Nanostructure formation and properties of ball-milled NiAl intermetallic compound

Binary Ni(x)A1(100-x) (46 less than or equal to x less than or equal to 60) compounds with ordered B2 structure were prepared by mechanical attrition of are-melted compounds. The average grain size of the as-milled powders (5-12 nm), the rms atomic-level strain, the stored enthalpy and the microhardness depend on the composition of the material. Varying the composition within the homogeneity range of the B2 phase field by adding elemental Ni and Al and subsequent mechanical alloying changes the grain size reversibly. Hence, the grain size depends on the intrinsic properties of the material. The results will be discussed with respect to models for the evolution of nanocrystalline grain sizes during milling based on the underlying mechanisms of plastic deformation and recovery for stoichiometric and off-stoichiometric compositions. (C) 1997 Elsevier Science S.A.