Vacancies as a constitutive element for the design of nanocluster-strengthened ferritic steels

Abstract

The existence of nanoclusters that are thermodynamically stable at elevated temperatures is truly intriguing because of its scientific implications and potential applications. Highly stable nanoclusters have been observed by atom probe tomography in iron-based alloys at temperatures close to 1400°C (0.92T_m) that appear to defy the stability constraints of artificially created nanostructured materials. The ∼4-nm-diameter Ti-, Y- and O-enriched nanoclusters are identified in the new form of a highly defective material state with vacancies as the critical alloying component and with (Ti + Y):O ratio different from the stable TiO₂ and Y₂Ti₂O₇ oxides. Vacancies play an indispensable role in enhancing the oxygen solubility and increasing the oxygen binding energy in the presence of Ti and Y, resulting in the stabilization of coherent nanoclusters. Atom probe tomography characterizations and theoretical predictions indicate that vacancies can be exploited for the first time as a nanoscale constituent to design materials with far superior high temperature properties.

Keywords

nanocluster / vacancy / ferritic alloy / nanoscale constituent / high temperature property

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Higher Education Press and Springer-Verlag Berlin Heidelberg