Mechanical properties of crystalline–amorphous composites: generalisation of Hall–Petch and inverse Hall–Petch behaviours

The strength, σy, of a polycrystal decreases with mean grain diameter D at D ≳ 50 atoms (i.e. Hall-Petch behaviour) and increases at D ≲ 50 (i.e. inverse-Hall-Petch behaviour). Our simulations generalise σy(D) to σy(D, l), where l is the mean thickness of grain boundaries. For various particle compositions, the maximum strength is reached at (D, l) ≃ (50, 6) particles for single-component facecentred-cubic solids and at (D, l) ≃ (50, 2) for bidispersed or body-centred-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.