Investigation of nano-clusters evolved with Ti and Zr in ferritic ODS steel and their effect on microstructure and mechanical properties

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In the present study, four nominal compositions Fe-15Cr-2W-0.3Y2O3-x (x = 0, 0.3Ti, 0.3Zr, 0.3Ti-0.3Zr) of ODS steel have been consolidated via spark-plasma-sintering of mechanically alloyed powders. All the samples were characterized via SEM, XRD, EBSD and TEM analysis and tested for hardness and compressive strength at room as well as elevated temperatures. Further, strength contributions of temperature dependent strengthening mechanisms were determined and correlated with the experimental values of compressive yield strength. Results suggest that contrary to Ti, addition of Zr was found with the precipitation of dense and much finer nano-clusters (∼3 nm) and observed to be more effective in enhancing the hardness and compressive strength at room as well as high temperatures. Composition containing both Ti and Zr solutes resulted in ultrafine grains of nearly uniform sizes and exhibited considerably enhanced hardness as well as compressive strength at all temperatures. However, it favoured the formation of Y-Zr-O nano-clusters instead of Y-Ti-O due to exhibiting lower formation enthalpy as determined from their reaction energies. As per the theoretically evaluated strength contributions, Orowan strengthening was found prevailed at high temperatures and it had a major contribution in compressive yield strength at room temperature as well. The study suggests the prevailing effect of formation of Y-Zr-O nano-clusters over Y-Ti-O nano-clusters in terms of obstacles to grain boundaries and mechanical properties which may provide an insight for the development of advanced nuclear materials.