Thin-Wall Debit in Creep of DS200 + Hf Alloy
Résumé
The thin-wall debit in creep life of the directionally solidified DS200 + Hf alloy at 900 °C has been investigated. A range of different applied loads and various directions with respect to the solidification direction was investigated. A direct comparison of creep properties in air between thin and massive specimens of DS200 + Hf was studied in detail. Creep results have shown that a substantial thin-wall debit in creep life and creep ductility is obtained along transverse directions compared with the longitudinal direction. The above creep performance was compared with the thin-wall loss in creep of the 〈001〉 single-crystal DS200 + Hf, for which almost no thickness debit in creep life was observed. The thin-wall debit in creep was mainly ascribed to the preferential oxidation of the grain boundaries. Besides, oxidized carbides were found to be cracked, and recrystallization was found in their vicinity. Finally, based on the produced experimental outcome, a coupled creep-oxidation modeling approach has been proposed to account for the thin-wall debit in creep life. This model takes into account creep anisotropy through the normalization by the ultimate tensile stress in both the Norton and Kachanov laws used in this modeling framework.