Orientation Dependence of Deformation Mode in Ti Single Crystals

Abstract

The deformation mode of Ti single crystals by plane-strain compression has been studied at room temperature by means of transmission electron microscopy. Rectangular specimens (l/4x 3/8 x 1/2″) were cut from a large single crystal grown by the transformation annealing method. The surfaces of the specimens were flattened by No. 0 Emery papers and subsequently polished by an electrochemical method in order to remove the mechanically affected zone by at least 5 microns. By an etch pit technique the dislocation density of the specimen thus prepared was found to be of the order of 106/cm2. The oxygen impurity level, which has been reported to drastically change the ratio of the resolved shear stresses on (0001) and ﹛100﹜, was 300 ppm. The plane normals of the specimens, determined by x-ray Laue method, are plotted in Fig. 2(A). It was found that twinning played a nominal role in specimen S1 01 whereas in S1 02 and S1 03 a great number of ﹛102﹜ were predominantly observed at the early stage of deformation (up to 2%). By attributing the catastrophic yield drop in S1 02 to twinning, the resolved shear stress for ﹛102﹜< 011> twins was derived to be 5.25 kg/mm2, which is roughly twice that of the prismatic slip.