Oxide dispersion strengthened (ODS) superalloys are generally considered to be promising candidate materials for high-temperature applications up to 1300 C because of their favorable combination of a highly elongated, coarse grain structure with dispersion strengthening by incoherent, fine, and homogeneously distributed Y 2 O 3 particles. [1] In particular, the creep behavior of the recently developed bcc ironbased ODS superalloy, PM 2000, and its British counterpart, MA 956, reveals partly contradictory and surprising results, which have not yet been clarified in the literature. [2±10] As an example, Figure 1 shows the true stress±true strain curves obtained from tensile specimens of PM 2000 at 1000 C. The material used in this study exhibits a grain structure typical of ferritic ODS superalloys. [5][6][7][8] Within the gauge length it consists merely of four large elongated grains oriented in the hard <111> orientation. [10] Beyond the elastic limit, the point of maximum deformation resistance (or maximum flow stress) is passed before the 0.2 % yield stress (see the dashed line) is attained, indicating an absence of work hardening. Secondly, a drastic decrease of s with increasing e follows, which is even more pronounced for lower strain rates, é. Consequently, strain-to-failure values of less than 1 % have been reported in long-term creep experiments. [7] This dramatic reduction of creep strength is accompanied by localized crystallographic shear deformation covering only a small fraction of the total gauge length of the specimen, see the macrograph (Fig. 2) after a plastic elongation of 1.5 % at é = 4´10 ±7 s ±1
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