Microstructure And Hydrogen Permeation Properties Of Nb-W-Ti-Ni Alloy

In recent years,based on the design principle of " two phases and multiple functions",the development of Nb-based hydrogen-separation alloys has become a research focus.Among them,the Nb-Ti-Ni ternary hydrogen-separation alloy has good hydrogen permeability and strong resistance to hydrogen embrittlement.However,the hydrogen embrittlement is serious.In this paper,a new Nb-W-Ti-Ni quaternary alloy was prepared by adding W element to replace some Nb in the alloy.Hydrogen permeation tests were carried out to investigate the effects of W element on the hydrogen permeation performance and hydrogen embrittlement resistance of alloys.Microstructures and phases were analyzed by means of SEM,EDS and XRD.The results of XRD,SEM and EDS showed that both Nb45-xWxTi27.5Ni27.5(x=0,5,10)and Nb56-xWxTi23Ni21(x=0,5,10,15)alloys consisted of two phases,primary bcc-Nb phase and eutectic phase.For Nb45-xWxTi27.5Ni27.5(x=0,5,10)alloys and Nb56Ti23Ni21 as well as Nb5iW5Ti23Ni2i alloys,as far as the eutectic phase considered,it is the type of bcc-Nb+B2-TiNi.For the Nb46WioTi23Ni21 and Nb4iW15Ti23Ni2i alloys,the divorced eutectic was obtained.The added W element completely dissolved in the primary bcc-Nb phase and suppressed the full developement of secondary dendritic arms.The experimental results of hydrogen dissolution tests showed that the addition of W element to Nb-Ti-Ni ternary alloys can reduce the hydrogen solubility.In addition,the dissolution of hydrogen atoms into the alloys is exothermic reaction.So,the higher the temperature is,the lower the hydrogen solubility becomes.Compared to Nb45-xWxTi27.5Ni27.5(x=0)alloy,the hydrogen permeability and diffusion coefficient were increased at low temperatures for the addition of 5%W element.With increasing temperature,the hydrogen permeability was decreased and the diffusion coefficient was barely changed.When the content of W element was 10%,the hydrogen permeability and diffusion coefficient of the alloy were obviously decreased.For Nb56-xWxTi23Ni21(x=0,10,15)alloys,Nb56Ti23Ni21 had excellent hydrogen permeability,howere,the resistance to hydrogen embrittlement was poor.With the addition of 10%W elements,the hydrogen permeability,diffusion coefficient and the resistance to hydrogen embrittlement were improved.With the addition of 15%W elements,the hydrogen permeability and diffusion coefficient were lowered and the resistance to hydrogen embrittlement was still good.Compared to Nb45-xWxTi27.5Ni27.5(x=0,5,10)alloys and Nb56-xWxTi23Ni2i(x=0,10)alloys,Nb41W15Ti23Ni2i alloy presents the best combinations of hydrogen permeability and resistance to hydrogen embrittlement.