Authors: W L Chan M W Fu
Publish Date: 2012/01/03
Volume: 62, Issue: 9-12, Pages: 989-1000
Abstract
Microforming process provides an efficient approach to fabricating microparts via microscaled plastic deformation However the material properties change and the size effect occur when the workpiece size is scaled down from macro to microlevel which makes the development of microforming system difficult It is thus necessary to study the size effect phenomena and microscaled deformation behaviors In this research the upsetting of annealed pure copper cylinders with different sizes from macro to microscale is conducted to investigate the interactive effect of specimen and grain sizes on material deformation behavior It is found that flow stress decreases and surface roughening and inhomogeneous flow take place with the increase of grain size and the decrease of specimen size Furthermore the properties of grain interior and grain boundary change and the properties of surface grains become significant in the overall deformation behavior It leads to the deviation between the Hall–Petch relation and the experimental results It is further revealed that the flow stress has a linear relationship with the ratio of specimen size to grain size D/d at a given strain and the change rate of the flow stress with D/d could be independent of strain By examining the changes of working hardening and slip distance it is found that there could be a delay in the formation of dislocation cell and the slip distance and the size of dislocation cell could increase with the decrease of D/d The presented size effect phenomena and the discussed physics thus provide a basis for the further exploration of the microscale plastic deformation behavior
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