Oxidation of Nb[sub 2]AlC and (Ti,Nb)[sub 2]AlC in Air

In this paper, we report on the oxidation kinetics in air of the ternary compounds (actual Nb:Al:C atomic ratios 1.95:1.05:0.95) and (actual Ti:Nb:Al:C ratios 0.94:1.06:0.93:0.94). In the 650-800°C temperature range, the oxidation reaction for the former occurs in two steps. First is At longer times and higher temperatures, and react to form for an overall reaction of In the 900-1200°C temperature range, oxidation of also occurs in two steps. First is At longer times and higher temperatures, and react to form for an overall reaction of In all cases, the oxidation occurs by the inward diffusion of oxygen. The formation of substantially enhances the oxidation resistance of relative to that of At 650 and 900°C the oxidation kinetics are subparabolic, with time exponents of and for and respectively. At 700 and 750°C, the oxidation kinetics of are linear, with rates comparable to those for the oxidation of pure Nb. The oxidation kinetics for at temperatures between 1000 and 1100°C start parabolic but become linear at longer times. At 1200°C, the oxidation is parabolic up to about 16 h; beyond that, the oxide layers tend to spall off. At 1200°C, a Nb-aluminide phase is observed at the oxide/material interface after 4 h of oxidation. Further oxidation leads to the formation of an -rich oxide phase at the oxide/substrate. Based on this work, the maximum extended-use temperature for in air is 650°C; for it is 900°C. © 2003 The Electrochemical Society. All rights reserved.