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| Malcharcziková J., Pešička J., Kursa M. |
| STRUCTURAL AND MICRO-STRUCTURAL ANALYSIS OF DIRECTIONALLY CRYSTALLISED INTER-METALLIC COMPOUND Ni3Al REALISED BY TEM |
Abstract
Structural and micro-structural analyses were performed on samples of Ni3Al with aluminium content of 25 at.%. Method of directional crystallisation was used for modification of their as-cast structure, as this method can influence structure and therefore also properties of final material. The samples were prepared by casting in vacuum induction furnace. Cast rollers with diameter 10 mm and length 95 mm were afterwards directionally crystallised by Bridgman method with vertical arrangement. Part of samples was prepared at the Department of non-ferrous metals, refining and recycling at VŠB-TU Ostrava, and remaining part of the samples was melted into electro-corundum tubes with specified apex angle on special equipment in Vladimir (Russia). Various rates of directional crystallisation were used for verification of the most suitable conditions for obtaining of homogenous structure. Suitable samples were adjusted by turning to tensile rods, which were then used for tensile tests with measurement of acoustic emissions. For these tests there were used short tensile rods of round section with length 55 mm and with diameter of central part of the rod 5 mm. During all measurements there was monitored intensive acoustic emission with characteristic dependence on time and with correlation to individual stages of deformation. The samples 139.2 and 139.3 show substantial improvement of ductility in comparison with normally prepared materials of this type. Metallographic evaluation was made on cross sections and longitudinal sections. Some of the formed structures are highly homogenous. In samples melted in electro-corundum tubes with specified angle a structure containing dislocation walls in the matrix was formed. Structure of samples was minutely analysed with use of transmission electron microscopy. Dislocation density in deformed and non-deformed state was determined on prepared foils.
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| Keywords: Ni-Al based intermetallic compounds|tensile tests|transmission electron microscopy|dislocation density| |
| No 4 (2007), p. 503-510 |
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