Papers by Keyword: Bridgman Growth

Abstract: Formation of microstructure defects at the phase boundaries in TRIP steels was investigated with the aid of microstructure analysis on a TRIP steel crystal, which was grown by the Bridgman technique. The microstructure studies comprised scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and transmission electron microscopy with high resolution (HRTEM). Initial XRD measurements revealed that the crystals under study consist of austenite and ferrite with extremely strong preferred orientations. Subsequent XRD pole figure measurements and EBSD scans have shown that the orientation relationship between austenite and ferrite can be described by the Nishiyama-Wassermann model. For a detailed description of the microstructure of the Bridgman crystal, the orientation distribution of crystallites within the individual phases was investigated using the XRD reciprocal space mapping and the rocking curve measurements. These experiments have shown that the density of microstructure defects is much lower in ferrite than in austenite. The direct information about the defect structures at the phase boundaries between austenite and ferrite was obtained from the TEM micrographs, which revealed complicated micro-twin structures at the boundaries between the neighbouring phases. HRTEM discovered very narrow stripes of ferrite embedded in austenite that were regarded as a source of the microstructure defects in austenite.

Abstract: The influence of the CO concentration in the gas phase on the distribution of carbon in Bridgman-grown, multicrystalline silicon is studied. The growth experiments were conducted in a high-vacuum induction furnace either under a CO enriched atmosphere or under CO free conditions. Furthermore, thermodynamic calculations in the system silicon/oxygen/carbon were done. In crystal growth under a CO enriched atmosphere a SiC-containing layer is formed on the top surface of the melt in agreement with the calculated phase diagram. In this case, the level of substitutional carbon in the cystal was found to be almost constant, whereas the axial carbon concentration in crystals grown under CO free conditions increases monotonously according to Scheil's law.