CO_(2) High Temperature Corrosion and Its Prevention of Chromia Forming Fe-base Alloys

High temperature corrosion of chromia forming Fe-base alloys by CO_(2) produces not only oxidation but also carburisation.The corrosion kinetics in CO_(2)-rich gas is found to be increased compared with that in air or oxygen.As a result,higher alloy chromium levels are required to achieve protective chromia formation in CO_(2).Corrosion reaction mechanisms in CO_(2) are examined and the internal carburisation of alloys in low carbon activity CO_(2) gases are analysed based on the variation of pO_(2) at the interface of oxide and metal.Carbon penetration through chromia oxide scale has been revealed by atom probe tomography.The strategies to resist CO_(2) corrosion are reviewed by alloying of Si and/or Mn,forming additional diffusion barrier layers,and by adding sulphur to modify oxide grain boundaries to reduce carbon diffusion along the grain boundaries.

Achieving a superior Na storage performance of Fe-based Prussian blue cathode by coating perylene tetracarboxylic dianhydride amine

Fe-based Prussian blue(Fe-PB)cathode material shows great application potential in sodium(Na)-ion batteries due to its high theoretical capacity,long cycle life,low cost,and simple preparation process.However,the crystalline water and vacancies of Fe-PB lattice,the low electrical conductivity,and the dissolution of metal ions lead to limited capacity and poor cycling stability.In this work,a perylene tetracarboxylic dianhydride amine(PTCDA)coating layer is successfully fabricated on the surface of Fe-PB by a liquid-phase method.The aminated PTCDA(PTCA)coating not only increases the specific surface area and electronic conductivity but also effectively reduces the crystalline water and vacancies,which avoids the erosion of Fe-PB by electrolyte.Consequently,the PTCA layer reduces the charge transfer resistance,enhances the Na-ion diffusion coefficient,and improves the structure stability.The PTCA-coated Fe-PB exhibits superior Na storage performance with a first discharge capacity of 145.2 mAh g^(−1) at 100 mA g^(−1).Long cycling tests exhibit minimal capacity decay of 0.027%per cycle over 1000 cycles at 1 A g^(−1).Therefore,this PTCA coating strategy has shown promising competence in enhancing the electrochemical performance of Fe-PB,which can potentially serve as a universal electrode coating strategy for Na-ion batteries.

Clean production of Fe-based amorphous soft magnetic alloys via smelting reduction of high-phosphorus iron ore and apatite

Separated preparation of prealloys and amorphous alloys results in severe solidification-remelting and beneficial element removal-readdition contradictions,which markedly increase energy consumption and emissions.This study offered a novel strategy for the direct production of FePC amorphous soft magnetic alloys via smelting reduction of high-phosphorus iron ore(HPIO)and apatite.First,the thermodynamic conditions and equilibrium states of the carbothermal reduction reactions in HPIO were calculated,and the element content in reduced alloys was theoretically determined.The phase and structural evolutions,as well as element migration and enrichment behaviors during the smelting reduction of HPIO and Ca_(3)(PO_(4))_(2),were then experimentally verified.The addition of Ca_(3)(PO_(4))_(2)in HPIO contributes to the enrichment of the P element in reduced alloys and the subsequent development of Fe_(3)P and Fe_(2)P phases.The content of P and C elements in the range of 1.52 wt% -14.63 wt% and 0.62 wt% -2.47 wt%,respectively,can be well tailored by adding 0-50 g Ca_(3)(PO_(4))_(2)and controlling the C/O mole ratio of 0.8-1.1,which is highly consistent with the calculated results.These FePC alloys were then successfully formed into amorphous ribbons and rods.The energy consumption of the proposed strategy was estimated to be 2.00×10^(8) kJ/t,which is reduced by 30% when compared with the conventional production process.These results are critical for the comprehensive utilization of mineral resources and pave the way for the clean production of Fe-based amorphous soft magnetic alloys.

Behavior of Medium-frequency Core Loss in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency have been investigated in the ranges of 100 Hz<= f<=25000 Hz and 0.1 T< =Bm <=1.0 T for three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys. The measured and calculated results showed that the total power loss per cycle clearly exhibited a nonlinear behavior in the range below 3 kHz～5 kHz depending on both the magnetic state and the value of Dm, whereas it showed a quasi-linear behavior above this range. The total loss was decomposed into hysteresis loss, classical eddy current loss and excess loss, the obvious nonlinear behavior has been confirmed to be completely determined by the dependence of the excess loss on frequency. It has been indicated that the change rate of the excess loss per cycle with respect to frequency sharp decreases with increasing frequency in the range below about 3 kHz～5 kHz, wherease the rate of change slowly varies above this range, thus leading to the quasilinear behavior of the total loss per cycle. In this paper, some linear expressions of the total loss per cycle has been given in a wider medium-frequency segment, which can be used for roughly estimating the total loss.

General Properties of Low-frequency Power Losses in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency f and amplitude flux density Bm have been investigated for the three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys in the ranges of 10 Hz<=f<=1000 Hz and 0.4 T<= Bm <=1.0 T. The total loss P is decomposed into the sum of the hysteresis loss Physt, the classical eddy current loss Pel and the excess loss Pexc. Physt has been found to be proportional to Bm^2 and f. The behavior of Pexc/f vs f being equivalent to P/f vs f clearly exhibits nonlinearity in the range not more than about 120 Hz, whereas the behavior of P/f vs f roughly shows linearity in the range far above 100 Hz and not more than 1000 Hz. In the range up to 1000 Hz, Physt is dominant in the original high permeability state and the state of low residual flux density, whereas Pexc in the state of high residual flux density is dominant in the wider range above about 100 Hz. The framework of the statistical theory of power loss has been used for representing the behavior of Pexc/f vs f. It has been found that the number n of the simultaneously active 'Magnetic Objects' linearly varies as n = n0 + Hexc/H0 as a function of the dynamic field Hexc in the range below about 120 Hz, whereas n approximately follows a law of the form n = n0 + (Hexc/H0)^m with 1 < m < 2 in the range far above 100 Hz and not more than 1000 Hz. The values of the field HO in principle related to the microstructure and the domain structure have been calculated for the three states.

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.

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.

Research Progress of Stress-Induced Magnetic Anisotropy in Fe-Based Amorphous and Nanocrystalline Alloys

Since it was discovered that stress annealing induced larger anisotropies compared to other annealing methods in amorphous and nanocrystalline alloys, there has been a lot of research done to explain this phenomenon. This has led to many suggestions about the origin of this stress-induced magnetic anisotropy, but till now the origin is explained with two competing models: the magnetoelastic effect model and the diatomic pair ordering model. In spite of these theories, the origin of the stress-induced anisotropy is still under discussion because direct observation of structural anisotropy is still lacking. In this paper, we have reviewed some of the characterization techniques which have been used to discuss the origin of stress-induced magnetic anisotropy and the progress which has been made thus far in unifying all the contrasting views which has been suggested to be the origin of the stress-induced anisotropy in FINEMET alloys.

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.

Prediction of the thermal conductivity of Mg–Al–La alloys by CALPHAD method

Mg-Al alloys have excellent strength and ductility but relatively low thermal conductivity due to Al addition.The accurate prediction of thermal conductivity is a prerequisite for designing Mg-Al alloys with high thermal conductivity.Thus,databases for predicting temperature-and composition-dependent thermal conductivities must be established.In this study,Mg-Al-La alloys with different contents of Al2La,Al3La,and Al11La3phases and solid solubility of Al in the α-Mg phase were designed.The influence of the second phase(s) and Al solid solubility on thermal conductivity was investigated.Experimental results revealed a second phase transformation from Al_(2)La to Al_(3)La and further to Al_(11)La_(3)with the increasing Al content at a constant La amount.The degree of the negative effect of the second phase(s) on thermal diffusivity followed the sequence of Al2La>Al3La>Al_(11)La_(3).Compared with the second phase,an increase in the solid solubility of Al in α-Mg remarkably reduced the thermal conductivity.On the basis of the experimental data,a database of the reciprocal thermal diffusivity of the Mg-Al-La system was established by calculation of the phase diagram (CALPHAD)method.With a standard error of±1.2 W/(m·K),the predicted results were in good agreement with the experimental data.The established database can be used to design Mg-Al alloys with high thermal conductivity and provide valuable guidance for expanding their application prospects.

Effect of icosahedral phase formation on the stress corrosion cracking(SCC)behaviors of the as-cast Mg-8%Li(in wt.%)based alloys

Through exploring the stress corrosion cracking(SCC)behaviors of the as-cast Mg-8%Li and Mg-8%Li-6%Zn-1.2%Y alloys in a 0.1 M NaCl solution,it revealed that the SCC susceptibility index(I_(SCC))of the Mg-8%Li alloy was 47%,whilst the I_(SCC)of the Mg-8%Li-6%Zn-1.2%Y alloy was 68%.Surface,cross-sectional and fractography observations indicated that for the Mg-8%Li alloy,theα-Mg/β-Li interfaces acted as the preferential crack initiation sites and propagation paths during the SCC process.With regard to the Mg-8%Li-6%Zn-1.2%Y alloy,the crack initiation sites included the I-phase and the interfaces of I-phase/β-Li andα-Mg/β-Li,and the preferential propagation paths were the I-phase/β-Li andα-Mg/β-Li interfaces.Moreover,the SCC of the two alloys was concerned with hydrogen embrittlement(HE)mechanism.

Ductile Fe-based amorphous alloys with high iron content

Fe-based amorphous alloys with high iron content of 76at%-80at%were synthesized in the Fe-Mo-Si-P-C-B alloy system by the single roller melt-spinning technique.The amorphous ribbons exhibit high Vickers microhardness and good ductility,which can be indented and bent 180°without breaking.A number of shear bands could be observed around the indents and the bending traces.Studies on the magnetic properties of the amorphous alloys show that they possess high saturation magnetizations of 1.34-1.6 T,which increases with the increase of iron content.The core losses of these Fe-based amorphous alloys at various magnetic inductions were tested and found to be significantly dependent on their components.The Fe-Mo-Si-P-C-B amorphous alloys with excellent mechanical properties and soft magnetic properties have promising potential in functional applications.

Formation and mechanical properties of ductile Fe-based amorphous alloys using a cast iron with minor addition of B and Al

Fe-based amorphous alloys with ductility were synthesized using the commercial cast iron QT50 (denoted as QT) with the combining minor addition of B and Al by single roller melt-spinning. The melt-spun (QT1-xBx)99Al1 (x is from 0.006wt% to 0.01wt%) amorphous alloys exhibit onset crystallization temperatures and Curie temperatures of 759-780 and 629-642 K respectively, and whi- ch increase with B content. The amorphous ribbons are ductile and can be bent 180° without breaking. With the increase in B content from 0.006wt% to 0.01wt%, the Vickers microhardness of the amorphous alloys increases from Hv 830 to Hv 1110. The effects of the additional B and Al elements on the glass forming ability and mechanical properties were also discussed.

Microstructures and micromechanical behaviors of high -entropy alloys investigated by synchrotron X-ray and neutron diffraction techniques: A review

High-entropy alloys(HEAs)possess outstanding features such as corrosion resistance,irradiation resistance,and good mechan-ical properties.A few HEAs have found applications in the fields of aerospace and defense.Extensive studies on the deformation mech-anisms of HEAs can guide microstructure control and toughness design,which is vital for understanding and studying state-of-the-art structural materials.Synchrotron X-ray and neutron diffraction are necessary techniques for materials science research,especially for in situ coupling of physical/chemical fields and for resolving macro/microcrystallographic information on materials.Recently,several re-searchers have applied synchrotron X-ray and neutron diffraction methods to study the deformation mechanisms,phase transformations,stress behaviors,and in situ processes of HEAs,such as variable-temperature,high-pressure,and hydrogenation processes.In this review,the principles and development of synchrotron X-ray and neutron diffraction are presented,and their applications in the deformation mechanisms of HEAs are discussed.The factors that influence the deformation mechanisms of HEAs are also outlined.This review fo-cuses on the microstructures and micromechanical behaviors during tension/compression or creep/fatigue deformation and the application of synchrotron X-ray and neutron diffraction methods to the characterization of dislocations,stacking faults,twins,phases,and intergrain/interphase stress changes.Perspectives on future developments of synchrotron X-ray and neutron diffraction and on research directions on the deformation mechanisms of novel metals are discussed.

Transformation of long-period stacking ordered structures in Mg-Gd-Y-Zn alloys upon synergistic characterization of first-principles calculation and experiment and its effects on mechanical properties

Based on experiments and first-principles calculations,the microstructures and mechanical properties of as-cast and solution treated Mg-10Gd-4Y-xZn-0.6Zr(x=0,1,2,wt.%)alloys are investigated.The transformation process of long-period stacking ordered(LPSO)structure during solidification and heat treatment and its effect on the mechanical properties of experimental alloys are discussed.Results reveal that the stacking faults and 18R LPSO phases appear in the as-cast Mg-10Gd-4Y-1Zn-0.6Zr and Mg-10Gd-4Y-2Zn-0.6Zr alloys,respectively.After solution treatment,the stacking faults and 18R LPSO phase transform into 14H LPSO phase.The Enthalpies of formation and reaction energy of 14H and 18R LPSO are calculated based on first-principles.Results show that the alloying ability of 18R is stronger than that of 14H.The reaction energies show that the 14H LPSO phase is more stable than the 18R LPSO.The elastic properties of the 14H and 18R LPSO phases are also evaluated by first-principles calculations,and the results are in good agreement with the experimental results.The precipitation of LPSO phase improves the tensile strength,yield strength and elongation of the alloy.After solution treatment,the Mg-10Gd-4Y-2Zn-0.6Zr alloy has the best mechanical properties,and its ultimate tensile strength and yield strength are 278.7 MPa and 196.4 MPa,respectively.The elongation of Mg-10Gd-4Y-2Zn-0.6Zr reaches 15.1,which is higher than that of Mg-10Gd-4Y0.6Zr alloy.The improving mechanism of elastic modulus by the LPSO phases and the influence on the alloy mechanical properties are also analyzed.

Ab initio molecular dynamics simulations of nano-crystallization of Fe-based amorphous alloys with early transition metals

The addition of early transition metals(ETMs)into Fe-based amorphous alloys is practically found to be effective in reducing theα-Fe grain size in crystallization process.In this paper,by using ab initio molecular dynamics simulations,the mechanism of the effect of two typical ETMs(Nb and W)on nano-crystallization is studied.It is found that the diffusion ability in amorphous alloy is mainly determined by the bonding energy of the atom rather than the size or weight of the atom.The alloying of B dramatically reduces the diffusion ability of the ETM atoms,which prevents the supply of Fe near the grain surface and consequently suppresses the growth ofα-Fe grains.Moreover,the difference in grain refining effectiveness between Nb and W could be attributed to the larger bonding energy between Nb and B than that between W and B.

Review on synergistic damage effect of irradiation and corrosion on reactor structural alloys

The synergistic damage effect of irradiation and corrosion of reactor structural materials has been a prominent research focus.This paper provides a comprehensive review of the synergistic effects on the third-and fourth-generation fission nuclear energy structural materials used in pressurized water reactors and molten salt reactors.The competitive mechanisms of multiple influencing factors,such as the irradiation dose,corrosion type,and environmental temperature,are summarized in this paper.Conceptual approaches are proposed to alleviate the synergistic damage caused by irradiation and corrosion,thereby promoting in-depth research in the future and solving this key challenge for the structural materials used in reactors.

Comparison of electrochemical behaviors of Ti-5Al-2Sn-4Zr-4Mo-2Cr-1Fe and Ti-6Al-4V titanium alloys in NaNO_(3) solution

The Ti-5Al-2Sn-4Zr-4Mo-2Cr-1Fe(β-CEZ)alloy is considered as a potential structural material in the aviation industry due to its outstanding strength and corrosion resistance.Electrochemical machining(ECM)is an efficient and low-cost technology for manufacturing theβ-CEZ alloy.In ECM,the machining parameter selection and tool design are based on the electrochemical dissolution behavior of the materials.In this study,the electrochemical dissolution behaviors of theβ-CEZ and Ti-6Al-4V(TC4)alloys in NaNO3solution are discussed.The open circuit potential(OCP),Tafel polarization,potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),and current efficiency curves of theβ-CEZ and TC4 alloys are analyzed.The results show that,compared to the TC4 alloy,the passivation film structure is denser and the charge transfer resistance in the dissolution process is greater for theβ-CEZ alloy.Moreover,the dissolved surface morphology of the two titanium-based alloys under different current densities are analyzed.Under low current densities,theβ-CEZ alloy surface comprises dissolution pits and dissolved products,while the TC4 alloy surface comprises a porous honeycomb structure.Under high current densities,the surface waviness of both the alloys improves and the TC4 alloy surface is flatter and smoother than theβ-CEZ alloy surface.Finally,the electrochemical dissolution models ofβ-CEZ and TC4 alloys are proposed.

New insights on the high-corrosion resistance of UHP Mg-Ge alloys tested in a simulated physiological environment

UHP Mg-Ge alloys was recently found to provide excellent corrosion resistance.This paper provides new insights on the mechanism of improved corrosion resistance of UHP Mg-Ge alloys in Hanks’solution.The studied UHP Mg-0.5Ge and UHP Mg-1Ge alloys showed superior corrosion resistance compared to UHP Mg and WE43,with the Mg-1Ge exhibiting the best corrosion performance.The exceptional corrosion resistance of the UHP alloy is attributed to(i)Mg_(2)Ge’s ability to suppress cathodic kinetics,(ii)Ge’s capability to accelerate the formation of a highly passive layer,and the(iii)low amounts of corrosion-accelerating impurities.