This study presents a general approach to derive the acoustic nonlinearity parameters induced by various types of dislocation configurations including dislocation strings （monopoles）, dislocation dipoles, dislocatio...This study presents a general approach to derive the acoustic nonlinearity parameters induced by various types of dislocation configurations including dislocation strings （monopoles）, dislocation dipoles, dislocation pileups and extended dislocations. It is found that expressions of the acoustic nonlinearity parameter induced by such a variety of dislocation con- figurations share a common mathematical form. They are all scaled with （Lch/b）n, where Lch is a characteristic length of the dislocation configuration, b is the magnitude of the Burgers vector, and n is either 3 or 4. Semiquantitative analysis is presented to compare the magnitudes of the acoustic nonlinearity parameters among different types of dislocation configurations.展开更多
The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been...The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes and the amount of porosity occurring at different Sr levels and pressure parameters. The results indicate that an increase in the filling pressure induces lower heat dissipation of the liquid close to the die/core surfaces, with the formation of slightly greater dendrite arms and coarser eutectic Si particles. On the other hand, the increase in the Sr level leads to finer microstructural scale and eutectic Si. The analysed variables, within the experimental conditions, do not affect the morphology of eutectic Si particles. Higher applied pressure and Sr content generate castings with lower amount of porosiW. However, as the filling pressure increases the flow of metal inside the die cavity is more turbulent, leading to the formation of oxide films and cold shots. In the analysed range of experimental conditions, the design of experiment methodology and the analysis of variance have been used to develop statistical models that accurately predict the average size of secondary dendrite arm spacing and the amount of porosity in the low-pressure die cast AISiTMg0.3 alloy.展开更多
Selective laser melting(SLM)has attracted great attention in the fabrication of magnesium-based biodegradable implants.However,current SLMed magnesium alloys are generally suffered from rapid corrosion,which is deadly...Selective laser melting(SLM)has attracted great attention in the fabrication of magnesium-based biodegradable implants.However,current SLMed magnesium alloys are generally suffered from rapid corrosion,which is deadly detrimental to their use.Herein,we thoroughly revealed why they are so vulnerable to corrosion through a typical SLMed AZ91D material model.An abnormally spatiotemporal“bulk erosion”mechanism was found,not the well-known“surface corrosion”mode of traditionally plastic-deformed alloys.The unique microstructure derived from SLM possesses high chemical reactivity,which is favorable for interactional attacks of fast fluid penetration,severe local corrosion and intensive micro-galvanic corrosion.Thus,it brings two orders of magnitude in corrosion rates compared with its plastic-deformed counterparts.In vitro,such fast-corrosion induced apparent cytotoxicity,cell damage,and further apoptosis to rat and mouse derived mesenchymal stem cells.In vivo,the material disintegrates into small pieces in a short period,and results in unexpected bone destruction and long-lasting foreign body reactions in Sprague Dawley rats.Close attention should be paid to this issue before SLMed Mg-based implants being applied in patients.展开更多
Strontium doped perovskite-type Nd0.7Sr0.3MnO3 ceramics were synthesized completely by high-energy ball milling raw oxides of Nd2O3, SrCO3 and MnO2. The optimal ball milling time and mass ratio of milling balls to raw...Strontium doped perovskite-type Nd0.7Sr0.3MnO3 ceramics were synthesized completely by high-energy ball milling raw oxides of Nd2O3, SrCO3 and MnO2. The optimal ball milling time and mass ratio of milling balls to raw materials are 4 h and 10：1, respectively. The grain size of as-milled Nd0.7Sr0.3MnO3 ceramics ranges from 51 to 93 nm, and the fine particles contain two phases of crystalline phase and amorphous phase. For the Nd0.7r0.3MnO3 synthesized by ball milling and sequent heat treatment, a remarkable colossal electroresistance （CER） effect is observed and the CER ratio reaches 900% at Curie temperature Tc when the load voltage increases from 0.1 to 0.8 V.展开更多
Yttrium hydride(YH_(x))is a highly promising neutron moderator material for nuclear reactors,known for its exceptional thermal stability and high hydrogen content.This study investigated the sintering mechanism and mi...Yttrium hydride(YH_(x))is a highly promising neutron moderator material for nuclear reactors,known for its exceptional thermal stability and high hydrogen content.This study investigated the sintering mechanism and microstructural evolution of YH_(x)monoliths processed by spark plasma sintering(SPS),with the effects of temperature,duration,and pressure.The results indicate that the sintering process can be divided into five stages:formation of sintering necks,rapid densification,anti-densification,recrystallization,and grain growth.The anti-densification behavior is attributed to hydrogen desorption,phase transformation-induced volumetric contraction,and vacancy coalescence from hydrogen migration,leaving residual pores and lattice defects.Furthermore,increasing the sintering temperature and duration promotes recrystallization and grain growth,whereas elevated pressure effectively suppresses grain boundary migration.This research establishes fundamental processing-structure correlations critical for optimizing YHx moderators in nuclear applications.展开更多
文摘This study presents a general approach to derive the acoustic nonlinearity parameters induced by various types of dislocation configurations including dislocation strings （monopoles）, dislocation dipoles, dislocation pileups and extended dislocations. It is found that expressions of the acoustic nonlinearity parameter induced by such a variety of dislocation con- figurations share a common mathematical form. They are all scaled with （Lch/b）n, where Lch is a characteristic length of the dislocation configuration, b is the magnitude of the Burgers vector, and n is either 3 or 4. Semiquantitative analysis is presented to compare the magnitudes of the acoustic nonlinearity parameters among different types of dislocation configurations.
文摘The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes and the amount of porosity occurring at different Sr levels and pressure parameters. The results indicate that an increase in the filling pressure induces lower heat dissipation of the liquid close to the die/core surfaces, with the formation of slightly greater dendrite arms and coarser eutectic Si particles. On the other hand, the increase in the Sr level leads to finer microstructural scale and eutectic Si. The analysed variables, within the experimental conditions, do not affect the morphology of eutectic Si particles. Higher applied pressure and Sr content generate castings with lower amount of porosiW. However, as the filling pressure increases the flow of metal inside the die cavity is more turbulent, leading to the formation of oxide films and cold shots. In the analysed range of experimental conditions, the design of experiment methodology and the analysis of variance have been used to develop statistical models that accurately predict the average size of secondary dendrite arm spacing and the amount of porosity in the low-pressure die cast AISiTMg0.3 alloy.
基金supported by the National Natural Science Foundation of China(Nos.52101283 and U22A20121)the National Key R&D Program of China(Nos.2021YFC2400700 and 2022YFC2406000)+6 种基金the Science and Technology Planning Project of Guangzhou(No.202201011454)the NSFC Incubation Program of GDPH(No.KY012021165)the High-level Hospital Construction Project(No.KJ012019520)the Special Fund Project of Guangdong Academy of Sciences(Nos.2022GDASZH-2022010107 and 2021GDASYL-20210102005)the GDAS Projects of International Cooperation Platform of Science and Technology(No.2022GDASZH-2022010203-003)the Guangdong Basic and Applied Basic Research Foundation(No.2022B1515250004)the Young Elite Scientist Sponsorship Program by China Association for Science and Technology(CAST)(No.YESS20210269).
文摘Selective laser melting(SLM)has attracted great attention in the fabrication of magnesium-based biodegradable implants.However,current SLMed magnesium alloys are generally suffered from rapid corrosion,which is deadly detrimental to their use.Herein,we thoroughly revealed why they are so vulnerable to corrosion through a typical SLMed AZ91D material model.An abnormally spatiotemporal“bulk erosion”mechanism was found,not the well-known“surface corrosion”mode of traditionally plastic-deformed alloys.The unique microstructure derived from SLM possesses high chemical reactivity,which is favorable for interactional attacks of fast fluid penetration,severe local corrosion and intensive micro-galvanic corrosion.Thus,it brings two orders of magnitude in corrosion rates compared with its plastic-deformed counterparts.In vitro,such fast-corrosion induced apparent cytotoxicity,cell damage,and further apoptosis to rat and mouse derived mesenchymal stem cells.In vivo,the material disintegrates into small pieces in a short period,and results in unexpected bone destruction and long-lasting foreign body reactions in Sprague Dawley rats.Close attention should be paid to this issue before SLMed Mg-based implants being applied in patients.
基金the National Natural Science Foundation of China (Grant No.10774040) and the joint Chinese-Russian Project for their financial supports
文摘Strontium doped perovskite-type Nd0.7Sr0.3MnO3 ceramics were synthesized completely by high-energy ball milling raw oxides of Nd2O3, SrCO3 and MnO2. The optimal ball milling time and mass ratio of milling balls to raw materials are 4 h and 10：1, respectively. The grain size of as-milled Nd0.7Sr0.3MnO3 ceramics ranges from 51 to 93 nm, and the fine particles contain two phases of crystalline phase and amorphous phase. For the Nd0.7r0.3MnO3 synthesized by ball milling and sequent heat treatment, a remarkable colossal electroresistance （CER） effect is observed and the CER ratio reaches 900% at Curie temperature Tc when the load voltage increases from 0.1 to 0.8 V.
基金supported by the Frontier Science Key Program of the Chinese Academy of Sciences(No.QYZDY-SSW-JSC016)Chinese Academy of Sciences President’s International Fellowship Initiative(No.2024VMA0012).
文摘Yttrium hydride(YH_(x))is a highly promising neutron moderator material for nuclear reactors,known for its exceptional thermal stability and high hydrogen content.This study investigated the sintering mechanism and microstructural evolution of YH_(x)monoliths processed by spark plasma sintering(SPS),with the effects of temperature,duration,and pressure.The results indicate that the sintering process can be divided into five stages:formation of sintering necks,rapid densification,anti-densification,recrystallization,and grain growth.The anti-densification behavior is attributed to hydrogen desorption,phase transformation-induced volumetric contraction,and vacancy coalescence from hydrogen migration,leaving residual pores and lattice defects.Furthermore,increasing the sintering temperature and duration promotes recrystallization and grain growth,whereas elevated pressure effectively suppresses grain boundary migration.This research establishes fundamental processing-structure correlations critical for optimizing YHx moderators in nuclear applications.
