The existence of nanoclusters that were thermodynamically stable at elevated temperatures was truly intriguing because of its scientific implications andpotential applications. Highly stable nanoclusters were observed by atom probe tomography in iron-based alloys at temperatures close to 1400C (0.92Tm) that appeared to defy the stability constraints of artificially created nanostructured materials. The ∼4nm-diameter Ti-, Y- and O-enriched nanoclusters were 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 played 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 indicated that vacancies could be exploited for the first time as a nanoscale constituent to design materials with far superior high temperature properties.

Vacancies as a Constitutive Element for the Design of Nanocluster-Strengthened Ferritic Steels. M.K.Miller, C.L.Fu, M.Krcmar, D.T.Hoelzer, C.T.Liu: Frontiers of Materials Science in China, 2009, 3[1], 9-14