Grain growth stagnation in fully dense nanocrystalline Y2O3 by spark plasma sintering

Nanocrystalline (nc) Y2O3 powders with 18 nm crystallite size were sintered using spark plasma sintering (SPS) at 1100 °C and 100 MPa for different durations. Specimens with 98% density and 106 ± 33 nm mean grain size were formed after 20 min. The grain size at the final stage of sintering first increased and then tended to stagnation with the SPS duration. The nanostructure consisted of convex tetrahedron shaped nano-pores at part of the grain boundary junctions. Theoretical calculations were made for grain growth stagnation imposed by either drag from nano-pores at grain junctions or from dense triple junctions; the experimental results were in agreement with grain growth stagnation due to nano-pore drag in nc-Y2O3. The conditions for the stabilization of the nanostructure in Y2O3 were determined. Extended SPS duration up to 40 min led to sudden grain coarsening and loss of the nanocrystalline character.