Effect of Nitrogen on Tensile Deformation Behavior and Development of Deformation Structure in Titanium

Ti-N alloys with different nitrogen content were tensile-tested, and then the effect of nitrogen on tensile properties and deformation structure were investigated. With increasing nitrogen content, the 0.2% proof stress and tensile stress were markedly increased accompanied with the lattice distortion of enlargement Of c/a ratio. Since the work hardening rate was also increased, the uniform elongation was not significantly decreased by the addition of nitrogen. However, the local elongation was reduced drastically through the occurrence of intergranular brittle fracture even by a small amount of nitrogen addition. In the tensile-deformed pure Ti, many deformation twins and dislocations were observed. On the other hand, few deformation twins and a high density of planar dislocation arrays were observed in the high nitrogen alloys. The changes in deformation structure might have caused the reduction of local elongation in nitrogen added alloys because of the intergranular brittle fracture derived from the suppression of twinning deformation and the stress concentration at grain boundary clue to piled-up dislocations in the planar array.