Papers by Keyword: Hydrogen Treatment

Abstract: The microstructural evolution of TIG welded joint in Ti-6.5Al-2Zr-1Mo-1V alloy treated by thermo hydrogen processing was investigated by optical microscopy, transmission electron microscopy and scanning electronic microscopy and the mechanical properties of welded joints were tested and analysed. The results showed that δ-hydride formed after hydrogenising at 700°C for 3 hours, and it is a face-centered cubic crystal. And these hydrides brought a strong fuzzy effect on microstructure. A lot of rhombic martensite phase α" generated in the area of welded joint. Metastable β(H) phase and α" phase were gradually decomposed to α and δ phases during aging. Hydrides were dissolved, the hydrogen was removed from the alloy and the recrystallization occurred in the process of annealing in vacuum. After hydrogen treatment, the refinement effect of grains in the fusion area was very obviously, that is, coarse columnar grains changed to finer equiaxed grains. Non-equilibrium phase reduced in grains. After hydrogen treatment (hydrogenization at 700°C for 3 hours, eutectoid at 300°C for 8 hours and annealing at 750°C for 8 hours in vacuum), the tensile strength of welded samples increased by 25.7%, and the elongation increased by 37.6% compared with welded samples without hydrogen treatment. After hydrogen treatment, the surface morphology of tensile fracture was relative flatness.

Abstract: Recently, Wang et. al. formulated a criterion for identifying the source of deep interface sates at the SiC/SiO2 interface, based on the known inefficiency of H2 passivation. We apply this criterion to a variety of excess carbon defects at the interface, which we have predicted to be energetically feasible. We find that, also with respect to this criterion, the simple C split interstitials are the most likely cause of the deep interface states among the examined defects.

Abstract: The effects of hydrogen on the microstructure and hot deformation behavior of Ti-6Al-4V alloy were studied, and the differences of microstructure and high temperature compressive behavior between the specimens hydrogenised various time at 700 oC and with the same hydrogen contents were analyzed. The results showed that the addition of hydrogen decreases the deformation resistance of Ti-6Al-4V alloy at high temperature. The flow stresses of specimens with the same hydrogen content declined as the prolongation of hydrogenating time. The microstructure observation indicated that stick-type microstructure was obtained in Ti-6Al-4V alloy annealed at 700 oC for 2 hours. Hydrogenation at 700 oC for 2 hours resulted in fine α plate in β transformed microstructure. When the hydrogenation time was prolonged to 6 hours, the volume fraction of newly-formed α plates increased and the prior α plates became coarser.