Equations(2)and(6)and the corresponding discussion in the paper[Chin.Phys.Lett.42,056301(2025)]have been corrected.These modiffcations do not affect the results derived in the paper.
By extending the concept of diffusion to the potential energy landscapes(PELs), we introduce the meansquared energy difference(MSED) as a novel quantity to investigate the intrinsic properties of supercooled liquids. ...By extending the concept of diffusion to the potential energy landscapes(PELs), we introduce the meansquared energy difference(MSED) as a novel quantity to investigate the intrinsic properties of supercooled liquids. MSED can provide a clear description of the “energy relaxation” process on a PEL. Through MSED analysis, we have obtained a characteristic time similar to that derived from structure analysis, namely τ_(α)^(*).Further, we establish a connection between MSED and the feature of PELs, providing a concise and quantitative description of PELs. The relaxation behavior of energy has been found to follow a stretched exponential form.As the temperature decreases, the roughness of the accessible PEL changes significantly around a characteristic temperature T_(x), which is 20% higher than the glass transition temperature T_(g) and is comparable to the critical temperature of the mode-coupling theory. More importantly, one of the PEL parameters is closely related to the Adam–Gibbs configurational entropy. The present research, which directly links the PEL to the relaxation process, provides avenues for further research of glasses.展开更多
The formation and evolution characteristics of bcc phase during the isothermal relaxation processes for supercooled-liquid and amorphous Pb were investigated by molecular dynamics simulation and cluster-type index met...The formation and evolution characteristics of bcc phase during the isothermal relaxation processes for supercooled-liquid and amorphous Pb were investigated by molecular dynamics simulation and cluster-type index method （CTIM）. It is found that during the relaxation process, the formation and evolution of bcc phase are closely dependent on the initial temperature and structure. During the simulation time scale, when the initial temperature is in the range of supercooled liquid region, the bcc phase can be formed and kept a long time; while it is in the range of glassy region, the bcc phase can be formed at first and then partially transformed into hcp phase; when it decreases to the lower one, the hcp and fcc phases can be directly transformed from the glassy structure without undergoing the metastable bcc phase. The Ostwald＇s ＂step rule＂ is impactful during the isothermal relaxation process of the supercooled and glassy Pb, and the metastable bcc phase plays an important role in the precursor of crystallization.展开更多
Research results on the viscous flow deformation behavior of bulk amorphous alloy in different systems are reviewed. The material exhibits an ideal Newtonian fluid at a high temperature. Analytical solution of lamella...Research results on the viscous flow deformation behavior of bulk amorphous alloy in different systems are reviewed. The material exhibits an ideal Newtonian fluid at a high temperature. Analytical solution of lamellar fluid flow behavior is used to discuss the viscous flow behavior of the bulk amorphous alloy in the supercooled liquid state. A material model, which describes such deformation behavior of Mg6oCusoYlo amorphous alloy, is introduced into the finite element method of microformin8 process. Surface feature size was investigated and found not sensitive to the micro formability. Bulk amorphous alloy may possibly be applied to microelectro-mechanical-systems （MEMS） fabrication.展开更多
This paper studied a snow event over North China on 21 February 2017,using aircraft in-situ data,a Lagrangian analysis tool,and WRF simulations with different microphysical schemes to investigate the supercooled layer...This paper studied a snow event over North China on 21 February 2017,using aircraft in-situ data,a Lagrangian analysis tool,and WRF simulations with different microphysical schemes to investigate the supercooled layer of warm conveyor belts(WCBs).Based on the aircraft data,we found a fine vertical structure within clouds in the WCB and highlighted a 1-2 km thin supercooled liquid water layer with a maximum Liquid Water Content(LWC) exceeding0.5 g kg^(-1) during the vertical aircraft observation.Although the main features of thermodynamic profiles were essentially captured by both modeling schemes,the microphysical quantities exhibited large diversity with different microphysics schemes.The conventional Morrison two-moment scheme showed remarkable agreement with in-situ observations,both in terms of the thermodynamic structure and the supercooled liquid water layer.However,the microphysical structure of the WCB clouds,in terms of LWC and IWC,was not apparent in HUJI fast bin scheme.To reduce such uncertainty,future work may focus on improving the representation of microphysics in bin schemes with in-situ data and using similar assumptions for all schemes to isolate the impact of physics.展开更多
By means of Gibbs-Bogoliubov (GB) thermodynamic variational calculation,the thermodynamic properties of the supercooled liquid metals,such as the 3rd family elements Al,Ga and Tl and transition metal Ti were calculate...By means of Gibbs-Bogoliubov (GB) thermodynamic variational calculation,the thermodynamic properties of the supercooled liquid metals,such as the 3rd family elements Al,Ga and Tl and transition metal Ti were calculated using the hard-sphere (HS) system as reference.The values of mean atomic volume,Helmholtz free energy,internal energy and entropy as well as specific heat at constant volume,isothermal bulk modulus,thermal expan- sion coefficient and specfic heat under constant pressure were evaluated.The glass transition temperature,T_g,is easily obtained from the C_p-T plot.The glass forming ability for metal can be predicted from T_g/T_m,which is in agreement with the experimental results.展开更多
The surface dynamics of supercooled liquid-glycerol is studied by scanning the thickness of the glycerol film with single photon detection. Measurements are performed at room temperature well above the glyeerol＇s gla...The surface dynamics of supercooled liquid-glycerol is studied by scanning the thickness of the glycerol film with single photon detection. Measurements are performed at room temperature well above the glyeerol＇s glass transition temperature. It is shown that the surface dynamics of the glycerol film is very sensitive to the temperature. The linear relationship between the thickness of the film and the viscosity predicted by the Vogel Pulcher-Tammann Hesse （VFTH） law is also presented experimentally.展开更多
In marginally jammed solids confined by walls,we calculate the particle and ensemble averaged value of an order parameter,Ψ(r),as a function of the distance to the wall,r.Being a microscopic indicator of structural d...In marginally jammed solids confined by walls,we calculate the particle and ensemble averaged value of an order parameter,Ψ(r),as a function of the distance to the wall,r.Being a microscopic indicator of structural disorder and particle mobility in solids,Ψis by definition the response of the mean square particle displacement to the increase of temperature in the harmonic approximation and can be directly calculated from the normal modes of vibration of the zerotemperature solids.We find that,in confined jammed solids,Ψ(r)curves at different pressures can collapse onto the same master curve following a scaling function,indicating the criticality of the jamming transition.The scaling collapse suggests a diverging length scale and marginal instability at the jamming transition,which should be accessible to sophisticatedly designed experiments.Moreover,Ψ(r)is found to be significantly suppressed when approaching the wall and anisotropic in directions perpendicular and parallel to the wall.This finding can be applied to understand the r-dependence and anisotropy of the structural relaxation in confined supercooled liquids,providing another example of understanding or predicting behaviors of supercooled liquids from the perspective of the zero-temperature amorphous solids.展开更多
Surface morphologies of Zr52.5 Al10 Ni10 Cu15 Be12.5 bulk metallic glass after being rolled at both a temperature around T9 and near （ Tx - 50） K were investigated with a scanning electron microscopy. Macroscopic an...Surface morphologies of Zr52.5 Al10 Ni10 Cu15 Be12.5 bulk metallic glass after being rolled at both a temperature around T9 and near （ Tx - 50） K were investigated with a scanning electron microscopy. Macroscopic and microscopic observation results show that squamae, cracks, steps and wedges exist on the surface when the samples were rolled at temperatures around Ty. However, a smooth and fiat surface appears when the samples were rolled at temperatures near （ Tx - 50） K. These results indicate that the mode of deformation in the supercooled liquid region is a partially homogeneous flow at a temperature around T9, and a fully homogeneous one at temperatures near （ Tx - 50） K. According to the results, it is more feasible to roll the amorphous alloys at temperatures near （ Tx - 50） K to obtain parts with smooth and fiat surface.展开更多
Local arrangement of atoms in supercooled liquid Ni_(80)P_(20) alloy has been investigated by using NPT-MD simulation techniques based on the effective pair Potentials derived for Ni-P system. Bond-orientational order...Local arrangement of atoms in supercooled liquid Ni_(80)P_(20) alloy has been investigated by using NPT-MD simulation techniques based on the effective pair Potentials derived for Ni-P system. Bond-orientational order, the long-range correlation function and symmetrical parameters by pair-analysis approach have been calculated for supercooled liquid Ni_(80)P_(20) alloy. Results show. that in case of Ni_(80) .P_(20) alloy, the local structure is all random-like whether the centre of cluster is located at atoms Ni or P. It indicates that the icosahedral symmetry is not the unique model to describe the microstructure in supercooled liquid metals.展开更多
Viscosity is a crucial dynamic property for alloy liquids.For alloy liquids with glass-forming ability,their viscosity undergoes a change of more than ten orders of magnitude upon cooling,and eventually,a transition f...Viscosity is a crucial dynamic property for alloy liquids.For alloy liquids with glass-forming ability,their viscosity undergoes a change of more than ten orders of magnitude upon cooling,and eventually,a transition from liquid to glassy state occurs when viscosity reaches 1012 Pa s.Nevertheless,the viscosity measurement in the supercooled liquid region(SLR)has been an experimental challenge.Here,in this work,by combining conventional and fast scanning calorimeters,the accurate viscosity of supercooled liquids for Au_(49)Ag_(5.5)Pd_(2.3)Cu_(26.9)Si_(16.3) and Zr_(44)Ti_(11)Cu_(10)Ni_(10)Be_(25) metallic glasses(MGs)was measured over a wide viscosity range of 10^(6)-10^(12) Pa s.Moreover,the viscosity range of 10^(6)-10^(8) Pa s is generally selected for thermoplastic forming(TPF),which takes advantage of the dramatic softening that MGs exhibit after being heated into the SLR.We further gave the TPF process window covering the range of processing temperature and time by utilizing the obtained viscosity data and timetemperature-transformation curves.The optimal time window avoiding property degradation was also determined,based on that there was no marked effect on the mechanical properties of MGs when crystallinity was below~5%.Our findings not only provide the accurate viscosity data in the SLR,but also determine the optimal process parameters for the TPF process.展开更多
Identifying supercooled liquid water(SLW)in clouds is critical for weather modification,aviation safety,and atmospheric radiation calculations.Currently,aircraft identification in the SLW area mostly depends on empric...Identifying supercooled liquid water(SLW)in clouds is critical for weather modification,aviation safety,and atmospheric radiation calculations.Currently,aircraft identification in the SLW area mostly depends on emprical estimation of cloud particle number concentration(N_(c))in China,and scientific verification and quantitative identification criteria are urgently needed.In this study,the observations are from the Fast Cloud Droplets Probe,Rosemount ice detector(RICE),and Cloud Particle Imager(CP_(i))onboard a King Air aircraft during seven flights in 2018 and 2019 over central and eastern China.Based on this,the correlation among N_(c),the proportion of spherical particles(P_(s)),and the probability of icing(P_(i))in supercooled stratiform and cumulus-stratus clouds is statistically analyzed.Subsequently,this study proposes a method to identify SLW areas using N_(c) in combination with ambient temperature.The reliability of this method is evaluated through the true skill statistics(TSS)and threat score(TS)methods.Numerous airborne observations during the seven flights reveal a strong correlation among Nc,P_(s),and P_(i)at the temperature from 0 to−18°C.When Nc is greater than a certain threshold of 5 cm^(−3),there is always the SLW,i.e.,P_(i)and P_(s)are high.Evaluation results demonstrate that the TSS and TS values for Nc=5 cm^(−3)are higher than those for Nc<5 cm^(−3),and a larger Nc threshold(>5 cm^(−3))corresponds to a higher SLW identification hit rate and a higher SLW content.Therefore,Nc=5 cm^(−3)can be used as the minimum criterion for identifying the SLW in clouds at temperature lower than 0°C.The SLW identification method proposed in this study is especially helpful in common situations where aircraft are equipped with only Nc probes and without the CP_(i)and RICE.展开更多
There is a lack of understanding of both the conversion of an unstable glass into a metastable supercooled liquid(MSL) upon heating and the metastability of MSLs. In this study, we investigated the time-and temperatur...There is a lack of understanding of both the conversion of an unstable glass into a metastable supercooled liquid(MSL) upon heating and the metastability of MSLs. In this study, we investigated the time-and temperature-dependent metastability of an MSL using an advanced nano-calorimetric technique. The chosen Au-based metallic glass(Au MG) allowed adequate probing of its MSL in a temperature range between 10 and 70 K above the standard glass transition temperature. We found that the survival time of the MSL state is a quadratic function of temperature. Beyond this duration threshold, the sample undergoes fast crystallization even if it is below the crystallization temperature that is measured using differential scanning calorimetry.Employing transmission electron microscopy, we observed the formation of clusters with a partially ordered lattice structure during relaxation in the Au MG sample fabricated using a nano-calorimeter. The atomic ordering within the clusters was enhanced by increasing time and temperature in the MSL region. Once the as-produced glass entered the MSL stage upon heating followed by a quenching stage at a given rate, the mechanical properties of the quenched glass remained the same regardless of its holding temperature and duration within the MSL region. This work provides insights into the glass-MSL-crystal transformation and offers guidance for designing standard metallic glasses for property characterizations.展开更多
Structural rejuvenation is vital and attractive for modulating the energetic state and structural heterogeneity of bulk metallic glasses(BMGs). In this paper, we show that cooling a BMG from a supercooled liquid regio...Structural rejuvenation is vital and attractive for modulating the energetic state and structural heterogeneity of bulk metallic glasses(BMGs). In this paper, we show that cooling a BMG from a supercooled liquid region at laboratory rates can reverse the relaxation enthalpy lost during the preceding structural relaxation. Increasing the cooling rate is beneficial for enhancing atomic mobility and dynamic mechanical relaxation intensity. Therefore, this rejuvenation methodology promotes tailoring the mechanical properties of BMGs and provides a comprehensive understanding of the rejuvenation mechanism.展开更多
As a common but critical dynamic crossover in glass-forming liquids(GFLs),the discovery of fragile-to-strong(F-S)transition promises a novel route for understanding supercooled liquid and glass transition.The present ...As a common but critical dynamic crossover in glass-forming liquids(GFLs),the discovery of fragile-to-strong(F-S)transition promises a novel route for understanding supercooled liquid and glass transition.The present work,for the first time,successfully realizes the quantitative prediction of the F-S transition in nine metallic glass-forming liquids,by a counter-intuitive approach that focuses on local atomic activation events,rather than relaxation,upon cooling.The dynamic crossover originates from a disorder-to-order transition by self-regulating behavior of atomic position within a cage controlled by finite atomic activation events,due to the appearance of local cooperative motion of nearest neighborhood atoms.Moreover,the dominant role of entropy in this anomaly has been discovered,and the correspondence between the crossover of configuration entropy involved in activation events and the occurrence of F-S transition has been found.Our work implies that the feature of atomic energy fluctuations reflected by atomic activation events has a close linkage to complex dynamic behaviors of disordered systems.展开更多
Bulk metallic glasses (BMGs) with large supercooled liquid region are promising materials for superplastic forming. In this paper, we demonstrate a microstructure-based strategy to pinpoint the composition with the la...Bulk metallic glasses (BMGs) with large supercooled liquid region are promising materials for superplastic forming. In this paper, we demonstrate a microstructure-based strategy to pinpoint the composition with the largest supercooled liquid region in La 86 x Al 14 Cu x (x=16 at%-20 at%) metallic glass system. By monitoring the changes in crystallization behavior of the glassy alloys with composition to search for the alloys exhibiting eutectic crystallization, the glassy alloys with the largest supercooled liquid region in the given alloy system can be found. The metallic glasses with Cu contents of 16 at%-19 at% exhibited two crystallization peaks, and the primary crystallization product was identified to be α-La by means of DSC, XRD and TEM. The increase in Cu content resulted in the decay of the primary crystallization peak and the increase in onset temperature of crystallization, leading to the enlargement of supercooled liquid region. By further suppressing the α-La primary crystallization with increasing Cu content up to 20 at%, the eutectic crystallization of α-La and LaCu 13 through one crystallization reaction occurred upon heating, where the largest supercooled liquid region of 65 K for La 66 Al 14 Cu 20 glassy alloy was located. This study indicats that, in a given glassy alloy system, a larger supercooled liquid region can be achieved by optimizing the alloy compositions to suppress the primary crystallization.展开更多
The theoretical challenges in understanding the nature of glass and glass transition raise significant questions in statistical and condensed matter physics.As a prototypical example of complex physical systems,glasse...The theoretical challenges in understanding the nature of glass and glass transition raise significant questions in statistical and condensed matter physics.As a prototypical example of complex physical systems,glasses and the vitrification process have been central research topics,consistently attracting broad scientific interest.This focus has driven extensive studies on phenomena such as aging,non-exponential relaxation,dynamic anomalies,glass-forming ability,and the mechanical response of glasses under stress.Recent advances in computational and experimental techniques have enabled rigorous testing of theoretical models,shedding new light on glass behavior.However,the intrinsic complexity of glass and the glass transition that lies in their physics,which spans multiple length and time scales,makes the system challenging to characterize.In this review,we emphasize the need to move beyond conventional approaches and propose a topological perspective as a promising alternative to address these challenges.Specifically,our findings reveal that the diversity in particle relaxation behavior is statistically linked to a global topological feature of the transient network structures formed by the particles in a given liquid.This direction offers opportunities to uncover novel phenomena that could fundamentally reshape our understanding of glassy materials.展开更多
As one of the most important forming technologies for industrial bulk metallic glass (BMG) parts withcomplex shapes, high-pressure die casting (HPDC) can fill a die cavity with a glass-forming metallic liquidin millis...As one of the most important forming technologies for industrial bulk metallic glass (BMG) parts withcomplex shapes, high-pressure die casting (HPDC) can fill a die cavity with a glass-forming metallic liquidin milliseconds. However, to our knowledge, the correlation between flow and crystallization behavior inthe HPDC process has never been established. In this study, we report on the solidification behavior ofZr_(55)Cu_(30)Ni_(5)Al_(10) glass forming liquid under various flow rates. Surprisingly, the resulting alloys display adecreasing content of amorphous phase with increase of flow rate, i.e. increase of cooling rate, suggestingthat crystallization kinetics of glass-forming metallic liquids in the HPDC process is strongly dependenton the flow field. Analysis reveals that the accelerated crystallization behavior is mainly ascribed to therapid increase in viscosity with a decreasing temperature as well as to the huge shear effect in the glassforming liquid at the end stage of the filling process when the temperature is close to the glass-transitionpoint;this results in a transition from diffusion- to advection-dominated transport. The current investigation suggests that flow-related crystallization must be considered to assess the intrinsic glass-formingability of BMGs produced via HPDC. The obtained results will not only improve the understanding ofcrystallization dynamics but also promote the high-quality production and large-scale application of BMGparts.展开更多
The Stokes–Einstein–Debye(SED)relation is proposed to be broken down in supercooled liquids by many studies.However,conclusions are usually drawn by testing some variants of the SED relation rather than its original...The Stokes–Einstein–Debye(SED)relation is proposed to be broken down in supercooled liquids by many studies.However,conclusions are usually drawn by testing some variants of the SED relation rather than its original formula.In this work,the rationality of the SED relation and its variants is examined by performing molecular dynamics simulations with the Lewis–Wahnstrom model of ortho-terphenyl(OTP).The results indicate the original SED relation is valid for OTP but the three variants are all broken down.The inconsistency between the SED relation and its variants is analyzed from the heterogeneous dynamics,the adopted assumptions and approximations as well as the interactions among molecules.Therefore,care should be taken when employing the variants to judge the validity of the SED relation in supercooled liquids.展开更多
High entropy metallic glasses（MGs） have attracted tremendous attentions owing to high entropy that benefits the probing of new MG-forming systems. However, the micro-formability of high entropy MGs is lack of invest...High entropy metallic glasses（MGs） have attracted tremendous attentions owing to high entropy that benefits the probing of new MG-forming systems. However, the micro-formability of high entropy MGs is lack of investigation in comparison with these conventional MG counterparts, which is crucial to the development of this kind of metallic alloys. In this work, the thermoplastic mciro-formability of TiZrHfNiCuBe high entropy MG was systemically investigated. Time-Temperature-Transformation（TTT）curve was first constructed based on isothermal crystallization experiments, which provides thermoplastic processing time of the supercooled high entropy MGs. By comparison with the deformation map,Newtonian flow was found beneficial to the thermoplastic formability. While the thermoplastic forming becomes arduous with reducing mould size to tens micrometer, because of the strong supercooled TiZrHfNiCuBe high entropy MG（fragility = 27）. Fortunately, the micro-formability of TiZrHfNiCuBe high entropy MG could be improved by vibration loading, as demonstrated by finite-element-method simulation. Our findings not only systemically evaluate the thermoplastic micro-formability of high entropy MG, but also provide fundamental understanding of the phenomenon.展开更多
文摘Equations(2)and(6)and the corresponding discussion in the paper[Chin.Phys.Lett.42,056301(2025)]have been corrected.These modiffcations do not affect the results derived in the paper.
基金supported by the National Key Research and Development Program of China (Grant No. 2022YFA1404603)by the National Natural Science Foundation of China (Grant Nos. 12274127 and 12188101)。
文摘By extending the concept of diffusion to the potential energy landscapes(PELs), we introduce the meansquared energy difference(MSED) as a novel quantity to investigate the intrinsic properties of supercooled liquids. MSED can provide a clear description of the “energy relaxation” process on a PEL. Through MSED analysis, we have obtained a characteristic time similar to that derived from structure analysis, namely τ_(α)^(*).Further, we establish a connection between MSED and the feature of PELs, providing a concise and quantitative description of PELs. The relaxation behavior of energy has been found to follow a stretched exponential form.As the temperature decreases, the roughness of the accessible PEL changes significantly around a characteristic temperature T_(x), which is 20% higher than the glass transition temperature T_(g) and is comparable to the critical temperature of the mode-coupling theory. More importantly, one of the PEL parameters is closely related to the Adam–Gibbs configurational entropy. The present research, which directly links the PEL to the relaxation process, provides avenues for further research of glasses.
基金Projects (50831003, 50571037) supported by the National Natural Science Foundation of China
文摘The formation and evolution characteristics of bcc phase during the isothermal relaxation processes for supercooled-liquid and amorphous Pb were investigated by molecular dynamics simulation and cluster-type index method （CTIM）. It is found that during the relaxation process, the formation and evolution of bcc phase are closely dependent on the initial temperature and structure. During the simulation time scale, when the initial temperature is in the range of supercooled liquid region, the bcc phase can be formed and kept a long time; while it is in the range of glassy region, the bcc phase can be formed at first and then partially transformed into hcp phase; when it decreases to the lower one, the hcp and fcc phases can be directly transformed from the glassy structure without undergoing the metastable bcc phase. The Ostwald＇s ＂step rule＂ is impactful during the isothermal relaxation process of the supercooled and glassy Pb, and the metastable bcc phase plays an important role in the precursor of crystallization.
基金supported by the National Natural Sci-ence Foundation of China under grant No. 50705092.
文摘Research results on the viscous flow deformation behavior of bulk amorphous alloy in different systems are reviewed. The material exhibits an ideal Newtonian fluid at a high temperature. Analytical solution of lamellar fluid flow behavior is used to discuss the viscous flow behavior of the bulk amorphous alloy in the supercooled liquid state. A material model, which describes such deformation behavior of Mg6oCusoYlo amorphous alloy, is introduced into the finite element method of microformin8 process. Surface feature size was investigated and found not sensitive to the micro formability. Bulk amorphous alloy may possibly be applied to microelectro-mechanical-systems （MEMS） fabrication.
基金jointly supported by the China National Science Foundation under Grant Nos.41875172 and 42075192。
文摘This paper studied a snow event over North China on 21 February 2017,using aircraft in-situ data,a Lagrangian analysis tool,and WRF simulations with different microphysical schemes to investigate the supercooled layer of warm conveyor belts(WCBs).Based on the aircraft data,we found a fine vertical structure within clouds in the WCB and highlighted a 1-2 km thin supercooled liquid water layer with a maximum Liquid Water Content(LWC) exceeding0.5 g kg^(-1) during the vertical aircraft observation.Although the main features of thermodynamic profiles were essentially captured by both modeling schemes,the microphysical quantities exhibited large diversity with different microphysics schemes.The conventional Morrison two-moment scheme showed remarkable agreement with in-situ observations,both in terms of the thermodynamic structure and the supercooled liquid water layer.However,the microphysical structure of the WCB clouds,in terms of LWC and IWC,was not apparent in HUJI fast bin scheme.To reduce such uncertainty,future work may focus on improving the representation of microphysics in bin schemes with in-situ data and using similar assumptions for all schemes to isolate the impact of physics.
文摘By means of Gibbs-Bogoliubov (GB) thermodynamic variational calculation,the thermodynamic properties of the supercooled liquid metals,such as the 3rd family elements Al,Ga and Tl and transition metal Ti were calculated using the hard-sphere (HS) system as reference.The values of mean atomic volume,Helmholtz free energy,internal energy and entropy as well as specific heat at constant volume,isothermal bulk modulus,thermal expan- sion coefficient and specfic heat under constant pressure were evaluated.The glass transition temperature,T_g,is easily obtained from the C_p-T plot.The glass forming ability for metal can be predicted from T_g/T_m,which is in agreement with the experimental results.
基金supported by the Natural Science Foundation of China (Grant No 10674086)973 Program of China (Grant Nos 2006CB921603,2006CB921102 and 2008CB317103)+4 种基金863 Program of China (Grant No 2009AA01Z319)NCET-06-0259the Shanxi Provincial Foundation for Leaders of Disciplines in Sciencethe Natural Science Foundation of Shanxi province,China (Grant No 2007011006)Shanxi Province Foundation for Returned scholars of China
文摘The surface dynamics of supercooled liquid-glycerol is studied by scanning the thickness of the glycerol film with single photon detection. Measurements are performed at room temperature well above the glyeerol＇s glass transition temperature. It is shown that the surface dynamics of the glycerol film is very sensitive to the temperature. The linear relationship between the thickness of the film and the viscosity predicted by the Vogel Pulcher-Tammann Hesse （VFTH） law is also presented experimentally.
基金Project supported by the National Natural Science Foundation of China(Grant No.11734014)。
文摘In marginally jammed solids confined by walls,we calculate the particle and ensemble averaged value of an order parameter,Ψ(r),as a function of the distance to the wall,r.Being a microscopic indicator of structural disorder and particle mobility in solids,Ψis by definition the response of the mean square particle displacement to the increase of temperature in the harmonic approximation and can be directly calculated from the normal modes of vibration of the zerotemperature solids.We find that,in confined jammed solids,Ψ(r)curves at different pressures can collapse onto the same master curve following a scaling function,indicating the criticality of the jamming transition.The scaling collapse suggests a diverging length scale and marginal instability at the jamming transition,which should be accessible to sophisticatedly designed experiments.Moreover,Ψ(r)is found to be significantly suppressed when approaching the wall and anisotropic in directions perpendicular and parallel to the wall.This finding can be applied to understand the r-dependence and anisotropy of the structural relaxation in confined supercooled liquids,providing another example of understanding or predicting behaviors of supercooled liquids from the perspective of the zero-temperature amorphous solids.
基金Project supported by National Natural Science Foundation of Chi-na (Grant Nos .50201009 ,50031010)
文摘Surface morphologies of Zr52.5 Al10 Ni10 Cu15 Be12.5 bulk metallic glass after being rolled at both a temperature around T9 and near （ Tx - 50） K were investigated with a scanning electron microscopy. Macroscopic and microscopic observation results show that squamae, cracks, steps and wedges exist on the surface when the samples were rolled at temperatures around Ty. However, a smooth and fiat surface appears when the samples were rolled at temperatures near （ Tx - 50） K. These results indicate that the mode of deformation in the supercooled liquid region is a partially homogeneous flow at a temperature around T9, and a fully homogeneous one at temperatures near （ Tx - 50） K. According to the results, it is more feasible to roll the amorphous alloys at temperatures near （ Tx - 50） K to obtain parts with smooth and fiat surface.
文摘Local arrangement of atoms in supercooled liquid Ni_(80)P_(20) alloy has been investigated by using NPT-MD simulation techniques based on the effective pair Potentials derived for Ni-P system. Bond-orientational order, the long-range correlation function and symmetrical parameters by pair-analysis approach have been calculated for supercooled liquid Ni_(80)P_(20) alloy. Results show. that in case of Ni_(80) .P_(20) alloy, the local structure is all random-like whether the centre of cluster is located at atoms Ni or P. It indicates that the icosahedral symmetry is not the unique model to describe the microstructure in supercooled liquid metals.
基金supported by the Taishan Scholars Program of Shandong Province(Grant No.tsqn201909010)the Key Basic and Applied Research Program of Guangdong Province(Grant No.2019B030302010)+1 种基金the National Natural Science Foundation of China(Grant Nos.51901139,51971120,and U1902221)the Key R&D Program of Shandong Province(Grant No.2022CXGC020308)。
文摘Viscosity is a crucial dynamic property for alloy liquids.For alloy liquids with glass-forming ability,their viscosity undergoes a change of more than ten orders of magnitude upon cooling,and eventually,a transition from liquid to glassy state occurs when viscosity reaches 1012 Pa s.Nevertheless,the viscosity measurement in the supercooled liquid region(SLR)has been an experimental challenge.Here,in this work,by combining conventional and fast scanning calorimeters,the accurate viscosity of supercooled liquids for Au_(49)Ag_(5.5)Pd_(2.3)Cu_(26.9)Si_(16.3) and Zr_(44)Ti_(11)Cu_(10)Ni_(10)Be_(25) metallic glasses(MGs)was measured over a wide viscosity range of 10^(6)-10^(12) Pa s.Moreover,the viscosity range of 10^(6)-10^(8) Pa s is generally selected for thermoplastic forming(TPF),which takes advantage of the dramatic softening that MGs exhibit after being heated into the SLR.We further gave the TPF process window covering the range of processing temperature and time by utilizing the obtained viscosity data and timetemperature-transformation curves.The optimal time window avoiding property degradation was also determined,based on that there was no marked effect on the mechanical properties of MGs when crystallinity was below~5%.Our findings not only provide the accurate viscosity data in the SLR,but also determine the optimal process parameters for the TPF process.
基金Supported by the National Key Research and Development Program of China(2016YFA0601701)Fengyun Application Pioneering Project(FY-APP-2021.0102)National High Technology Research and Development Program of China(2012AA120902).
文摘Identifying supercooled liquid water(SLW)in clouds is critical for weather modification,aviation safety,and atmospheric radiation calculations.Currently,aircraft identification in the SLW area mostly depends on emprical estimation of cloud particle number concentration(N_(c))in China,and scientific verification and quantitative identification criteria are urgently needed.In this study,the observations are from the Fast Cloud Droplets Probe,Rosemount ice detector(RICE),and Cloud Particle Imager(CP_(i))onboard a King Air aircraft during seven flights in 2018 and 2019 over central and eastern China.Based on this,the correlation among N_(c),the proportion of spherical particles(P_(s)),and the probability of icing(P_(i))in supercooled stratiform and cumulus-stratus clouds is statistically analyzed.Subsequently,this study proposes a method to identify SLW areas using N_(c) in combination with ambient temperature.The reliability of this method is evaluated through the true skill statistics(TSS)and threat score(TS)methods.Numerous airborne observations during the seven flights reveal a strong correlation among Nc,P_(s),and P_(i)at the temperature from 0 to−18°C.When Nc is greater than a certain threshold of 5 cm^(−3),there is always the SLW,i.e.,P_(i)and P_(s)are high.Evaluation results demonstrate that the TSS and TS values for Nc=5 cm^(−3)are higher than those for Nc<5 cm^(−3),and a larger Nc threshold(>5 cm^(−3))corresponds to a higher SLW identification hit rate and a higher SLW content.Therefore,Nc=5 cm^(−3)can be used as the minimum criterion for identifying the SLW in clouds at temperature lower than 0°C.The SLW identification method proposed in this study is especially helpful in common situations where aircraft are equipped with only Nc probes and without the CP_(i)and RICE.
基金supported by the Songshan Lake Materials Laboratory (Grant No. 2021SLABFN05)the National Natural Science Foundation of China (Grant Nos. 51971120, 51901139)+2 种基金the Taishan Scholars Program of Shandong Province (Grant No. tsqn201909010)the Key Basic and Applied Research Program of Guangdong Province(Grant No. 2019B030302010)the Sao Paulo Research Foundation–FAPESP (Grant No.#2013/07793-6)。
文摘There is a lack of understanding of both the conversion of an unstable glass into a metastable supercooled liquid(MSL) upon heating and the metastability of MSLs. In this study, we investigated the time-and temperature-dependent metastability of an MSL using an advanced nano-calorimetric technique. The chosen Au-based metallic glass(Au MG) allowed adequate probing of its MSL in a temperature range between 10 and 70 K above the standard glass transition temperature. We found that the survival time of the MSL state is a quadratic function of temperature. Beyond this duration threshold, the sample undergoes fast crystallization even if it is below the crystallization temperature that is measured using differential scanning calorimetry.Employing transmission electron microscopy, we observed the formation of clusters with a partially ordered lattice structure during relaxation in the Au MG sample fabricated using a nano-calorimeter. The atomic ordering within the clusters was enhanced by increasing time and temperature in the MSL region. Once the as-produced glass entered the MSL stage upon heating followed by a quenching stage at a given rate, the mechanical properties of the quenched glass remained the same regardless of its holding temperature and duration within the MSL region. This work provides insights into the glass-MSL-crystal transformation and offers guidance for designing standard metallic glasses for property characterizations.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51971178 and 52271153)financially supported by National Natural Science Foundation of China (Grant No. 12072344)+4 种基金the Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(Grant No. 2021JC-12)the Natural Science Foundation of Chongqing(Grant No. cstc2020jcyj-jq X0001)sponsored by the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University (Grant No. CX2021015)the Youth Innovation Promotion Association of the Chinese Academy of Sciencesfinancial support from Research Grant Council (RGC) and the Hong Kong government through the General Research Fund (GRF)(Grant Nos.U11200719 and U11213118)。
文摘Structural rejuvenation is vital and attractive for modulating the energetic state and structural heterogeneity of bulk metallic glasses(BMGs). In this paper, we show that cooling a BMG from a supercooled liquid region at laboratory rates can reverse the relaxation enthalpy lost during the preceding structural relaxation. Increasing the cooling rate is beneficial for enhancing atomic mobility and dynamic mechanical relaxation intensity. Therefore, this rejuvenation methodology promotes tailoring the mechanical properties of BMGs and provides a comprehensive understanding of the rejuvenation mechanism.
基金supported by the National Natural Science Foundation of China(Grant Nos.51901139,U1902221,51971120,and 51971093)the Taishan Scholars Program of Shandong Province(Grant No.tsqn201909010)the Key Basic and Applied Research Program of Guangdong Province(Grant No.2019B030302010)。
文摘As a common but critical dynamic crossover in glass-forming liquids(GFLs),the discovery of fragile-to-strong(F-S)transition promises a novel route for understanding supercooled liquid and glass transition.The present work,for the first time,successfully realizes the quantitative prediction of the F-S transition in nine metallic glass-forming liquids,by a counter-intuitive approach that focuses on local atomic activation events,rather than relaxation,upon cooling.The dynamic crossover originates from a disorder-to-order transition by self-regulating behavior of atomic position within a cage controlled by finite atomic activation events,due to the appearance of local cooperative motion of nearest neighborhood atoms.Moreover,the dominant role of entropy in this anomaly has been discovered,and the correspondence between the crossover of configuration entropy involved in activation events and the occurrence of F-S transition has been found.Our work implies that the feature of atomic energy fluctuations reflected by atomic activation events has a close linkage to complex dynamic behaviors of disordered systems.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50631010, 50771005 and 50771006)the National Basic Research Program of China (Grant No. 2007CB613900)
文摘Bulk metallic glasses (BMGs) with large supercooled liquid region are promising materials for superplastic forming. In this paper, we demonstrate a microstructure-based strategy to pinpoint the composition with the largest supercooled liquid region in La 86 x Al 14 Cu x (x=16 at%-20 at%) metallic glass system. By monitoring the changes in crystallization behavior of the glassy alloys with composition to search for the alloys exhibiting eutectic crystallization, the glassy alloys with the largest supercooled liquid region in the given alloy system can be found. The metallic glasses with Cu contents of 16 at%-19 at% exhibited two crystallization peaks, and the primary crystallization product was identified to be α-La by means of DSC, XRD and TEM. The increase in Cu content resulted in the decay of the primary crystallization peak and the increase in onset temperature of crystallization, leading to the enlargement of supercooled liquid region. By further suppressing the α-La primary crystallization with increasing Cu content up to 20 at%, the eutectic crystallization of α-La and LaCu 13 through one crystallization reaction occurred upon heating, where the largest supercooled liquid region of 65 K for La 66 Al 14 Cu 20 glassy alloy was located. This study indicats that, in a given glassy alloy system, a larger supercooled liquid region can be achieved by optimizing the alloy compositions to suppress the primary crystallization.
基金supported by the National Natural Science Foundation of China(Grant Nos.12474184,52031016,11804027)。
文摘The theoretical challenges in understanding the nature of glass and glass transition raise significant questions in statistical and condensed matter physics.As a prototypical example of complex physical systems,glasses and the vitrification process have been central research topics,consistently attracting broad scientific interest.This focus has driven extensive studies on phenomena such as aging,non-exponential relaxation,dynamic anomalies,glass-forming ability,and the mechanical response of glasses under stress.Recent advances in computational and experimental techniques have enabled rigorous testing of theoretical models,shedding new light on glass behavior.However,the intrinsic complexity of glass and the glass transition that lies in their physics,which spans multiple length and time scales,makes the system challenging to characterize.In this review,we emphasize the need to move beyond conventional approaches and propose a topological perspective as a promising alternative to address these challenges.Specifically,our findings reveal that the diversity in particle relaxation behavior is statistically linked to a global topological feature of the transient network structures formed by the particles in a given liquid.This direction offers opportunities to uncover novel phenomena that could fundamentally reshape our understanding of glassy materials.
基金L.H.Liu would like to thank the financial support from the National Natural Science Foundation of China(No.52001123)the China Postdoctoral Science Foundation(Nos.2019TQ0099 and 2019M662908)+5 种基金Guangdong Basic and the Applied Basic Research Foundation(No.2019A1515110215)the Foundation for Distinguished Young Talents in Higher Education of Guangdong(No.2019KQNCX003)the Fundamental Research Funds for the Central Universities(No.2020ZYGXZR030)the Open Fund of National Engineering Research Center of Near-net-shape Forming for Metallic Materials(No.2019003)C.Yang would like to thank the financial support from the Key Basic and Applied Research Program of Guangdong Province(No.2019B030302010)the National Natural Science Foundation of China(No.51971149).
文摘As one of the most important forming technologies for industrial bulk metallic glass (BMG) parts withcomplex shapes, high-pressure die casting (HPDC) can fill a die cavity with a glass-forming metallic liquidin milliseconds. However, to our knowledge, the correlation between flow and crystallization behavior inthe HPDC process has never been established. In this study, we report on the solidification behavior ofZr_(55)Cu_(30)Ni_(5)Al_(10) glass forming liquid under various flow rates. Surprisingly, the resulting alloys display adecreasing content of amorphous phase with increase of flow rate, i.e. increase of cooling rate, suggestingthat crystallization kinetics of glass-forming metallic liquids in the HPDC process is strongly dependenton the flow field. Analysis reveals that the accelerated crystallization behavior is mainly ascribed to therapid increase in viscosity with a decreasing temperature as well as to the huge shear effect in the glassforming liquid at the end stage of the filling process when the temperature is close to the glass-transitionpoint;this results in a transition from diffusion- to advection-dominated transport. The current investigation suggests that flow-related crystallization must be considered to assess the intrinsic glass-formingability of BMGs produced via HPDC. The obtained results will not only improve the understanding ofcrystallization dynamics but also promote the high-quality production and large-scale application of BMGparts.
基金supported by the National Natural Science Foundation of China (No. 12104502)the Natural Science Foundation of Sichuan Province (No. 2023YFG0308)
文摘The Stokes–Einstein–Debye(SED)relation is proposed to be broken down in supercooled liquids by many studies.However,conclusions are usually drawn by testing some variants of the SED relation rather than its original formula.In this work,the rationality of the SED relation and its variants is examined by performing molecular dynamics simulations with the Lewis–Wahnstrom model of ortho-terphenyl(OTP).The results indicate the original SED relation is valid for OTP but the three variants are all broken down.The inconsistency between the SED relation and its variants is analyzed from the heterogeneous dynamics,the adopted assumptions and approximations as well as the interactions among molecules.Therefore,care should be taken when employing the variants to judge the validity of the SED relation in supercooled liquids.
基金supported by the National Natural Science Foundation of China [Grant Nos. 51671090, 51725504, 51435007]the funds of the the State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology [number AWJ-17M06]
文摘High entropy metallic glasses（MGs） have attracted tremendous attentions owing to high entropy that benefits the probing of new MG-forming systems. However, the micro-formability of high entropy MGs is lack of investigation in comparison with these conventional MG counterparts, which is crucial to the development of this kind of metallic alloys. In this work, the thermoplastic mciro-formability of TiZrHfNiCuBe high entropy MG was systemically investigated. Time-Temperature-Transformation（TTT）curve was first constructed based on isothermal crystallization experiments, which provides thermoplastic processing time of the supercooled high entropy MGs. By comparison with the deformation map,Newtonian flow was found beneficial to the thermoplastic formability. While the thermoplastic forming becomes arduous with reducing mould size to tens micrometer, because of the strong supercooled TiZrHfNiCuBe high entropy MG（fragility = 27）. Fortunately, the micro-formability of TiZrHfNiCuBe high entropy MG could be improved by vibration loading, as demonstrated by finite-element-method simulation. Our findings not only systemically evaluate the thermoplastic micro-formability of high entropy MG, but also provide fundamental understanding of the phenomenon.
