Although intermetallics are attractive for their high strength, many of them are often brittle at room temperature, thereby severely limiting their potential as structural materials. Here, we report on a previously unidentified deformable nanocrystalline CoAl intermetallics with Co-rich thick grain boundaries (GBs). In situ micropillar compression studies show that nanocrystalline CoAl with thick GBs exhibits ultrahigh yield strength, exceeding 4.5 gigapascals. Unexpectedly, nanocrystalline CoAl intermetallics also show prominent work hardening to a flow stress of 5.7 gigapascals up to 20% compressive strain. Transmission electron microscopy studies show that deformation induces abundant dislocations inside CoAl grains with thick GBs, which accommodate plastic deformation. Molecular dynamics simulations reveal that the Co-rich thick GBs play a vital role in promoting nucleation of dislocations at the Co/CoAl interfaces, thereby enhancing the plasticity of the intermetallics. This study provides a perspective to promoting the plasticity of intermetallics via the introduction of thick GBs.
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