Study On The Microstructure And Properties Of La₂O₃ Copper Matrix Composite Prepared By Liquid-liquid In-situ Reaction

The hexagonal structure of La₂O₃ and its unique outer electronic structure have a great influence on the comprehensive properties of the materials,so it has been widely concerned in the research and application of various fields.The reinforcement phase of La₂O₃-Cu matrix composite prepared by the traditional external method is mainly distributed on the grain boundary,where stress-strain concentration and microcracks are easy to occur when the material deforms;high stress/strain will make the combination of reinforcement phase and copper matrix unstable,lead to particle fracture,and then lead to material failure.Therefore,the La₂O₃-Cu matrix composite obtained by traditional external method can't meet the demand of deep processing of plastic deformation.In this paper,La₂O₃-Cu matrix composites were prepared by a liquid-liquid in-situ reaction method.The influence factors in the preparation process of La₂O₃-Cu matrix composites and the microstructure and properties of different content of La₂O₃-Cu matrix composites were studied and analyzed.The results are as follows:The calcination temperature is the key factor for the preparation of La₂CuO₄ powder.In this studied the best calcination temperature was 800?.At this temperature,the precursor is completely burned and the La₂CuO₄ powder has no obvious impurities.At the temperature of680?,the La₂CuO₄ powder can be reduced to La₂O₃ and Cu.Combination.The effect of ball milling time on the composite powder was found.Under the condition of 30 h ball milling,the composite powder was relatively small,and the reinforcing phase La₂O₃ was evenly distributed on the copper powder.Comparing the density of the composite material under different initial sintering pressures,it was found that the initial pressure was 1.5 MPa.When the content of La₂O₃ is 3 vol.%,comparing the microstructure and properties of the composites at different SPS sintering temperatures,it is found that when the sintering temperature is 800?,the composites have the highest density,reaching 98.55%,the composites have the smallest grains and the largest hardness 92.6 HV,the conductivity is also the largest,83%IACS.The density,microstructure,mechanical properties and electrical properties of La₂O₃-Cu matrix composites with different La₂O₃ content prepared by liquid-liquid in-situ reaction method and external method were compared.It was found that the density of La₂O₃-Cu matrix composites prepared by liquid-liquid in-situ reaction method was higher than that by external method,and the hardness and conductivity of La₂O₃-Cu matrix composites prepared by liquid-liquid in-situ reaction method were higher than those by external method.With the increase of the content of La₂O₃,the grain size of the composite decreases obviously.Because of the fine grain strengthening,the hardness of the composite increased from 66 HV to 107 HV and the conductivity decreases slightly.Comparing the tribological properties of La₂O₃-Cu matrix composites with different La₂O₃content prepared by the two methods,it is found that when the load is 50 N,with the increase of La₂O₃ content,the wear surface of the composites becomes relatively smooth and complete from rough,and the wear resistance of the composites increases;when the content of La₂O₃ is fixed,the larger the load is,the more serious the wear of the composites,the lower the friction coefficient.The wear resistance of La₂O₃-Cu composite prepared by liquid-liquid in-situ reaction is higher than that by external addition.A uniaxial compression test was performed on a 3vol.%La₂O₃ reinforced copper-based composite prepared by different preparation methods on a Gleeble-1500D thermal simulation tester.At the initial stage of deformation,as the amount of deformation increases,the flow stress of the composite first increases linearly and rapidly.When the amount of deformation reaches a certain value,the flow stress value slowly increases with the increase of the amount of deformation,and the slope of the curve decreases,and finally changes in a steady state.When the amount of deformation and the temperature of the deformation are constant,the flow changes with the increase of the strain rate.The stress will also increase;and at the same strain rate and deformation,the flow stress will decrease as the temperature increases;The peak stress of La₂O₃-Cu matrix composite prepared by liquid-liquid in-situ reaction is smaller than that of La₂O₃-Cu matrix composite,and its plasticity is better.