High Temperature Softening Behavior Of Hydrogenated Titanium Alloys Andpure Zirconium And Its Effect On Forging Deformation

Thermo hydrogen processing of titanium alloy, which hydrogen is used as a temporary alloying element, for improving the properties of titanium alloy through changing plasticity, microstructure and reversible effects. Hydrogen induced titanium alloy high temperature softening is one of the most important aspect of thermo hydrogen processing, and the main mechanism is hydrogen promotes αâ†'β phase transition decresing transition temperature and increasing volume fraction of β phase. The physical essence of the special effect of hydrogen on titanium elements is related to lattice structure and atomic structure of the metals. But the research on the effect of hydrogen on high tempareture deformation behavior of titanium elements is not comprehensive at present, and the theory of hydrogen induced titanium elements high temperature softening has not been established.The effect of hydrogen on pure titanium elements Ti and Zr high temperature deformation behavior is studied in this paper, which is used to research the law of hydrogen induced high temperature softening without the other impurities, and the mechanism of hydrogen induced titanium elements high temperature softening can be interpreted from lattice structure and atomic structure. And then the effect of hydrogen on Ti6Al4V alloy high temperature deformation behavior is compared with that of titanium elements.The high temperature softening behavior of hydrogenated titanium alloys and pure zirconium is researched in this paper. The quantitative relationship between hydrogen content and steady stress is founded, and hydrogenation induced microstructure and phase evolution is related to mechanical properties changing. The theory of hydrogen induced titanium elements and alloys high temperature softening is improved. The high temperature deformation behavior of Ti-xH, Zr-xH and Ti6Al4V-xH system are researched by isothermal hot compression test. The experiments cover α, α+β and β regions through changing deformation temperature and hydrogen content. The results show that, the effect of hydrogen on high temperature deformation behavior of titanium and zirconium are similar. In α+β region, the relationship between steady stress and hydrogen content is inverse linear; in β region, the relationship between steady stress and hydrogen content is linear when hydrogen induced hardening. In β region of Ti6Al4V-xH, the relationship between steady stress and hydrogen content is always linear. In addition, hydrogen induced β phase softening is found.Optical microscope (OM), scanning electron microscope (SEM and EBSD) and transmission electron microscope (TEM) are used to study the influence of hydrogen on the microstructures evolution. The dislocation density in hydrogenated samples is lower than in unhydrogenated, and dynamic recover (DRV) in α phase is promoted by hydrogenation.hydrogenation induced α phase high temperature softening and hydrogenation promoting αâ†'β phase transition are the main reasons for hydrogen induced high temperature softening. The hydrogenation induced α phase high temperature softening are illustrated as follows: firstly, hydrogenation induced a weaker bond decreases the shear modulus (G), which decreases the critical shear stress of dislocation motion (η); secondly, the spanking diffusion and segregation which is sensitive to pressure reduces pining and piling up of dislocation, and dislocation motion is promoted; thirdly, solid solution strengthening effect is not notable, because the solubility of hydrogen is not high and lattice dislocation is small. Hydrogenation induced softening or strengthening for β phase is decided by the competition of the two aspects: firstly, softening effect caused by spanking diffusion and segregation; secondly, hydrogenation induced a harder bond increasing η and solid solution strengthening effect of hydrogen.Dehydrogenation process of Ti6Al4V-xH is researched in this paper, and the results show that, between450℃and500℃, the rate of dehydrogenation increases rapidly, which means the rate of hydrogen diffusion increases rapidly. The phenomenon of hydrogen induced softening appears at480℃, so hydrogen diffusion is the main reason of hydrogen induced softening. After vacuum heat treatment at700℃by4h, hydrogen content can be reduced to safe range (CH≤0.015wt.%).The high temperature deformation behavior of hydrogenated near α titanium alloy Ti600and β titanium alloy Ti40are researched. The reasons of hydrogen induced high temperature deformation resistance decreasing are verified, which includes hydrogen induced α phase softening and promoting αâ†'β phase transition. And the linear relationship between hydrogen content and steady stress are tested in hydrogen induced β phase strengthening.The application of hydrogen induced softening to Ti6Al4V alloy blade isothermal forging is studied. The results show that, compareing with unhydrogenated blade forged at950℃, the room temperature and high temperature strength of hydrogenated blade forged at850℃increases by around11%, and the forging load of them are similar. Mechanical properties of both blades can meet the need of aircraft engine. It provides a reference for industrial application of thermo hydrogen processing.