Phase transformation is one of the factors that would significantly influence the ability to resist cavitation erosion of stainless steels. Due to the specific properties of duplex stainless steel, the heat treatment ...Phase transformation is one of the factors that would significantly influence the ability to resist cavitation erosion of stainless steels. Due to the specific properties of duplex stainless steel, the heat treatment would bring about significant phase transformations. In this paper, we have examined the previous studies on the phase transition of stainless steel, including the literature on the classification of stainless steel, spinodal decomposition, sigma phase transformation, and cavitation erosion of double stainless steel. Through these literature investigations, the destruction of cavitation erosion on duplex stainless steel can be clearly known, and the causes of failure of duplex stainless steel in seawater can be clarified, thus providing a theoretical basis for subsequent scientific research. And the review is about to help assess the possibility of using bulk heat treatment to improve the cavitation erosion (CE) behaviour of the duplex stainless steel 7MoPLUS.展开更多
Both furnace cooled and as-cast eutectoid Zn-Al alloys were investigated under external tensile stress at 100℃. It was observed that the external tensile stress caused decomposition of two metastable phases η’T and...Both furnace cooled and as-cast eutectoid Zn-Al alloys were investigated under external tensile stress at 100℃. It was observed that the external tensile stress caused decomposition of two metastable phases η’T and η’S which derived from both original state of the alloy, and a phase transformation, αf +ε→T’ +η, in both furnace cooled and as-cast eutectoid Zn-Al alloys. Also spheroidized structure formed partially during tensile testing. Superplasticity of the alloy has been discussed correlating with the phase transformations and microstructural changes.展开更多
A new continuous multi-phase transformation field model was established for liquid-solid-eutectoid transformation. Taking Fe-C alloy as an example, the model was used to simulate the evolution of the micro-morphology ...A new continuous multi-phase transformation field model was established for liquid-solid-eutectoid transformation. Taking Fe-C alloy as an example, the model was used to simulate the evolution of the micro-morphology of the liquid-solid phase transition, and the effects of temperature, solute and free energy on the nucleation of pearlite after the liquid-solid phase transition were analyzed. The micro-morphology of pearlite was simulated. The simulation results show that the austenite structure has hereditary effect on the pearlite, the morphology of pearlite structure was similar to that of the parent austenite. The eutectoid structure at the front of pearlite grows toward the interior of austenite grains in a bifurcation manner and in the spherical coronal shape. In addition, the growth rate of pearlite was related to the shape of concave-convex interface at the nucleation site, and the growth rate at the convex interface was faster than that at the concave interface.展开更多
Rare-earth(RE)elements,known as“industrial vitamins”,have permeated modern lives,especially in high-tech applications.Although the RE elements possess close chemical similarities and have been treated as“one elemen...Rare-earth(RE)elements,known as“industrial vitamins”,have permeated modern lives,especially in high-tech applications.Although the RE elements possess close chemical similarities and have been treated as“one element”in the periodic table,their characteristics differ from each other.The RE microalloying effect is the crux to ameliorate the physicomechanical and thermochemical properties of materials,thereby the study of RE-related phase diagrams becomes indispensable to the design and optimization of RE-containing materials.However,in reality,the knowledge base in this area is considerably scarce compared with that of other commonly-used elements.In this work,the phase equilibria,phase diagrams,phase transformations,and some recent examples of RE-containing materials design are summarized,with which one can predict the RE solubilities,the RE precipitates,as well as the corresponding service behaviors.The attainment of enhanced materials’properties suggests that the thermodynamic rules extracted from the phase diagrams could serve as fundamental criteria for the successful development of novel RE-containing materials.展开更多
Effects of solute rare earth(RE)on continuous cooling transformation of a low-alloy Cr–Mo–V bainitic steel are investigated in detail by dilatometry,optical microscopy(OM),scanning electron microscopy(SEM)and transm...Effects of solute rare earth(RE)on continuous cooling transformation of a low-alloy Cr–Mo–V bainitic steel are investigated in detail by dilatometry,optical microscopy(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Microstructures appeared in thermal dilatometric samples of both low-alloy Cr–Mo–V(RE)steels are composed of quasi-polygonal ferrite(QPF),degenerate pearlite(DP),granular bainite(GB),lath bainite(LB),and martensite(M)depending on cooling rate.When cooling rate is lower than 2°C/s,the addition of RE suppresses QPF transformation,and thereby inducing a broader transformation region of GB.When cooling rate ranges from 2 to 100°C/s,the addition of RE decreases the start temperature of bainitic transformation distinctly,which results in finer bainitic ferrite grain size and higher dislocation density.The addition of RE can enhance the hardness of the low alloy Cr–Mo–V steel by affecting the aforementioned diffusional and/or partly displacive transformation.However,when cooling rate increases up to 150°C/s,two steels have the same hardness value of about 435 HV due to only martensite obtained by displacive transformation.展开更多
The mechanism involved in the phase transformation process of pyrolusite (MnO_(2)) during roasting in a reducing atmosphere was systematically elucidated in this study,with the aim of effectively using low-grade compl...The mechanism involved in the phase transformation process of pyrolusite (MnO_(2)) during roasting in a reducing atmosphere was systematically elucidated in this study,with the aim of effectively using low-grade complex manganese ore resources.According to single-factor experiment results,the roasted product with a divalent manganese (Mn^(2+)) distribution rate of 95.30% was obtained at a roasting time of 25 min,a roasting temperature of 700℃,a CO concentration of 20at%,and a total gas volume of 500 mL·min^(-1),in which the manganese was mainly in the form of manganosite (MnO).Scanning electron microscopy and Brunauer–Emmett–Teller theory demonstrated the microstructural evolution of the roasted product and the gradual reduction in the pyrolusite ore from the surface to the core Thermodynamic calculations,X-ray photoelectron spectroscopy,and X-ray diffractometry analyses determined that the phase transformation of pyrolusite followed the order of MnO_(2)→Mn_(2)O_(3)→Mn_(3)O_(4)→MnO phase by phase,and the reduction of manganese oxides in each valence state proceeded simultaneously.展开更多
A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth.Results reveal a retarded transformation from the shock-induced Bi-Ⅴphase to a metastable Bi-...A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth.Results reveal a retarded transformation from the shock-induced Bi-Ⅴphase to a metastable Bi-Ⅳphase during the shock release,instead of the thermodynamically stable Bi-Ⅲphase.The emergence of the metastable Bi-Ⅳphase is understood by the competitive interplay between two transformation pathways towards the Bi-Ⅳand Bi-Ⅲ,respectively.The former is more rapid than the latter because the Bi-Ⅴto B-Ⅳtransformation is driven by interaction between the closest atoms while the Bi-Ⅴto B-Ⅲtransformation requires interaction between the second-closest atoms.The nucleation time for the Bi-Ⅴto Bi-Ⅳtransformation is determined to be 5.1±0.9 ns according to a classical nucleation model.This observation demonstrates the importance of the formation of the transient metastable phases,which can change the phase transformation pathway in a dynamic process.展开更多
Various solid state phase transformations exist in metastable β-type Ti alloys,which can be employed to optimize the mechanical properties.In this paper,synchrotron X-ray diffraction(SXRD)experiments were carried out...Various solid state phase transformations exist in metastable β-type Ti alloys,which can be employed to optimize the mechanical properties.In this paper,synchrotron X-ray diffraction(SXRD)experiments were carried out to study the phase transformations of a Ti36Nb5Zr alloy subjected to different thermomechanical treatments.Furthermore,the correlation between the phase constitutions and the mechanical properties was discussed.The a" texture formed,and high-density defects were introduced after cold rolling of the solution treated specimen,leading to the decrease in Young’s modulus and the increase in strength.The cold-rolled specimens were then annealed at temperatures from 423 to 773 K for 30 min.Both the Young’s modulus and strength increased with annealing temperatures increasing up to 673 K,which resulted from the precipitation of the ω and/or α phases.With further increase in annealing temperatures to 773 K,the β→α precipitation replaced the β→ω_(iso) phase transformation,and the density of defects decreased,leading to the decrease in both the Young’s modulus and strength.These results provide theoretical basis for the design biomedical Ti alloys with both low Young’s modulus and high strength.展开更多
Thermally induced evolution of phase transformations is a basic physical-chemical process in the dissociation of gas hydrate in sediment (GHS). Heat transfer leads to the weakening of the bed soil and the simultaneous...Thermally induced evolution of phase transformations is a basic physical-chemical process in the dissociation of gas hydrate in sediment (GHS). Heat transfer leads to the weakening of the bed soil and the simultaneous establishment of a time varying stress field accompanied by seepage of fluids and deformation of the soil. As a consequence, ground failure could occur causing engineering damage or/and environmental disaster. This paper presents a simplified analysis of the thermal process by assuming that thermal conduction can be decoupled from the flow and deformation process. It is further assumed that phase transformations take place instantaneously. Analytical and numerical results are given for several examples of simplified geometry. Experiments using Tetra-hydro-furan hydrate sediments were carried out in our laboratory to check the theory. By comparison, the theoretical, numerical and experimental results on the evolution of dissociation fronts and temperature in the sediment are found to be in good agreement.展开更多
The phase transformations during thermomechanical processing can be employed to optimize mechanical properties of β-type Ti alloys.However,such understandings are still lacking for the alloy consisting of dual β+α&...The phase transformations during thermomechanical processing can be employed to optimize mechanical properties of β-type Ti alloys.However,such understandings are still lacking for the alloy consisting of dual β+α" phases in solution-treated and quenched state.In this paper,the phase transformations in a Ti38 Nb model alloy subjected to different thermomechanical processing were investigated by using synchrotron X-ray diffraction(SXRD) experiments,and their influence on the Young’s modulus was discussed.The results indicated that highdensity dislocations introduced by cold rolling still existed after annealing at temperatures lower than 573 K,which can decrease the martensitic transformation start temperature to below room temperature.With annealing temperatures increasing,the α"→β,β→ω_(iso),and β→α phase transformations occurred successively.At annealing temperature of 473 K,the specimen consisted of a trace of α"and ω phases as well as dominant β phase which was kept to room temperature by the high density of dislocations,rather than by the chemical stabilization.As a result,an ultralow Young’s modulus of 25.9 GPa was realized.Our investigation not only provides in-depth understandings of the phase transformations during thermomechanical processing of β-type Ti alloys,but also sheds light on designing biomedical Ti alloys with ultralow Young’s modulus.展开更多
While there have been multiple recent reports in the literature focusing on the effects of magnetic field on the phase transformation behaviors,the research conducted with an ultra-high magnetic field greater than 20 ...While there have been multiple recent reports in the literature focusing on the effects of magnetic field on the phase transformation behaviors,the research conducted with an ultra-high magnetic field greater than 20 T is still preliminary.In the current study,the structure evolution of Co-B alloys are experimentally studied with undercooling.The effects of a 25 T magnetic field on the solidification behavior and the subsequent solid-state phase transformation behavior have been investigated.The 25 T magnetic field is confirmed to have little effect on the homogeneous nucleation,but have some influence on the heterogeneous nucleation of Co_(3) B and Co_(23)B6 phases by modifying the wetting angleθ.The decomposition of Co_(23)B6 phase in the subsequent cooling process can be effectively suppressed by applying the 25 T magnetic field.The present work might be helpful for not only theoretically understanding the influence of ultra-high magnetic field on the phase transformation behaviors but a potential technology of field-manipulation of magnetic materials.展开更多
The solid-phase transformations of metal materials under high magnetic fields are an important topic in research on the electromagnetic processing of materials.Progress in research on the diffusional phase transformat...The solid-phase transformations of metal materials under high magnetic fields are an important topic in research on the electromagnetic processing of materials.Progress in research on the diffusional phase transformations of Fe–C alloys under high magnetic fields is reviewed.The effects of high magnetic fields on the microstructural evolution in diffusional phase transformations in Fe–C alloys are discussed.The kinetics of ferrite transformations,pearlite transformations,and the precipitation of carbides under high magnetic fields are reviewed in terms of the thermodynamics of phase transformations and the diffusion behavior of carbon atoms.Finally,future trends in research on diffusional phase transformations of Fe–C alloys under high magnetic fields are discussed.展开更多
We investigate the critical nuclei morphology in phase transformation by combining two effective ingredients,with the first being the phase field modeling of the relevant energetics which has been a popular approach f...We investigate the critical nuclei morphology in phase transformation by combining two effective ingredients,with the first being the phase field modeling of the relevant energetics which has been a popular approach for phase transitions and the second being shrinking dimer dynamics and its variants for computing saddle points and transition states.In particular,the newly formulated generalized shrinking dimer dynamics is proposed by adopting the Cahn-Hilliard dynamics for the generalized gradient system.As illustrations,a couple of typical cases are considered,including a generic system modeling heterogeneous nucleation and a specific material system modeling the precipitate nucleation in FeCr alloys.While the standard shrinking dimer dynamics can be applied to study the non-conserved case of generic heterogeneous nucleation directly,the generalized shrinking dimer dynamics is efficient to compute precipitate nucleation in FeCr alloys due to the conservation of concentration.Numerical simulations are provided to demonstrate both the complex morphology associated with nucleation events and the effectiveness of generalized shrinking dimer dynamics based on phase field models.展开更多
Tin(Sn)holds great promise as an anode material for next-generation lithium(Li)ion batteries but suffers from massive volume change and poor cycling performance.To clarify the dynamic chemical and microstructural evol...Tin(Sn)holds great promise as an anode material for next-generation lithium(Li)ion batteries but suffers from massive volume change and poor cycling performance.To clarify the dynamic chemical and microstructural evolution of Sn anode during lithiation and delithiation,synchrotron X-ray energydispersive diffraction and X-ray tomography are simultaneously employed during Li/Sn cell operation.The intermediate Li-Sn alloy phases during de/lithiation are identified,and their dynamic phase transformation is unraveled which is further correlated with the volume variation of the Sn at particle-and electrode-level.Moreover,we find that the Sn particle expansion/shrinkage induced particle displacement is anisotropic:the displacement perpendicular to the electrode surface(z-axis)is more pronounced compared to the directions(x-and y-axis)along the electrode surface.This anisotropic particle displacement leads to an anisotropic volume variation at the electrode level and eventually generates a net electrode expansion towards the separator after cycling,which could be one of the root causes of mechanical detachment and delamination of electrodes during long-term operation.The unraveled chemical evolution of Li-Sn and deep insights into the microstructural evolution of Sn anode provided here could guide future design and engineering of Sn and other alloy anodes for high energy density Li-and Na-ion batteries.展开更多
An accurate flow stress model was established by considering the parameters of strain rate,strain and temperature as well asβ→a+βphase transformation in order to develop the plastic forming theory of TC18 titanium ...An accurate flow stress model was established by considering the parameters of strain rate,strain and temperature as well asβ→a+βphase transformation in order to develop the plastic forming theory of TC18 titanium alloy.Firstly,the phase transition kinetics of TC18 titanium alloy during isothermal and continuous cooling at 1073 and 1273 K was studied by thermodynamic calculation,meanwhile,the relationship of volume fraction of phase transition with temperature and time was obtained.Constitutive models were calculated by investigating flow behaviors under hot compression tests with the strain rates of 0.001-1s^(-1) and temperatures of 973-1223 K in the singleβand a+βregions in TC18 titanium alloy,respectively.By combining the phase transformation dynamic kinetics with constitutive models,an accurate flow stress model was established,providing theoretical basis and data support for the hot forging of TC18 titanium alloy.展开更多
To explore the effect of temperature on the phase transformation of HCP→FCC during compression, the uniaxial compression process of AZ31 magnesium alloy was simulated by the molecular dynamics method, and the changes...To explore the effect of temperature on the phase transformation of HCP→FCC during compression, the uniaxial compression process of AZ31 magnesium alloy was simulated by the molecular dynamics method, and the changes of crystal structure and dislocation evolution were observed. The effects of temperature on mechanical properties, crystal structure, and dislocation evolution of magnesium alloy during compression were analyzed. It is concluded that some of the Shockley partial dislocation is related to FCC stacking faults. With the help of TEM characterization, the correctness of the correlation between some of the dislocations and FCC stacking faults is verified. Through the combination of simulation and experiment, this paper provides an idea for the in-depth study of the solid-phase transformation of magnesium alloys and provides reference and guidance for the design of magnesium alloys with good plasticity and formability at room temperature.展开更多
The negative thermal expansion(NTE) phenomenon is of great significance in fabricating zero thermal expansion(ZTE) materials to avoid thermal shock during heating and cooling. NTE is observed in limited groups of mate...The negative thermal expansion(NTE) phenomenon is of great significance in fabricating zero thermal expansion(ZTE) materials to avoid thermal shock during heating and cooling. NTE is observed in limited groups of materials, e.g., metal cyanides, oxometallates, and metalorganic frameworks, but has not been reported in the family of metal hydrides. Herein, a colossal and continuous negative thermal expansion is firstly developed in the low-temperature phases of LT1-and LT2-Mg_(2)NiH_(4) between 488 K and 733 K from in-situ transmission electron microscope(TEM) video, with the volume contraction reaching 18.7% and 11.3%, respectively. The mechanisms for volume contraction of LT1 and LT2 phases are elucidated from the viewpoints of phase transformation, magnetic transition, and dehydrogenation, which is different from common NTE materials containing flexible polyhedra units in the structure. The linear volume shrinkage of LT2 in the temperature of 488-553 K corresponds to the phase transition of LT2→HT with a thermal expansion coefficient of -799.7 × 10^(-6) K^(-1) revealed by in-situ synchrotron powder X-ray diffraction. The sudden volume contraction in LT1 between 488 and 493 K may be caused by the rapid dehydrogenation of LT1 to Mg_(2)Ni. The revealed phenomenon in single composite material with different structures would be significant for preparing zero thermal expansion materials by tuning the fraction of LT1 and LT2 phases.展开更多
The improved microstructure and enhanced elevated temperature mechanical properties of Ti-44Al-5Nb-(Mo,V,B)alloys were obtained by vacuum arc re-melting(VAR)and primary annealing heat treatment(HT)of 1260℃/6 h/Furnac...The improved microstructure and enhanced elevated temperature mechanical properties of Ti-44Al-5Nb-(Mo,V,B)alloys were obtained by vacuum arc re-melting(VAR)and primary annealing heat treatment(HT)of 1260℃/6 h/Furnace cooling(FC).The phase transformation,microstructure evolution and tensile properties for as-cast and HTed alloys were investigated.Results indicate that three main phase transformation points are determined,T_(eut)=1164.3℃,T_(γsolv)=1268.3℃and T_(βtrans)=1382.8℃.There are coarse lamellar colonies(300μm in length)and neighbor reticular B2 andγgrain(3-5μm)in as-cast alloy,while lamellar colonies are markedly refined and multi-oriented(20-50μm)as well as the volume fraction and grain sizes of equiaxedγand B2 phases(about 15μm)significantly increase in as-HTed alloy.Phase transformations involvingα+γ→α+γ+β/B2 and discontinuousγcoarsening contribute to the above characteristics.Borides(1-3μm)act as nucleation sites forβ_(eutectic) and produce massiveβgrains with different orientations,thus effectively refining the lamellar colonies and forming homogeneous multi-phase microstructure.Tensile curves show both the alloys exhibit suitable performance at 800℃.As-cast alloy shows a higher ultimate tensile stress of 647 MPa,while a better total elongation of more than 41%is obtained for as-HTed alloy.The mechanical properties improvement is mainly attributed to fine,multi-oriented lamellar colonies,coordinated deformation of homogeneous multi-phase microstructure and borides within lamellar interface preventing crack propagation.展开更多
The coupling effect of heat absorption and release exists in the thermal decomposition of a few chemical materials.However,the impact of the above coupling on thermal hazard assessment is not considered in the literat...The coupling effect of heat absorption and release exists in the thermal decomposition of a few chemical materials.However,the impact of the above coupling on thermal hazard assessment is not considered in the literature studies.In this work,nitroguanidine(NQ)and 1,3,5-trinitro-1,3,5-triazine(RDX)are selected as representative materials to explore the influence of the coupling effect on the thermal hazard assessment of chemical materials.The linear heating experiments of NQ and RDX are carried out by a microcalorimeter and synchronous thermal analyser.The thermal decomposition curves are decoupled by advanced thermokinetics software.The thermal decomposition and kinetic parameters before and after decoupling are calculated.The results of TG experiment show that both NQ and RDX began to lose mass during the endothermic stage.The endothermic melting and exothermic decomposition of NQ and RDX are coupled within this stage.The coupling effect has different degrees of influence on its initial decomposition temperature and safety parameters.Compared with the parameters in the coupling state,the initial decomposition temperature and adiabatic induction period after decoupling decrease.The self-accelerating decomposition temperature increases,and internal thermal runaway time decreases.In the thermal hazard assessment of chemical materials with coupling effects,the calculated parameters after decoupling should be taken as an important safety index。展开更多
To study the formation and transformation mechanism of long-period stacked ordered(LPSO)structures,a systematic atomic scale analysis was conducted for the structural evolution of long-period stacked ordered(LPSO)stru...To study the formation and transformation mechanism of long-period stacked ordered(LPSO)structures,a systematic atomic scale analysis was conducted for the structural evolution of long-period stacked ordered(LPSO)structures in the Mg-Gd-Y-Zn-Zr alloy annealed at 300℃~500℃.Various types of metastable LPSO building block clusters were found to exist in alloy structures at different temperatures,which precipitate during the solidification and homogenization process.The stability of Zn/Y clusters is explained by the first principles of density functional theory.The LPSO structure is distinguished by the arrangement of its different Zn/Y enriched LPSO structural units,which comprises local fcc stacking sequences upon a tightly packed plane.The presence of solute atoms causes local lattice distortion,thereby enabling the rearrangement of Mg atoms in the different configurations in the local lattice,and local HCP-FCC transitions occur between Mg and Zn atoms occupying the nearest neighbor positions.This finding indicates that LPSO structures can generate necessary Schockley partial dislocations on specific slip surfaces,providing direct evidence of the transition from 18R to 14H.Growth of the LPSO,devoid of any defects and non-coherent interfaces,was observed separately from other precipitated phases.As a result,the precipitation sequence of LPSO in the solidification stage was as follows:Zn/Ycluster+Mg layers→various metastable LPSO building block clusters→18R/24R LPSO;whereas the precipitation sequence of LPSO during homogenization treatment was observed to be as follows:18R LPSO→various metastable LPSO building block clusters→14H LPSO.Of these,14H LPSO was found to be the most thermodynamically stable structure.展开更多
文摘Phase transformation is one of the factors that would significantly influence the ability to resist cavitation erosion of stainless steels. Due to the specific properties of duplex stainless steel, the heat treatment would bring about significant phase transformations. In this paper, we have examined the previous studies on the phase transition of stainless steel, including the literature on the classification of stainless steel, spinodal decomposition, sigma phase transformation, and cavitation erosion of double stainless steel. Through these literature investigations, the destruction of cavitation erosion on duplex stainless steel can be clearly known, and the causes of failure of duplex stainless steel in seawater can be clarified, thus providing a theoretical basis for subsequent scientific research. And the review is about to help assess the possibility of using bulk heat treatment to improve the cavitation erosion (CE) behaviour of the duplex stainless steel 7MoPLUS.
文摘Both furnace cooled and as-cast eutectoid Zn-Al alloys were investigated under external tensile stress at 100℃. It was observed that the external tensile stress caused decomposition of two metastable phases η’T and η’S which derived from both original state of the alloy, and a phase transformation, αf +ε→T’ +η, in both furnace cooled and as-cast eutectoid Zn-Al alloys. Also spheroidized structure formed partially during tensile testing. Superplasticity of the alloy has been discussed correlating with the phase transformations and microstructural changes.
基金This work was financially supported by the National Natural Science Foundation of China(Grant Nos.:11504149,51661020)thc Natural Scicnce Toundation of Gansu Province of China(Grant No:18JR3RA147).
文摘A new continuous multi-phase transformation field model was established for liquid-solid-eutectoid transformation. Taking Fe-C alloy as an example, the model was used to simulate the evolution of the micro-morphology of the liquid-solid phase transition, and the effects of temperature, solute and free energy on the nucleation of pearlite after the liquid-solid phase transition were analyzed. The micro-morphology of pearlite was simulated. The simulation results show that the austenite structure has hereditary effect on the pearlite, the morphology of pearlite structure was similar to that of the parent austenite. The eutectoid structure at the front of pearlite grows toward the interior of austenite grains in a bifurcation manner and in the spherical coronal shape. In addition, the growth rate of pearlite was related to the shape of concave-convex interface at the nucleation site, and the growth rate at the convex interface was faster than that at the concave interface.
基金the National Natural Science Foundation of China(Nos.52101026 and 52222507)the Natural Science Foundation of Zhejiang Province(No.LQ20E010004)+2 种基金the“Pioneer”and“Leading Goose”R&D Program of Zhejiang(No.2022C01017)the National Natural Science Foundation of China(52101108)the Ningbo 3315 Innovation Team(Nos.2019A-18-C and 2020A-03-C)is gratefully acknowledged.
文摘Rare-earth(RE)elements,known as“industrial vitamins”,have permeated modern lives,especially in high-tech applications.Although the RE elements possess close chemical similarities and have been treated as“one element”in the periodic table,their characteristics differ from each other.The RE microalloying effect is the crux to ameliorate the physicomechanical and thermochemical properties of materials,thereby the study of RE-related phase diagrams becomes indispensable to the design and optimization of RE-containing materials.However,in reality,the knowledge base in this area is considerably scarce compared with that of other commonly-used elements.In this work,the phase equilibria,phase diagrams,phase transformations,and some recent examples of RE-containing materials design are summarized,with which one can predict the RE solubilities,the RE precipitates,as well as the corresponding service behaviors.The attainment of enhanced materials’properties suggests that the thermodynamic rules extracted from the phase diagrams could serve as fundamental criteria for the successful development of novel RE-containing materials.
基金This work was supported by the National Natural Science Foundation of China(Grant No.52101059)the Shenyang National Laboratory for Materials Science(Grant No.L2019F48).
文摘Effects of solute rare earth(RE)on continuous cooling transformation of a low-alloy Cr–Mo–V bainitic steel are investigated in detail by dilatometry,optical microscopy(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Microstructures appeared in thermal dilatometric samples of both low-alloy Cr–Mo–V(RE)steels are composed of quasi-polygonal ferrite(QPF),degenerate pearlite(DP),granular bainite(GB),lath bainite(LB),and martensite(M)depending on cooling rate.When cooling rate is lower than 2°C/s,the addition of RE suppresses QPF transformation,and thereby inducing a broader transformation region of GB.When cooling rate ranges from 2 to 100°C/s,the addition of RE decreases the start temperature of bainitic transformation distinctly,which results in finer bainitic ferrite grain size and higher dislocation density.The addition of RE can enhance the hardness of the low alloy Cr–Mo–V steel by affecting the aforementioned diffusional and/or partly displacive transformation.However,when cooling rate increases up to 150°C/s,two steels have the same hardness value of about 435 HV due to only martensite obtained by displacive transformation.
基金financially supported by the National Key Research and Development Program of China (No.2023YFC2909000)the National Natural Science Foundation of China(No.52174240)the Open Foundation of State Key Laboratory of Mineral Processing (No.BGRIMM-KJSKL-2023-15)。
文摘The mechanism involved in the phase transformation process of pyrolusite (MnO_(2)) during roasting in a reducing atmosphere was systematically elucidated in this study,with the aim of effectively using low-grade complex manganese ore resources.According to single-factor experiment results,the roasted product with a divalent manganese (Mn^(2+)) distribution rate of 95.30% was obtained at a roasting time of 25 min,a roasting temperature of 700℃,a CO concentration of 20at%,and a total gas volume of 500 mL·min^(-1),in which the manganese was mainly in the form of manganosite (MnO).Scanning electron microscopy and Brunauer–Emmett–Teller theory demonstrated the microstructural evolution of the roasted product and the gradual reduction in the pyrolusite ore from the surface to the core Thermodynamic calculations,X-ray photoelectron spectroscopy,and X-ray diffractometry analyses determined that the phase transformation of pyrolusite followed the order of MnO_(2)→Mn_(2)O_(3)→Mn_(3)O_(4)→MnO phase by phase,and the reduction of manganese oxides in each valence state proceeded simultaneously.
基金supported by the National Natural Science Foundation of China (Grant No.12072331)the Science Challenge Project (Grant No.TZ2018001)+2 种基金the Japan Society for the Promotion of Science (Grant Nos.17H04820 and 21H01677)the Foundation of the United Laboratory of High-Pressure Physics and Earthquake Scienceperformed under the approval of the Photon Factory Program Advisory Committee (Proposal Nos.2016S2-006 and 2020G680)。
文摘A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth.Results reveal a retarded transformation from the shock-induced Bi-Ⅴphase to a metastable Bi-Ⅳphase during the shock release,instead of the thermodynamically stable Bi-Ⅲphase.The emergence of the metastable Bi-Ⅳphase is understood by the competitive interplay between two transformation pathways towards the Bi-Ⅳand Bi-Ⅲ,respectively.The former is more rapid than the latter because the Bi-Ⅴto B-Ⅳtransformation is driven by interaction between the closest atoms while the Bi-Ⅴto B-Ⅲtransformation requires interaction between the second-closest atoms.The nucleation time for the Bi-Ⅴto Bi-Ⅳtransformation is determined to be 5.1±0.9 ns according to a classical nucleation model.This observation demonstrates the importance of the formation of the transient metastable phases,which can change the phase transformation pathway in a dynamic process.
基金This work was financially supported by the Fundamental Research Funds for the Central Universities(No.2017QNA04)Qing-Kun Meng thanks Prof.Yu-Chen Karen Chen-Wiegart at Stony Brook University and Dr.Jian-Ming Bai,Dr.Hui Zhong and Dr.Sanjit Ghose at National Synchrotron Light Source II for their assistance in the synchrotron experiments.This research used 28-ID-2(XPD)beamline of the National Synchrotron Light Source II,a U.S.Department of Energy(DOE)Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No.DE-SC0012704.
文摘Various solid state phase transformations exist in metastable β-type Ti alloys,which can be employed to optimize the mechanical properties.In this paper,synchrotron X-ray diffraction(SXRD)experiments were carried out to study the phase transformations of a Ti36Nb5Zr alloy subjected to different thermomechanical treatments.Furthermore,the correlation between the phase constitutions and the mechanical properties was discussed.The a" texture formed,and high-density defects were introduced after cold rolling of the solution treated specimen,leading to the decrease in Young’s modulus and the increase in strength.The cold-rolled specimens were then annealed at temperatures from 423 to 773 K for 30 min.Both the Young’s modulus and strength increased with annealing temperatures increasing up to 673 K,which resulted from the precipitation of the ω and/or α phases.With further increase in annealing temperatures to 773 K,the β→α precipitation replaced the β→ω_(iso) phase transformation,and the density of defects decreased,leading to the decrease in both the Young’s modulus and strength.These results provide theoretical basis for the design biomedical Ti alloys with both low Young’s modulus and high strength.
基金supported by the National High Technology Research and Development Program of China (Grant N. 2006AA09A209-7)the Major Oil and Gas Program of China (Grant No. 2008ZX05026-04-011)+1 种基金Knowledge Innovative Program of the Chinese Academy of Sciences (Grant No. KJCX2-YW-L02)the National Natural Science Foundation of China (Grant No. 1077218)
文摘Thermally induced evolution of phase transformations is a basic physical-chemical process in the dissociation of gas hydrate in sediment (GHS). Heat transfer leads to the weakening of the bed soil and the simultaneous establishment of a time varying stress field accompanied by seepage of fluids and deformation of the soil. As a consequence, ground failure could occur causing engineering damage or/and environmental disaster. This paper presents a simplified analysis of the thermal process by assuming that thermal conduction can be decoupled from the flow and deformation process. It is further assumed that phase transformations take place instantaneously. Analytical and numerical results are given for several examples of simplified geometry. Experiments using Tetra-hydro-furan hydrate sediments were carried out in our laboratory to check the theory. By comparison, the theoretical, numerical and experimental results on the evolution of dissociation fronts and temperature in the sediment are found to be in good agreement.
基金financially supported by the Fundamental Research Funds for the Central Universities (No.2017QNA04)。
文摘The phase transformations during thermomechanical processing can be employed to optimize mechanical properties of β-type Ti alloys.However,such understandings are still lacking for the alloy consisting of dual β+α" phases in solution-treated and quenched state.In this paper,the phase transformations in a Ti38 Nb model alloy subjected to different thermomechanical processing were investigated by using synchrotron X-ray diffraction(SXRD) experiments,and their influence on the Young’s modulus was discussed.The results indicated that highdensity dislocations introduced by cold rolling still existed after annealing at temperatures lower than 573 K,which can decrease the martensitic transformation start temperature to below room temperature.With annealing temperatures increasing,the α"→β,β→ω_(iso),and β→α phase transformations occurred successively.At annealing temperature of 473 K,the specimen consisted of a trace of α"and ω phases as well as dominant β phase which was kept to room temperature by the high density of dislocations,rather than by the chemical stabilization.As a result,an ultralow Young’s modulus of 25.9 GPa was realized.Our investigation not only provides in-depth understandings of the phase transformations during thermomechanical processing of β-type Ti alloys,but also sheds light on designing biomedical Ti alloys with ultralow Young’s modulus.
基金supported by the National Natural Science Foundation of China(No.51690164)the fund of National Key Laboratory for Precision Hot Processing of Metals(6142909200104)+2 种基金National Training Program of Innovation and Entrepreneurship for Undergraduates(S202010699137)the Fundamental Research Funds for the Central Universitiesthe support of the LNCMI-CNRS。
文摘While there have been multiple recent reports in the literature focusing on the effects of magnetic field on the phase transformation behaviors,the research conducted with an ultra-high magnetic field greater than 20 T is still preliminary.In the current study,the structure evolution of Co-B alloys are experimentally studied with undercooling.The effects of a 25 T magnetic field on the solidification behavior and the subsequent solid-state phase transformation behavior have been investigated.The 25 T magnetic field is confirmed to have little effect on the homogeneous nucleation,but have some influence on the heterogeneous nucleation of Co_(3) B and Co_(23)B6 phases by modifying the wetting angleθ.The decomposition of Co_(23)B6 phase in the subsequent cooling process can be effectively suppressed by applying the 25 T magnetic field.The present work might be helpful for not only theoretically understanding the influence of ultra-high magnetic field on the phase transformation behaviors but a potential technology of field-manipulation of magnetic materials.
基金supported by the National Natural Science Foundation of China(Grant No.51690162)Liaoning Revitalization Talents Program(Grant No.XLYC1908002)Fundamental Research Funds for the Central Universities(Grant No.N180912004).
文摘The solid-phase transformations of metal materials under high magnetic fields are an important topic in research on the electromagnetic processing of materials.Progress in research on the diffusional phase transformations of Fe–C alloys under high magnetic fields is reviewed.The effects of high magnetic fields on the microstructural evolution in diffusional phase transformations in Fe–C alloys are discussed.The kinetics of ferrite transformations,pearlite transformations,and the precipitation of carbides under high magnetic fields are reviewed in terms of the thermodynamics of phase transformations and the diffusion behavior of carbon atoms.Finally,future trends in research on diffusional phase transformations of Fe–C alloys under high magnetic fields are discussed.
基金NSF-DMS 1016073 and 1318586,and the Recruitment Program of Global Youth Experts in China.
文摘We investigate the critical nuclei morphology in phase transformation by combining two effective ingredients,with the first being the phase field modeling of the relevant energetics which has been a popular approach for phase transitions and the second being shrinking dimer dynamics and its variants for computing saddle points and transition states.In particular,the newly formulated generalized shrinking dimer dynamics is proposed by adopting the Cahn-Hilliard dynamics for the generalized gradient system.As illustrations,a couple of typical cases are considered,including a generic system modeling heterogeneous nucleation and a specific material system modeling the precipitate nucleation in FeCr alloys.While the standard shrinking dimer dynamics can be applied to study the non-conserved case of generic heterogeneous nucleation directly,the generalized shrinking dimer dynamics is efficient to compute precipitate nucleation in FeCr alloys due to the conservation of concentration.Numerical simulations are provided to demonstrate both the complex morphology associated with nucleation events and the effectiveness of generalized shrinking dimer dynamics based on phase field models.
基金sponsored by the Helmholtz Association,the China Scholarship Council(CSC)partially funded by the German Research Foundation,DFG(Project No.MA 5039/4-1)。
文摘Tin(Sn)holds great promise as an anode material for next-generation lithium(Li)ion batteries but suffers from massive volume change and poor cycling performance.To clarify the dynamic chemical and microstructural evolution of Sn anode during lithiation and delithiation,synchrotron X-ray energydispersive diffraction and X-ray tomography are simultaneously employed during Li/Sn cell operation.The intermediate Li-Sn alloy phases during de/lithiation are identified,and their dynamic phase transformation is unraveled which is further correlated with the volume variation of the Sn at particle-and electrode-level.Moreover,we find that the Sn particle expansion/shrinkage induced particle displacement is anisotropic:the displacement perpendicular to the electrode surface(z-axis)is more pronounced compared to the directions(x-and y-axis)along the electrode surface.This anisotropic particle displacement leads to an anisotropic volume variation at the electrode level and eventually generates a net electrode expansion towards the separator after cycling,which could be one of the root causes of mechanical detachment and delamination of electrodes during long-term operation.The unraveled chemical evolution of Li-Sn and deep insights into the microstructural evolution of Sn anode provided here could guide future design and engineering of Sn and other alloy anodes for high energy density Li-and Na-ion batteries.
基金Funded by the National Natural Science Foundation of China(No.52075058)the Natural Science Foundation of Chongqing(No.cstc2021jcyj-msxmX1112)the Research and Demonstration of Key Technologies for Forging High-performance Aluminum Alloys for Aerospace Applications(No.Z20210348)。
文摘An accurate flow stress model was established by considering the parameters of strain rate,strain and temperature as well asβ→a+βphase transformation in order to develop the plastic forming theory of TC18 titanium alloy.Firstly,the phase transition kinetics of TC18 titanium alloy during isothermal and continuous cooling at 1073 and 1273 K was studied by thermodynamic calculation,meanwhile,the relationship of volume fraction of phase transition with temperature and time was obtained.Constitutive models were calculated by investigating flow behaviors under hot compression tests with the strain rates of 0.001-1s^(-1) and temperatures of 973-1223 K in the singleβand a+βregions in TC18 titanium alloy,respectively.By combining the phase transformation dynamic kinetics with constitutive models,an accurate flow stress model was established,providing theoretical basis and data support for the hot forging of TC18 titanium alloy.
基金supported by the National Key Research and Development Project (2018YFB1307902)Shanxi Province Joint Student Training Base Talent Training Project(No.2018JD33)+5 种基金Shanxi young top talent projectShanxi Province Science Foundation for Youths (201901D211312)Excellent young academic leaders in Shanxi colleges and universities(No.2019045)Excellent Achievements Cultivation Project of Shanxi Higher Education Institutions(No.2019KJ028)Shanxi Province emerging industry leader talent projectShanxi Graduate Education Innovation Project(No.2019SY482)。
文摘To explore the effect of temperature on the phase transformation of HCP→FCC during compression, the uniaxial compression process of AZ31 magnesium alloy was simulated by the molecular dynamics method, and the changes of crystal structure and dislocation evolution were observed. The effects of temperature on mechanical properties, crystal structure, and dislocation evolution of magnesium alloy during compression were analyzed. It is concluded that some of the Shockley partial dislocation is related to FCC stacking faults. With the help of TEM characterization, the correctness of the correlation between some of the dislocations and FCC stacking faults is verified. Through the combination of simulation and experiment, this paper provides an idea for the in-depth study of the solid-phase transformation of magnesium alloys and provides reference and guidance for the design of magnesium alloys with good plasticity and formability at room temperature.
基金supported by the National Key Research and Development Program of China (2021YFB3701001)the National Natural Science Foundation of China (51871143)+1 种基金Shanghai Engineering Research Center for Metal Parts Green Remanufacture (No.19DZ2252900) from Shanghai Engineering Research Center Construction ProjectShanghai Rising-Star Program (21QA1403200)。
文摘The negative thermal expansion(NTE) phenomenon is of great significance in fabricating zero thermal expansion(ZTE) materials to avoid thermal shock during heating and cooling. NTE is observed in limited groups of materials, e.g., metal cyanides, oxometallates, and metalorganic frameworks, but has not been reported in the family of metal hydrides. Herein, a colossal and continuous negative thermal expansion is firstly developed in the low-temperature phases of LT1-and LT2-Mg_(2)NiH_(4) between 488 K and 733 K from in-situ transmission electron microscope(TEM) video, with the volume contraction reaching 18.7% and 11.3%, respectively. The mechanisms for volume contraction of LT1 and LT2 phases are elucidated from the viewpoints of phase transformation, magnetic transition, and dehydrogenation, which is different from common NTE materials containing flexible polyhedra units in the structure. The linear volume shrinkage of LT2 in the temperature of 488-553 K corresponds to the phase transition of LT2→HT with a thermal expansion coefficient of -799.7 × 10^(-6) K^(-1) revealed by in-situ synchrotron powder X-ray diffraction. The sudden volume contraction in LT1 between 488 and 493 K may be caused by the rapid dehydrogenation of LT1 to Mg_(2)Ni. The revealed phenomenon in single composite material with different structures would be significant for preparing zero thermal expansion materials by tuning the fraction of LT1 and LT2 phases.
基金Funded by the National Natural Science Foundation of China(No.52071065)Fundamental Research Funds for the Central Universities(No.N2007007)。
文摘The improved microstructure and enhanced elevated temperature mechanical properties of Ti-44Al-5Nb-(Mo,V,B)alloys were obtained by vacuum arc re-melting(VAR)and primary annealing heat treatment(HT)of 1260℃/6 h/Furnace cooling(FC).The phase transformation,microstructure evolution and tensile properties for as-cast and HTed alloys were investigated.Results indicate that three main phase transformation points are determined,T_(eut)=1164.3℃,T_(γsolv)=1268.3℃and T_(βtrans)=1382.8℃.There are coarse lamellar colonies(300μm in length)and neighbor reticular B2 andγgrain(3-5μm)in as-cast alloy,while lamellar colonies are markedly refined and multi-oriented(20-50μm)as well as the volume fraction and grain sizes of equiaxedγand B2 phases(about 15μm)significantly increase in as-HTed alloy.Phase transformations involvingα+γ→α+γ+β/B2 and discontinuousγcoarsening contribute to the above characteristics.Borides(1-3μm)act as nucleation sites forβ_(eutectic) and produce massiveβgrains with different orientations,thus effectively refining the lamellar colonies and forming homogeneous multi-phase microstructure.Tensile curves show both the alloys exhibit suitable performance at 800℃.As-cast alloy shows a higher ultimate tensile stress of 647 MPa,while a better total elongation of more than 41%is obtained for as-HTed alloy.The mechanical properties improvement is mainly attributed to fine,multi-oriented lamellar colonies,coordinated deformation of homogeneous multi-phase microstructure and borides within lamellar interface preventing crack propagation.
基金the project of the Open Research Fund Program of Science and Technology on Aerospace Chemical Power Laboratory(Grant No.STACPL320221B04)Key Laboratory of Explosion Science and Technology(Beijing Institute of Technology)The project number is ZDKT21-01.
文摘The coupling effect of heat absorption and release exists in the thermal decomposition of a few chemical materials.However,the impact of the above coupling on thermal hazard assessment is not considered in the literature studies.In this work,nitroguanidine(NQ)and 1,3,5-trinitro-1,3,5-triazine(RDX)are selected as representative materials to explore the influence of the coupling effect on the thermal hazard assessment of chemical materials.The linear heating experiments of NQ and RDX are carried out by a microcalorimeter and synchronous thermal analyser.The thermal decomposition curves are decoupled by advanced thermokinetics software.The thermal decomposition and kinetic parameters before and after decoupling are calculated.The results of TG experiment show that both NQ and RDX began to lose mass during the endothermic stage.The endothermic melting and exothermic decomposition of NQ and RDX are coupled within this stage.The coupling effect has different degrees of influence on its initial decomposition temperature and safety parameters.Compared with the parameters in the coupling state,the initial decomposition temperature and adiabatic induction period after decoupling decrease.The self-accelerating decomposition temperature increases,and internal thermal runaway time decreases.In the thermal hazard assessment of chemical materials with coupling effects,the calculated parameters after decoupling should be taken as an important safety index。
基金financially funded by Natural Science Basic Research Program of Shaanxi(grant number 2022JM-239)Key Research and Development Project of Shaanxi Provincial(grant number 2021LLRH-05–08)。
文摘To study the formation and transformation mechanism of long-period stacked ordered(LPSO)structures,a systematic atomic scale analysis was conducted for the structural evolution of long-period stacked ordered(LPSO)structures in the Mg-Gd-Y-Zn-Zr alloy annealed at 300℃~500℃.Various types of metastable LPSO building block clusters were found to exist in alloy structures at different temperatures,which precipitate during the solidification and homogenization process.The stability of Zn/Y clusters is explained by the first principles of density functional theory.The LPSO structure is distinguished by the arrangement of its different Zn/Y enriched LPSO structural units,which comprises local fcc stacking sequences upon a tightly packed plane.The presence of solute atoms causes local lattice distortion,thereby enabling the rearrangement of Mg atoms in the different configurations in the local lattice,and local HCP-FCC transitions occur between Mg and Zn atoms occupying the nearest neighbor positions.This finding indicates that LPSO structures can generate necessary Schockley partial dislocations on specific slip surfaces,providing direct evidence of the transition from 18R to 14H.Growth of the LPSO,devoid of any defects and non-coherent interfaces,was observed separately from other precipitated phases.As a result,the precipitation sequence of LPSO in the solidification stage was as follows:Zn/Ycluster+Mg layers→various metastable LPSO building block clusters→18R/24R LPSO;whereas the precipitation sequence of LPSO during homogenization treatment was observed to be as follows:18R LPSO→various metastable LPSO building block clusters→14H LPSO.Of these,14H LPSO was found to be the most thermodynamically stable structure.