Abstract: The processing of synthesizing nano Y-TZP materials by hot-pressing was investigated. It was found that there were large crack-like pores in the sintered samples. The
reason of this new phenomena was that the soft agglomerate in the powder was not efficiently destroyed. When sintered, the soft agglomerate sintered quickly
and turned into hard agglomerate, as a result of the interaction between the hard agglomerate and the matrix, large pores formed. On the other hand, the applied
pressure was limited because the low stress tolerance of the graphite die, so no plastic displacement could happen and those large pores could not be "squashed",
As a result, the density of the samples sintered by hot-pressing was lower than that by pressureless sintering at the same sintering temperature. To overcome this
shortage of hot-pressing, sinter-forging was applied and nano Y-TZP materials with grain size of about 85nm and relative density of 99% could be obtained when sintered at 1100℃.

Key words: hot-pressing, nano structured materials, Y-TZP