Study Of Grain Growth And Diffusion Phase Field Method In Solid-state Sintering Process

Solid state sintering is a process in which pressed powder is gradually transformed into a solid whole with a certain geometric shape by means of particle adhesion and material transfer between bodies under the action of high temperatures below the melting point,resulting in pore discharge,volume contraction,and strength improvement.Sintering technology has played an important role in many fields such as science and technology,industry,medical treatment,aviation,and so on.However,factors such as the physical and chemical properties,particle size distribution,shape characteristics,and temperature distribution of the sintered material system all affect the sintering process.Therefore,in order to produce high-performance sintered materials,it is necessary to understand the evolution of microstructure during the sintering process,in order to make more targeted improvements to the sintering technology.In this paper,the phase field parameters during the sintering process,the effects of inert particles,and temperature on grain growth were studied using a twin crystal and polycrystalline phase field model.The reasons for the changes in grain microstructure during the sintering process were analyzed from the perspectives of neck length,small grain change rate,and average grain size.The phase field dynamics equations are solved by the finite difference method.The main conclusions are as follows:Surface diffusion is the dominant mechanism for neck formation,and grain boundary diffusion plays an auxiliary role in the neck formation stage;Increasing grain boundary mobility only accelerates grain boundary migration and does not affect the neck growth stage;The chemical free energy coefficient does not affect the grain morphology,but has a significant impact on the final equilibrium configuration;The larger the gradient energy coefficient,the longer the neck length,and the faster the neck growth rate.Inert particles in different spatial positions will cause different grain morphology,and when inert particles are located above the matrix,the grains will grow obviously abnormally.When the inert particles are located at the diagonal of the matrix,the abnormally grown grains are obviously better than those when the inert particles are distributed above the matrix.When inert particles are uniformly distributed in the matrix,the grain size is relatively consistent;There is a critical value for the volume fraction of inert particles.Too little inert particles can promote the grain growth,while too much inert particles can not obviously improve the grain refinement effect.The larger the radius of inert particles is,the weaker the hindrance to grains,while the smaller the radius of inert particles is,the stronger the pinning effect on grains,which is the result of the competition between particle size and particle number.In the case of coupled temperature field,the growth rate of neck is accelerated;The higher the temperature,the larger the average grain size;The neck growth rate and the maximum neck length increase with the increase of thermal diffusion coefficient.