THE EFFECT OF CRYSTAL ORIENTATION AND BOUNDARY MISORIENTATION ON TENSILE CAVITATION DURING HOT TENSION DEFORMATION OF Ti-6Al-4V

摘要

Cavitation during hot tensile deformation in Ti alloys is commonly observed. Prior work has indicated that cavities are often located at grain boundaries perpendicular to the tension axis where the lamellae appear nearly parallel to the tension axis. Since lamellar colony interfaces tend to include the c-axis, it had been hypothesized that cavities develop preferentially at boundaries that have the hard c-axis orientation parallel to the tension axis. A tension specimen deformed at 815℃ and 0.1/s strain rate was analyzed to evaluate this hypothesis using orientation imaging microscopy, by measuring the crystal orientations surrounding nucleated cavities. Small cavities observed far from the fracture surface were in agreement with the hypothesis. In regions with more strain, more cavity growth was apparent when a small fraction of soft orientations with a non-c-axis orientation was also at or near the cavity. The constraint of the hard orientations and the preferential deformation of the softer orientations around relatively undeformable c-axis orientations was concluded to stimulate tensile conditions that favor cavity growth.