Microstructure, mechanical properties and machining performance of spark plasma sintered Al2O3-ZrO2-TiCN nanocomposites

The effect of addition of nanocrystalline ZrO2 and TiCN to ultrafine Al2O3 on mechanical properties and microstructure of the composites developed by spark plasma sintering (SPS) was investigated. The distribution of the nanoparticles was dependent on their overall concentration. Maximum hardness (21 GPa) and indentation toughness (5.5 MPa m1/2) was obtained with 23 vol% nanoparticles, which was considered as the optimum composition. The Zener pinning criteria were also satisfied at this composition with grain size of the restraining nanoparticles ∼63-65 nm. Hardness of the composites follows the rule of mixtures; crack deflection and crack arrest by nanoparticles at grain boundaries along with mixed fracture mode led to high toughness in the nanocomposites. Cutting tool inserts were developed by SPS with the optimized composition and their machining performance was compared with commercial alumina based inserts. Increased toughness in the nanocomposite inserts reflects in the machining performance as the tool life improves drastically compared to that of the commercial inserts at high cutting speeds ≥500 m min−1. This was attributed to differences in their failure modes; the commercial inserts fail catastrophically by fracture due to their low toughness whereas the nanocomposite inserts reach the tool failure criteria by crater wear at all machining conditions.