LOADING MODE DEPENDENCE OF DEFORMATION MICROSTRUCTURE IN A HIGH-PURITY TITANIUM SINGLE-CRYSTAL ORIENTED FOR DIFFICULT GLIDE

A special high-purity titanium single crystal was prepared to study th e effect of loading mode on deformation microstructure. Six rectangula rly sectioned specimens were cut from the same single crystal. The loa ding axis of the specimens was parallel to the C-axis of the crystal, and the wide surface was parallel to the prism plane {1010}, with the narrow surface {1210}. Mechanical tests were conducted within the cham ber of a scanning electron microscope JSM35C using a specially designe d apparatus with closed-loop computer control. Five loading modes were used: monotonic tension, tension-tension fatigue, and tension-compres sion fatigue with three different stress amplitudes. The surface appea rance of the specimens was registered with SEM periodically, and the c yclic twins as well as persistent slip bands were identified using tra ce analysis technique. The substructures of the tested specimens were examined with a transmission electron microscope on foils cut from the specimens parallel to the wide surface. The dislocation structures of specimens tested in different modes were observed, and the slip syste ms and twinning modes for each case are discussed.