TABLE OF CONTENTS Modelling the Origins of Defects
Nathan R. Barton
Department of Mechanical and Aerospace Engineering, University of California, San Diego, USA
Paul R. Dawson
Sibley School of Mechanical and Aerospace Engineering, Cornell University, New York, USA
Defects can occur from hot working operations of titanium alloys in relation to several features of their microstructures. One possibility is for voids to form as a consequence of cavitation. These may be associated with grain boundaries where the lattices are highly misoriented, especially if the hexagonal close packed c-axis lies parallel to the tension direction in one grain [BIE 01]. For alloys with lamellar microstructures, the failure of the hot working process to transform the lamellae into more equiaxed grains can leave the material with what is regarded as a defect, namely the retained lamellar structure. Dynamic globularization denotes the breakup of the lamellar micro-structure that is an intended goal of the hot working operations. Recent articles report on globularization and cavitation observed experimentally using orientation imaging microscopy (OIM) [BIE 02], as well as the flow softening that is apparent during the breakdown forming operations. With the purpose of better understanding the origins of processing defects in titanium alloys, finite element simulations have been conducted at the scale of the lamellar microstructure. Results from [BIE 02] and from the references contained therein in large part motivate the issues examined via the modeling reported here.
With lamellae of hexagonal close packed ? and body centered cubic ?, the colony microstructures...
