Abstract
IT has recently been reported that unnotched single crystals of zone-melted molybdenum are ductile in impact well below room temperature1. Although the impurity content of this material was very low it was felt that the improvement may be due to the single crystal structure and not the purity. Some crystals were therefore forged and recrystallized to give a poly crystalline material of grain size 4/cm. The specimens were turned to ¼in. diameter and electro-polished to produce a surface similar to that of the zone-melted crystals. Tested in a 10 ft./lb. Charpy impact machine these gave a 5 ft./lb. transition temperature of −80°C. compared with −140°C. for similar purity single crystals. A graph of the two sets of results is shown in Fig. 1, the points and full line refer to polycrystals and the broken line to single crystals.
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