The effect of high pressure on self-diffusion in beta-titanium
Jeffery, Rondo Nelden
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https://hdl.handle.net/2142/25850
Description
Title
The effect of high pressure on self-diffusion in beta-titanium
Author(s)
Jeffery, Rondo Nelden
Issue Date
1970
Doctoral Committee Chair(s)
Lazarus, David
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
high pressure
self-diffusion
beta-titanium
lathe-sectioning technique
Language
en
Abstract
"Diffusion of Ti44 into beta-titanium has been measured as a function of
pressure at approximately 10000C using standard lathe-sectioning techniques.
The diffusion coefficient is found to decrease with pressure, indicating a
positive activation volume. This result is in contradiction of earlier
reports of negative activation volumes for diffusion of Fe in S-Ti and U in
y-U.
The value obtained for the activation volume for self-diffusion in S-Ti
is approximately 3.6 ± 1.0 cm3/mOle, corresponding to ~V/VM = 0.33 + 0.1,
where VM is the molar volume. Comparison is made with atomic.models and
various proposed mechanisms for diffusion in the anomalous body-centered
cubic metals. The magnitude of ~V appears to be too large to be consistent
with the ""extrinsic"" vacancy mechanism of Kidson, but smaller than would
normally be expected for simple vacancy diffusion in bcc metals; It is
concluded that diffusion in beta-titanium most probably proceeds via a
combination of vacancy and short dislocation-path diffusion, known as the
Hart mechanism. Non-gaussian penetration profiles were observed in some of
the runs. This has been interpreted in terms of oxide hold-up of the tracer
at the surface and possible diffusion of the tracer as an oxide along dislocation
pipes or grain boundaries near the surface prior to dissociation."
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