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Title:The effect of high pressure on self-diffusion in beta-titanium
Author(s):Jeffery, Rondo Nelden
Doctoral Committee Chair(s):Lazarus, David
Department / Program:Physics
Subject(s):high pressure
lathe-sectioning technique
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.
Issue Date:1970
Genre:Dissertation / Thesis
Rights Information:1970 Rondo Nelden Jeffery
Date Available in IDEALS:2011-07-26
Identifier in Online Catalog:6053442

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