Porosity distribution and stress concentration in ZrN as a surrogate for PuN: Comparisons between 2-D and 3-D measurements and models

A serial sectioning process was used to develop a three-dimensional (3D) representation of the microstructure of a ZrN dense pellet sintered in Argon at 1600°0C Twenty five two-dimensional (2D) images of the microstructure obtained by imaging with an optical microscope at 200X (slides spaced 2μm apart from each other) were used as a basis for reconstructing the 3D microstructure of the ceramic for structural modeling. This representation allows the quantification of the spatial distribution of porosity in the samples as well as the creation of a three-dimensional finite-element model (FEM) that accounts for effects of the presence of pores in structural behavior. Furthermore, another model was obtained using 3D Computer Aided Design (CAD) software to simulate stress-strain behavior of the reconstructed volume subjected to tensile stress and study critical regions for stress concentration. Correlations of the 3D models with existing 2D models and experimental results obtained at Los Alamos National Laboratory (LANL) show that there is good correlation among experimentally measured pellet density and 2D as well as 3D estimations of porosity. It was also found that the highest stress concentrations occur at the grain boundaries, both in the 2D and 3D models. Work supported under the Global Nuclear Energy Partnership (GNEP) and the Advanced Fuel Cycle Initiative (AFCI), DOE/NE Agreement # DE-FC07-05ID14654.