The microstructure in Y 2 O 3 -stabilized tetragonal zirconia polycrystal (Y-TZP) sintered at 1300°-1500°C was examined to clarify the role of Y 3؉ ions on grain growth and the formation of cubic phase. The grain size and the fraction of the cubic phase in Y-TZP increased as the sintering temperature increased. Both the fraction of the tetragonal phase and the Y 2 O 3 concentration within the tetragonal phase decreased with increasing fraction of the cubic phase. Scanning transmission electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) measurements revealed that cubic phase regions in grain interiors in Y-TZP generated as the sintering temperature increased. High-resolution electron microscopy and nanoprobe EDS measurements revealed that no amorphous layer or second phase existed along the grainboundary faces in Y-TZP and Y 3؉ ions segregated at their grain boundaries over a width of ϳ10 nm. Taking into account these results, it was clarified that cubic phase regions in grain interiors started to form from grain boundaries and the triple junctions in which Y 3؉ ions segregated. The cubic-formation and grain-growth mechanisms in Y-TZP can be explained using the grain boundary segregation-induced phase transformation model and the solute drag effect of Y 3؉ ions segregating along the grain boundary, respectively.

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ȬɋɐɲȪય‫ك‬ᓺᅀᇋɀɳȻɓȪএệᇋΧǽḩᨕіኝ◧Iᭀং ነ̡ӟ̘ɿগDŽЈ‫‬ɿগ⛡ᥴᗁɿ۱ᨀ⇠ೢଉ ɿ‫ڤ‬ғʶଉ ଉ ኇɅʀጋ‫ك‬༔‫⓯ݨ‬ƗȤࢫ746-8501 ୮‫ۑ‬᭔‫ٷܦ‬లϣ༔ᨊ 4560 ଉ ᴗ⒅შᗕ͆ᢼɿቦᄦᮾ᳣ᑿᐦቦᄦᮾ᳣ཀࢫ305-0047 ⇹᭔dzǞǿల٣ᥰ 1-2-1 ଉ ଉ ኇ̸গકগકрకકṾᮾ᳣ᲇἕ۰ᮾ᳣ᑿᐦࢫ113-8656 ኇ̸ȩᄙ̸ٚ೯᧯ 2-11-16The microstructure in 2.9 molಚ Y 2 O 3 -stabilized tetragonal zirconia polycrystal Y-TZP sintered at 1100c -1650c C was examined to clarify the role of Y 3ࢪ ions on the cubic-formation and grain growth processes. The cubic phase in Y-TZP stared to appear at 1300c C and the fraction of the cubic phase increased with the increasing sintering temperature. Scanning transmission electron microscopy and nanoprobe X-ray energy dispersive spectroscopy EDS measurements revealed that the Y 3ࢪ ion distribution in the grain interiors in Y-TZP was nearly homogeneous up to 1300c C and cubic phase regions in the grain interiors were formed clearly over 1300c C. The cubic phase region in the grain interior was extended as the sintering temperature increased. High-resolution electron microscopy and nanoprobe EDS measurements revealed that no amorphous layer existed along the grainboundary faces in Y-TZP, and Y 3ࢪ ions segregated at their grain boundaries over a width of ࣽ10 nm. The segregation peak of Y 3ࢪ ions was clearly seen at 1300c C, and above this temperature, Y 3ࢪ ions segregated at the grain boundaries not only between tetragonal grains but also between tetragonal and cubic grains. These results show that cubic phase regions started to be transformed from the grain boundaries andor the triple junctions in which Y 3ࢪ ions segregated. The cubic-formation mechanism in Y-TZP can be reasonably explained from the viewpoint of the Grain Boundary Segregation-Induced Phase Transformation model, and the grain-growth behavior is probably controlled by the solute drag effect of Y 3ࢪ ions segregating along the grain boundary.

The sinterabilities of fine zirconia powders including 5 mass% Y 2 O 3 were investigated, with emphasis on the effect of Al 2 O 3 at the initial sintering stage. The shrinkage of powder compact was measured under constant rates of heating (CRH). The powder compact including a small amount of Al 2 O 3 increased the densification rate with elevating temperature. The activation energies at the initial stage of sintering were determined by analyzing the densification curves. The activation energy of powder compact including Al 2 O 3 was lower than that of a powder compact without Al 2 O 3 . The diffusion mechanisms at the initial sintering stage were determined using the new analytical equation applied for CRH techniques. This analysis exhibited that Al 2 O 3 included in a powder compact changed the diffusion mechanism from grain boundary to volume diffusions (VD). Therefore, it is concluded that the effect of Al 2 O 3 enhanced the densification rate because of decrease in the activation energy of VD at the initial sintering stage.

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