Oxidation of columbium (niobium) and coated columbium alloys

Microstructure and High Temperature Oxidation Performance of Silicide Coating on Nb-Based Alloy C-103

“…6) and only a very thin glassy silica layer at 1100°C (Fig. 11) are consistent with the fact that SiO 2 phase turns glassy above about 1150°C [8]. From the nature of the oxide layer that formed after isothermal oxidation at 1300°C (Fig.…”

“…However, EPMA mapping for Nb and Si taken from the above layer clearly suggested the layer to consist of a Nb-rich silicide phase. Based on the binary Nb-Si phase diagram [21] and the reported literature on silicide coatings on niobium alloys [8,9,13,22], the inner layer is expected to consist of Nb 5 Si 3 phase. It is clear from Fig.…”

“…Similarly, the high temperature oxidation behaviour of these coatings has also been reported using weight change measurements and oxide scale characterization [8,20]. However, detailed characterization of the oxide scale that forms on the coating during oxidation exposure and also the coating degradation process, have not been well reported.…”

“…These compounds can be applied in form of coatings to enhance the oxidation resistance of Nb-alloys. Although aluminide coatings have exhibited good oxidation performance on some Nb-alloys [7], silicide coatings most often offer better oxidation resistance to these alloys [8][9][10]. Both simple silicide coatings as well as coatings modified with elements such as Al, B, Ge, Fe and Cr have been reported for oxidation protection to Nb-alloys [8][9][10].…”

Tantalum, niobium and their alloys

“…The chronological pattern of oxidation the niobium alloy WD 15 with a coating of 60 % Si, 20 % Co and 20 % Cr with (•) and without (x) 2 % boron in air between 1473 and 1673 K [30] In order to improve the performance of gas turbines with simultaneous decrease in the fuel consumption, it would be desirable to increase the operating temperature to, say, 1643 to 1703 K. But since this would then involve considerable expenditure on cooling if nickelbase alloys are used, the use of niobium alloys could be considered if their oxidation rate could be kept within acceptable limits. This problem was studied in a detailed investigation when alloys resistant to high temperature with the composition Nb18.5W3.6Hf0.145C (SU-31) and Nb27.6Ta10.6W0.94Zr (FS-85) were oxidized between 813 and 1753 K in a current of air [33]. The SU 31 alloy was the more resistant of the two alloys, although even this alloy cannot be used in gas turbines above 1363 K without protective surface coating.…”