Outstanding high-temperature strength of novel Fe–Cr–Ni–Al–V ferritic alloys with hierarchical B2–NiAl precipitates

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We designed and developed a novel ferritic alloy, which reveals excellent high-temperature yield strength enhanced by coherent hierarchical precipitates. The composition of designed ferritic alloy was tailored via addition of Vanadium into a Fe–Cr–Ni–Al alloy to control the size and volume fractions of coherent B2–NiAl precipitates. The evolutions of microstructures, mechanical properties, and strengthening mechanisms at 973 K were examined by the experimental efforts coupled with theoretical approach, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction, compressive mechanical tests at 973 K, and theoretical (strengthening calculations) approach. It was found that the vanadium results in the reduction of the lattice misfit between B2–NiAl precipitate and matrix and decrease of the precipitate size. Furthermore, a hierarchical structure in the precipitate, i.e., nano-scale Fe23Zr6 phase within the B2–NiAl precipitate, was established in V-containing ferritic alloys, which plays a vital role in enhancing the yield strength at 973 K.