| Nano-structured oxide dispersion strengthened (ODS) steels are the important structural material candidates for first wall application in fusion reactor due to their excellent radiation resistance and good high temperature mechanical properties, which come from ultra-high density of Y-Ti-O-enriched nanoscale precipitates, high-densities of dislocations and ultrafine grains. However, the formation mechanism of Y-Ti-O precipitates is not understood comprehensively yet. In this study, four kinds of 9Cr-ODS steels with different Y/Ti atomic ratio were produced by mechanical alloying (MA) and hot isostatic pressing (HIP). The microstructure of the ODS steels were characterized by HRTEM, STEM, TEM and EBSD. The relative density, hardness and tensile properties were also measured. The following results were obtained:(1) The four kinds of 9Cr-ODS steels with different Y/Ti atom ratios were produced by MA and HIP. The relative density of four ODS steels are all more than 98%.(2) High-density of Y-Ti-O enriched nanoclusters, Y2Ti2O7 precipitates and large MnCr2O4 phases are formed in Ti-containing ODS steels. There are high-density of Y-0 clusters or Y2O3, Cr2O3 and MnCr2O4 precipitates in Ti-free ODS steel.(3) In the ODS steel with Y/Ti=0.42, the density of nanoscle precipitates is the highest, the average size is the smallest. In the ODS steel with Y/Ti=0.989, the density of nanoscle precipitates is the lowest, the average size is the largest.(4) The Vickers hardness of Ti-containing ODS steels is similar and is higher than that of Ti-free ODS steel.(5) The ODS steel with Y/Ti=0.42 exhibits the best strength and toughness, compared to Ti-free ODS steel and Ti-containing ODS steels with Y/Ti=0.14 and Y/Ti=0.989. |
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