DEVELOPMENT OF ORIENTATION COHERENCE IN PLANE-STRAIN DEFORMATION

Spatial orientation coherence in 20 pct channel-die compressed aluminum ingot is investigated using the two-point orientation coherence function (OCF) constructed from individual crystallite orientation measurements. It is found that orientation coherence clusters formed in the initially coherence-free ingot during deformation. The orientation coherence cluster consists of a central grain with lattice orientation (φ1, φ{symbol}, φ2) surrounded by grains with lattice orientation (π + φ1, φ{symbol}, φ2); this coincides with one of the processing-symmetry orientations of the central grain. The observed clustering is compared with simulations of structure evolution based upon the classical full-constraint Taylor model. As is expected, no coherence structure develops in these simulations. A mechanism of formation for the orientation coherence cluster is proposed based upon a requirement of stress equilibrium between neighboring grains, while maintaining, on average, strain compatibility with the overall plane-strain compression deformation mode. A simplified Fourier representation of the conditional two-point OCF is described, and a numerical scheme to obtain the expansion coefficients is proposed and tested. © 1990 The Metallurgical of Society of AIME.