Modification of BCC phase and the enhanced reversible hydrogen storage properties of Ti-V-Fe-Mn alloys with varied V/Fe ratios

Ti-V-based alloys are proved of huge potential in storing hydrogen,but the incomplete reversible hydrogen storage capacity caused by overstability of V hydride has limited the large-scale application.In this study,Ti_(32)V_(40+x)Fe_(23-x)Mn_(5)(x=0,4,8,12,at.%)alloys were designed,and the effects of V/Fe ratio on phase constitution and hydrogen storage properties were investigated.The main phase of the alloys is body-centered cubic(BCC)phase,and the lattice constants of the BCC phase decrease with the decrease of V/Fe ratio.Moreover,C14 Laves phase exists in alloys with a Fe content of 19at.%to 23at.%.For hydrogenation,the C14 Laves phase can accelerate the hydrogen absorption rate,but the hydrogen absorption capacity is reduced.With the decrease of V/Fe ratio,the hydride gradually destabilizes.Owing to its large lattice constant and high hydrogen absorption phase content,the Ti_(32)V_(52)Fe_(11)Mn_(5)alloy shows the most enhanced hydrogen storage properties with hydrogenation and dehydrogenation capacities of 3.588wt.%at 298 K and 1.688wt.%at 343 K,respectively.The hydrogen absorption capacity of this alloy can be reserved to 3.574wt.%after 20 cycles of hydrogen absorption and desorption.

Mechanism on the Effect of Al upon the γ→ε Martensite Transformation in the Fe-Mn Alloys

The structure of the solid solution treated and deformed Fe-25Mn-(0-3.11)Al-0.15C alloys was examined by means of metallograph and X-ray diffraction, which has confirmed that Al restrains the γ→ε transformation in the Fe-Mn alloys. The mechanism on the restraining effect of Al has been discussed on the basis of the efFect of Al upon the stacking fault energy in the Fe-Mn alloys.Aluminium increases thermodynamically the stability of the Fe-Mn austenite and the driving force limit necessitated to be overcome for the γ→ε transformation, because the thermodynamicalcalculation indicates that Al increases the stacking fault energy in the Fe-Mn alloys at 300 K.Al will decrease the number and the size for the ε-martensite nucleus according to the stacking fault mechanism of the ε-martensite nucleation

Utlra-fast hydrolysis performance of MgH_(2) catalyzed by Ti-Zr-Fe-Mn-Cr-V high-entropy alloys

Hydrogen energy is one of the ideal energy alternatives and the upstream of the hydrogen industry chain is hydrogen production,which can be achieved via the reaction of inorganic materials with water,known as hydrolysis.Among inorganic materials,the high hydrogen capacity for hydrolysis of MgH_(2)(15.2 wt%)makes it a promising material for hydrogen production via hydrolysis.However,the dense Mg(OH)_(2) passivation layer will block the reaction between MgH_(2) and the solution,resulting in low hydrogen yield and sluggish hydrolysis kinetics.In this work,the hydrogenyield and hydrogen generation rate of MgH_(2) are considerably enhanced by adding Ti-Zr-Fe-Mn-Cr-V high-entropy alloys(HEAs) for the first time.In particular.the MgH_(2)-3 wt% TiZrFe_(1.5)MnCrV_(0.5)(labelled as MgH_(2)-3 wt% Fe_(1.5)) composite releases 1526.70 mL/g H_(2) within 5 min at 40℃,and the final hydrolysis conversion rate reaches 95.62% within 10 min.The mean hydrogen generation rate of the MgH_(2)-3 wt% Fe_(1.5) composite is 289.16 mL/g/min,which is 2.38 times faster than that of pure MgH_(2).Meanwhile,the activation energy of the MgH_(2)-3 wt% Fe_(1.5) composite is calculated to be 12.53 kJ/mol. The density functional theory(DFT) calculation reveals that the addition of HEAs weakens the Mg-H bonds and accelerates the electron transfer between MgH_(2) and HEAs,Combined with the cocktail effect of HEAs as well as the formation of more interfaces and micro protocells,the hydrolysis performance of MgH_(2) is considerably improved.This work provides an appealing prospect for real-time hydrogen supply and offers a new effective strategy for improving the hydrolysis performance of MgH_(2).

THERMODYNAMICS OF MARTENSITIC TRANSFORMATION IN Fe-Mn-C AND Fe-Ni-C ALLOYS

A Central Atom Model is introduced and the LFG and Hsu models are modified in order to evaluate the driving force for the martensitic transformation in Fe-Mn-C and Fe-Ni-C al- loys.The results show that the relationship between the driving force and the yield strength of austenite at Ms temperature,σ_(0.2)~γ/M_s,fits Hsu's formula;ΔG~=2.1σ_(0.2)~γ/M_s+907 J/mol.The M_s temperatures of Fe-Mn-C and Fe-Ni-C alloys are also calculated.The calculated results are in good agreement with experimental values.

X-ray Peak-Shift Determination of Deformation Fault Probability in Fe-Mn-Si Alloys

The X-ray diffraction peak-shift method was introduced into the determination of deformation fault probability (a) of Fe-Mn-Si alloys with various Mn contents and thermomechanical cycling numbers. The precise lattice constants required were obtained by numerical calculation instead of using standard sample without any fault. The influence of internal stress on the determined a has been evaluated, and the caused relative error was determined as about 4% and thus negligible. The results show that the deformation fault probability increases with decreasing Mn-content and increasing cycle number, which are qualitatively consistent with those results of Psf determined by peak-broadening method.

STUDY ON THE MAGNETISM AND PHASE TRANSFORMATIONIN Fe-Mn-Si-C SHAPE MEMORY ALLOYS

The hyperfine interactions of two shape memory alloys have been studied by Mossbauer effect measurement at various temperatures. The Mossbauer spectra exhibit a mag-netic change from antiferro magnetic state to paramagnetic state when the temperuture rises. The Fe-Mn-Si alloys have a small hyperfine field and silicon element increases the hyperfine field and magnetic susceptibility. Thermo-induced γ→ ε trunsforma-tions are suppressed by Neel transition and by increasing carbon content, whereas stress induced γ→ ε transformation occurs in both alloys. Antiferromagnetic spin order can suppress thermo-induced γ→εtransformations efficiently, but cannot sup-press stress induced γ → ε transformation.

EFFECTS OF TEMPERING TEMPERATURE AND TIME ON SHEAR MODULUS OF Fe-Mn BASED ALLOYS

Effects of the tempering temperature and time on the shear modulus of Fe-Mn based alloys have been studied.The results show that(ΔG/G)-Tcurves of tempered alloys containing Cr and Ti have two extreme values—maximum and minimum,and that the curves of tem- pered alloys containing Cr,Ni,W and C only have a maximum value.This is the reason that Ni,W and C decrease the transformation point T_N of the antiferromagnetism.The ΔG_λ ef- feet increases gradually with the rise of tempering temperature or with the increase of tem- pering time.

Relations between the Lattice Parameter and the Stability of Austenite against ε Martensite for the Fe-Mn Based Alloys

The influences of lattice parameter of austenite, the electron concentration, the yield strength of parent phase on γ→ε martensite start temperature Ms in the Fe-Mn alloys containing C, Al, Ge and Si have been experimentally investigated. The results show that the lattice parameter of austenite is more important than the electron concentration and the yield strength of parent phase in governing the γ→ε martensitic transformation in Fe-Mn based alloys. A relation between the Ms and lattice parameter of austenite in Fe-Mn based alloys is suggested. The elements Mn, C, Al, Ge, which increase the lattice parameter of austenite lower the Ms; while the element Si, which decreases the lattice parameter increases the MS. The depressing effect of antiferromagnetic transition on the γ→ε martensitic transformation may be related to the increase of lattice parameter due to the positive magnetostriction during the antiferromagnetic transition.

Martensitic Transformation in Fe-Mn-Si Based Shape Memory Alloys

The critical driving force for martensitic transformation fcc ( gamma ) yields hcp ( epsilon ) in ternary Fe-Mn-Si alloys increases with the content of Mn and decreases with that of Si. Thermodynamical prediction of M//s in ternary Fe-Mn-Si alloys was established. The fcc ( gamma ) yields hcp ( epsilon ) martensitic transformation in Fe-Mn-Si is a semi-thermoelastic and the nucleation process does not strongly depend on soft mode. Nucleation occurs directly through an overlapping of stacking fault rather than pole mechanism, and it is suggested that stacking fault energy (SFE) is the main factor controlling nucleation. Based on the phenomenological theory of martensite crystallography, a shuffle on (0001)//h//c//p plane is required when d//1//1//1 does not equal d//0//0//0//2. The derived principal strain in Bain distortion is smaller, i, e., more reasonable than the values given by Christian. Alloying elements strengthening the austenite, lowering SFE of gamma phase and reducing T//N** gamma temperature may be beneficial to shape memory effect of Fe-Mn-Si based alloys. Accordingly, Fe-Mn-Si-RE and Fe-Mn-Si-Cr-N (or Fe-Mn-Si-Ni-Cr-N) are worthy to be recommended as shape memory materials with improved shape memory effect. (Edited author abstract) 48 Refs.

Accelerated design of high-performance Mg-Mn-based magnesium alloys based on novel bayesian optimization

Magnesium(Mg),being the lightest structural metal,holds immense potential for widespread applications in various fields.The development of high-performance and cost-effective Mg alloys is crucial to further advancing their commercial utilization.With the rapid advancement of machine learning(ML)technology in recent years,the“data-driven''approach for alloy design has provided new perspectives and opportunities for enhancing the performance of Mg alloys.This paper introduces a novel regression-based Bayesian optimization active learning model(RBOALM)for the development of high-performance Mg-Mn-based wrought alloys.RBOALM employs active learning to automatically explore optimal alloy compositions and process parameters within predefined ranges,facilitating the discovery of superior alloy combinations.This model further integrates pre-established regression models as surrogate functions in Bayesian optimization,significantly enhancing the precision of the design process.Leveraging RBOALM,several new high-performance alloys have been successfully designed and prepared.Notably,after mechanical property testing of the designed alloys,the Mg-2.1Zn-2.0Mn-0.5Sn-0.1Ca alloy demonstrates exceptional mechanical properties,including an ultimate tensile strength of 406 MPa,a yield strength of 287 MPa,and a 23%fracture elongation.Furthermore,the Mg-2.7Mn-0.5Al-0.1Ca alloy exhibits an ultimate tensile strength of 211 MPa,coupled with a remarkable 41%fracture elongation.

Relationship between the unique microstructures and behaviors of high-entropy alloys

High-entropy alloys(HEAs),which were introduced as a pioneering concept in 2004,have captured the keen interest of nu-merous researchers.Entropy,in this context,can be perceived as representing disorder and randomness.By contrast,elemental composi-tions within alloy systems occupy specific structural sites in space,a concept referred to as structure.In accordance with Shannon entropy,structure is analogous to information.Generally,the arrangement of atoms within a material,termed its structure,plays a pivotal role in dictating its properties.In addition to expanding the array of options for alloy composites,HEAs afford ample opportunities for diverse structural designs.The profound influence of distinct structural features on the exceptional behaviors of alloys is underscored by numer-ous examples.These features include remarkably high fracture strength with excellent ductility,antiballistic capability,exceptional radi-ation resistance,and corrosion resistance.In this paper,we delve into various unique material structures and properties while elucidating the intricate relationship between structure and performance.

Influence of Metalloid Elements on the Magnetic Properties and Anisotropy of FeNi-based Amorphous Alloys

The magnetic properties and anisotropy of amor- phous(Fe_(80)Ni_(20))_(78)Si_xB_(22-x).alloys have been investigated systematically.The maximum permeability,coercive force and remanence have been determined for as-prepared and annealed samples,The results on the technical magnetic properties of this alloy system have been discussed and compared with Masumoto's.

CONSTITUTIONAL DIAGRAM OF Fe-Mn-C ALLOYS AFTER SOLUTION TREATMENT AT 1000℃

On the basis of experimental results of 76 points of composition and previous relevant conclu- sions,a relatively complete constitutional diagram of solid solution treating Fe-Mn-C sys- tem alloy at 1000℃ has been constructed with austenite zones of different stabilities.The chemical composition range and structure change of steels with various Mn have also been discussed.Thus,the reasonable selection of composition and structure may be available for the manganese steel with commercial purposes.

Creep Behaviour of Fe-Mn Binary Alloys

Tensile creep behaviour of fine-grained Fe-Mn binary alloys containing 0.42-1.21 wt. % Mn has been investigated in the temperature range from room temperature to 475K under 10-50 MPa. Tensile tests are carried out with a constant cross-head speed under uniaxial load at a strain rate 10^-4s^-1. Stress exponent and activation energy are determined to clarify deformation mechanism. The obtained variation of steady state creep rate with respect to the applied stress for Fe-Mn binary alloys exhibits two distinct regimes at about 20 MPa, indicating a possible change in creep mechanism. The average stress exponent is approximately 2.2, which is a characteristic of grain boundary sliding in the alloys. The activation energy for plastic flow varies from 135 to 92k J/mol, depending on the Mn content.

INFLUENCE OF AUSTENITE STRENGTHENING ON MARTENSITIC TRANSFORMATION IN Fe-Mn-C ALLOYS

The M_s temperature and the yield strength of austenite at M_s temperature have been meas- ured for five Fe-Mn-C alloys.The experimental results show that there is a linear relation- ship between them.The effect of the solution strengthening of austenite on martensite morphology is also studied.It is pointed out that there is a characteristic temperature T_c in austenite strengthening.Martensite morphology is mainly of dislocated laths when M_s>T_c, and is mainly of twinned plates when M_s<T_c.A theoretical analysis is given which is in good agreement with experimental results.

SHAPE MEMORY EFFECT OF POLYCRYSTALLINE Fe-Mn-Si ALLOYS

The influence of quenching temperature on the shape memory effect(SME)of the Fe-Mn-Si polycrystalline alloys and their martensitic transformation temperature have been studied.The SME of the hot-rolled specimen may be remarkably enhanced by selecting quenching temperature of 600—800℃.It has been shown that SME is influenced not only by the distribution of ε-phase morphology but also by its pre-existence.

Microstructure and damping properties of LPSO phase dominant Mg-Ni-Y and Mg-Zn-Ni-Y alloys

This work studied the microstructure,mechanical properties and damping properties of Mg_(95.34)Ni_(2)Y_(2.66) and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys systematically.The difference in the evolution of the long-period stacked ordered(LPSO)phase in the two alloys during heat treatment was the focus.The morphology of the as-cast Mg_(95.34)Ni_(2)Y_(2.66)presented a disordered network.After heat treatment at 773 K for 2 hours,the eutectic phase was integrated into the matrix,and the LPSO phase maintained the 18R structure.As Zn partially replaced Ni,the crystal grains became rounded in the cast alloy,and lamellar LPSO phases and more solid solution atoms were contained in the matrix after heat treatment of the Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloy.Both Zn and the heat treatment had a significant effect on damping.Obvious dislocation internal friction peaks and grain boundary internal friction peaks were found after temperature-dependent damping of the Mg_(95.34)Ni_(2)Y_(2.66)and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys.After heat treatment,the dislocation peak was significantly increased,especially in the alloy Mg_(95.34)Ni_(2)Y_(2).66.The annealed Mg_(95.34)Ni_(2)Y_(2.66)alloy with a rod-shaped LPSO phase exhibited a good damping performance of 0.14 atε=10^(−3),which was due to the difference between the second phase and solid solution atom content.These factors also affected the dynamic modulus of the alloy.The results of this study will help in further development of high-damping magnesium alloys.

Recent innovations in laser additive manufacturing of titanium alloys

Titanium(Ti)alloys are widely used in high-tech fields like aerospace and biomedical engineering.Laser additive manufacturing(LAM),as an innovative technology,is the key driver for the development of Ti alloys.Despite the significant advancements in LAM of Ti alloys,there remain challenges that need further research and development efforts.To recap the potential of LAM high-performance Ti alloy,this article systematically reviews LAM Ti alloys with up-to-date information on process,materials,and properties.Several feasible solutions to advance LAM Ti alloys are reviewed,including intelligent process parameters optimization,LAM process innovation with auxiliary fields and novel Ti alloys customization for LAM.The auxiliary energy fields(e.g.thermal,acoustic,mechanical deformation and magnetic fields)can affect the melt pool dynamics and solidification behaviour during LAM of Ti alloys,altering microstructures and mechanical performances.Different kinds of novel Ti alloys customized for LAM,like peritecticα-Ti,eutectoid(α+β)-Ti,hybrid(α+β)-Ti,isomorphousβ-Ti and eutecticβ-Ti alloys are reviewed in detail.Furthermore,machine learning in accelerating the LAM process optimization and new materials development is also outlooked.This review summarizes the material properties and performance envelops and benchmarks the research achievements in LAM of Ti alloys.In addition,the perspectives and further trends in LAM of Ti alloys are also highlighted.

Effect of Compound Rare Earth on Shape Memory Effect of Fe-Mn-Si-Ni-C Alloys

Effect of compound rare earth (RE) on shape memory effect (SME) of Fe-Mn-Si-Ni-C shape memory alloy was studied by bent measurement,thermal cycle training, SEM and XRD etc. The results show that metallurgic microstructure is refined and SME improved evidently with the addition of compound RE. The alloy appears little two-way shape memory effect. The former training and addition of compound RE are two effective ways to restrain martensitic stability. XRD analysis also indicates that ε→γ reversible transition ratio increases by training greatly help to improve SME of the alloy.

Microstructures,corrosion behavior and mechanical properties of as-cast Mg-6Zn-2X(Fe/Cu/Ni)alloys for plugging tool applications

Mg-6Zn-2X(Fe/Cu/Ni)alloys were prepared through semi-continuous casting,with the aim of identifying a degradable magnesium(Mg)alloy suitable for use in fracturing balls.A comparative analysis was conducted to assess the impacts of adding Cu and Ni,which result in finer grains and the formation of galvanic corrosion sites.Scanner electronic microscopy examination revealed that precipitated phases concentrated at grain boundaries,forming a semi-continuous network structure that facilitated corrosion penetration in Mg-6Zn-2Cu and Mg-6Zn-2Ni alloys.Pitting corrosion was observed in Mg-6Zn-2Fe,while galvanic corrosion was identified as the primary mechanism in Mg-6Zn-2Cu and Mg-6Zn-2Ni alloys.Among the tests,the Mg-6Zn-2Ni alloy exhibited the highest corrosion rate(approximately 932.9 mm/a)due to its significant potential difference.Mechanical testing showed that Mg-6Zn-2Ni alloy possessed suitable ultimate compressive strength,making it a potential candidate material for degradable fracturing balls,effectively addressing the challenges of balancing strength and degradation rate in fracturing applications.