Mechanical Twinning of Titanium Single Crystals

摘要

Compression tests were performed on titanium single crystals at room temperature and at -196C, and the twinning mode was investigated using metallographic, electron microscopy and X-ray diffraction studies. Four crystallographic orientations, each different with respect to the compression axis, were selected in order to make the prospective twinning system planes, , , and , subject to a maximum resolved shear stress, i.e., Schmid factor = 0.5. type twins were the most frequently observed in all the crystals tested and type twins were the second most frequent. The second undistorted planes of twinning, K sub 2, for (-1-121) and (10-12) twins were determined to be the (0001) plane and (-1012) plane, respectively, from the inflection angle of small angle boundaries which had been sheared by twinning. In order to examine the critical resolved shear stress law Schmid factor analysis has been made. Twinning systems with Schmid factors less than 0.5 were not easily activated possibly because the required shear stress was much higher than the systems with a Schmid factor of 0.5. Consequently, the possible existence of CRSS law in twinning is negative. (Author)