Formation of ultra-fine grained materials by machining and the characteristics of the deformation fields

Formation of ultra-fine structure in several materials by severe plastic deformation has been studied by plane strain machining. The microstructure generated in machined chips was characterized by optical microscopy and transmission electron microscopy as ultra-fine grains. A theoretical model was adopted to evaluate large plastic deformation in the primary deformation zone, the results show that the typical shear strains generated at the shear plane are in the range of 2-10. A more realistic finite element model was developed to characterize the deformation field associated with chip formation in plain orthogonal machining. The numerical results show that most of the grain refinement associated with the formation of ultra-fine grained chip can be attributed to the large shear strain imposed in the deformation zone. It could be feasible to take machining as a method to preparing ultra-fine grained materials and a type of experiment method to study severe plastic deformation. (C) 2008 Elsevier B.V. All rights reserved.