Theoretical modeling of densification during activated solid-state sintering
Theoretical modeling of densification during activated solid-state sintering
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DOI：
10.1007/bf02648421
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发表时间：
1996-02-01
影响因子：
2.8
通讯作者：
German, RM
中科院分区：
文献类型：
--
作者：
Johnson, JL;German, RM
活化固态烧结依赖于添加低浓度的晶界偏析物质来增加扩散速率。在这篇文章中，增强扩散通过激活层在晶界已被建模的情况下，钨烧结过渡元素添加。恒定升温速率和等温烧结被认为是。在经典的治疗，烧结分为三个阶段，但修改建议的基础上，最近的观察和理论，包装协调，孔隙形态，孔隙位置，晶粒生长，和孔隙-晶界分离。允许烧结的中间和最终阶段基于闭合孔隙率的量重叠，以解释过程中早期的孔隙闭合和填充协调与致密化的逐渐增加。采用平均曲率理论估算烧结中间阶段的气孔曲率。在最后阶段中，在四面体的角和其正方形小平面上对孔隙进行建模。孔隙位置对致密化的影响很小，而晶界流动性是一个更重要的因素。该模型允许孔隙晶界分离，以匹配实验测量的晶粒尺寸。模型预测进行比较，纯钨和钨烧结添加钴，铁，镍，和钯的电阻曲线。对于Co和Fe活化的样品，该模型被修改，以占扩散活化能的增加，由于在钨中的活化剂的溶解。
Activated solid-state sintering relies on the addition of low concentrations of grain boundary segregating species to increase diffusion rates. In this article, enhanced diffusion through an activated layer at the grain boundaries has been modeled for the case of tungsten sintered with transition element additions. Both constant heating rates and isothermal sintering are considered. As in classical treatments, sintering is divided into three stages, but modifications are proposed based on recent observations and theories regarding packing coordination, pore morphology, pore location, grain growth, and pore-grain boundary separation. The intermediate and final stages of sintering are allowed to overlap based on the amount of closed porosity to account for both pore closure early in the process and the gradual increase in packing coordination with densification. Mean curvature theory is used to estimate pore curvature during the intermediate stage of sintering. In the final stage, pores are modeled on both the corners of a tetrakaidecahedron and on its square facets. The pore location has only a small effect on densification, while the grain boundary mobility is more of a factor. The model allows pore-grain boundary separation to match experimentally measured grain sizes. The model predictions are compared to dilatometer curves of pure tungsten and tungsten sintered with additions of Co, Fe, Ni, and Pd. For the Co- and Fe-activated samples, the model is modified to account for an increase in diffusional activation energy due to dissolution of the activator in tungsten.