Chemically induced grain boundary migration
Abstract
Experimental evidence is presented, showing that gram boundary motion can be induced by changing the composition by means of grain boundary diffusion. The experiments were carried out by treating specimens of pure iron in an atmosphere of zinc or iron-zinc specimens in an atmosphere with a lower zinc potential. The reaction resembles the grain boundary migration in discontinuous precipitation and provides an experimental method of isolating grain boundary migration for study.
The experimental results can be used to evaluate rather directly the grain boundary diffusivity and mobility. The diffusivities thus obtained are several orders of magnitude larzer than the values reported for stationary boundaries. It is concluded that the boundary diffusivity is greatly enhanced by grain boundary motion.
Résumé
On présente une preuve expérimentale du fait que l'on peut faire migrer un joint grains en changeant la composition par diffusion intergranulaire. Dans ces expériences, on a traité des échantillons de ter pur dans une atmosphère de zinc et des échantillons de fer et de zinc dans une atmosphère dont le potentiel de zinc était plus faible. La réaction ressemble à la migration des joints de grains dans la précipitation discontinue et elle fournit une méthode expérimentale pour isoler la migration intergranulaire en vue de son étude.
On peut utiliser les résultats expérimentaux pour évaluer assez directement la diffusivité et la mobilité des joints de grains. Les valeurs de la diffusivité que l'on obtient ainsi sont supérieures de plusieurs ordres de grandeur à celles qu'on a publiées pour les joints stationnaires. On en déduit que la diffusivité d'un joint est fortement augmentée par son déplacement.
Zusammenfassung
Es werden experimentelle Hinweise vorgelegt dafür, daβ eine Korngrenzbewegung durch die Änderung der Zusammensetzung über Korngrenzendiffusion eingeleitet werden kann. Zur Durchführung der Experimente wurden Proben aus reinem Eisen in einer Zink-Atmosphäre und Proben aus Zink-Eisen in einer Atmosphäre mit kleinerem Zink-Potential behandelt. Die Reaktion ähnelt der Korngrenzbewegung unter diskontinuierlicher Auscheidung und stellt eine experimentelle Methode dar, die Korngrenzbewegung für die Untersuchung zu isolieren.
Mit den experimentellen Ergebnissen lassen sich Korngrenzendiffusivität und beweglichkeit ziemlich direkt auswerten. Die so erhaltenen Diffusivitäten sind um mehrere Gröβenordnungen gröβer als diejenigen, die für stationäre Korngrenzen angegeben werden. Aus den Ergebnissen wird gefolgert, daβ die Korngrenzdiffusivität durch Korngrenzbewegung beträchtlich verstärkt wird.
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Permanent address: Department of Metallurgy and Materials Science, McMaster University, Hamilton, Ontario, Canada.