The Effect of Orientation on the Yielding and Flow of Molybdenum Single Crystals

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Abstract
The influence of the orientation with respect to the direction of stresses has been investigated over the temperature range 77 to 413 °K. At temperatures below 300 °K the limit of the proportionality of strain to stress and the rate of work‐hardening depend markedly on the orientation. At temperatures above 300 °K the yield stress is practically independent of the orientation and the crystals can experience a large elongation without necking. Crystals with the tensile axis orientated in a direction near the centre of the unit stereographic triangle exhibit three work‐hardening stages. Slip lines and etch pit observations have shown that profuse cross‐slip of screw dislocations is a characteristic feature of the deformation of molybdenum single crystals. An explanation, based on the mobility of the jogs in screw dislocations, is proposed for the orientation dependence of the yield stress.