Solid-phase synthesis in Ni-Mg and Ni-Mg-C systems upon ball milling of powder mixtures

Abstract

It is shown by X-ray diffraction analysis and differential scanning calorimetry that phase formation in mechanochemical synthesis (MS) of two-component mixtures in the Ni-Mg system occurs through amorphization. The final product of the MS of Ni75Mg25 mixture is the nonequilibrium nanocrystalline Ni-7.5 at % Mg solid solution with a lattice constant a = 0.3602 nm (aNi = 0.3526 nm). Milling of a mixture with a higher magnesium content (Ni66.7Mg33.3) yields a two-phase mixture composed of an amorphous phase and Ni(Mg) solid solution. MS of three-component mixtures in the Ni-Mg-C system, regardless of the form of the initial components (Ni60Mg25C20 mixtures of elementary components or a mixture of Ni2Mg intermetallic compound, Ni powder, and graphite), yields double cubic carbide of antiperovskite type, Ni3MgC0.75 (E21 structure type), with a lattice constant of 0.3782 nm. It is shown that the initial milling stage for a mixture of this elementary components in the presence of graphite is characterized by the distortion of Mg particles with the formation of texture in the (002) basic plane.