Anomalous diffusion in the BCC phases of IVB-metals and their alloys
- Univ. of Muenster (Germany, F.R.)
Anomalous fast self-diffusion, resulting in small values of the frequency factor and the activation energy in the temperature range close to the phase transformation, is observed in the bcc-phases of the IVb-metal and IVb-metal alloys. Previous explanations of this behavior are briefly reviewed. Results of the temperature dependence of self-diffusion and of the isotope effect in {beta}-Zr and {beta}-Hf are presented. Remarkably curved Arrhenius plots were obtained for Zr-tracer diffusion in bcc alloys of Zr with Nb and Ti, which stabilize the {beta}-phase. Corresponding experiments in the Zr-Sc system are in progress. The results are explained assuming a monovacancy mechanism in combination with phonon assisted diffusion jumps, which become increasingly important as the temperature of the phase transformation is approached. In the bcc lattice the LA-2/3(111) phonon mode shows a considerable softening. As a consequence atomic fluctuations may be very much promoted by this mode thus reducing the effective migration energy for jumps in the <111> direction.
- OSTI ID:
- 5311103
- Report Number(s):
- CONF-840909--
- Journal Information:
- TMS (The Metallurgical Society) Paper Selection; (USA), Journal Name: TMS (The Metallurgical Society) Paper Selection; (USA) Vol. 56; ISSN 0197-1689; ISSN TMPSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360102* -- Metals & Alloys-- Structure & Phase Studies
ACTIVATION ENERGY
ALLOYS
ARRHENIUS EQUATION
BCC LATTICES
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
CUBIC LATTICES
DIFFUSION
ELEMENTS
ENERGY
EQUATIONS
HAFNIUM
METALS
NIOBIUM ALLOYS
PHASE TRANSFORMATIONS
SCANDIUM ALLOYS
SELF-DIFFUSION
TEMPERATURE DEPENDENCE
TITANIUM ALLOYS
TRANSITION ELEMENTS
ZIRCONIUM
ZIRCONIUM ALLOYS
ZIRCONIUM BASE ALLOYS