Isothermal oxidation behavior of TribaloyTM T400 and T800. (December 2018) - Peng, Jian
Abstract TribaloyTM alloys are well-known as wear-resistant alloys, however, their oxidation kinetics and mechanisms are not well studied, especially their long-term oxidation behavior. In this work, the long-term isothermal oxidation behavior of TribaloyTM T400 and T800 in synthetic air at 900 °C for up to 1000 h was investigated. The mass gains of the samples were continuously recorded during the experiments with a thermobalance. Post mortem inspection of the samples was performed and the oxidation mechanism was analyzed. The results show that T800 has a better oxidation resistance than T400. The parabolic rate constant kp of T800 is 4.9·10−14 g2 ·cm−4 ·s−1, which is approximately one order of magnitude lower than 4.8·10−13 g2 ·cm−4 ·s−1 for T400. The penetration depth of the oxides in T800 is less than half of that in T400 and steady state oxidation is attained after approximately 200 h, compared to 350 h for T400. The better oxidation resistance of T800 correlates with its higher Cr content whereby protective Cr2 O3 scales form more readily. Oxidation: chromium essential to resistance Long-term oxidation of two commercial Tribaloy™ compositions shows lower chromium content is detrimental to protective scale formation. A team led by Jian Peng from the Max-Planck Institut für Eisenforschung in Germany held T400 and T800, two Co or Ni-based superalloys with lower and higher chromium content respectively, at 900 °C in air for up to 1000 h. They confirmed that T800 resists oxidation better than T400, and attributed this to the higher fraction of chromium(III) oxide in the mixed oxide scale. Because T400 has less chromium, a confluence of factors such as slower formation of chromium(III) oxide, no continuous chromium(III) oxide layer, and preferential oxidation of the Laves phases with a shell of cobalt oxide and a core of chromium(III) oxide. Better understanding corrosion scales may lead to longer component lifetimes.