SJi et al. / Journal of the European Ceramic Society 25(2005)301-317 been carried out on monolithIc CAS and other plagio- clase feldspars under uniaxial compression(o1>02 o3=0)at ambient pressure, -ll it remains uncertain if the results from small strain creep tests are able to be apolated to other conditions because a small amount of strain is usually insufficient for steady-state microstruc ture to occur. 12 Cavitation often occurs in the sam- ples deformed at ambient pressure. -Furthermore the application of CAs-based ceramic composites to high temperature and high pressure environment was largely hinder ab aural any y little knowledge of me- CAS-based composites from laboratory tests. (2)CAS crystal is triclinic with the lowest crystallographic symmetry. The relative activity of different slip systems and dynamic recrystallization in dislocation creeping 目 CAS under varying physical and chemical conditions are still poorly known. The investigation of CAs mi- crostructure and texture can further our understanding of plastic deformation mechanism and textural devel- opment in triclinic crystalline materials. In spite of its importance, CAS has a much smaller textural database than other crystalline materials such as metals and min- erals(mainly olivine, quartz and calcite). Reasons for this are purely technical because CAs is triclinic crystallographic orientations of CAs cannot be deter- mined using conventional X-ray due to the large number of overlapping diffraction peaks. The texture of triclinic albite(NaAlSi3Os) has been measured by employing synchrotron X-ray goniometry, 7 but this technique is expensive and not widely available. Neutron diffraction goniometry has been applied to the measurements of ICAS plagioclase texture, 18,19 however, relatively large vol- umes of sample material (l cm' which is often larger 的数山m than most of samples deformed experimentally Fig 1. Photograph(a) and photo raph(b)of a hot isostatical pressed are needed for this type of measurements because layered Qtz-CAS composite neutron flux densities are generally low. CAS texture an be determined but its grain size should be larger than 20-30 um and and sharp interfaces(Fig. 1), which was created during cold the measurement is time-consuming. Recently, it was pressing and subsequently thinned during HIP. The layering shown that the most powerful technique for success- in cylindrical LC samples is characterized by the ratio of the fully measuring texture of triclinic crystals is electron diameter() to the thickness(h)of material layers. The PC backscattering diffraction(EBSD) equipped in a scan- is a homogeneous mixture of equal volume fraction of Qtz ning electron microscope(SEM).21-23 Thus, this new and CAS(Fig 2a) technique was used in collecting representative CAs Commercial powders of CAS(An98. Oro.2Abo. ) glass texture from our deformed samples (Schott GmbH, Germany) and quartz Johnson-Matthey GmbH, Germany) were used as the starting material The same Cas glass powder has been used in previous 2. Samples studies. 16,22 The CAS glass powder with particle size less than <60 um was first predried in an oven at a constant Four categories of samples were prepared, using hot iso- temperature of 393k for at least 100 h to drive off ad- atic pressing(HIP)techniques, for mechanical tests. They sorbed water. The powder was then encapsulated into a are layered composites (LC, Fig. 1), particulate composites steel jacket(= 15 mm, I= 25 mm) and cold-pressed (PC, Fig 2a) of quartz(Qtz)and CAs, and the pure CAs under an axial stress of about 150 MPa. Each cold-pressed (Fig 2b)and Qtz(Fig. 2c)polycrystalline aggregates. The pellet was HIPed and statistically annealed at 1123K for LC contains alternating Qtz and CAS layers with strong I h, 1323 K for I h and then 1473 K for 3 h at a confin-302 S. Ji et al. / Journal of the European Ceramic Society 25 (2005) 301–311 been carried out on monolithic CAS and other plagio￾clase feldspars under uniaxial compression (σ1 > σ2 = σ3 = 0) at ambient pressure,5–11 it remains uncertain if the results from small strain creep tests are able to be ex￾trapolated to other conditions because a small amount of strain is usually insufficient for steady-state microstruc￾ture to occur.12 Cavitation often occurs in the sam￾ples deformed at ambient pressure.5–11 Furthermore, the application of CAS-based ceramic composites to a high temperature and high pressure environment was largely hindered by the relatively little knowledge of me￾chanical, microstructural and textural data of CAS and CAS-based composites from laboratory tests.11,13–16 (2) CAS crystal is triclinic with the lowest crystallographic symmetry. The relative activity of different slip systems and dynamic recrystallization in dislocation creeping CAS under varying physical and chemical conditions are still poorly known. The investigation of CAS mi￾crostructure and texture can further our understanding of plastic deformation mechanism and textural devel￾opment in triclinic crystalline materials. In spite of its importance, CAS has a much smaller textural database than other crystalline materials such as metals and min￾erals (mainly olivine, quartz and calcite). Reasons for this are purely technical because CAS is triclinic. Full crystallographic orientations of CAS cannot be deter￾mined using conventional X-ray due to the large number of overlapping diffraction peaks. The texture of triclinic albite (NaAlSi3O8) has been measured by employing synchrotron X-ray goniometry,17 but this technique is expensive and not widely available. Neutron diffraction goniometry has been applied to the measurements of plagioclase texture,18,19 however, relatively large vol￾umes of sample material (>1 cm3 which is often larger than most of samples deformed experimentally8–11) are needed for this type of measurements because neutron flux densities are generally low. CAS texture can be determined using optical U-stage method18,20, but its grain size should be larger than 20–30
m and the measurement is time-consuming. Recently, it was shown that the most powerful technique for success￾fully measuring texture of triclinic crystals is electron backscattering diffraction (EBSD) equipped in a scan￾ning electron microscope (SEM).21–23 Thus, this new technique was used in collecting representative CAS texture from our deformed samples. 2. Samples Four categories of samples were prepared, using hot iso￾static pressing (HIP) techniques, for mechanical tests. They are layered composites (LC, Fig. 1), particulate composites (PC, Fig. 2a) of quartz (Qtz) and CAS, and the pure CAS (Fig. 2b) and Qtz (Fig. 2c) polycrystalline aggregates. The LC contains alternating Qtz and CAS layers with strong Fig. 1. Photograph (a) and photomicrograph (b) of a hot isostatical pressed layered Qtz–CAS composite. and sharp interfaces (Fig. 1), which was created during cold pressing and subsequently thinned during HIP. The layering in cylindrical LC samples is characterized by the ratio of the diameter (d) to the thickness (h) of material layers. The PC is a homogeneous mixture of equal volume fraction of Qtz and CAS (Fig. 2a). Commercial powders of CAS (An98.9Or0.2Ab0.9) glass (Schott GmbH, Germany) and quartz (Johnson-Matthey GmbH, Germany) were used as the starting materials. The same CAS glass powder has been used in previous studies.16,22 The CAS glass powder with particle size less than <60
m was first predried in an oven at a constant temperature of 393 K for at least 100 h to drive off ad￾sorbed water. The powder was then encapsulated into a steel jacket (φ = 15 mm, l = 25 mm) and cold-pressed under an axial stress of about 150 MPa. Each cold-pressed pellet was HIPed and statistically annealed at 1123 K for 1 h, 1323 K for 1 h and then 1473 K for 3 h at a confin-