The Oxidation Behavior of Ti6242S–Ti4822 Composites

Abstract

Motivated by emerging interests in high temperature multimaterial topology optimized blisk structures, accelerated characterization of the oxidation behavior of composites comprised of consolidated near-α Ti alloy Ti6242S and γ-TiAl-based Ti4822 powders is investigated. Oxidation tests of seven compositions (0, 10, 25, 50, 75, 90, and 100 wt% Ti4822) were carried out in air between the upper use temperature of 600 °C and a higher temperature of 850 °C intended to accelerate the rate of oxidation. After oxidation for 24–50 h, monolithic Ti6242S showed significant mass gain during oxidation at (and beyond) 600 °C while Ti4822 required exposure at 750 °C and above to define the oxidation kinetics. The experimental oxidation behavior of both the terminal compositions and composites was adequately modelled by the parabolic oxidation model. Interestingly, the data reveal a similar temperature dependence (i.e. activation energy) for all composites investigated. The mass gain data of the composites reveal that the oxidation resistance, as indicated by the logarithm of the parabolic rate constant, increases linearly with the addition of Ti4822. This correlated with previously published observations that the oxidation of many Ti alloys scales linearly with the Al content in the alloy and with the fact that the reaction layer between the Ti6242S and the Ti4822 particle domains is rich in α₂ Ti₃Al phase, which has an oxidation behavior intermediate to that of the “pure” alloys. Based on these experimental data, a “go, no-go” constraint was developed for preliminary design using topology optimization algorithms to select candidate materials for hot, oxygen-exposed surface regions of multi-material structures.