Mechanical properties of crystalline-amorphous composites: generalization of Hall–Petch and inverse Hall–Petch behaviors

The strength, σy, of a polycrystal decreases with mean grain diameter D at D ≳ 50 atoms (i.e. Hall–Petch behavior) and increases at D ≲ 50 (i.e. inverse Hall–Petch behavior). Our simulations generalize σy(D) to σy(D, l), where l is the mean thickness of amorphous grain boundaries of crystalline–amorphous composites. The maximum strength is reached at (D, l) ≈ (50, 6) atoms for single-component face-centered-cubic solids and at (D, l) ≈ (50, 2) for bidispersed or body-centered-cubic solids because of the different activation stresses of dislocation motions. The results explain recent alloy experiments and provide a way to exceed the maximum strength of polycrystals. Ductility and elastic moduli are also measured in the broad (D, l) space. The regimes without a strength–ductility trade-off, the maximum ductility and ductile–brittle transitions are identified. These results obtained in (D, l) space are important in solid mechanics and can guide the fabrication of crystalline–amorphous composites with outstanding mechanical properties.