A study of microalloyed pure aluminum for superconductor stabilizer applications /
The effects of microalloying on the strength, resistivity,
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1994.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=741965581&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The effects of microalloying on the strength, resistivity, and resistivity degradation characteristics of high purity aluminum at 4.2 K have been examined. Testing methods primarily consisted of monitoring electrical and mechanical properties during simulated conductor operating conditions of 0︢.001 strain at 4.2 K. Variables concerning solutes are element type (Au, B, Ca, Ce, Ga, Sn, or Y), concentration (O to 90 wppm), and the initial material condition, which is dependent on processing. The results show that microalloying at levels of about 10 appm are beneficial for strengthening and for inhibiting resistivity degradation; elements which appear to be particularly effective are Ce and Y. However, although evidence for Cottrell atmospheres was found with solute concentrations below 10 appm, improvements attributed to microalloying are actually an indirect result of grain refinement that occurs with microalloying. A fine grain structure results in a higher work hardening rate and a lower overall degradation; limited evidence suggests that texture may be significant as well. TEM observations show that cyclic deformation within a strain range of 0︢.001 at 4.2 K does not produce a well defined dislocation subcell structure in high purity aluminum; the dislocation arrangement is best described as a high density of heterogeneously distributed dislocations. Results from materials in an annealed condition indicate that resistivity coefficients for Au, B, Ca, Ce, Ga, Sn, and Y, at concentrations below 100 wppm, are 0.016, 0.004, 0.039, 0.001, 0.009, 0.005, and 0.015 n[ ]cm/wppm, respectively. Contributions to the resistivity by the RRR of the base metal is reduced from -10,000 to not less than 2,500. Finally, observations of microsegregated particles that form during solidification of the microalloys indicate that the solubilities of B and Ca in aluminum at room temperature are close to zero appm; solubilities of other elements appear to be higher than those levels tested. |
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| Item Description: | Vita. "Major Subject: Mechanical Engineering". |
| Physical Description: | xix, 271 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |