The Influence Of W And Pd Alloying On Microstructure And Hydrogen Transport Properties Of Nb₅₆Ti₂₃Ni₂₁ Alloy

The hydrogen separation alloys Nb₅₆Ti₂₃Ni₂₁ based on theory of "multiphase composition,functional sharing" have good hydrogen permeation properties,but they have insufficient hydrogen embrittlement resistance.In this paper,new hydrogen separation alloy were formed by 3 different methods of replacing elements based on the alloy Nb₅₆Ti₂₃Ni₂₁.The first way is to replace part of Nb by W and Pd.The second way is to replace part of Nb by W?to replace part of Ti Ni by Pd.And the last way is to replace part of Nb by W?to replace part of Ni by Pd.The microstructure and hydrogen transport properties were studied.The effects of W and Pd on the properties of the alloys were investigated,and hydrogen permeation materials with high hydrogen permeation properties and good hydrogen embrittlement res istance were developed.Nb₅₆Ti₂₃Ni₂₁ series alloys with W and Pd were tested by XRD,SEM and EDS and the results show that the main phases composition of the alloy are Bcc-Nb phase and B2-Ti Ni phase.The mainly microstructure of alloy maintains the primary BccNb phase and the eutectic phase [Bcc Nb + B2-Ti Ni].W mainly exists in the primary Nb phase in a solid solution and Pd mainly exist in the Ti Ni solid solution.The first effect of the addition element W on the microstructure of the alloy is to make the lateral branches of the primary Nb phase undeveloped.This is mainly because the addition of high melting point element W causes the liquidus temperature of the alloy to increase,and the precipitation of bcc-?Nb,W?can occur at a higher temperature.In addition,element W promotes the the phenomenon of "Halo" occuring in the primary Nb phase,and promotes the contents of Bcc-Nb to decrease and B2-Ti Ni to increase in the eutectic phase.The addition of element Pd transforms eutectic from lamellar to reticular,whose morphology is divorced eutectic or even non-eutectic.The element W and Pd work together to make the dissolving structure appear in the alloy.Hydrogen percolation experiments of Nb₅₆Ti₂₃Ni₂₁ series alloys with added elements W and Pd show that hydrogen penetrating flow J×L and pressure ?P0.5 of the alloy in high pressure does not comply with the laws of Sieverts.The effect of replacing Nb with elements W and Pd is not good,and the more elements W and Pd are added,the worse the hydrogen permeability of the alloy is.Nb56 series alloys obtained by element W replacing Nb and element Pd replacing Ti Ni or Ni have bet ter hydrogen permeability.The Nb51W5Ti23Ni16Pd5 alloy shows the highest hydrogen permeability coefficient.The hydrogen brittleness resistance of alloy Nb₅₆Ti₂₃Ni₂₁ is poorer,and broke down at 220 ?.But the hydrogen brittleness resistance of W and Pd alloying Nb₅₆Ti₂₃Ni₂₁ series alloy can be very good,they do not broke down in the process of slow cooling.The addition of element W and Pd effectively improved the hydrogen brittleness of the alloy.The hydrogen dissolution test was performed on the alloy of W and Pd alloyed Nb₅₆Ti₂₃Ni₂₁ series,and experiments showed that the addition of elements W and Pd effectively reduces the hydrogen solubility of the alloy.W and Pd can reduce the hydrogen dissolution of the alloy,and the more of added elements,the more reduction of hydrogen solubility.When W replaces some Nb and Pd replaces some Ti Ni,the hydrogen dissolution of alloy will also be reduced,but the reduction is less than the way of W and Pd replacing part of Nb.When W replaces some Nb and Pd replaces some Ni,the reduction of the hydrogen dissolution is least.At 523K⁶73K,the hydrogen solubility of Nb41W7.5Pd7.5Ti23Ni21 alloy was the lowest,while that of Nb51W5Ti23Ni16Pd5 alloy was the highest,but all of them were smaller than the basic alloy Nb₅₆Ti₂₃Ni₂₁.The driving hydrogen diffusion model based on the chemical potential,is used to explain the hydrogen diffusion of W and Pd alloying Nb₅₆Ti₂₃Ni₂₁ performance.The results show that adding elements W,Pd alloy refers to the former factor B0 decreases in varying degree.The more content of Pd and W,referring to former factor,the smaller B0,alloy Nb41W7.5Pd7.5Ti23Ni21 refers to the former factor to the minimum.B0 of W replacing Nb and Pd replacing Ni is maximum.Element W and Pd replacement elements Nb and W replacement Nb replacement,Pd,Ni in both cases,all can increase the permeability of hydrogen diffusion activation,and W and Pd content increase,the permeability of hydrogen diffusion activation energy,the greater the spread,the more difficult;In the case of element W replacing Nb and Pd replacing Ti Ni,diffusion activation energy can be reduced and hydrogen can be diffused.Among the four types of Nb₅₆Ti₂₃Ni₂₁ alloy that W and Pd alloyed,Nb51W5Ti23Ni16Pd5 alloy has the largest hydrogen permeability at all temperatures,which is 2.996×10-8 mol H2m-2s-1pa-0.5,and has good anti-hydrogen brittleness and the best comprehensive performance.