Abstract
A lamellar (L12 + B2) AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA) was severely deformed by a novel hybrid-rolling process. During hybrid-rolling, the deformation was carried out in two stages, namely cryo-rolling followed by warm-rolling at 600 °C. The strain (ε) imparted in each of these steps was identical ~1.2, resulting in a total strain of ε~2.4 (corresponding to 90% reduction in thickness). The novel processing strategy resulted in an extremely heterogeneous microstructure consisting of retained lamellar and transformed nanocrystalline regions. Each of these regions consisted of different phases having different crystal structures and chemical compositions. The novel structure-composition dual heterogeneous microstructure originated from the stored energy of the cryo-rolling which accelerated transformations during subsequent low temperature warm-rolling. The dual heterogeneous microstructure yielded an unprecedented combination of strength (~2000 MPa) and ductility (~8%). The present study for the first time demonstrated that dual structure-composition heterogeneities can be a novel microstructural design strategy for achieving outstanding strength-ductility combination in multiphase high entropy alloys.
Highlights
Ni individual domains again consisted of multiscale architecture ranging from ultrafine recrystallized FCC grains to coarse recovered B2 grains, which resulted in simultaneous enhancement in strength and ductility
When compared to high pressure torsion (HPT) processed alloys[35], the novel hybrid processing route enjoys the distinct advantage of bulk processing, overcoming the limitations of small specimen size that can be fabricated by HPT
The most striking aspect of the hybrid-rolled eutectic high entropy alloy (EHEA) is the development of an extremely heterogeneous microstructure featured by the dual structural-compositional heterogeneities
Summary
Ni individual domains again consisted of multiscale architecture ranging from ultrafine recrystallized FCC grains to coarse recovered B2 grains, which resulted in simultaneous enhancement in strength and ductility. It is important to recognize that the phase compositions in these HEAs can be metastable, so that novel processing routes can accentuate precipitations or transformation of completely new phases even in single phase HEAs34. Significant potential for the control of compositional heterogeneities exists in addition to microstructural heterogeneities. This novel approach seems rather exciting, surprisingly it has not been demonstrated as yet. We have investigated the effect of a novel TMP route combining cryo-rolling followed by warm-rolling ( referred to as hybrid-rolling) on the AlCoCrFeNi2.1 EHEA. The novel processing strategy results in a novel heterogeneous nanostructure combining unprecedented strength and ductility. We further envisage that this novel processing strategy will open up unexplored avenues for developing a new class of HEAs with advanced properties
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