Automated crystal orientation mapping - a new tool for ceramic composites investigations
Marek Faryna Uniwesytet Jagielloński, Środowiskowe Laboratorium Analiz Fizykochemicznych i Badań Strukturalych, ul. Ingardena 3, 30-060 Kraków
Annals 2 No. 5, 2002 pages 267-272
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abstract Automated crystal orientation measurements preformed by use backscattered diffraction (EBSD) in the scanning electron microscope (SEM) (Fig. 1) provided the basis for a quantitative investigation of microstructure in an yttria stabilised, tetragonal zirconia-based (Y-TZP) composites. This technique known also as orientation imaging microscopy (OIMTM) can be preferable to transmission electron microscopy (TEM) for microstructural characterisation, since no sample thinning is required, extensive crystal data is already available, and the analysis area is greatly increased. Two carbides, mainly TaC and NbC, chemically stable in relation to the zirconia, have been selected as reinforcing inclusions. The incorporation of carbides, showing similar mechanical properties, into the Y-TZP matrix leads to ceramics of significantly better mechanical properties (Tab. 1). The way of explaining such a phenomenon is to investigate crystallographic relationships between oxide and carbide phases which influence the strength of the interphase boundaries and, finally, lead to the increase of fracture toughness and wear resistance of the composites. Several such crystallographic relationships have been found. Examples of stereographic projections of different crystallographic directions have been presented (Figs 2 and 3) and misorientation distribution functions (NDFs) for both phases (e.g. Fig. 4) have also been calculated. However, such composites were difficult to investigate in the EBSD/SEM since there are non-conductive, the Y-TZP grain size, in some cases, of order of system resolution, and the sample surface, though carefully prepared, reveals a distinctive microtopography. In this paper, some useful solutions have been given to omit these problems. The data confirming, crystallographic relationships, established previously by TEM, investigations, have also been presented. Electron backscattered diffraction is also an essential tool for measuring the amount of coincident site lattice (CSL) boundaries. Figure 5 shows an example of such measurements, mainly the fraction of CSL boundaries formed in the Y-TZP/NbC composite.