M. N. Mungole, M. Surender, S. Bhargava
May 2, 2013
Characterization of oxide scale and α-casing in Ti6Al4V titanium alloy oxidized at 1050, 1150, 1250 and 1340 K for 2, 4, 6, 8 and 12 h in a dynamic oxygen gas atmosphere has been analyzed. The oxide scale exhibited a spalling tendency. Its thickness systematically increased with the temperature and the duration of the oxidation. At a later stage the scale exhibited a catastrophic growth due to the increased porosity. The oxygen stabilized α-phase and its volume fraction as well as its hardness decreased with the distance in the metal matrix (α-casing). Estimated oxygen diffusion coefficients based on the hardness profiles across α-casing were 7.0 × 10 −14 , 8.5 × 10 −14 , and 1.2 × 10 −13 , 1.8 × 10 −13 m 2 /s at 1050, 1150, 1250, and 1340 K, respectively. Similarly, the overall activation energy for diffusion of oxygen in the alloy was 105 kJ mol −1 . EDS analysis across α-casing in the internal oxidation zone revealed sharp concentration wells for Ti and Al. Titanium concentration decreased and that of aluminum increased in these wells.