Bulk Nanostructured Zirconia Ceramics with High Hardness and Toughness via Integration of High-Pressure Torsion and Spark Plasma Sintering

TL;DR

This study combines high-pressure torsion and spark plasma sintering to produce nanostructured zirconia ceramics with high hardness and toughness, overcoming challenges of conventional sintering.

Contribution

It introduces a novel integration of HPT and SPS for nanostructured bulk zirconia with enhanced mechanical properties.

Findings

Achieved mean grain size of 80 nm in zirconia ceramics.

Demonstrated high hardness of 1500 Hv and good fracture toughness.

Observed phase transformations that contribute to mechanical performance.

Abstract

Developing nanostructured bulk ceramics is a major challenge when conventional high-temperature sintering is employed for consolidation. In the current investigation, yttria-stabilized zirconia (YSZ) with a composition of ZrO2 - 3 mol% Y2O3 is first treated using high-pressure torsion (HPT) and further consolidated using spark plasma sintering (SPS) to produce a nanostructured bulk sample. The material demonstrates phase transformations from tetragonal to dislocation-decorated monoclinic by HPT and reversely transforms to the tetragonal phase after the SPS process while maintaining a mean grain size of 80 nm and large numbers of dislocations. The consolidated ceramic exhibits a density of 6.07 g/cm3 (99% relative density) with a high hardness of 1500 Hv, which is reasonably consistent with the prediction of the Hall-Petch relationship. Examination of the indented areas during the hardness test confirms the absence of cracks, indicating good fracture toughness (KIC) because of the presence of dislocations, while the sample processed only by SPS and without HPT processing forms numerous cracks by indentation and exhibits low KIC.