Abstract
Existing oxide dispersion strengthened (ODS) alloys are, besides Ni-based superalloy single crystals, the most creep-resistant materials. The creep resistance of the ODS alloys may, moreover, be significantly improved thanks to increasing the volume fraction of the nano oxides by more than one order of magnitude so that the oxides play a decisive role in strengthening. The present experimental study deals with two systems of such a high-volume fraction of nano oxides, namely, the Fe-11Al-1O and Fe-17Cr-7Al-4Y2O3 systems prepared by mechanical alloying and hot rolling leading to a rather stable fine-grained microstructure. This microstructure undergoes static recrystallization at high temperatures. The kinetics of static recrystallization and coarsening of nano oxides in recrystallized grains is determined for both systems. The difference in kinetics of coarsening of Al-based and Y-based oxides in the Fe-11Al-1O and Fe-17Cr-7Al-4Y2O3 systems is expressive and predetermines the Fe-17Cr-7Al-4Y2O3 system or similar ones to become the new leading system among creep- and oxidation-resistant materials for applications up to 1200 °C.
Highlights
To meet growing demands on energy and economic efficiency, new creep- and oxidation-resistant structural materials are being intensively examined in the searched for a radical breakthrough.The existing leading metallic materials are represented by two classical groups: (i) Ni-based superalloy single crystals and (ii) oxide dispersion strengthened (ODS) coarse-grained ferritic alloys.The excellent creep properties of Ni-based superalloy single crystals are due to their microstructure, which consists of ordered cube-shaped γ’-precipitates of a volume fraction of about 70% separated by thin channels of disordered γ matrix
Coarse-grained alloys strengthened by nano oxides of several percent of volume fraction are promising creep-resistant materials for very high temperatures thanks to high stability of oxides against coarsening
Static recrystallization occurs in the Fe-11Al-1O system at 1000 ◦ C and in the Fe-17Cr-7Al-4Y2 O3 system at 1120 ◦ C with nearly the same kinetics leading to practically the same coarse-grained
Summary
To meet growing demands on energy and economic efficiency, new creep- and oxidation-resistant structural materials are being intensively examined in the searched for a radical breakthrough.The existing leading metallic materials are represented by two classical groups: (i) Ni-based superalloy single crystals and (ii) oxide dispersion strengthened (ODS) coarse-grained ferritic alloys.The excellent creep properties of Ni-based superalloy single crystals are due to their microstructure, which consists of ordered cube-shaped γ’-precipitates of a volume fraction of about 70% separated by thin channels of disordered γ matrix. To meet growing demands on energy and economic efficiency, new creep- and oxidation-resistant structural materials are being intensively examined in the searched for a radical breakthrough. The existing leading metallic materials are represented by two classical groups: (i) Ni-based superalloy single crystals and (ii) oxide dispersion strengthened (ODS) coarse-grained ferritic alloys. The excellent creep properties of Ni-based superalloy single crystals are due to their microstructure, which consists of ordered cube-shaped γ’-precipitates of a volume fraction of about 70% separated by thin channels of disordered γ matrix. The mechanisms of creep are summarized in the overview paper [1], showing that plastic deformation starts by dislocation slip in the γ-channels, which is very difficult in the γ’-precipitates. Micromechanical unit cell models [2,3] account for all decisive creep mechanisms inclusive of microstructure evolution and fit well to experiments. The instability of the γ-precipitates due to directional coalescence and/or coarsening above 900 ◦ C and enormous processing costs (higher generations contain considerable amounts of expensive Re and Ru) seem to be the greatest drawback of the superalloy single crystals
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