Microstructure evolution and creep strength of new-generation oxide dispersion strengthened alloys with high volume fraction of nano-oxides

Abstract Four creep resistant Fe-based oxide dispersion strengthened (ODS) alloys with a significantly high amount of dispersed oxide nanoprecipitates have been investigated. One Fe-Al-O and three Fe-Al-Cr-Mo-Y2O3 systems with different chemical composition strengthened by yttrium nano-oxides have been prepared by mechanical alloying of powders and consolidation by hot rolling leading to ultrafine grained microstructure due to dynamic recrystallization. The thermal stability of the precipitates, effects of the processing on the microstructure (grain and precipitate size) and mechanical properties at high temperatures have been evaluated. It has been found that the rolling temperature has a significant effect on the static recrystallization process during the subsequent heat treatment and on the resulting grain size of the alloys and does not affect the size of nano-oxides and their dispersion. Tensile tests performed at a low constant rate of 10-6 s-1 allow a quick estimate of the creep strength and helps to a quick identification of optimum processing conditions. It was found that the mechanism of the fracture is changing from trans-granular to inter-granular between 600 and 800 °C which leads to a significant drop of ductility. The set of mechanical tests has been completed also for 1100 °C indicating a rather high applicability potential of the investigated system.