• Yokokawa, Tadaharu
• Tabata, Chihiro
• Kawagishi, Kyoko
• Suzuki, Shinsuke
• Osada, Toshio
• Ikeda, Ayako

Abstract

<jats:title>Abstract</jats:title><jats:p>To clarify the effect of solution heat-treatment on the oxidation resistance of Ni-base single-crystal superalloy TMS-238, the evaluation of dendrite/inter-dendrite segregation of alloying elements in the as-cast and heat-treated samples, and its effect on cyclic oxidation resistance were investigated. Cyclic oxidation test results at 1100 °C for up to 150 cycles clearly showed that the as-cast samples with element segregations had lower oxidation resistance compared to heat-treated samples with homogeneous structure. Further, for the as-cast sample, rapid growth and spallation of oxide consisting of NiO, Cr<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>, and Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> were observed around the dendrite core for 10 cycles of oxidation. Analysis of sub-surface on sample isothermally oxidized at 1100 °C for 10 minutes showed that rapid oxide growth is due to the formation of discontinuous Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> layer at dendrite core with lower Al concentration. Furthermore, in this study, the threshold value of Al concentration and Gibbs energy for the formation of continuous Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> layer were estimated and determined to be around 5.2 wt pct and − 556.6 ± 0.5 kJ/mol, respectively. This indicated that the solution heat-treatment for TMS-238 should be conducted above 1305 °C for exhibiting oxidation resistance at 1100 °C, to meet the threshold value within the whole region between dendrite and inter-dendrite.</jats:p>

Topics

• impedance spectroscopy
• surface
• superalloy