Preparation of Y‐TZP Nanoceramics by Gelcasting‐Pressing Method and Pressureless Sintering

Abstract

There is worldwide interest in the Y-TZP (tetragonal zirconia polycrystals stabilized by yttria) nanoceramics, which are believed to have some special characteristics such as superplasticity at low temperature. [1] However, fabrication of dense bulk nanocrystalline ceramics is very challenging since inevitable grain growth occurs at relatively high sintering temperatures needed for densification. The fabrication process usually involves forming and sintering. Duran and other researchers [2][3][4][5][6] have shown that green compacts with homogeneous microstructure, small pore size and narrow pore size distribution are necessary to ensure the low temperature sintering. Therefore, one main objective in a forming process is to produce uniform green body with homogeneous microstructure, small pore size and narrow pore size distribution. Previous studies have indicated that microstructural defects such as delamination, microcracks and large pores in the product are caused at drying forming. Recently, colloidal forming processes such as gelcasting [7] and direct coagulation casting (DCC), [8] in which ceramic powder is dispersed in a water-based suspension and held in a gel network, have attracted great interest. Among these methods, the gelcasting has significant advantages over the other processes, in terms of dimensional accuracy, the uniform structure and high strength of the green bodies, simplicity, and as well reduced manufacturing cost. Gelcasting has rapidly developed in the past decade as a promising colloidal in situ forming technique. It has been utilized in the forming of many sorts of ceramic material systems. [9][10][11][12] However, few reports about the use of this method for nanoceramics are found in the literature.Though gelcasting forming processes can improve the uniformity of green bodies and reduce structural defects but because of some characteristics of the nano powders itself, it is very difficult to preparation of a concentrated suspension with high solid volume loading in gelcasting, therefore the density of the green body is unsatisfactory. An optimal approach would be a combination of gelcasting and dry pressing processes, bringing together their advantages. Based on this concept, a new ceramics-forming process, gelcastingpressing, is developed by the authors.In addition, lots of methods, including hot-pressing, sinter-forging, hot-isostatic pressing and spark plasma sintering, have been used to fabricate nano-ceramics. [13][14][15] Among these methods, pressureless sintering is still a most promising one because of its low cost and easy technique. In this work, Y-TZP nanoceramics were prepared by gelcasting-pressing and pressureless sintering, while the microstructure, the pore distribution and sintering behavior of the green body were studied.Characteristics of powders and green bodies. Characteristics of nano-powders: The X-ray diffraction (XRD) patterns of nanopowders calcinated at different temperatures for 2 h are shown in Figure 2. It is seen that there is no diffraction peaks and t...

Fabrication of complex-shaped Y-TZP/Al2O3 nanocomposites

“…The washed precipitates mentioned above were dried in an oven for 24 h and calcined at 1200 • C for 2 h. After that, the product was then ground in an agate mortar, and nano-sized powders were obtained. The complex-shaped Y-TZP/Al 2 O 3 nanocomposites were prepared by gelcasting (Zhang et al, 2005(Zhang et al, , 2006b; the flow chart of the proceeding is outlined in Fig. 1.…”

“…On this basis, Y-TZP nanoceramics were prepared successfully using gelcasting-pressing and pressureless-sintering by the authors (Zhang et al, 2005(Zhang et al, , 2006b. In this work, complex-shaped Y-TZP/Al 2 O 3 nanocomposites were prepared by gelcasting and pressureless-sintering, while the microstructure and the sintering behavior of the green body were studied.…”

Densification and Phase Transformation During Pressureless Sintering of Nanocrystalline ZrO2–Y2O3–CuO Ternary System

“…Thus, it seemed interesting to prepare ZrO 2 (3Y)‐based mixed oxides and to study their structural and sintering behavior. Similar materials are also of interest in the field of preparation of Y‐TZP based ceramics as engineering materials 4–7 …”

“…In addition, a number of methods, including hot‐pressing, sinter‐forging, hot‐isostatic pressing, and spark plasma sintering, have been used to fabricate nanoceramics 14–16 . Among these methods, pressureless sintering is still the most promising one because of its low cost and easy technique 4–6 . In this work, ZrO 2 –Y 2 O 3 –CuO nanosized powders with various CuO contents have been synthesized by the chemical coprecipitation technique.…”

“…Similar materials are also of interest in the field of preparation of Y-TZP based ceramics as engineering materials. [4][5][6][7] Hwang and colleagues [8][9][10][11][12][13] studied the processing, microstructure, and tribology of coarse-grained CuO doped commercial 3Y-TZP composite ceramics. Their results showed that this group of materials has attractive properties such as superplastic behavior at elevated temperature and low friction coefficients under dry sliding conditions.…”