Theoretical Study On Temperature/size Dependent Properties For Particle Reinforced Metal Matrix Composites And Ferromagnetic/ferroelectric Materials

With the rapid development of high-end equipment such as aerospace equipment,high-performance weapons equipment and fourth generation nuclear power equipment,particle reinforced metal matrix composites are more and more widely used at different temperatures.Yield strength is a key mechanical property index of material design in engineering,and it is very sensitive to temperature.Therefore,the research on the yield strength of particle reinforced metal matrix composites at different temperatures has become one of the most active fields of high and new technology.At present,the existing studies on the temperature dependent yield strength of particle reinforced metal matrix composites are mainly depends on experiments,which not only faces the problems of time consumption and energy consumption,but also cannot fully reveal the evolution law of material properties with temperature.And there are only a few theoretical models of temperature dependent yield strength of particle reinforced metal matrix composites.Therefore,it is of great theoretical significance and engineering application value to study various mechanisms for controlling the yield strength of particle reinforced metal matrix composites at different temperatures,especially at high temperatures,and their evolution with temperature,and establish a theoretical characterization model of temperature dependent yield strength.As the indispensable functional materials in the scientific and industrial development of modern science and technology society,ferroelectric materials and ferromagnetic materials have been widely used in the high and new technology fields such as magnetostrictive materials and information storage materials due to their excellent performance of good memory and active adjustment of their own actions.The ferromagnetic materials in the practical application also often face different environment temperature.As one of the key factors controlling the macroscopic properties of magnetostrictive materials and magnetic storage materials,magnetocrystalline anisotropy energy is significantly affected by temperature.Therefore,the study on the theoretical characterization of temperature dependent magnetocrystalline anisotropy energy is helpful to the design and development of magnetic functional materials.In addition,with the rapid development of information science,in order to achieve higher storage density,people need to pursue the size of the memory point has been in the nanoscale.The physical properties of ferroelectric and ferromagnetic nanomaterials in different sizes are obviously different from that of bulk materials,and the existing theoretical models that characterize the effect of size on the physical properties for ferroelectric and ferromagnetic nanomaterials still need to be improved.Moreover,phase transition is a key problem in the process of preparing the corresponding materials.It is necessary to study the scientific problems related to the phase transition of ferroelectric and ferromagnetic nanomaterials at different sizes.It is of great theoretical significance and engineering application value to analyze the key material parameters affecting the phase change temperature at different sizes and its evolution with size,and establish a theoretical characterization model of size dependent phase change temperature.In this paper,the force-heat equivalence energy density principle is applied to the theoretical characterization of the properties for particle reinforced metal matrix composites,ferromagnetic,ferroelectric and superconducting materials.The corresponding theoretical characterization models of temperature dependent mechanical properties and temperature/size dependent physical properties are established.The specific research work is as follows:(1)Combined with the theoretical model of temperature dependent yield strength for metal materials established by the research group in the early stage and the existing strengthening theory applicable to room temperature,the evolution law of the main strengthening mechanism with temperature is studied,and a temperature dependent yield strength model of particle reinforced metal matrix composites without fitting parameters is established,which takes into account the comprehensive effects of load transfer strengthening,dislocation density strengthening,grain refinement strengthening and work hardening strengthening.It provides a new method for predicting yield strength at different temperatures.The model was used to analyze the variation law of the yield strength contribution of various strengthening mechanisms to the composites with the temperature,and study the effects of particle size on the main strengthening mechanisms and yield strength of composites.(2)In this study,it is assumed that there is an equivalent relationship between the magnetocrystalline anisotropy energy and the heat energy.A temperature dependent theoretical model of first order magnetocrystalline anisotropy constant without any fitting parameters for ferromagnetic metals is developed.The model establishes the quantitative relationship between temperature dependent first order magnetocrystalline anisotropy constant,heat capacity and volume expansion coefficient.The predicted results of our model are all in good agreement with the available experimental results of first order magnetocrystalline anisotropy constants at different temperatures for dysprosium,terbium,holmium,iron and cobalt.Compared with existing models,this study provides a more convenient and simple method to predict the first order magnetocrystalline anisotropy constant at different temperatures and the temperature where the first order magnetocrystalline anisotropy constant decreases to zero.(3)In this study,by establishing the equivalent relationship between interfacial energy and internal energy,a novel theoretical model without any fitting parameters is established to quantitatively characterize the influence of size on the critical transition temperature of nanocrystals.A good agreement between the predicted results of our model and experimental results of ferroelectric,ferromagnetic and superconductive nanocrystals which have been widely studied is obtained.The quantitative relationship between the size dependent critical temperature,melting enthalpy,melting point and atomic diameter is uncovered by the present model.Particularly,compared with the existing models,our model can more reasonably predict the change trend of V shape that the critical temperature of the transformation from ferromagnetism to paramagnetism decreases rapidly with the increase of the size when the size is less than a certain minimum value,and increases with the increase of the size when the size is larger than the value for ferromagnetic nanomaterials.Moreover,our model can more reasonably predict the critical size at which ferroelectric properties of ferroelectric materials disappear.This study provides a convenient and practical method to further explore the change law of critical temperature with size.