Enhanced Mechanical Properties of Al2O3 Nanoceramics via Low Temperature Spark Plasma Sintering of Amorphous Powders

Abstract

In this work, Al2O3 nanoceramics were prepared by spark plasma sintering of amorphous powders and polycrystalline powders with similar particle sizes. Effective comparisons of sintering processes and ultimate products depending on starting powder conditions were explored. To ensure near-full density higher than 98% of the Al2O3 nanoceramics, the threshold temperature in SPS is 1450 °C for polycrystalline Al2O3 powders and 1300 °C for amorphous powders. The low SPS temperature for amorphous powders is attributed to the metastable state with high free energy of amorphous powders. The Al2O3 nanoceramics prepared by amorphous powders display a mean grain size of 170 nm, and superior mechanical properties, including high bending strength of 870 MPa, Vickers hardness of 20.5 GPa and fracture toughness of 4.3 MPa∙m1/2. Furthermore, the Al2O3 nanoceramics prepared by amorphous powders showed a larger dynamic strength and dynamic strain. The toughening mechanism with predominant transgranular fracture is explained based on the separation of quasi-boundaries.

Alumina Ceramics for Armor Protection via 3D Printing Using Different Monomers

“…Considering that the major mechanism of deformation in brittle materials, including ceramics, is the propagation of cracks [ 41 , 42 ], in dynamic mechanical tests, the speed of crack propagation was much lower than the loading rate, and the cracks are unable to propagate quickly. The delay of crack propagation led to delayed sample fracture, achieving higher strength and strain values for the alumina ceramics at higher strain rates [ 43 , 44 ].…”

“…For ceramics with a bending strength of about 400 MPa, the compressive strength can be up to 2 GPa [9]. On the other hand, the compressive strength is much higher in dynamic tests than in quasi-static state due to the delay of crack propagation at high strain rates [43,44].…”