Study On Microstructure And Hydrogen Permeation Behavior Of NbFe Based Hydrogen Filtration Alloys

At present,industrial hydrogen is mainly obtained through the reforming of fossil fuels such as natural gas and the removal of impurities and by-products（N₂,H₂S,etc）through separation technology.Pd based membranes have generally low permeability and high cost,and 5B group metals have a special Bcc structure with higher hydrogen permeability compared to Pd’s Fcc structure.The previous work of the research group has shown that the Nb₅Ti₆₀Fe₃₅ system alloy has significant advantages as a low-cost and high-performance hydrogen permeation material,as well as poor resistance to hydrogen embrittlement under low temperature conditions.This article improves the comprehensive performance of hydrogen filtration membranes through the use of"composition control methods"（i.e.reducing Ti metal content and adding hydrogen repelling alloy elements）,and conducts detailed research on the microstructure,hydrogen permeation,hydrogen dissolution,and hydrogen diffusion performance of the aforementioned materials using various experimental methods.The details are as follows:（1）The Nb-Fe binary system alloy was prepared by removing the high impact hydrogen absorption Ti element.The phase microstructure,hydrogen permeation performance,and hydrogen solubility of five different alloys with different contents were studied.It was found that when the Nb content was 58.6 at.%,a eutectic Bcc-Nb+Fe₇Nb₆ phase structure was formed,otherwise some of the primary Bcc-Nb phases and Fe₇Nb₆ phases precipitated.The change in hydrogen absorption decreases to varying degrees with increasing temperature,and the failure hydrogen permeation performance based on mechanical properties cannot be tested;Modify the sample by high-temperature heat treatment and study its microstructure and hydrogen transfer characteristics under this heat treatment parameter.It was found that after being treated at an appropriate temperature for 24 hours,the hydrogen embrittlement resistance of the alloy was partially improved.After heat treatment,the hydrogen permeation performance of Nb₇₀Fe₃₀ alloy was about 2.81×10^-8 mol·H₂·m^-1·s^-1·Pa^-1/2at 673 K,which is1.75 times the Pd under the same conditions,indicates that Nb-Fe binary alloys can be used as alternative materials for hydrogen permeation separation membranes.（2）Replacing 2 at%transitional hydrogen repelling elements（Cu,Co,Mo,etc.）in the original Nb-Ti-Fe alloy to form a quaternary Nb-Ti-Fe-M alloy system,and studying the influence of various alloy additions on the microstructure and hydrogen permeation performance.The results show that the internal structure of the alloy is still composed of eutectic{Bcc-（Nb,Ti,M）+B2-（Ti,M）Fe}phases,indicating that the dependence of the microstructure type on the type of alloy elements is relatively small.However,the hydrogen permeation performance of the alloy is closely related to the type of hydrogen repelling alloy:the hydrogen embrittlement resistance of the alloy decreases sharply after the addition of W,Mo,and Cr;After adding Pd,Al,and Ni,the hydrogen permeation performance of the alloy is improved,but the hydrogen brittleness resistance is not significantly improved;After the addition of Cu,the hydrogen embrittlement resistance and hydrogen permeation performance of the alloy were improved,and the hydrogen permeability of the alloy reached4.32×10^-8 mol·H₂·m^-1·s^-1·Pa^-1/2 at 673 K.Hydrogen dissolution measurements were conducted on as cast condition alloys using PCT equipment,and a mechanism diagram of ductile brittle transition was constructed for the aforementioned quaternary alloy body.（3）On the basis of the above research,the hydrogen permeation model of alloy was constructed and the hydrogen transport process under the influence of concentration gradient,chemical potential gradient and other factors was introduced.The influence of alloy type,composition and inherent characteristics（strength,microhardness,electronic energy level,etc）on microstructure and hydrogen permeation performance was emphatically expounded:the hydrogen transport process under low hydrogen pressure concentration was controlled by hydrogen concentration gradient;The chemical potential gradient at high hydrogen pressure concentration can more accurately describe the hydrogen transport process of alloys.The hydrogen permeability of alloys is controlled by multiple parameters,among which the alloy type,component content,and electronic energy level have a relatively large impact,while phase orientation and physicochemical properties have a relatively small impact.Finally,compared with Nb based hydrogen filtration alloys in the literature,the design concept of hydrogen separation alloying was proposed by comparing and analyzing the hydrogen permeation correlation under the influence of multiple parameters.