| Cu alloy with high strength and conductivity is a key functional material in modern industry. The in-situ deformed Cu-Fe composite is an attractive strength conductor due to the good properties and lower price. This research is supported by the National High Technology Research and Development Program of China (Grant No.2007AA03Z519), the Fundamental Research Funds for the Central Universities (Grant No.N100609004) and Doctoral Dissertation Support Program of Northeastern University. Controlling solidification structure and Heat treatment are two important methods to improve the combination properties of strength and conductivity. The electromagnetic stirring (EMS) and high magnetic field (HMF) are imposed in the solidification and heat treatment, respectively. So in this thesis, the effects of EMS and HMF on the microstructure and properties of deformed Cu-Fe composites are investigated. And the growth of a-Fe particle and precipitation processes in Cu-Fe alloy under HMF are also investigated.The experiment results of solidification process under EMS in Cu-Fe alloy show that, grain refinement of Cu-Fe alloy is mainly dependent on Fe element and the amount of Fe. The EMS can effectively refine the grain in Cu-Fe alloy with lower Fe content instead of the one with high Fe content. And, the EMS also can break the Fe dendrites and refine the size and spacing of Fe dendrite arms. When the EMS current is over 100 A, the Fe phases separate to ingot surface due to heavily stirring level. So,100A is a better EMS current.According to microstructure heredity, the EMS can refine the indirectly refine the microstructure in the deformed Cu-Fe alloy/composite. The deformed Cu-2%Fe alloys prepared by EMS have a finer grain, and the Cu-6%Fe composites (original composition is 8%Fe) prepared by EMS have the finer filament spacing, width and thickness. The spacing and amount of Fe filaments are increasing with the increasing Fe content.The Cu-2%Fe alloy and Cu-6%Fe composites prepared by EMS own the higher strength. And the strength of Cu-Fe composite is increases with increasing Fe content. EMS can’t influence the conductivity of Cu-Fe alloy/composite. Therefore, the EMS is effective method to improve the combination properties of strength and conductivity.The experiment results of HMF annealing treatment of Cu-12.8%Fe show that, when the annealing temperature is at 450℃, the spacing and morphology of Fe filaments are not changed with the rising annealing time, and the HMF can’t change the morphology of Fe filament and the Fe solubility. When the composites are annealed at 700℃, the HMF can increase filament spacing, and accelerate the thermal instability of Fe filament and dissolution of Fe element. At 450℃, conductivity gradually increases with annealing time, and strength reduces with annealing time. The strength and conductivity are not changed by EMS. At 700℃, HMF can reduce the strength and conductivity at the same time. Therefore, at the better annealing temperature of 450℃, the HMF can’t effectively improve the microstructure and properties of Cu-Fe composites.The experiment results of Fe filament instability show that the dominant instability of the Fe fibers is the longitudinal boundary splitting which is determined by the greater cross sectional aspect ratio (width/thickness, w/t) and the larger ratio of boundary to interfacial energy (γB/γs).The longitudinal boundary splitting makes the ribbon-like Fe fibers evolve into a series of cylindrical fibers. Then the cylindrical Fe fibers undergo the instability process in terms of the breakup, growth and coarsening concurrently. The breakup times are accurately predicted by the Rayleigh perturbation model. The growth process primarily contributes to the higher increasing rate of the fiber radius during isothermal annealing at 700℃ than that calculated by the coarsening theory developed for cylindrical fibers, since the Cu-matrix of composites is highly supersaturated after casting/cold-working process.The study of conductivity mechanism in Cu-Fe composites reveals that the resistivity of impurity scattering ρimp is the main contributor to the resistivity of the Cu-Fe composites if the phonon and dislocation scattering contributions to the electrical resistivity are considered to be constants. At annealing temperatures below 500℃, an increase of filament spacing and reduction of interface area in unit volume result in a marginal decrease of the resistivity with temperatures. Above 500℃, the Fe solubility in Cu-matrix rapidly increases with temperature, which directly causes the increase of composites resistivity.The orientation relationship between the a-Fe particle and Cu-matrix is K-S relationship, i.e. (111)f/(101)b, [101]f//[111]b, [121]f//[121]b. The shape of a-Fe particle is lath-shaped particle, and the angle between the growth direction (long-axis direction) and close-packed direction [101]f//[111]b is 8-9°, and can be calculated by invariant-line model. The HMF can’t influence the basic crystallographic characteristics. When the HMF is nearly parallel to the growth direction, the growth will be accelerated. When the HMF is nearly normal to growth direction, the growth speed will not be changed.The investigation results of aging treatment under HMF shows that, the coherent y-Fe particles precipitate from Cu-matrix after 450℃ aging, and the HMF doesn’t change the precipitates size. When the composites aged at 700℃, the size of precipitates is larger than that aged at 450℃, and the HMF can obviously increase the precipitates size. A lot of misfit dislocations will be released from γ-Fe/Cu interface with the rising precipitates size. At the aging temperature of 450℃ the HMF can’t influence the Fe solubility and conductivity. However, the HMF can reduce the Fe solubility in Cu-matrix and increase the conductivity, so the HMF can promote the precipitation process at 700℃. |
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