Rajendra K. Bordia, Eugene Olevsky*, Christophe Martin**

Clemson University, USA
*Diego State University, USA
**DUniv. Grenoble Alpes, CNRS, SIMaP, Grenoble F-38000, France

In many cases, a porous body is subjected to non-hydrostatic stresses during sintering. Two practically important cases are sintering under external uniaxial stress (sinter-forging) and constrained sintering of ceramic coatings and films. In this talk, the densification and evolution of the microstructure, during sinter-forging and constrained sintering, will be discussed. For these cases, although the stress state is different, there is an equivalence in the strain state.

Experimentally and using multi-scale, we show that the pore shape evolution during stress assisted sintering is dependent on the size of the pore. We define two types of pores – intrinsic small inter-particle pores, and extrinsic significantly larger than the intrinsic pores. We present experimental results on the development of pore shape anisotropy during sintering under nonhydrostatic stresses of ceramics containing both type of pores. The effect of stress on the microstructure is investigated. As expected during sintering under non-hydrostatic stress, the pore shape becomes anisotropic and the pores orient preferentially. However, the orientation of the pores, depends on both the size of the pores (intrinsic or extrinsic) and the anisotropic nature of the strain. Multiscale numerical simulations provide insights into the origin of this behavior. Based on these results, we also provide a fundamental definition of the transition pore size – pore size at which the behavior changers from intrinsic to extrinsic.