Self-diffusion of 44Ti is measured in β-Ti under UHV conditions in the whole range of existence of the b.c.c. phase. The Arrhenius plot shows a strong upward curvature in agreement with previous investigations of Murdock et al. The anomalous diffusion behaviour is related to the experimentally observed softening of the LA ⅔〈111〉 phonon mode and is explained by a monovacancy mechanism with a temperature-dependent migration enthalpy. When separating the phonon related diffusion contribution the analysis yields a frequency factor and an activation enthalpy consistent with normal vacancy diffusion parameters.



Die Selbstdiffusion von 44Ti wird unter UHV-Bedingungen in β-Ti im gesamten Existenzbereich der k.r.z.-Phase gemessen. Die Arrheniusdarstellung ergibt eine stark aufwarts gekrummte Kurve in Ubereinstimmung mit fruheren Untersuchungen von Murdock et al. Das anomale Diffusions-verhalten wird mit der experimentell beobachteten Aufweichung der LA ⅔〈111〉-Phononmode verknupft und mit einem Einzelleerstellenmechanismus mit temperaturabhangiger Wanderungsenthalpie erklart. Bei Abspaltung des phononbeeinflusten Diffusionsbeitrages ergibt die Analyse einen Frequenzfaktor und eine Aktivierungsenthalpie, die mit Parametern fur normale Leerstellendiffusion ubereinstimmt.

On the Anomalous Self-Diffusion in B.C.C. Titanium

Interdiffusion in β-Ti–Zr binary alloys

Interdiffusion in the body cubic centeredβ-phase of Ta–Ti alloys

Tracer diffusion of 95Zr and 95Nb has been measured in a set of β-Zr-Nb alloys (Zr-5.5 at. % Nb, Zr-16.3 at. % Nb, and Zr-28.1 at. % Nb) in a wide temperature range from 1035 to 1871 K. All experimental concentration profiles revealed a Gaussian-like behavior over two to three decades in logarithm of concentrations. Experimental data were analyzed in terms of the Manning’s random alloy model and the partial correlation factors were calculated as functions of temperature. The partial correlation factors vary smoothly over the whole temperature range, whereas the diffusivity shows a pronounced curvature of the Arrhenius plots. A correlation was found between the degree of deviation from the Arrhenius behavior of the diffusion coefficients of both components and the lattice dynamics features of the measured phonon dispersions in their dependence on the Nb content in these alloys. The temperature dependence of the isotope effect parameter E of Zr diffusion was measured in the Zr-5.5 at.% Nb alloy. E essentially increases with temperature and the energy transfer factor ΔK deduced for the alloy was found to be somewhat larger than the corresponding values for pure β-Zr, especially at low temperatures. The whole set of experimental data leads to the conclusion that only one diffusion mechanism—the vacancy mechanism—is operating in the whole investigated temperature range.

U. KÖhler

Papers

The influence of scandium on the anomalous self-diffusion in b.c.c.-zirconium