Design And Preparation Of Nb Based Solid Solution Alloy And Its Hydrogen Permeation Study

The inhibition of hydrogen embrittlement failure and the improvement of hydrogen permeation performance are the focus of research on hydrogen separation alloy membranes at home and abroad.This research has important theoretical significance and broad application prospects for the study of element doping and alloying modification of Nb-based hydrogen separation alloy membranes with solid solution structure.In this paper,the changes of crystal structure,hydrogenation thermodynamics,hydrogen diffusion kinetics and mechanical properties of Nb-based solid solution alloys with different amounts and different kinds of alloying elements were studied,and the hydrogen permeation properties of the alloy membranes were investigated.The anti-hydrogen embrittlement properties were analyzed.Main points can be obtained as the following:1)Nb_100-xW_x(x=2,5,8,10,16)alloy samples were prepared by arc melting.The results indicated that melting-prepared Nb_100-xW_x samples are Nb-based solid solutions with bcc structure.W-doping will induce the lattice distortion and shrink,the distortion behavior is more obvious with the increase of W-doping content.Non-equilibrium transformation microstructure is observed in these Nb_100-xW_xsamples,which presents dendritic morphology with W-poor region dispersed in W-rich matrix.Dense and refined dendritic morphology is observed obviously in Nb_100-xW_x(x=10,16)samples.W-doping results in the increase of the value of hydride-formation enthalpy,and benefits H-release of corresponding hydride.Higher H-diffusion coefficient(D_H=1.66×10^-9 cm²·s^-1)is obtained in Nb₈₄W₁₆ sample,which is about 1.8 times that of Nb₉₈W₂ sample.W-doping also improve the anti-hydrogen embrittlement capacity,Nb₈₄W₁₆ sample has the largest maximum load(85.43N)and maximum displacement(0.85mm),which is about 2.5 and2.6 times that of Nb₉₈W₂ sample respectively,indicating that the improvement of mechanical properties is related to its microstructure.2)Nb₉₀W₅M₅ alloy was prepared by partially replacing Nb with 5 mol%of alloying elements M(M=Co,Ni,Mo,Ti).The results indicated that all Nb₉₀W₅M₅ samples are solo Nb solid-solution phase(Nb-bcc),the degree of lattice distortion of these samples are affected by atomic radius of doped element.Bigger Crystal cell-volume distortion contraction and small lattice parameter was observed in Nb₉₀W₅Co₅sample,where Co-rich Nb Co solid solution structure is precipitated at grain boundaries and intracrystalline defects of Nb solid solution.Nb₉₀W₅Co₅sample has lower absolute value of hydride formation(-22.3 KJ/mol),higher hydrogen-diffusion coefficient(1.57 x 10^-9 cm²/s),and higher critical load(78.4 N),which exhibits good bending mechanical properties and hydrogen penetration properties.Experimental studies have shown that the ternary doping and Co-rich Nb Co solid solution structure is more favorable for the hydrogen permeability and hydrogen embrittlement resistance of Nb-based solid solution alloys.3)The structure and properties of Nb_95-xW₅Co_x(x=1,2,3,5)alloys were further studied.Comparative experiments show that the Co-rich solid solution were precipitated from the grain boundary of the Nb solid solution when doped with 1 mol%Co.As the amount of Co doping increases,the Co-rich solid solution continues to be precipitated from the Nb solid solution intragranular defect.Moreover,the lattice constant of the alloy decrease and the value of the hydride formation enthalpy,the hydrogen diffusion coefficient and the maximum load are continuously increased,indicating that the Co-rich solid solution structure is beneficial to the improvement of the hydrogen permeability and hydrogen embrittlement resistance of the alloy.