In-situ SEM micropillar compression of porous and dense zirconia materials

The reduction of failure rates of small-sized zirconia devices depends on the understanding of their micro mechanical properties. This paper reports the micromechanical behaviors of porous and dense zirconia materials using in-situ micropillar compression with a flat diamond indenter in a scanning electron microscope (SEM). Porous and dense zirconia micropillars were made using focused ion beam (FIB) milling technique in the SEM. They were then subject to in-situ SEM compression to identify their Young's moduli, yield stresses, plastic deformation, compressive and fracture strengths, damage accumulations, and failure mechanisms. We found that while both porous and dense zirconia microstructures exhibited plastic behaviors, the former had much lower Young's moduli, strengths (yield, compression and fracture), resilience and toughness but higher ductility, resulting in significant buckling than the latter. In plastic regions, alternative strain softening and hardening may have caused stress variations in porous zirconia while dislocation movement contributed to strain hardening in dense zirconia. Although both zirconia materials had quasi-brittle failures, there were different damage mechanisms. The quasi-brittle failure for porous state was due to mushrooming buckling damage driven by breaking of weak interconnected pore networks, resulting in severe compaction and pulverization, microcracks and material piling. The quasi-brittle failure for dense state was identified as plastic crushing damage, involving microcrack initiation and propagation, cleavage and intergranular fractures, and delamination. The mechanical properties of porous and dense zirconia micropillars investigated contributed to the knowledge on deformation and damage mechanisms of zirconia materials at the small scale.