Oxidation resistance of refractory γ-TiAlW coatings

The resistance to oxidation of the W-alloyed magnetron sputtered γ-TiAl fine-crystalline 4 μm thick coatings have were investigated in this work. The oxidation tests were performed in an atmosphere of pure oxygen or in the air at a temperature of 1173 K for 120 h. The resistance to high-temperature oxidation was investigated by means of micro-thermogravimetric analysis with continuous or stepwise control of the substrate weight. Before and after the oxidation the morphology of the coatings as well as their chemical and phase composition were investigated by SEM, EDS and EBSD, respectively. The results have been compared with those obtained for the uncoated γ-TiAl substrate. It was found that: (1) the W-alloyed γ-TiAl coatings have a considerably higher oxidation resistance (about four orders of magnitude) than the uncoated γ-TiAl substrates and that their resistance to oxidation increases with the concentration of alloying element in the range of the concentrations investigated in the work; (2) the high resistance to oxidation of the coatings is a result of the thin α-Al 2O 3 layer formation on the surface of the substrate during oxidation; (3) the formation of dense and uniform α-Al 2O 3 layer on the coating surface is due to a fine-crystalline structure of the magnetron deposited γ-TiAlW coating.