A general method to determine optimal thermal cycles based on solid-state sintering fundamentals

Abstract

Most technical ceramics require processing up to and including final-stage sintering to obtain a high-density bulk while inhibiting grain growth as dominant sintering process as far as possible. The literature typically highlights the qualitative interdependence of the sintering variables and microstructural parameters, focusing on very simple particulate systems. However, a quantitative method to achieve optimum sintering of actual polycrystalline solids is still lacking.This paper puts forward such a method, which has been satisfactorily tested by the authors. The method consists of a mathematical model, based on the physical phenomena that take place during solid-state sintering. The method leads to two differential equations: a densification rate and a pore-dragged normal grain growth rate equation during final-stage sintering, which mainly depend on sintering temperature and shaping conditions. Simultaneous numerical integration of these two rate equations allows design of an optimal thermal cycle (enhancing densification and controlling grain growth) to obtain the targeted sintered polycrystalline microstructure. Application of this method yields staggered thermal cycles, in addition to the number of steps, as well as the sintering temperature and dwell time in each step.