The relation between the plastic deformation of aluminium single crystals and polycrystals

Publisher Website
Google Scholar
Abstract
Single crystals of 〈100〉, 〈111〉 and 〈110〉 axial orientation, and poly-crystals, both of 99·99% pure aluminium, were deformed in tension at temperatures of 27%, 200°c, 400°c and 600°c. The experiments on single crystals reveal that as the temperature is increased, the shear stress-shear strain curves for the three orientations become more and more similar until at 600°c they are identical. On the other hand, the surface appearance of the crystals strained at 600°c indicates that the mode of deformation depends drastically on orientation. Taylor's criterion for the comparison of the stress–strain curves of single and Folycrystals was found to be valid at 27°c. As the temperature is raised, however, the criterion ceases to be applicable. From the results of these experiments it is proposed that at the lower temperatures in both single crystals and polycrystals the principal hardening mechanism is the formation of Lomer–Cottrell barriers that act as obstacles against which glide dislocations can pile up. As the temperature is raised these barriers become ineffective as obstacles to slip, whereas grain boundaries in polycrystals continue to be effective in causing dislocation pile-ups.