The Microstructure And Hydrogen Transportation Performance Of Nb-Mo-Ti-Ni Alloys

In this paper, the effect of Mo addition on the microstructure and hydrogen transportation properties of Nb-Ti-Ni alloy is studied. In the experiment, four groups’ alloy are smelted by using the electric arc furnace: group a: Nb15-x Mox Ti42.5Ni42.5(x = 0,5,10), group b: Nb20-x Mox Ti40Ni40(x = 0,5,10), group c: Nb30-x Mox Ti35Ni35(x = 0,5,10), group d: Nb40-x Mox Ti30Ni30(x = 0,5,10). By using scanning electron microscopy and Xray diffraction analyzer, these four groups of alloy’s microstructure and phase composition are analyzed, the relationship between the composition and alloy is explained, the answer of Mo’s influence to the alloy’s solidification path is illustrated. According to the organization analysis, group d alloy is selected to test hydrogen transportation performance. The connection between Nb-Mo-Ti-Ni alloy’s composition, microstructure and hydrogen transportation performance is summarized.The results of SEM and XRD shows that the addition of Mo could lead the solidification of the alloy to the Nb-rich and Ni-rich region. With the increase of Mo content, the composition of group a and group b from primary Ti Ni and binary eutectic [bcc-Nb+Ti Ni] change into primary bcc-Nb and Ti Ni. In Nb15Mo5Ti40Ni40 alloy, the eutectic phase is ternary eutectic {[bcc-Nb+Ti Ni]+Ti2Ni}, and Ti2 Ni phase is found in Nb5Mo10Ti42.5Ni42.5 and Nb10Mo10Ti40Ni40 alloy; group c and group d alloy in Mo content 5% remain the primary bcc-Nb with binary eutectic phase [bcc-Nb+Ti Ni] phase composition,they accord with the "multi phase composition, function sharing" hydrogen separation principle of alloy design, when Mo content is 10%, a little amount of ternary eutectic phase is found.Hydrogen absorption and hydrogen permeation tests are performed in the group d, which has the best performance of hydrogen permeation. The results showed that, with the addition of Mo, the hydrogen solubility of the alloys decreased significantly, the hydrogen diffusion and hydrogen permeation properties increased first and then decreased. Among three alloys, the Nb35Mo5Ti30Ni30 alloy has the highest hydrogen permeability, up to 3.15×10-8 mol H2·m-1·s-1·Pa-0.5 in 673 K, which is about 1.98 times of pure Pd in the same condition. Through the pressure-constant slow-cooling test, Nb30Mo10Ti30Ni30 alloy shows the best property against hydrogen embrittlement, which means that Mo’s addition can improve the resistance to hydrogen embrittlement.Permeation hydrogen in the alloy follows the dissolution and diffusion, the acts occurred mainly in the primary bcc-Nb and Mo addition can reduce primary phase gap size, lead alloy hydrogen solubility decrease, and the hydrogen embrittlement resistance can improve, and reduce the hydrogen hopping gap distance increases the permeability and diffusion performance gold, but with Mo content further increased, the alloy in low energy gap, high energy gap resulted in the reduction of hydrogen atoms in the film diffusion rate greatly reduced. In addition, Nb30Mo10Ti30Ni30 alloy between upstream and downstream hydrogen concentration gradient lower, the hydrogen atom diffusion, lack of motivation is the leading cause of the hydrogen diffusion and permeation properties followed by the reasons for the decline.