Abstract
Dislocation activity is critical to ductility and the mechanical strength of metals. Dislocations are the primary drivers of plastic deformation, and their interactions with each other and with other microstructural features such as grain boundaries (GBs) lead to strengthening of metals. In general, suppressing dislocation activity leads to brittleness of polycrystalline materials. Here, we find an intermetallic that can accommodate large plastic strain without the help of dislocations. For small grain sizes, the primary deformation mechanism is GB sliding, whereas for larger grain sizes the material deforms by direct amorphization along shear planes. The unusual deformation mechanisms lead to the absence of traditional Hall-Petch (HP) relation commonly observed in metals and to an extended regime of strength weakening with grain refinement, referred to as the inverse HP relation. The results are first predicted in simulations and then confirmed experimentally.
Highlights
Dislocation activity is critical to ductility and the mechanical strength of metals
In non-fcc metallic systems, the inverse HP relation has been previously predicted by molecular dynamics (MD) simulations[14,15,16], but it has been generally absent in experiments[3,5,6,17,18,19]
By investigating grain size dependence of strength, we reveal that SmCo5 is characterized by a clear and large regime of the inverse HP relation in contrast to typical observations reported for metallic systems[7,8]
Summary
Dislocation activity is critical to ductility and the mechanical strength of metals. Dislocations are the primary drivers of plastic deformation, and their interactions with each other and with other microstructural features such as grain boundaries (GBs) lead to strengthening of metals. In the past couple of decades, it has been established that the scaling of strength with grain size described by HP relation may breakdown in face centered cubic (fcc) metals and even lead to weakening of the materials with continued grain refinement when the grain size is below ~12–15 nm[7,8,9,10,11,12,13] This breakdown is often referred to as the inverse HP relation and it has been attributed to the dominant role played by GBs in strain accommodation in the small grain size regime. By investigating grain size dependence of strength, we reveal that SmCo5 is characterized by a clear and large regime of the inverse HP relation in contrast to typical observations reported for metallic systems[7,8]
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