Research Of The Rmal-elastic-diffusion Theory Combine With Phase Field Method

Current assisted sintering technology have advantage of heating fast,short sintering time,high density and less internal defect,which make it widely used in manufacture of ceramic materials,functional gradient materials and nanometer materials.The green body and compaction powder could achieve high density after a short period of time sintering under high temperature and high temperature gradient which caused by thousands Ampere current through the mould.Although this technology has been developed quickly,the sintering mechanism is still in dispute.As for non-conductive powder,pulse electric current sintering process could be treated as microstructure evolution problems under applied pressure,high heating rate and temperature gradient,the quantitative description of thermal-elastic-diffusion coupling effect and numerical calculation are keys to that problem.In this work,the classical thermo-elastic-diffusion coupling equations in equilibrium states are extended to the non-equilibrium status combining with Phase Field method to simulate a full coupling thermo-elastic-diffusion in non-isothermal process without phase transition.Thermodynamic and kinetic coefficients are chosen through the parametric analysis of the asymptotic phase interface to meet the requirements of sharp interface model.This method could evaluate the interaction influence between temperature,deformation and concentration in the process of microstructural evolution.As an example,a four-sphere diffusion model under heating and applied pressure is utilized to simulate microstructural evolution.More over,in view of the non-Fourier heat conduction problem through diffusion interface,the influence of introducing diffusion interface on temperature field distribution are discussed.Basing on non-Fourier heat conduction law,the temperature distribution through the sharp interface and that through diffusion interface are compared in the paper,and the characteristics of temperature field of three different diffusion interface interpolation schemes are analyzed.Then,the influence of different interpolation schemes on diffusion driving force are analyzed.This paper is described as the following.In first chapter,we briefly introduce the research of the thermal-elastic-diffusion coupling theory and sintering numerical simulation method of SPS technology,and have a synopsis of this paper.In second chapter,the theory of thermal-elastic-diffusion considering non-equilibrium state is introduced and verifies the generalized thermodynamic compatibility by numerical method.In third chapter,a typical four sintered powder particle model is introduced to analysis the coupling effect between temperature,concentration and stress under the condition of different applied pressure and temperature boundary condition.The results show that stress field has little influence on diffusion,while the stress change caused by the concentration change in the diffusion behavior is obvious.On the other hand,the temperature and temperature gradient have a significant influence on the evolution,and the temperature field is not sensitive to the change of concentration field.In forth chapter,for non-Fourier heat conduction problem containing diffusion interface,the influence on temperature field distribution of three different numerical schemes are analyzed,and the stability of our thermal-elastic-diffusion coupling theory under different numerical treatment schemes is discussed.The distribution of temperature field near the diffusion interface would be significantly changed by different interpolation schemes under non-fourier heat conduction law,which greatly changes the local thermal stress.While the the different numerical treatment scheme of diffusion interface has little influence on the microstructure evolution process which is solving by our thermal-elastic-diffusion coupling theory,and it it proved the stability of our coupling theory.