Different Ball Milling Time Effect on Tungsten Copper Powder Phase II

After high-energy ball milling, tungsten copper powder usually has lattice deformation, high-density defects and nano structure, which differ the thermodynamic and kinetic characteristics of powder system from conventional solid-state reaction and has a deviation from equilibrium properties.

It includes: 1. the continuous decrease of effective grain size and the peak movement will cause the formation of amorphous alloy; 2. the reaction component diffraction peak intensity decreased, broad-based amorphous gradually increase intensity; 3. intermediate (intermetallic compound) pre-form is further milled, resulting in an intermediate product amorphization. Overall, tungsten copper powder during the milling process after repeated deformation, cold welding distortion and tear in high energy state, also formed alternately layered structure and ultrafine microstructure, with time, each component of X-ray diffraction same position, the strength decreased.

Actually, there are several reasons: 1. High-density bit early milling wrong form, the stress field increased the elemental powders of free energy to form an alloy of the main driving forces; 2. Nano crystal formed after the high-energy ball milling with a high volume fraction of grain boundaries, the grain boundaries to store large amounts of excess enthalpy; 3. Phase boundary energy is driven alloying and system constraints in the single-phase metastable important factor; 4.Narrow composite layered structure, in a ball mill further broken into small pieces, the tip having a radius of curvature as small as 1nm, the surface tension of the solution may also be driven atoms.

Therefore, the related researchers thought atomic solid solution has two patterns, one is the crystal lattice get into solvent and resulting in lattice constant changing; and another is nano crystalline solvent provide a large number of grain boundaries, some solute atoms segregate in grain boundary, which makes the atoms in grain boundary lose the diffractive characteristic. In addition, X-ray and electron diffraction showed a single phase under construction, apparently at this time is not the solute and solvent atoms in the neighboring state, namely sub-miscible state.

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