The effect of hydrogen on the mechanical properties of iron whiskers
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but this treatment is welt known to cause severe embrittlement in bulk samples of iron and steel. 130/~m diam iron wire, tested under identical conditions, showed a significant decrease in elongation. The strength of whisker crystals increases as the size (i.e. diameter and length) of the crystals is decreased, and with considerable scatter extrapolates to the theoretical cohesive strength of the perfect crystal at the smallest whisker diameters2 It is therefore necessary, in order to estimate the true theoretical cohesive strengths, to test a large m e m b e r of whiskers. Figure 1 shows the ultimate tensile strength of as-grown iron whiskers plotted vs their effective diameter. As might be expected from the difficulties of handling the whiskers, and the limitations of the equipment, the scatter is large. It is clear that whiskers below ~ 10/tm diam are needed to achieve the theoretical strength of 13 GPa. The measurement of ultimate tensile strength vs whisker diameter was repeated for whiskers precharged with hydrogen for one half hour. The results are shown in Fig. 2. There appears to be no significant difference
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(/.Lm ) Fig. l--The strength of as-grown iron whiskers as a function of diameter.
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K. S. LEE, formerly with the Metallurgy and Materials Science Division of the Department of Energy and Environment, Brookhaven National Laboratory, is now with the HTGR Safety Division of the Department of Nuclear Energy, Brookhaven National Laboratory, Upton, NY 11973. DAVID DEW-HUGHES, formerly with the Metallurgy and Materials Science Division of the Department of Energy and Environment, Brookhaven National Laboratory, Upton, NY, is now with the Department of Engineering Science, University of Oxford, Oxford, United Kingdom. Manuscript submitted October 9, 1979.
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DIAMETER (/.L m ) Fig. 2--The strength of iron whiskers precharged with hydrogen as a function of diameter.
ISSN 0360-2133/80/0711-1227500.75/0 METALLURGICAL TRANSACTIONS A 9 1980 AMERICAN SOCIETY FOR METALS AND THE METALLURGICAL SOCIETY OF AIME
VOLUME 11A, JULY 1980--1227
Fig. 3--The strength of iron whiskers continuously charged with hydrogen as a function of diameter.
Fig. 4--SEM micrograph of fractured (I 10) iron whisker. This fracture is typical of all whiskers studied.
between these results and those in Fig. 1 for the as-grown whiskers. It is possible that any precharged hydrogen could have diffused out of the crystals during the time interval, usually ~ 1 / 2 h between the charging process and the tensile test. This is particularly likely in view of the small dimensions of, and absence of traps in, the whiskers. The tensile machine was
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