Grain-size-dependent non-monotonic lattice parameter variation in nanocrystalline W: The role of non-equilibrium grain boundary structure

The grain size dependency of lattice parameter during high-energy ball milling of W has been investigated. The lattice parameter varies non-monotonically with grain size during milling with a lattice contraction initially followed by an expansion. The lattice parameters were calculated in view of the non-equilibrium grain boundary structure that evolved during milling using excess free volume and the interfacial stresses at the grain boundaries. The calculated lattice parameters closely match the experimentally observed values.