In order to investigate the damage tolerance of a metastable Ti-5Al-3V-3Mo-2Cr-2Zr-1Nb-1Fe(Ti5321)alloy with bimodal microstructure using void growth quantification and micromechanical modeling,in situ tensile testing...In order to investigate the damage tolerance of a metastable Ti-5Al-3V-3Mo-2Cr-2Zr-1Nb-1Fe(Ti5321)alloy with bimodal microstructure using void growth quantification and micromechanical modeling,in situ tensile testing was performed during X-ray microtomography experiments.Compared with investigations of surface voids by traditional two-dimensional(2D)methods involving post-mortem characterization,three-dimensional(3D)information on void evolution inside optically opaque samples obtained through X-ray microtomography is essential.The Rice and Tracey model and Huang model were applied to predict void growth and show good agreement with experimental data using calibration of the damage parameterα.The void growth kinetics of Ti5321 with bimodal microstructure was analyzed by comparing theαvalue with that of Ti64 for different microstructure morphologies.The damage mechanism of ductile fracture of Ti5321 with bimodal microstructure is discussed.It was found that the size of the voids apparently increases with the triaxiality of stress.Post-mortem scanning electron microscopy(SEM)was also used to demonstrate this damage mechanism of ductile fracture of Ti5321.展开更多
The heterogeneity of glasses has critical influences on the properties.How heterogeneity evolves during annealing is an intriguing cutting-edge question.In this work,the heterogeneity of the annealed metal-lic and pol...The heterogeneity of glasses has critical influences on the properties.How heterogeneity evolves during annealing is an intriguing cutting-edge question.In this work,the heterogeneity of the annealed metal-lic and polymer glasses has been studied systematically by using stress relaxation and nanoindentation tests.The stress relaxation processes are analyzed using Kohlrausch-Williams-Watts(KWW)equation.We surprisingly find that the heterogeneous factor βkww in KWW equation does not change monotonously but increases first and then decreases along with the annealing time.The two-stage process implies that glasses do not evolve as expected toward the more homogeneous glassy state but become homogeneous first and then more heterogeneous.This is further verified by the evolution of critical shear stress for local plasticity.It is revealed that the two-stage process is correlated with different relaxation modes,which is further interpreted using a phenomenological model.These findings not only give insights into understanding the nature of glasses,but also are useful for designing glasses with superior properties.展开更多
Metallic glasses have aroused considerable interest in the past decades because they exhibit fascinating properties. First, this article briefly outlines the mechanical, thermal properties and application of the metal...Metallic glasses have aroused considerable interest in the past decades because they exhibit fascinating properties. First, this article briefly outlines the mechanical, thermal properties and application of the metallic glasses. In addition, we focus on the dynamic mechanical relaxation behaviors, i.e. main （α） and secondary （β） relaxations, in metallic glasses. The mechanical relaxation behaviors are connected to the mechanical properties and physical properties in glassy materials. The main relaxation in glassy materials is related to the glass transition phenomenon and viscous flow. On the other hand, the β relaxation is linked to many fundamental issues in metallic glasses. In these materials relaxation processes are directly related to the plastic deformation mechanism. The mechanical relaxations, particularly, the β relaxation provides an excellent opportunity to design metallic glasses with desired physical and mechanical properties. We demonstrate the universal characteristics of main relaxation in metallic glasses. The phenomenological models and the physical theories are introduced to describe the main relaxation in metallic glasses. In parallel, we show the dependence of the α. and β relaxations on the thermal treatments in metallic glasses. Finally, we analyze the correlation between the atomic mobility and the thermo-mechanical treatments in metallic glasses. On the one hand, the atomic mobility in metallic glasses is reduced by physical aging or crystallization. On the other hand, the atomic mobility in metallic glass is enhanced by deformation （i.e. compression and cold rolling）. Importantly, to analyze the atomic mobility in amorphous materials, a physical theory is introduced. This model invokes the concept of quasi-point defects, which correspond to the density fluctuations in the glassy materials.展开更多
Non-isothermal crystallization transformation kinetics and isothermal crystallization kinetics in super-cooled liquid region（SLR） in Zr55Cu30Ni5Al10 bulk metallic glasses were studied by differential scanning calori...Non-isothermal crystallization transformation kinetics and isothermal crystallization kinetics in super-cooled liquid region（SLR） in Zr55Cu30Ni5Al10 bulk metallic glasses were studied by differential scanning calorimetry（DSC） and X-ray diffraction（XRD）.In isochronal mode,the average values of activation energy in Zr55Cu30Ni5Al10 bulk metallic glass determined by different models（Kissinger method,Flynn-Wall-Ozawa method and Augis-Bennett method） are in good agreement with each other.In addition,the isothermal transformation kinetics in Zr55Cu30Ni5Al10 bulk metallic glasses was described by the Johnson-Mehl-Avrami（JMA） model.For Zr55Cu30Ni5Al10 bulk metallic glass,the Avrami exponent n ranges from 2.2 to 2.9,indicating that crystallization mechanism in the bulk metallic glass was mainly diffusion-controlled;crystal growth is controlled by long range ordering diffusion in three-dimensional growth during isothermal crystallization process.The average value of activation energy in Zr55Cu30Ni5Al10 bulk metallic glass is 469 kJ/mol in isothermal transformation process.展开更多
Dynamic relaxation processes are fundamental to understand the mechanical and physical properties of metallic glasses. In the current work, mechanical relaxations in a La30Ce30Al15Co25 bulk metallic glass were probed ...Dynamic relaxation processes are fundamental to understand the mechanical and physical properties of metallic glasses. In the current work, mechanical relaxations in a La30Ce30Al15Co25 bulk metallic glass were probed by dynamic mechanical analysis. In contrast to many metallic glasses, La30Ce30Al15Co25 metallic glass shows a pronounced slow β relaxation peak. Physical aging below the glass transition temperature Tgleads to an increase of the apparent activation energy and a decrease of the slow β relaxation magnitude. The correlation between the slow β relaxation and the main α relaxation is discussed.展开更多
Non-equiatomic high entropy bulk metallic glasses were reported recently and show unique mechanical and physical properties.Dynamic mechanical relaxation behavior of Zr_(35)Hf_(17.5)Ti_(5.5)Al_(12.5)Co_(7.5)Ni_(12)Cu_...Non-equiatomic high entropy bulk metallic glasses were reported recently and show unique mechanical and physical properties.Dynamic mechanical relaxation behavior of Zr_(35)Hf_(17.5)Ti_(5.5)Al_(12.5)Co_(7.5)Ni_(12)Cu_(10)high entropy bulk metallic glass was investigated by dynamic mechanical analysis(DMA)and the mechanical spectra could be well described by the quasi-point defects(QPD)theory.Compared to typical metallic glasses,the intensity of theβrelaxation of Zr_(35)Hf_(17.5)Ti_(5.5)Al_(12.5)Co_(7.5)Ni_(12)Cu_(10)high entropy bulk metallic glass is lower due to the sluggish diffusion.At the same time,the correlation factor is higher than that of conventional metallic glasses and this is ascribed to the high configuration entropy.In parallel,physical aging below the glass transition temperature leads to a decrease of atomic mobility,caused by a decrease of the concentration of defects.展开更多
The dynamic mechanical relaxation behavior of Ti36.2Zr30.3Cu8.3Fe4Be21.2 bulk metallic glass with good glass-forming ability was investigated by mechanical spectroscopy.The mechanical relaxation behavior was analyzed ...The dynamic mechanical relaxation behavior of Ti36.2Zr30.3Cu8.3Fe4Be21.2 bulk metallic glass with good glass-forming ability was investigated by mechanical spectroscopy.The mechanical relaxation behavior was analyzed in the framework of quasi-point defects model.The experimental results demonstrate that the atomic mobility of the metallic glass is closely associated with the correlation factorχ.The physical aging below the glass transition temperature T g shows a non-Debye relaxation behavior,which could be well described by stretched Kohlrausch exponential equation.The Kohlrausch exponentβaging reflects the dynamic heterogeneities of the metallic glass.Both concentration of"defects"and atomic mobility decrease caused by the in situ successive heating during the mechanical spectroscopy experiments.展开更多
The anelastic deformation behavior of Pd_(20)Pt_(20)Cu_(20)Ni_(20)P_(20) high-entropy metallic glass was probed by monitoring the stress relaxation and recovery processes. The stress relaxation under consecutive strai...The anelastic deformation behavior of Pd_(20)Pt_(20)Cu_(20)Ni_(20)P_(20) high-entropy metallic glass was probed by monitoring the stress relaxation and recovery processes. The stress relaxation under consecutive strain steps can be described by the Kohlrausch-Williams-Watts(KWW) function. In addition, considering a hierarchy of relaxation processes related to the structural heterogeneity, a constitutive model is proposed in order to describe the whole process of stress relaxation and determine the contribution of different time scales. Moreover, a crossover from stochastic activation to percolation of flow defects with the ultimate strain can be observed during stress relaxation process. The anelastic recovery process after a strain step is studied as a function of the initial strain level and characterized by means of a direct spectrum analysis. The peaks in the recovery time-spectra revealed the evolution of flow defects in Pd_(20)Pt_(20)Cu_(20)Ni_(20)P_(20) high-entropy metallic glass. The understanding of the atomic free-volume zones effect and the anelastic deformation provides important insight into how atomic structural features affect the deformation behavior of high-entropy metallic glasses, and may provide a new avenue into the improvement of their mechanical properties.展开更多
Dear Editor,Minimally invasive glaucoma surgery (MIGS) is a lessinvasive surgical alternative to filtering surgery for reducing intraocular pressure (IOP). This technique has been shown to offer long-term outcomes equ...Dear Editor,Minimally invasive glaucoma surgery (MIGS) is a lessinvasive surgical alternative to filtering surgery for reducing intraocular pressure (IOP). This technique has been shown to offer long-term outcomes equivalent to filtering surgery[1]. The XEN gel implant (Allergan Inc., CA, USA) is one of MIGS procedures. This implant consists of a 6-mm tube of collagen-derived gelatin cross-linked with glutaraldehyde, preloaded in an injector.展开更多
Understanding mechanical relaxation, such as primary（α） and secondary（β） relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses....Understanding mechanical relaxation, such as primary（α） and secondary（β） relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses. At a fundamental level, relaxation, plastic deformation, glass transition, and crystallization of metallic glasses are intimately linked to each other, which can be related to atomic packing, inter-atomic diffusion, and cooperative atom movement. Conceptually, βrelaxation is usually associated with structural heterogeneities intrinsic to metallic glasses. However, the details of such structural heterogeneities, being masked by the meta-stable disordered long-range structure, are yet to be understood. In this paper, we briefly review the recent experimental and simulation results that were attempted to elucidate structural heterogeneities in metallic glasses within the framework of β relaxation. In particular, we will discuss the correlation amongβ relaxation, structural heterogeneity, and mechanical properties of metallic glasses.展开更多
TiNi-based shape memory alloys(SMAs)have been used as damping materials to eliminate noise and mechanical vibration.However,their application is limited by low working temperatures and damping capacity.In this work,tw...TiNi-based shape memory alloys(SMAs)have been used as damping materials to eliminate noise and mechanical vibration.However,their application is limited by low working temperatures and damping capacity.In this work,two novel Ti-Zr-Hf-Ni-Co-Cu high entropy shape memory alloys(HESMAs)with different transformation temperatures and damping properties were investigated.The results show that Ti_(25)Zr_(8)Hf_(17)Ni_(30)Co_(5)Cu_(15) has superior damping performance arising from martensitic transformation,shape memory effect(thermal cycle at constant load)as well as superelasticity.Compared to traditional TiNi-based SMAs,the as-cast HESMAs exhibit a much higher ultrahigh yield strength(∼2 GPa)and storage modulus(∼50 GPa).The high configuration entropy of the HESMAs with high uneven internal stress and severe lattice distortion is revealed as the underlying mechanisms governing distinctive damping performance.The effects of high configuration entropy and microheterogeneity on the martensitic transforma-tion behavior and damping performance of HESMAs are clarified in this work,which provides a basis for designing alloys with superior damping properties.展开更多
ntergranular slow crack growth in zirconia polycrystal is described with a cohesive zone model that simulate mechanically the reaction-rupture mechanism underlying stress and environ- mentally assisted failure. A 2D p...ntergranular slow crack growth in zirconia polycrystal is described with a cohesive zone model that simulate mechanically the reaction-rupture mechanism underlying stress and environ- mentally assisted failure. A 2D polycrystal is considered with cohesive surfaces inserted along the grain boundaries. The anisotropic elastic modulus and grain-to-grain misorientation are accounted for together with an initial stress state related to the processing. A minimum load threshold is shown to originate from the onset of the reaction-rupture mechanism to proceed where a minimum traction is reached locally and from the magnitude of the initial compression stresses. This work aims at providing reliable predictions in long lasting applications of ceramics.展开更多
The power-law relationship between creep rate decay and time is one of the intrinsic characteristics of metallic glasses.In the current work,a La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10) high-entropy metallic glass was select...The power-law relationship between creep rate decay and time is one of the intrinsic characteristics of metallic glasses.In the current work,a La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10) high-entropy metallic glass was selected as the model alloy to test the influences of physical aging and cyclic loading on the power-law creep mechanism,which was probed by the dynamic mechanical analysis in terms of the stochastic activation,and contiguous interplay and permeation of shear transformation zones.It is demonstrated that a notable discrepancy appears between thermal treatment and mechanical treatment on the power-law creep mechanism of this high-entropy metallic glass.On the one hand,physical aging below the glass transition temperature introduces the annihilation of potential shear transformation zones which contribute to creep.On the other hand,cyclic loading can tailor the“forward”jump operations competing with the“backward”ones of shear transformation zones by controlling the interval time(recovery time).The current research offers a new pathway towards understanding the creep mechanism of high-entropy metallic glasses.展开更多
BACKGROUND We report a case of post-coronavirus disease(COVID)immune hepatitis occurring in a young male with no pre-existing comorbidities.CASE SUMMARY A previously healthy 21-year-old male patient was admitted to ou...BACKGROUND We report a case of post-coronavirus disease(COVID)immune hepatitis occurring in a young male with no pre-existing comorbidities.CASE SUMMARY A previously healthy 21-year-old male patient was admitted to our hospital with mild COVID-19.During the course of in-hospital isolation and monitoring,he developed an alanine aminotransferase(ALT)and aspartate aminotransferase(AST)increase,with the enzymes peaking at day 24(ALT 15 times the upper normal limit),with preserved liver function.The liver enzyme increase occurred 20 d after the complete clinical remission of COVID-19,and ALT dynamics paralleled the increase in total antibodies against severe acute respiratory syndrome coronavirus 2(SARS-CoV-2).The case was interpreted as post-COVID immune hepatitis,with extensive laboratory investigations excluding other potential causes.The hepatocytolysis remitted 20 d after the peak ALT,without further intervention,with complete recovery,but the total anti-SARS-CoV-2 antibodies continued to increase the next 5 mo following the acute infection.CONCLUSION Close attention should also be paid to young patients with mild forms of disease,and a high index of suspicion should be maintained for post-COVID complications.展开更多
To develop durable bone healing strategies through improved control of bone repair,it is of critical importance to understand the mechanisms of bone mechanical integrity when in contact with biomaterials and implants....To develop durable bone healing strategies through improved control of bone repair,it is of critical importance to understand the mechanisms of bone mechanical integrity when in contact with biomaterials and implants.Bone mechanical integrity is defined here as the adaptation of structural properties of remodeled bone in regard to an applied mechanical loading.Accordingly,the authors present why future investigations in bone repair and regeneration should emphasize on the matrix surrounding the osteocytes.Osteocytes are mechanosensitive cells considered as the orchestrators of bone remodeling,which is the biological process involved in bone homeostasis.These bone cells are trapped in an interconnected porous network,the lacunocanalicular network,which is embedded in a bone mineralized extracellular matrix.As a consequence of an applied mechanical loading,the bone deformation results in the deformation of this lacunocanalicular network inducing a shift in interstitial fluid pressure and velocity,thus resulting in osteocyte stimulation.The material environment surrounding each osteocyte,the so called perilacunar and pericellular matrices properties,define its mechanosensitivity.While this mechanical stimulation pathway is well known,the laws used to predict bone remodeling are based on strains developing at a tissue scale,suggesting that these strains are related to the shift in fluid pressure and velocity at the lacunocanalicular scale.While this relationship has been validated through observation in healthy bone,the fluid behavior at the bone-implant interface is more complex.The presence of the implant modifies fluid behavior,so that for the same strain at a tissue scale,the shift in fluid pressure and velocity will be different than in a healthy bone tissue.In that context,new markers for bone mechanical integrity,considering fluid behavior,have to be defined.The viewpoint exposed by the authors indicates that the properties of the pericellular and the perilacunar matrices have to be systematically investigated and used as structural markers of fluid behavior in the course of bone biomaterial development.展开更多
This study specifically investigated the influence of the composition of aluminosilicate material <i>i.e.</span><span> </span></span><span><span><span style="font-fami...This study specifically investigated the influence of the composition of aluminosilicate material <i>i.e.</span><span> </span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"></i> the substitution of metakaolin by rice husk ash and the nature of alkaline activators (Na<sup>+</sup>/K<sup>+</sup>) on mineralogical, structural, physical and mechanical properties of geopolymer binders. This influence was evaluated based on X-ray diffraction (XRD), Fourier Transform InfraRed spectroscopy (FTIR) and Scanning Electron Microscope (SEM analyses, apparent density, water accessible porosity, compressive strength and thermal properties. Two types of geopolymer binder were synthesized according to the type of alkali activator used, the NaOH-based geopolymer and the KOH-based geopolymer. The results of characterization performed after 14 days of curing of geopolymer samples showed that the activation of the aluminosilicate powder using alkaline solution led to change in their micro</span><span style="font-family:Verdana;">structure. The highest compressive strength was obtained with the</span><span style="font-family:Verdana;"> NaOH-based geopolymer.展开更多
基金supported by the China Postdoctoral Science Foundation(No.2022M720399).
文摘In order to investigate the damage tolerance of a metastable Ti-5Al-3V-3Mo-2Cr-2Zr-1Nb-1Fe(Ti5321)alloy with bimodal microstructure using void growth quantification and micromechanical modeling,in situ tensile testing was performed during X-ray microtomography experiments.Compared with investigations of surface voids by traditional two-dimensional(2D)methods involving post-mortem characterization,three-dimensional(3D)information on void evolution inside optically opaque samples obtained through X-ray microtomography is essential.The Rice and Tracey model and Huang model were applied to predict void growth and show good agreement with experimental data using calibration of the damage parameterα.The void growth kinetics of Ti5321 with bimodal microstructure was analyzed by comparing theαvalue with that of Ti64 for different microstructure morphologies.The damage mechanism of ductile fracture of Ti5321 with bimodal microstructure is discussed.It was found that the size of the voids apparently increases with the triaxiality of stress.Post-mortem scanning electron microscopy(SEM)was also used to demonstrate this damage mechanism of ductile fracture of Ti5321.
基金National Natural Science Foundation of China(Nos.52201193,51922102,92163108 and 52001319)National Key R&D Program of China(No.2018YFA0703600)+3 种基金Ningbo Natural Science Foundation of Ningbo City(No.2022J310)"Pioneer and Leading Goose"R&D Program of Zhejiang(No.2022C01023)‘Proyecto PID2020–112975GB-I00 de investigación financiado por MCIN/AEI/10.13039/501100011033′Generalitat de Catalunya AGAUR grant 2017-SGR-42.
文摘The heterogeneity of glasses has critical influences on the properties.How heterogeneity evolves during annealing is an intriguing cutting-edge question.In this work,the heterogeneity of the annealed metal-lic and polymer glasses has been studied systematically by using stress relaxation and nanoindentation tests.The stress relaxation processes are analyzed using Kohlrausch-Williams-Watts(KWW)equation.We surprisingly find that the heterogeneous factor βkww in KWW equation does not change monotonously but increases first and then decreases along with the annealing time.The two-stage process implies that glasses do not evolve as expected toward the more homogeneous glassy state but become homogeneous first and then more heterogeneous.This is further verified by the evolution of critical shear stress for local plasticity.It is revealed that the two-stage process is correlated with different relaxation modes,which is further interpreted using a phenomenological model.These findings not only give insights into understanding the nature of glasses,but also are useful for designing glasses with superior properties.
基金the Centre National de la Recherche Scientifique (CNRS) for providing the postdoctoral financial support
文摘Metallic glasses have aroused considerable interest in the past decades because they exhibit fascinating properties. First, this article briefly outlines the mechanical, thermal properties and application of the metallic glasses. In addition, we focus on the dynamic mechanical relaxation behaviors, i.e. main （α） and secondary （β） relaxations, in metallic glasses. The mechanical relaxation behaviors are connected to the mechanical properties and physical properties in glassy materials. The main relaxation in glassy materials is related to the glass transition phenomenon and viscous flow. On the other hand, the β relaxation is linked to many fundamental issues in metallic glasses. In these materials relaxation processes are directly related to the plastic deformation mechanism. The mechanical relaxations, particularly, the β relaxation provides an excellent opportunity to design metallic glasses with desired physical and mechanical properties. We demonstrate the universal characteristics of main relaxation in metallic glasses. The phenomenological models and the physical theories are introduced to describe the main relaxation in metallic glasses. In parallel, we show the dependence of the α. and β relaxations on the thermal treatments in metallic glasses. Finally, we analyze the correlation between the atomic mobility and the thermo-mechanical treatments in metallic glasses. On the one hand, the atomic mobility in metallic glasses is reduced by physical aging or crystallization. On the other hand, the atomic mobility in metallic glass is enhanced by deformation （i.e. compression and cold rolling）. Importantly, to analyze the atomic mobility in amorphous materials, a physical theory is introduced. This model invokes the concept of quasi-point defects, which correspond to the density fluctuations in the glassy materials.
文摘Non-isothermal crystallization transformation kinetics and isothermal crystallization kinetics in super-cooled liquid region（SLR） in Zr55Cu30Ni5Al10 bulk metallic glasses were studied by differential scanning calorimetry（DSC） and X-ray diffraction（XRD）.In isochronal mode,the average values of activation energy in Zr55Cu30Ni5Al10 bulk metallic glass determined by different models（Kissinger method,Flynn-Wall-Ozawa method and Augis-Bennett method） are in good agreement with each other.In addition,the isothermal transformation kinetics in Zr55Cu30Ni5Al10 bulk metallic glasses was described by the Johnson-Mehl-Avrami（JMA） model.For Zr55Cu30Ni5Al10 bulk metallic glass,the Avrami exponent n ranges from 2.2 to 2.9,indicating that crystallization mechanism in the bulk metallic glass was mainly diffusion-controlled;crystal growth is controlled by long range ordering diffusion in three-dimensional growth during isothermal crystallization process.The average value of activation energy in Zr55Cu30Ni5Al10 bulk metallic glass is 469 kJ/mol in isothermal transformation process.
基金supported by the National Natural Science Foundation of China(Grant No.51611130120,11772257 and11572249)supported by the Fundamental Research Funds for the Central Universities(No.3102017HQZZ012 and3102018ZY010)+1 种基金the Astronautics Supporting Technology Foundation of Chinathe support of the Office of Naval Research for the work at NRL
文摘Dynamic relaxation processes are fundamental to understand the mechanical and physical properties of metallic glasses. In the current work, mechanical relaxations in a La30Ce30Al15Co25 bulk metallic glass were probed by dynamic mechanical analysis. In contrast to many metallic glasses, La30Ce30Al15Co25 metallic glass shows a pronounced slow β relaxation peak. Physical aging below the glass transition temperature Tgleads to an increase of the apparent activation energy and a decrease of the slow β relaxation magnitude. The correlation between the slow β relaxation and the main α relaxation is discussed.
基金financially supported by the National Natural Science Foundation of China(No.51971178)the Fundamental Research Funds for the Central Universities(Nos.3102019ghxm007 and 3102017JC01003)+4 种基金Astronautics Supporting Technology Foundation of China(No.2019-HT-XG)the Natural Science Foundation of Shaanxi Province(No.2019JM-344)the Construction Project of Postgraduate Course of Northwestern Polytechnical Universitythe financial support from MINECO(grant FIS2017-82625-P)Generalitat de Catalunya(grant 2017SGR0042)。
文摘Non-equiatomic high entropy bulk metallic glasses were reported recently and show unique mechanical and physical properties.Dynamic mechanical relaxation behavior of Zr_(35)Hf_(17.5)Ti_(5.5)Al_(12.5)Co_(7.5)Ni_(12)Cu_(10)high entropy bulk metallic glass was investigated by dynamic mechanical analysis(DMA)and the mechanical spectra could be well described by the quasi-point defects(QPD)theory.Compared to typical metallic glasses,the intensity of theβrelaxation of Zr_(35)Hf_(17.5)Ti_(5.5)Al_(12.5)Co_(7.5)Ni_(12)Cu_(10)high entropy bulk metallic glass is lower due to the sluggish diffusion.At the same time,the correlation factor is higher than that of conventional metallic glasses and this is ascribed to the high configuration entropy.In parallel,physical aging below the glass transition temperature leads to a decrease of atomic mobility,caused by a decrease of the concentration of defects.
基金supported by the National Natural Science Foundation of China (Nos. 51611130120, 11772257, 11572249, 51871132)supported by the Fundamental Research Funds for the Central Universities (Nos. 3102018ZY010, 3102017HQZZ012)
文摘The dynamic mechanical relaxation behavior of Ti36.2Zr30.3Cu8.3Fe4Be21.2 bulk metallic glass with good glass-forming ability was investigated by mechanical spectroscopy.The mechanical relaxation behavior was analyzed in the framework of quasi-point defects model.The experimental results demonstrate that the atomic mobility of the metallic glass is closely associated with the correlation factorχ.The physical aging below the glass transition temperature T g shows a non-Debye relaxation behavior,which could be well described by stretched Kohlrausch exponential equation.The Kohlrausch exponentβaging reflects the dynamic heterogeneities of the metallic glass.Both concentration of"defects"and atomic mobility decrease caused by the in situ successive heating during the mechanical spectroscopy experiments.
基金supported by the NSFC (Grant No. 51971178)the Natural Science Foundation of Shaanxi Province (Grant No. 2021JC-12)+3 种基金financial support from MICINN (grant FIS2017–82625-P)Generalitat de Catalunya (Grant 2017SGR0042)sponsored by Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University (No. CX202031)China Scholarship Council (CSC) under Grant 202006290092。
文摘The anelastic deformation behavior of Pd_(20)Pt_(20)Cu_(20)Ni_(20)P_(20) high-entropy metallic glass was probed by monitoring the stress relaxation and recovery processes. The stress relaxation under consecutive strain steps can be described by the Kohlrausch-Williams-Watts(KWW) function. In addition, considering a hierarchy of relaxation processes related to the structural heterogeneity, a constitutive model is proposed in order to describe the whole process of stress relaxation and determine the contribution of different time scales. Moreover, a crossover from stochastic activation to percolation of flow defects with the ultimate strain can be observed during stress relaxation process. The anelastic recovery process after a strain step is studied as a function of the initial strain level and characterized by means of a direct spectrum analysis. The peaks in the recovery time-spectra revealed the evolution of flow defects in Pd_(20)Pt_(20)Cu_(20)Ni_(20)P_(20) high-entropy metallic glass. The understanding of the atomic free-volume zones effect and the anelastic deformation provides important insight into how atomic structural features affect the deformation behavior of high-entropy metallic glasses, and may provide a new avenue into the improvement of their mechanical properties.
文摘Dear Editor,Minimally invasive glaucoma surgery (MIGS) is a lessinvasive surgical alternative to filtering surgery for reducing intraocular pressure (IOP). This technique has been shown to offer long-term outcomes equivalent to filtering surgery[1]. The XEN gel implant (Allergan Inc., CA, USA) is one of MIGS procedures. This implant consists of a 6-mm tube of collagen-derived gelatin cross-linked with glutaraldehyde, preloaded in an injector.
基金supported by the National Natural Science Foundation of China(Grant Nos.51401192 and 51611130120)the Natural Science Foundation of Shaanxi Province,China(Grant No.2016JM5009)+5 种基金the Fundamental Research Funds for the Central Universities of China(Grant Nos.3102015ZY027 and 3102015BJ(Ⅱ)JGZ019)the Aeronautical Science Foundation of China(Grant No.2015ZF53072)supported by the Hong Kong Scholar Program of China(Grant No.XJ2015056)the support of MINECO(Grant No.FIS2014-54734-P)Generalitat de Catalunya(Grant No.2014SGR00581)supported by the Research Grant Council,the Hong Kong City of China,through the General Research Fund(Grant No.City U11214914)
文摘Understanding mechanical relaxation, such as primary（α） and secondary（β） relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses. At a fundamental level, relaxation, plastic deformation, glass transition, and crystallization of metallic glasses are intimately linked to each other, which can be related to atomic packing, inter-atomic diffusion, and cooperative atom movement. Conceptually, βrelaxation is usually associated with structural heterogeneities intrinsic to metallic glasses. However, the details of such structural heterogeneities, being masked by the meta-stable disordered long-range structure, are yet to be understood. In this paper, we briefly review the recent experimental and simulation results that were attempted to elucidate structural heterogeneities in metallic glasses within the framework of β relaxation. In particular, we will discuss the correlation amongβ relaxation, structural heterogeneity, and mechanical properties of metallic glasses.
基金supported by the National Natural Science Foundation of China (NSFC) (Grant Nos.51971178,52271153 and 51871132)the Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province (Grant No.2021JC-12)+1 种基金the Natural Science Foundation of Chongqing (Grant No.cstc2020jcyj-jqX0001)the Youth Innovation Promotion Association CAS (2021188).
文摘TiNi-based shape memory alloys(SMAs)have been used as damping materials to eliminate noise and mechanical vibration.However,their application is limited by low working temperatures and damping capacity.In this work,two novel Ti-Zr-Hf-Ni-Co-Cu high entropy shape memory alloys(HESMAs)with different transformation temperatures and damping properties were investigated.The results show that Ti_(25)Zr_(8)Hf_(17)Ni_(30)Co_(5)Cu_(15) has superior damping performance arising from martensitic transformation,shape memory effect(thermal cycle at constant load)as well as superelasticity.Compared to traditional TiNi-based SMAs,the as-cast HESMAs exhibit a much higher ultrahigh yield strength(∼2 GPa)and storage modulus(∼50 GPa).The high configuration entropy of the HESMAs with high uneven internal stress and severe lattice distortion is revealed as the underlying mechanisms governing distinctive damping performance.The effects of high configuration entropy and microheterogeneity on the martensitic transforma-tion behavior and damping performance of HESMAs are clarified in this work,which provides a basis for designing alloys with superior damping properties.
文摘ntergranular slow crack growth in zirconia polycrystal is described with a cohesive zone model that simulate mechanically the reaction-rupture mechanism underlying stress and environ- mentally assisted failure. A 2D polycrystal is considered with cohesive surfaces inserted along the grain boundaries. The anisotropic elastic modulus and grain-to-grain misorientation are accounted for together with an initial stress state related to the processing. A minimum load threshold is shown to originate from the onset of the reaction-rupture mechanism to proceed where a minimum traction is reached locally and from the magnitude of the initial compression stresses. This work aims at providing reliable predictions in long lasting applications of ceramics.
基金the National Natural Science Foundation of China(NSFC,No.51971178)the Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(No.2021JC-12)+3 种基金the Natural Science Foundation of Chongqing(No.cstc2020jcyj-jq X0001)sponsored by Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX2021015)financial support from MICINN(grant PID2020112975GB-I00)Generalitat de Catalunya(grant 2017SGR0042)。
文摘The power-law relationship between creep rate decay and time is one of the intrinsic characteristics of metallic glasses.In the current work,a La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10) high-entropy metallic glass was selected as the model alloy to test the influences of physical aging and cyclic loading on the power-law creep mechanism,which was probed by the dynamic mechanical analysis in terms of the stochastic activation,and contiguous interplay and permeation of shear transformation zones.It is demonstrated that a notable discrepancy appears between thermal treatment and mechanical treatment on the power-law creep mechanism of this high-entropy metallic glass.On the one hand,physical aging below the glass transition temperature introduces the annihilation of potential shear transformation zones which contribute to creep.On the other hand,cyclic loading can tailor the“forward”jump operations competing with the“backward”ones of shear transformation zones by controlling the interval time(recovery time).The current research offers a new pathway towards understanding the creep mechanism of high-entropy metallic glasses.
文摘BACKGROUND We report a case of post-coronavirus disease(COVID)immune hepatitis occurring in a young male with no pre-existing comorbidities.CASE SUMMARY A previously healthy 21-year-old male patient was admitted to our hospital with mild COVID-19.During the course of in-hospital isolation and monitoring,he developed an alanine aminotransferase(ALT)and aspartate aminotransferase(AST)increase,with the enzymes peaking at day 24(ALT 15 times the upper normal limit),with preserved liver function.The liver enzyme increase occurred 20 d after the complete clinical remission of COVID-19,and ALT dynamics paralleled the increase in total antibodies against severe acute respiratory syndrome coronavirus 2(SARS-CoV-2).The case was interpreted as post-COVID immune hepatitis,with extensive laboratory investigations excluding other potential causes.The hepatocytolysis remitted 20 d after the peak ALT,without further intervention,with complete recovery,but the total anti-SARS-CoV-2 antibodies continued to increase the next 5 mo following the acute infection.CONCLUSION Close attention should also be paid to young patients with mild forms of disease,and a high index of suspicion should be maintained for post-COVID complications.
文摘To develop durable bone healing strategies through improved control of bone repair,it is of critical importance to understand the mechanisms of bone mechanical integrity when in contact with biomaterials and implants.Bone mechanical integrity is defined here as the adaptation of structural properties of remodeled bone in regard to an applied mechanical loading.Accordingly,the authors present why future investigations in bone repair and regeneration should emphasize on the matrix surrounding the osteocytes.Osteocytes are mechanosensitive cells considered as the orchestrators of bone remodeling,which is the biological process involved in bone homeostasis.These bone cells are trapped in an interconnected porous network,the lacunocanalicular network,which is embedded in a bone mineralized extracellular matrix.As a consequence of an applied mechanical loading,the bone deformation results in the deformation of this lacunocanalicular network inducing a shift in interstitial fluid pressure and velocity,thus resulting in osteocyte stimulation.The material environment surrounding each osteocyte,the so called perilacunar and pericellular matrices properties,define its mechanosensitivity.While this mechanical stimulation pathway is well known,the laws used to predict bone remodeling are based on strains developing at a tissue scale,suggesting that these strains are related to the shift in fluid pressure and velocity at the lacunocanalicular scale.While this relationship has been validated through observation in healthy bone,the fluid behavior at the bone-implant interface is more complex.The presence of the implant modifies fluid behavior,so that for the same strain at a tissue scale,the shift in fluid pressure and velocity will be different than in a healthy bone tissue.In that context,new markers for bone mechanical integrity,considering fluid behavior,have to be defined.The viewpoint exposed by the authors indicates that the properties of the pericellular and the perilacunar matrices have to be systematically investigated and used as structural markers of fluid behavior in the course of bone biomaterial development.
文摘This study specifically investigated the influence of the composition of aluminosilicate material <i>i.e.</span><span> </span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"></i> the substitution of metakaolin by rice husk ash and the nature of alkaline activators (Na<sup>+</sup>/K<sup>+</sup>) on mineralogical, structural, physical and mechanical properties of geopolymer binders. This influence was evaluated based on X-ray diffraction (XRD), Fourier Transform InfraRed spectroscopy (FTIR) and Scanning Electron Microscope (SEM analyses, apparent density, water accessible porosity, compressive strength and thermal properties. Two types of geopolymer binder were synthesized according to the type of alkali activator used, the NaOH-based geopolymer and the KOH-based geopolymer. The results of characterization performed after 14 days of curing of geopolymer samples showed that the activation of the aluminosilicate powder using alkaline solution led to change in their micro</span><span style="font-family:Verdana;">structure. The highest compressive strength was obtained with the</span><span style="font-family:Verdana;"> NaOH-based geopolymer.
