Effect of 1 wt% LiF additive on the densification of nanocrystalline Y_2O_3 ceramics by spark plasma sintering

摘要

Densification of nanocrystalline cubic yttria (nc-Y_2O_3) powder, with 18 nm crystal size and 1 wt% LiF as a sintering additive was investigated. Specimens were fabricated by spark plasma sintering at 100 MPa, within the temperature range of 700-1500 °C. Sintering at 700 °C for 5 and 20 min resulted in 95% and 99.7% dense specimens, with an average grain size of 84 and 130 nm, respectively. nc-Y_2O_3 without additive was only 65% dense at 700 °C for 5 min. The presence of LiF at low sintering temperatures facilitated rapid densification by particle sliding and jamming release. Sintering at high temperatures resulted in segregation of LiF to the grain boundaries and its entrapment as globular phase within the fast growing Y_2O_3 grains. The sintering enhancement advantage of LiF was lost at high SPS temperatures.