Research Of Elastic-Plastic Deformation Mechanism In Ti-H System

Due to the high activity and small radius of hydrogen, hydrogen is inclined to be in an unstable state if the external environmental condition has changed. So the behavior and role of hydrogen in titanium and titanium alloys is very complex., Recently, microscopic mechanisms between hydrogen and titanium have been proposed according to experimental facts. However, the conflicting views exist and the microscopic mechanism of hydrogen-induced plasticity of titanium is lack of theoretical basis. If the phenomena and problems of hydrogen-induced plasticity in titanium cannot be explain and resolve reasonably, the development of heat hydrogen treatment techniques will be limited. Therefore, further study of the behavior and mechanism of hydrogen in titanium and titanium alloys is necessary. And the simulated calculation and experiments are designed to focus on the nature of elastic deformation and plastic deformation properties in Ti-H system. This paper will also adopt the first-principles method to study the behavior and mechanism of hydrogen in titanium from electronic and atomic scale.First principles simulation results show that: the hydrogen atom in α phase and β phase tend to occupy octahedral because hydrogen atom dissolved in the octahedral release more energy than in the tetrahedral. If the solute atom hydrogen occupy octahedral in α-Ti, then hydrogen will cause lattice distortion and volume expansion to a degree. When the value of solute atom hydrogen exceeds a certain value, the crystal distortion will be too large, the crystal structure would trend to convert from hcp to bcc. For the study concerning electronic structure of Ti-H, the new energy of gap has emerged because the electrons in 1s orbit of H atoms interact with that in 3p, 3d and 4s orbit of the nearest Ti atoms. For the α-Ti, the kibbutz number and the electron density of the nearest titanium atom decrease with increasing hydrogen content, so hydrogen would induce the weak bonds in α-Ti. For the β-Ti, the situation is opposite and hydrogen would induce the strong bonds in β-Ti. Meanwhile, for Ti-H system, the bulk modulus is positively correlated with the hydrogen content. Noticeably, the shear and Young’s modulus is negative with hydrogen content in α-Ti and positive in β-Ti.Internal friction experiments showed that in the high temperature zone the internal friction of recrystallization and the relaxation peak Pb of boundary are negative with the hydrogen content. It implies that the hydrogen w ould promote recovery and suppress recrystallization. The internal friction concerning hydrogen and dislocations and dislocations and point defects will more obvious when hydrogen content increase, which reveals the hydrogen facilitate the movement of dislocations. The internal friction peak P4 caused by solute atoms and dislocations peak is negative with the hydrogen content, indicating that hydrogen weakened the interaction between dislocations and solute atoms. Sno ek internal friction peak is proportional to the hydrogen content because the hydrogen-enhanced diffusion. Elastic modulus has been measured in the α-phase, β-phase and two-phase zone, the results of experiment confirm the theory of hydrogen-induced α-Ti weak bonds and hydrogen-induced β-Ti strong bonds, and a mathematical model has been proposed.Lastly, we conduct the hot compression and tensile tests to explore hydrogen-induced plasticity mechanisms in different parameters. S pecifically, the difference of the role and behavior of hydrogen in tension and compression deformation has been summarized. And the microstructure will be observed by optical, scanning electron and transmission electron microscopy. In the hot compression test, the value of steady stress and yield strength are negative with increasing hydrogen content. According to the mechanical performance characteristics, it can be found that hydrogen facilitate d islocation motion and dynamic recovery, while inhibiting the occurrence of dynamic recrystallization. The steady stress dropped significantly from 0.09 to 0.22 wt. % because of hydrogen-induced phase transition. In the process of hot tensile test, breaking stress and yield strength decrease with increasing hydrogen content, but the tensile elongation is not positively correlated with the hydrogen content. There is an optimum processing parameters for hot tensile deformation. The different texture and the local softening effect caused by hydrogen resulting in difference of mechanical properties in tension and compression. The change of mechanical properties of different crystal orientation caused by hydrogen is different.