Optimization of B2/L21 hierarchical precipitate structure to improve creep resistance of a ferritic Fe-Ni-Al-Cr-Ti superalloy via thermal treatments

The effect of precipitate structures of a B2-NiAl/L2(1)-Ni2TiAl hierarchical precipitate-strengthened ferritic alloy on the precipitate/matrix interface, elastic strain, and creep resistance has been investigated by systematic heat treatments and creep experiments. The experimental results reveal that the highest creep strength was achieved in a heat-treated sample containing the largest coherent precipitate with fine internal networks, whereas the semi-coherent precipitate results in a sharp drop of the creep strength. It was found that the strong elastic strain field, affected by the internal structure within the precipitate, plays a crucial role in improving the creep resistance. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.