Energy state estimation of mechanocomposites containing fusible components based on analysis of fine structure parameters and thermal effects

Energy state of composites obtained by mechanical alloying of the Cu-Sn and Fe-Ga powder mixtures during high-energy processing in the planetary ball mill is evaluated by the methods of X-ray diffraction analysis (XRD) and differential scanning calorimetry (DSC). It is shown that during mechanical alloying the total amount of accumulated energy can reach 80 % of the composite melting enthalpy. The greatest contribution to the structuralphase transformations is made by the phase changes of elastic deformations and grain boundaries. The obtained XRD data are consistent with the DSC data. Three endothermic effects are established at temperatures of 507, 792 and 905–1085 °C for the mechanocomposite with the composition Cu20Sn, the value of these thermal effects is significantly reduced (to 0.79, 16.29 and 36 J/g, respectively) relative to an alloy of similar composition obtained by metallurgical methods. The following criteria of estimation of the most probable processes of structural-phase transformations are proposed based on the energy state of mechanocomposites: the structure of the composite is activated at ΔEε << ΔEs; new phases (solid solutions, intermetallic compounds) are formed at ΔEε ≈ ΔEs; the structure ordering processes take place at ΔEε > ΔEs. The decrease in the values of the energy of elastic deformations ΔEε during prolonged mechanical alloying may indicate the increase of the role of the diffusion processes and the formation of ordered structures, which will contribute to the increase of thermal stability of the grain boundaries. According to these criteria, the dose of the introduced mechanical energy to obtain hardened mechanocomposites of the Cu-Sn composition is to meet the conditions: D ≥ 3.4 kJ/g for Cu-Sn mechanocomposites; D ≥ 37.8 kJ/g for Fe-Ga mechanocomposites.