TWINNING AND THE LOW TEMPERATURE MECHANICAL PROPERTIES OF POLYCRYSTALLINE COLUMBIUM AND MOLYBDENUM.
Final technical rept. Feb 65-Jan 66,
WESTINGHOUSE RESEARCH LABS PITTSBURGH PA
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Mechanical properties of Cb and Mo have been investigated over a range of grain sizes from 20 C to minus 269 C. Interpretation of the load elongation curves, in compression and tension, along with detailed metallographic investigation has led to the following conclusions 1 Twinning can occur more readily in coarse grain than fine grain material, 2 Twins can occur over the entire range of temperature 20 C to minus 269 C in molybdenum but only in the range minus 150 to minus 269 C in columbium at Epsilon 0.00042sec and 3 Enhanced stresses ahead of a crack can cause twinning but there is no definite evidence to show that twins cause cracking. These results have been interpreted in terms of a model independent hypothesis, based on simple considerations of the dissipation of energy by various deformation mechanisms. Author