固相烧结——Ⅰ气孔显微结构模型及其热力学稳定性,致密化方程

SOLID STATE SINTERING I——PORE MICROSTRUCTURAL MODEL AND THERMODYNAMIC STABILITY,DENSIFICATION EQUATIONS

讨论了二维及三维闭口气孔的稳定性，发现二维状态时气孔的稳定性问题可以用数学方法根据气孔的颗粒配位数和二面角的大小解析；而三维状态时气孔则可借助球形气孔模型近似地确定。在这一模型的基础上，建立了烧结中期和后期的气孔显微结构模型，并由此推导了固相烧结中、后期作用于气孔的烧结应力和固相烧结中期和后期的致密化方程。根据所推导的致密化方程，得到了烧结中期和后期的气孔收缩判据。讨论了气孔尺寸分布，素坯密度和烧结后期包裹气体对致密化的影响。描述无压烧结的致密化方程经一定的变化可以容易地用于描述热压和热等静压烧结的致密化过程。

The stability of closed pores in 2 and 3dimension is discussed.It is found that stability of pores in 2dimension can be determined mathematically based on their particle coordination number and dihedral angle;while stability of those in 3dimension can be approximately determined by a spherical pore model.This model is set up by first excluding the effect of interface tension,so the pore is supposed to be spherical,and then the tensile stress induced by interface tension is supposed to act on this hypothesized spherical pore.On the basis of the spherical pore model,pore microstructure models for the intermediate and final stages of sintering have been set up;while on the basis of the pore microstructure models, densification equations are derived for the above stages of sintering.With the models and the derived densification equations,the criteria of the pore stability both in the intermediate and final stages of sintering are obtained.The effects of pore size distribution,green densitiy and the entrapped pore gas pressure in the final stage of sintering are discussed.The densification equations for pressureless solid state sintering can be easily extended for describing the densification behaviour during hot pressing or hot isostatic pressing.