Influences Of Hydrogen Treatment On Microstructure Of Titanium Alloy And Theoretical Calculation And Process Simulation

Hydrogen treatment (HT) is a peculiar heat treatment approach of titanium alloys. HT, or the use of hydrogen as a temporary element by using the reversible function, can modify the microstructure of titanium alloys. The processability and service performance will be enhanced after HT.The TC4alloy after HT (hydrogenation at750℃, and then dehydrogenation at700℃) has been investigated by optical microscope (OM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The microstructures after dehydrogenation of the specimens with different hydrogen contents have been observed. The phase transformation during hydrogen treatment has been studied. The refining mechanisms of microstructure after HT have been analysed. The relationship between hardness of hydrogenation specimens after dehygenation and hydrogen content has been gained. Furthermore, the relationship between hydrogen pressure and hydrogen content of titanium alloys in the process of hydrogenation has been calculated by thermodynamic calculation, and the diffusion processes of hydrogen during hydrogenation and dehydrogenation have been simulated. The main results are as follows:(1) There are two kinds of microstructure in TC4alloy treated by hydrogenation and dehydrogenation, one is primary a phase, and the other is β transformed microstructure which is composed of a and β phase. The microstructure of TC4alloy is refined after hydrogenation and dehydrogenation which is a result of decrease of volume fraction of primary a phase, refinement of primary a phase, refining of β transformed microstructure.(2) The hardness of hydrogenated TC4after dehydrogenation increases with hydrogen content increasing.(3) The relationship among hydrogen content XH, hydrogen pressure pH2and interaction energy Ⅰof Ti-H can be expressed as follows: pH2=XH2·pθ/exp[333192-2(1-XH)2I/973R]Combining the equality above,the plot of hydrogen content in titanium alloy VS. hydrogen pressure is obtained in balanced system of hydrogenation by regression of interaction energy I.(4)After hydrogented for900s,the center hydrogen content of titanium alloy specimen with a size of30mm×10mm×2mm reaches99.85％of the target hydrogen content,after dehydrogented for1800s,the highest hydrogen content is6.67×10-3ppm.