Study On Microstructure And Hydrogen Transport Behaviors Of V(Nb)-Ti-Fe Alloys

Hydrogen energy is a renewable and clean energy.The finished hydrogen produced in industrial hydrogen production（such as:fossil energy reforming hydrogen production）contains many by-products,such as H₂S,N₂,CO and CO₂,etc.Therefore,“hydrogen separation technology”has become an important technical link for obtaining pure hydrogen.At present,Pd membrane materials have been commercially used in the field of hydrogen separation,but their cost is high,and it is particularly important to develop new membrane materials with cheap and excellent hydrogen permeability.In this context,Group 5B metals（Nb,V and Ta,etc.）have become the focus of research by scholars at domestic and foreign.However,the above pure metals are prone to hydrogen embrittlement during hydrogen permeation and cannot be used in the hydrogen separation process.According to existing literature reports,V-based alloys（V-Ni,V-Fe and V-Ti Ni,etc.）have high advantages in hydrogen permeability and are ideal hydrogen separation membrane materials to replace commercial Pd membranes.But so far,no research on V-Ti-Fe hydrogen separation alloys has been carried out at domestic and foreign.Based on this,the V-Ti-Fe alloys system was selected as the research object in this paper,and the phase diagram,microstructure,hydrogen transport behavior,heat treatment process and hydrogen embrittlement resistance of V-Ti-Fe alloys were studied in detail.as follows:1.The representative(Ti₆₅Fe₃₅)_100-xV_x（x=0,2.5,5,10,15,25）alloys was selected as the research object,and the above 6 different alloys were successfully prepared by non-consumable arc melting furnace equipment.Firstly,the effects of different V contents on the alloys microstructure,phase types（Ti Fe,Ti Fe₂ and bcc-（V,Ti））and phase volume fraction were investigated.When the V content is the same,the hydrogen solubility of the alloys increases with the increase of temperature,and when the V content increases gradually,the hydrogen solubility of the alloy increases gradually.On the basis of the above and combined with the hydrogen permeation behavior of different alloys,the ductile-brittle transition hydrogen concentration region（DBTC）of V-based alloys was explored,that is,the ductile-brittle transition region of V-based dual-phase alloys was about 0.42-0.48 H/M,this part of the work provides a new idea for the subsequent design of V-based hydrogen permeable alloys.2.On the basis of“1”,expand the alloys composition design from“line”to“surface”,that is,expand the research scope to 31 composition points,and systematically study its microstructure,phase composition,mechanical properties and hydrogen permeation performance.Considering the research results,the above alloys are divided into three regions,namely Ti Fe phase region（consisting of primary Ti Fe phase and{Ti Fe+bcc-（V,Ti）}eutectic structure）,Ti Fe₂ phase region（consisting of primary Ti Fe phase,Ti Fe₂ phase and bcc-（V,Ti）}solid solution phase）and bcc-（V,Ti）phase region（composed of primary Ti Fe phase and bcc-（V,Ti）}solid solution phase）.Among them,alloys in Ti Fe₂ and bcc-（V,Ti）phase regions are not suitable for hydrogen separation due to their poor mechanical properties.In the Ti Fe phase region,the mechanical properties of V_2.5Ti6_2.5Fe₃₅ dual-phase alloy were significantly improved after annealing at 1173K and 18h,and its hydrogen flux value was 4.6 mol H₂ m^-2 s^-1,which was the same as that of pure Pd under the same conditions 1.3 times,and good resistance to hydrogen embrittlement.In addition,the eutectic morphology of the alloys structure has a great influence on the hydrogen permeability,and the mechanical properties of the alloys are closely related to the types and contents of Ti Fe₂ and Ti₂Fe phases.3.Based on the research of Nb/V-based alloys DBTC,the design concept of 5B group metal dual-phase alloys is proposed.Based on this,the applicability of the above concept in the design of Nb-Ti-Fe hydrogen separation alloys is systematically studied.The research shows that the hydrogen solubility（temperature less than 673 K）of alloys containing primary Ti Fe phase is lower than 0.72 H/M,on the contrary,the hydrogen solubility（temperature less than 673 K）of alloys containing primary Nb phase is greater than 0.72 H/M.In addition,the interfacial area of the Ti Fe phase in the alloy eutectic is inversely proportional to the hydrogen permeation performance.Among them,the Nb₅Ti₆₀Fe₃₅ alloy with the smallest Ti Fe phase interface exhibits the highest hydrogen permeation performance at 673 K,namely:3.82×10^-8 mol H₂ m^-1 s^-1 Pa^-0.5.Finally,a Nb₅Ti₅₈Fe₃₅Cu₂ alloy with high hydrogen permeability(4.32×10^-8 mol H₂ m^-1 s^-1 Pa^-0.5)and excellent resistance to hydrogen embrittlement was developed based on the design concept of 5B group metal dual-phase alloy.