Deformation behaviour of copper in ultramicrotomy

Abstract

The dislocation microstructure of ultra microtomed copper chips less than 350 nm thick has been characterised, and the observed texture compared with that computed on the basis of continuity of primary shear. The good agreement between the observed and calculated textures suggests both that the primary shear is continuous and that the deformation in the secondary zone is not one of shear. Evidence of twinning in this region is presented, and it is demonstrated how a moiré technique can be used to analyse the large rémanent elastic strains in the chip. Although the study described in this paper indicates that the main deformation mode is continuous this is not to say that discontinuous deformation may not occur in many practical machining situations. It is suggested that the observed lamellae and banded form of disolation microstructure which might, initially, be thought to arise from discontinuous deformation is in fact, the result of the partial plastic relaxation of the resultant stress field. It is concluded that the conditions prevailing at the interface between the tool and the chip are important in determining a material's machinability by influencing the mode of deformation within it.