on the oxidation resistance of WB2?z coatings

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 thin films was experimentally investigated at temperatures up 700 °C. Ta alloying in sputter deposited WB2?z coatings led decelerated oxide scale growth changed mode from paralinear more linear (but retarded) behavior with increasing content. The corresponding rate constants decrease kp* = 6.3 ? 10?4 µm2/s for WB2?z, 1.1 W0.66Ta0.34B2?z as well kl 2.6 10?5 µm/s TaB2?z, underlined by decreasing thicknesses ranging 1170 nm (WB2?z), over 610 (W0.66Ta0.34B2?z) 320 (TaB2?z) after 10 min Dense adherent scales exhibit an increased tantalum content (columnar oxides), which suppresses volatile tungsten-rich boron oxides, hence being key-factor resistance. Thus, adding (in range x 0.2–0.3) ?-structured does not only positively influence thermal but also drastically increases