Microstructural, Mechanical And Electrical Characteristics Of Cu-Fe Filamentary Microcomposites

Cu-Fe in situ microcomposites are of particular interest because of the good strengthening effect of Fe filaments and the relatively low cost of iron constituent. However, the relatively high solubility of iron in copper at high temperatures coupled with the slow kinetics of iron precipitation at low temperatures in the Cu-Fe system can reduce the electrical conductivity. For this reason, optimizing strength and conductivity is the key issue recently. Many investigations are focused on the processes, mechanical and electrical properties etc.The Cu-Fe filamentary microcomposites were prepared by prior heat treatments and heavy cold drawing treatments. The evolution of filamentary microstructure was investigated and the mechanical and electrical properties were measured during the deformation process. The relationship between the microstructure and properties were analyzed. The calculation models responsible for the strengthening and electrical resistivity were modified and built up. The strain compatibility behavior between the different components was analyzed. The effects of rare earth elements on microstructural, mechanical and electrical characteristics of the alloys were investigated. Moreover, the influence on the microstructure and properties were investigated by introducing heat treatments prior to or after drawing deformation.Quenching and aging treatment or homogenizing treatment prior to drawing deformation refine the primary dendrites, remove the solute segregation along Cu grain boundaries and promote the precipitation of secondary Fe particles. Heat treatments prior to drawing deformation remarkably improve the strength levels and electrical properties during the deformation process. During the prior homogenizing treatment and cold drawing, a filamentary structure dispersed in Cu matrix is formed from the primary Fe phase. Some Fe precipitates produced in prior homogenizing treatments can also evolve into thin filaments during drawing.During cold drawing, Strong deformation texture appeared formed in the filaments. The drawing strain resulted in the crystal orientation and texture distribution change in both Cu and Fe phases. Cu matrix and Fe phase display different strain levels and strain increase rates during different stages of drawing deformation, which show a non-synchronous strain between both phases. The Fe filamentary structures of Cu-Fe alloys result in high strain strengthening but low electrical conductivity. At high strain, the fibrous structure further increases the strength level and resistivity of the alloys. The secondary Fe filaments can also improve the strength and conductivity in low strain range.The strengthening model for Cu-Fe based on rule of mixture has been improved, which indicate the evolution of strengthening mechanism during the deformation process. The strength dependent on the filament spacing accords with the Hall-Petch relationship when the filament spacing is greater than a certain scale. When the filament spacing is less than the certain scale, the strength dependent on the filament spacing deviates from the Hall-Petch relationship. And the strengthening mechanism transforms into the athermal obstacles at the boundaries and interfaces. The tensile strength increases linearly with the increase in phase boundary density.The enhanced scattering of interface results the resistivity increase of the Cu-Fe alloys with drawing strain. The relationship between resistivity and drawing strain based on interfacial scattering model has been built up. The electrical resistivity increases linearly with the increase in phase boundary density.The strength, hardness and elastic modulus decrease and the electrical conductivity and plastic deformation capacity increase with the increase in annealing temperature for the Cu-12% Fe microcomposites annealed at different temperatures.Adding rare earth elements into Cu-6%Fe alloy can refine the as-cast microstructure, facilitate the precipitation of secondary Fe particles and effectively improve the conductivity at high strain. Moreover, the thermal stability was improved of the heavy drawn microcomposites during high temperature annealing due to the contribution of rare earth elements.