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ASTM Selected Technical Papers
Eddy-Current Characterization of Materials and Structures
By
G Birnbaum
G Birnbaum
1
National Bureau of Standards
,
Washington, D.C. 20234
;
co-chairman and co-editor
Search for other works by this author on:
G Free
G Free
2
National Bureau of Standards
,
Washington, D.C. 20234
;
co-chairman and co-editor
Search for other works by this author on:
ISBN-10:
0-8031-0752-8
ISBN:
978-0-8031-0752-6
No. of Pages:
518
Publisher:
ASTM International
Publication date:
1981

Even though casting technology has a 5000-year history, the understanding and control of the process still has significance to current metal producers. Non-destructive evaluation is usually applied to finished or semifinished product; however, in casting, when the evaluation is moved to the point of production, the testing procedure can be incorporated into the casting control. The metallurgical impetus for such casting control and evaluation cannot be simply stated since the needs are process and product dependent. The main technical advantage of applying eddy-current analysis to the study of solidification is that eddy currents have a reasonable sensitivity to continuous and discontinuous conductivity changes. A drawback in the examination of the liquid-solid interfaces is that the eddy-current signals are integrated over a substantial volume, which averages out detailed information such as dendrite structure. To successfully use the technique of eddy-current analysis, one must utilize postmortem metallographic examination of specimens for standards and detailed mathematical modeling of the solidification response, which cover probable morphologies. Laboratory measurements of freezing of a Pb-20Sn alloy demonstrate that directional solidification can be identified. Finally, two techniques of data analysis for processing eddy-current signals are presented and discussed.

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