By the emission electron microscope a high-contrast picture of grain structure is obtained with thermal or photoelectric release of electrons. The "memory effect" (MORLIN, TREMMEL) marks the individual steps of the grain boundary movement through volume expansion or thermal etching when releasing electrons by electrons or ions. The existence of an oxide layer on the surface of e.g. molybdenum and tungsten is starting the recrystallization and influencing the recrystallization temperature. Oxide layers are formed in selected areas corresponding to the distribution of surface seeds and the oxygen bombardment. Carbon atoms accumulate preferably at the grain boundaries as carbides, so decorating the crystallites in forming mixed crystals. -It may be assumed that the carbon solved in tungsten and molybdenum fixes the dislocations a t the grain boundaries. I n contradiction to all theories of secondary recrystallization "ring crystals" are formed. Mit Hilfe des Emissionselektronenmikroskops werden bei thermischer oder photoelektrischer Elektronenauslosung kontrastreiche Abbildungen des Korngefuges erhalten. Das ,,Elrinnorungsvermogen" (MORLIN, TREMMEL) h41t bei Elektronenauslosung durch Ebktronen oder Ionen die einzelnen Schritte des ..Kernwachstums durch unterschiedliche Volumenausdehnung oder thermische Atzunq fest. Die Anwesenheit einer Oxidschicht auf der Oberfliiche von z. B. Molybdan und Wolfram lost die Rekristallisation aus und beeinflul3t deren Temperatur. Die Oxidschichten werden in gesonderten Oberfliichengebieten, die zur Verteilung der Oberfliichenkeime und des Sauerstoffbeschusses in Beziehung stehen, gebildet. Die Kohlenstoffatome reichern sich vorzugsweise in den Korngrenzen an und dekorieren so die Kristallite unter Bildung von Mischkristallen. -Man kann annehmen, da13 der in Molybdiin und Wolfram geloste Kohlenstoff die Versetzungen in den Korngrenzen fixiert. I m Gegensatz zu den Theorien uber die sekundhre Rekristallisation werden ,,Ringkristalle" gehildet.
Preliminary noticeFor detailed investigations of the process of primary and secondary recrystallization t h e co:itinuous observation of the course of this process is a prerequisite. The possibilities offered by t h e light microscope or the high-temperature microscope are rather limited, because in this case chemical or physical etching methods enable only the initial or final states t o be observed. I n addition, recrystallization generally proceeds so quickly for t h e individual crystal grain t h a t t h e process can completely be recorded only kinematically on film. Owing t o its imaging conditions t h e emission microscope meets several requirements for the investigation of recrystallization and has already repeatedly been used for this purpose (MORLIN, TREMMEL ; ZAMINER; SASAKI, FUKOTOMI).
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