With the rapid development of 3C industries,the demand for high-thermal-conductivity magnesium alloys with high mechanical performance is increasing quickly.However,the thermal conductivities of most common Mg foundry...With the rapid development of 3C industries,the demand for high-thermal-conductivity magnesium alloys with high mechanical performance is increasing quickly.However,the thermal conductivities of most common Mg foundry alloys(such as Mg-9wt%-1wt%Zn)are still relatively low.In this study,we developed a high-thermal-conductivity Mg-4Al-4Zn-4RE-1Ca(wt%,AZEX4441)alloy with good mechanical properties for ultrathin-walled cellphone components via high-pressure die casting(HPDC).The HPDC AZEX4441 alloy exhibited a fine homogeneous microstructure(average grain size of 2.8μm)with granular Al_(11)RE_(3),fibrous Al_(2)REZn_(2),and networked Ca_(6)Mg_(2)Zn_(3) phases distributed at the grain boundaries.The room-temperature thermal conductivity of the HPDC AZEX4441 alloy was 94.4 W·m^(-1)·K^(-1),which was much higher than 53.7 W·m^(-1)·K^(-1) of the HPDC AZ91D alloy.Al and Zn in the AZEX4441 alloy were largely consumed by the formation of Al_(11)RE_(3),Al_(2)REZn_(2),and Ca_(2)Mg_(6)Zn_(3) phases because of the addition of RE and Ca.Therefore,the lattice distortion induced by solute atoms of the AZEX4441 alloy(0.171%)was much lower than that of the AZ91D alloy(0.441%),which was responsible for the high thermal conductivity of the AZEX4441 alloy.The AZEX4441 alloy exhibited a high yield strength of~185 MPa,an ultimate tensile strength of~233 MPa,and an elongation of~4.2%.This result indicated that the tensile properties were comparable with those of the AZ91D alloy.Therefore,this study contributed to the development of high-performance Mg alloys with a combination of high thermal conductivity,high strength,and good castability.展开更多
γ-Fe nano-particles with size of 20-40 nm were produced by SF6-sensitized CW CO2 laser-induced gaseous pyrolysis of Fe(Co) 5, The γ-Fe stabte in reaction zone at above 910℃ was formed.The rapid quenching prevents f...γ-Fe nano-particles with size of 20-40 nm were produced by SF6-sensitized CW CO2 laser-induced gaseous pyrolysis of Fe(Co) 5, The γ-Fe stabte in reaction zone at above 910℃ was formed.The rapid quenching prevents from the γ-Fe transforming to α-Fe as rapidly cooling from high temperature to room temperature, The characteristics of the particles were examined at room temperature by TEM. electron diffraction and XRD. It was proved that about 70% of γ-Fe phase in the particles was present. In addition. the lattice constant of the γ-Fe was 0.364 nm in place of 0.360 nm展开更多
Exploring the phase transition of high entropy alloys(HEAs)with multiple major elements is of great importance for understanding the underlying physical mechanisms.Macroscopic martensitic phase tran-sition has been fr...Exploring the phase transition of high entropy alloys(HEAs)with multiple major elements is of great importance for understanding the underlying physical mechanisms.Macroscopic martensitic phase tran-sition has been frequently reported in HEAs,however,nanoscale microstructural phase evolution has not been investigated to the same extent.Herein,we have prepared the Ti_(33)Nb_(15)Zr_(25)Hf_(25)O_(2)HEA and investi-gated the strain glass transition and its associated properties using dynamic mechanical analysis and mi-crostructure characterization.We have found that the elastic modulus in Ti_(33)Nb_(15)Zr_(25)Hf_(25)O_(2)HEA deviates from Wachtman’s equation and observed the Elinvar effect in the form of temperature-independent mod-ulus in the temperature range from 150 K to 450 K and frequency-dependence modulus around 220 K.The strain glass transition has been evidenced in Ti_(33)Nb_(15)Zr_(25)Hf_(25)O_(2)HEA by the formation and growth of nano-sized domains during in-situ transmission electron microscopy(TEM)cooling,and substantiated by the broken ergodicity during zero-field-cooling/field-cooling.The strain glass transition is believed to account for the Elinvar effect,where the modulus hardening of nano-sized domains compensates dynam-ically with the modulus softening of the transformable matrix.展开更多
In this study,a novel strategy for developingα+βdual-phase titanium alloys with low Young's modulus and high yield strength was proposed,and a Ti-15Nb-5Zr-4Sn-1 Fe alloy was developed through theoretical composi...In this study,a novel strategy for developingα+βdual-phase titanium alloys with low Young's modulus and high yield strength was proposed,and a Ti-15Nb-5Zr-4Sn-1 Fe alloy was developed through theoretical composition design and microstructure manipulation.After hot-rolling and subsequent annealing,a high volume fraction of ultrafine grainedαphase embedded in metastableβ-matrix was formed in the microstructure as intended.Consequently,this alloy exhibits both low Young's modulus(61 GPa)and high yield strength(912 MPa).The experimental results prove that the proposed strategy is appropriate for developing titanium alloys with superior yield strength-to-modulus ratio than those of conventional metallic biomedical materials.Present study might shed light on the research and development of advanced biomedical titanium alloys with low Young's modulus and high yield strength.展开更多
Fe-Ni alloys exhibiting temperature-independent elastic modulus(Elinvar)and thermal expansion(Invar)properties have found wide and significant applications,such as liquefied natural gas tanks,micrometers,reed relays,h...Fe-Ni alloys exhibiting temperature-independent elastic modulus(Elinvar)and thermal expansion(Invar)properties have found wide and significant applications,such as liquefied natural gas tanks,micrometers,reed relays,hairsprings,etc.[1].Owing to the technical and theoretical importance of Invar and Elinvar effects,the underlying mechanisms of such effects have been展开更多
Fe-Ni based Elinvar alloys performing temperature-independent elastic modulus over a wide temperature range have found wide and significant applications. Although numerous models involved with magnetism have been prop...Fe-Ni based Elinvar alloys performing temperature-independent elastic modulus over a wide temperature range have found wide and significant applications. Although numerous models involved with magnetism have been proposed to explain the Elinvar anomaly, some of the puzzles concerning the anomaly have not been fully understood. In this work, a remarkable discrepancy between the inflection temperature of modulus and the Curie temperature in a typical Fe-Ni-Cr Elinvar alloy was found,challenging the magnetic mechanism for Elinvar anomaly. Microstructural characterization and dynamic mechanical analysis demonstrate the occurrence of a strain glass transition with continuous formation of nanodomains. Accompanying such a transition, the gradual softening in the elastic modulus of austenite offsets the modulus hardening due to the vibrational anharmonicity of nanodomains upon cooling, leading to the Elinvar effect. As a result, the inflection temperature of modulus corresponds to the initiation of nanodomains' formation instead of magnetic transition. Our findings specify the association of Elinvar anomaly with structural aspects, and provide new insights into the mechanism of Elinvar anomaly in Fe-Ni based alloy.展开更多
The microstructural evolution,oxidation resistance and mechanical properties of Ti-6.5Al-2Sn-4Hf-2 Nbbased alloys with different contents of tungsten(W)additions ranging from 0 to 4.0 wt.%have been investigated in thi...The microstructural evolution,oxidation resistance and mechanical properties of Ti-6.5Al-2Sn-4Hf-2 Nbbased alloys with different contents of tungsten(W)additions ranging from 0 to 4.0 wt.%have been investigated in this study.The addition of W changed the microstructure from Widmanstatten colony of the W-free alloy to basketweave microstructure.After thermal exposure at 650℃ for 1000 h,the retainedβphase became less continuous,and secondaryβnano-particles with high W concentration were precipitated fromαlamellas.Withinαlamellas,the W was found to mainly partitioned into the secondaryβphase and refined the ordered α_(2)-Ti_(3)Al precipitates due to increased solubility of Nb in α_(2) phase.High W addition increased activation energy for oxidation,promoting the formation of more uniform and compact compound oxides,therefore substantially enhanced the oxidation resistance of the alloy.Besides,the W addition also improved the room and high-temperature yield strength without obviously losing plasticity after long-time thermal exposure.The improved mechanical performance was mainly attributed to the introduction of moreα/βinterfaces,the precipitation of secondaryβphase and the refinedα_(2) phase with Nb segregation.展开更多
In this study,PCR-denaturing gradient gel electrophoresis(DGGE)was applied to analyze the microbial communities in lake sediments from Lake Xuanwu,Lake Mochou in Nanjing and Lake Taihu in Wuxi.Sediment samples from se...In this study,PCR-denaturing gradient gel electrophoresis(DGGE)was applied to analyze the microbial communities in lake sediments from Lake Xuanwu,Lake Mochou in Nanjing and Lake Taihu in Wuxi.Sediment samples from seven locations in three lakes were collected and their genomic DNAs were extracted.The DNA yields of the sediments of Lake Xuanwu and Lake Mochou were high(10 mg/g),while that of sediments in Lake Taihu was relatively low.After DNA purification,the 16S rDNA genes(V3 to V5 region)were amplified and the amplified DNA fragments were separated by parallel DGGE.The DGGE profiles showed that there were five common bands in all the lake sediment samples indicating that there were similarities among the populations of microorganisms in all the lake sediments.The DGGE profiles of Lake Xuanwu and Lake Mochou were similar and about 20 types of micro-organisms were identified in the sediment samples of both lakes.These results suggest that the sediment samples of these two city lakes(Xuanwu,Mochou)have similar microbial communities.However,the DGGE profiles of sediment samples in Lake Taihu were significantly different from these two lakes.Furthermore,the DGGE profiles of sediment samples in different locations in Lake Taihu were also different,suggesting that the microbial communities in Lake Taihu are more diversified than those in Lake Xuanwu and Lake Mochou.The differences in microbial diversity may be caused by the different environmental conditions,such as redox potential,pH,and the concentrations of organic matters.Seven major bands of 16S rDNA genes fragments from the DGGE profiles of sediment samples were further reamplified and sequenced.The results of sequencing analysis indicate that five sequences shared 99%-100%homology with known sequences(Bacillus and Brevibacillus,uncultured bacteria),while the other two sequences shared 93%-96%homology with known sequences(Acinetobacter,and Bacillus).The study shows that the PCR-DGGE technique combined with sequence analysis is a feasible and efficient method for the determination of microbial communities in sediment samples.展开更多
Marine streptomycetes are rich sources of natural products with novel structures and interesting biological activities,and genome mining of marine streptomycetes facilitates rapid discovery of their useful products.In...Marine streptomycetes are rich sources of natural products with novel structures and interesting biological activities,and genome mining of marine streptomycetes facilitates rapid discovery of their useful products.In this study,a marine-derived Streptomyces sp.M10 was revealed to share a 99.02%16S rDNA sequence identity with that of Streptomyces marokkonensis Ap1T,and was thus named S.marokkonensis M10.To further evaluate its biosynthetic potential,the 7,207,169 bps of S.marokkonensis M10 genome was sequenced.Genomic sequence analysis for potential secondary metaboliteassociated gene clusters led to the identification of at least three polyketide synthases(PKSs),six non-ribosomal peptide synthases(NRPSs),one hybrid NRPS-PKS,two lantibiotic and five terpene biosynthetic gene clusters.One type I PKS gene cluster was revealed to share high nucleotide similarity with the candicidin/FR008 gene cluster,indicating the capacity of this microorganism to produce polyene macrolides.This assumption was further verified by isolation of two polyene family compounds PF1 and PF2,which have the characteristic UV adsorption at 269,278,290 nm(PF1)and 363,386 and 408 nm(PF2),respectively.S.marokkonensis M10 is therefore a new source of polyene metabolites.Further studies on S.marokkonensis M10 will provide more insights into natural product biosynthesis potential of related streptomycetes.This is also the first report to describe the genome sequence of S.marokkonensis-related strain.展开更多
基金The authors are grateful for the financial support by the National Key Research and Development Program of China(No.2016YFB0301103)the National Natural Science Foundation of China(NSFC,No.51401010).
文摘With the rapid development of 3C industries,the demand for high-thermal-conductivity magnesium alloys with high mechanical performance is increasing quickly.However,the thermal conductivities of most common Mg foundry alloys(such as Mg-9wt%-1wt%Zn)are still relatively low.In this study,we developed a high-thermal-conductivity Mg-4Al-4Zn-4RE-1Ca(wt%,AZEX4441)alloy with good mechanical properties for ultrathin-walled cellphone components via high-pressure die casting(HPDC).The HPDC AZEX4441 alloy exhibited a fine homogeneous microstructure(average grain size of 2.8μm)with granular Al_(11)RE_(3),fibrous Al_(2)REZn_(2),and networked Ca_(6)Mg_(2)Zn_(3) phases distributed at the grain boundaries.The room-temperature thermal conductivity of the HPDC AZEX4441 alloy was 94.4 W·m^(-1)·K^(-1),which was much higher than 53.7 W·m^(-1)·K^(-1) of the HPDC AZ91D alloy.Al and Zn in the AZEX4441 alloy were largely consumed by the formation of Al_(11)RE_(3),Al_(2)REZn_(2),and Ca_(2)Mg_(6)Zn_(3) phases because of the addition of RE and Ca.Therefore,the lattice distortion induced by solute atoms of the AZEX4441 alloy(0.171%)was much lower than that of the AZ91D alloy(0.441%),which was responsible for the high thermal conductivity of the AZEX4441 alloy.The AZEX4441 alloy exhibited a high yield strength of~185 MPa,an ultimate tensile strength of~233 MPa,and an elongation of~4.2%.This result indicated that the tensile properties were comparable with those of the AZ91D alloy.Therefore,this study contributed to the development of high-performance Mg alloys with a combination of high thermal conductivity,high strength,and good castability.
文摘γ-Fe nano-particles with size of 20-40 nm were produced by SF6-sensitized CW CO2 laser-induced gaseous pyrolysis of Fe(Co) 5, The γ-Fe stabte in reaction zone at above 910℃ was formed.The rapid quenching prevents from the γ-Fe transforming to α-Fe as rapidly cooling from high temperature to room temperature, The characteristics of the particles were examined at room temperature by TEM. electron diffraction and XRD. It was proved that about 70% of γ-Fe phase in the particles was present. In addition. the lattice constant of the γ-Fe was 0.364 nm in place of 0.360 nm
基金supported by the National Key Research and De-velopment Program of China(No.2022YFB3800052)the National Natural Science Foundation of China(Nos.12002013,51971009,and 51831006)+1 种基金the Zhejiang Natural Science Foundation(No.LZ23E010004).H.L.Hou also acknowledges the support of the Fundamental Research Funds for the Central Universities(No.501LKQB2020105028)the Opening Fund of the State Key Lab-oratory of Nonlinear Mechanics.
文摘Exploring the phase transition of high entropy alloys(HEAs)with multiple major elements is of great importance for understanding the underlying physical mechanisms.Macroscopic martensitic phase tran-sition has been frequently reported in HEAs,however,nanoscale microstructural phase evolution has not been investigated to the same extent.Herein,we have prepared the Ti_(33)Nb_(15)Zr_(25)Hf_(25)O_(2)HEA and investi-gated the strain glass transition and its associated properties using dynamic mechanical analysis and mi-crostructure characterization.We have found that the elastic modulus in Ti_(33)Nb_(15)Zr_(25)Hf_(25)O_(2)HEA deviates from Wachtman’s equation and observed the Elinvar effect in the form of temperature-independent mod-ulus in the temperature range from 150 K to 450 K and frequency-dependence modulus around 220 K.The strain glass transition has been evidenced in Ti_(33)Nb_(15)Zr_(25)Hf_(25)O_(2)HEA by the formation and growth of nano-sized domains during in-situ transmission electron microscopy(TEM)cooling,and substantiated by the broken ergodicity during zero-field-cooling/field-cooling.The strain glass transition is believed to account for the Elinvar effect,where the modulus hardening of nano-sized domains compensates dynam-ically with the modulus softening of the transformable matrix.
基金the National Natural Science Foundation of China(Nos.51671012,51831006 and 51971009)the International Science and Technology Cooperation Program of China(No.2015DFA51430)the Fundamental Research Funds for the Central Universities。
文摘In this study,a novel strategy for developingα+βdual-phase titanium alloys with low Young's modulus and high yield strength was proposed,and a Ti-15Nb-5Zr-4Sn-1 Fe alloy was developed through theoretical composition design and microstructure manipulation.After hot-rolling and subsequent annealing,a high volume fraction of ultrafine grainedαphase embedded in metastableβ-matrix was formed in the microstructure as intended.Consequently,this alloy exhibits both low Young's modulus(61 GPa)and high yield strength(912 MPa).The experimental results prove that the proposed strategy is appropriate for developing titanium alloys with superior yield strength-to-modulus ratio than those of conventional metallic biomedical materials.Present study might shed light on the research and development of advanced biomedical titanium alloys with low Young's modulus and high yield strength.
基金supported by the National Natural Science Foundation of China (51431007,51771012)
文摘Fe-Ni alloys exhibiting temperature-independent elastic modulus(Elinvar)and thermal expansion(Invar)properties have found wide and significant applications,such as liquefied natural gas tanks,micrometers,reed relays,hairsprings,etc.[1].Owing to the technical and theoretical importance of Invar and Elinvar effects,the underlying mechanisms of such effects have been
基金supported financially by the National Natural Science Foundation of China (Nos. 51431007, 51831006 and 51771012)
文摘Fe-Ni based Elinvar alloys performing temperature-independent elastic modulus over a wide temperature range have found wide and significant applications. Although numerous models involved with magnetism have been proposed to explain the Elinvar anomaly, some of the puzzles concerning the anomaly have not been fully understood. In this work, a remarkable discrepancy between the inflection temperature of modulus and the Curie temperature in a typical Fe-Ni-Cr Elinvar alloy was found,challenging the magnetic mechanism for Elinvar anomaly. Microstructural characterization and dynamic mechanical analysis demonstrate the occurrence of a strain glass transition with continuous formation of nanodomains. Accompanying such a transition, the gradual softening in the elastic modulus of austenite offsets the modulus hardening due to the vibrational anharmonicity of nanodomains upon cooling, leading to the Elinvar effect. As a result, the inflection temperature of modulus corresponds to the initiation of nanodomains' formation instead of magnetic transition. Our findings specify the association of Elinvar anomaly with structural aspects, and provide new insights into the mechanism of Elinvar anomaly in Fe-Ni based alloy.
基金supported by National Key Research and Development Program of China(No.2017YFB0306205)the National Natural Science Foundation of China(Grant No.51671012,51831006,51971009)the Fundamental Research Funds for the Central Universities。
文摘The microstructural evolution,oxidation resistance and mechanical properties of Ti-6.5Al-2Sn-4Hf-2 Nbbased alloys with different contents of tungsten(W)additions ranging from 0 to 4.0 wt.%have been investigated in this study.The addition of W changed the microstructure from Widmanstatten colony of the W-free alloy to basketweave microstructure.After thermal exposure at 650℃ for 1000 h,the retainedβphase became less continuous,and secondaryβnano-particles with high W concentration were precipitated fromαlamellas.Withinαlamellas,the W was found to mainly partitioned into the secondaryβphase and refined the ordered α_(2)-Ti_(3)Al precipitates due to increased solubility of Nb in α_(2) phase.High W addition increased activation energy for oxidation,promoting the formation of more uniform and compact compound oxides,therefore substantially enhanced the oxidation resistance of the alloy.Besides,the W addition also improved the room and high-temperature yield strength without obviously losing plasticity after long-time thermal exposure.The improved mechanical performance was mainly attributed to the introduction of moreα/βinterfaces,the precipitation of secondaryβphase and the refinedα_(2) phase with Nb segregation.
基金This study is supported by the National Basic Research Program(2002CB412307)the National High Technology Research and Development Program of China(Water Environment Program)(2002AA601011).
文摘In this study,PCR-denaturing gradient gel electrophoresis(DGGE)was applied to analyze the microbial communities in lake sediments from Lake Xuanwu,Lake Mochou in Nanjing and Lake Taihu in Wuxi.Sediment samples from seven locations in three lakes were collected and their genomic DNAs were extracted.The DNA yields of the sediments of Lake Xuanwu and Lake Mochou were high(10 mg/g),while that of sediments in Lake Taihu was relatively low.After DNA purification,the 16S rDNA genes(V3 to V5 region)were amplified and the amplified DNA fragments were separated by parallel DGGE.The DGGE profiles showed that there were five common bands in all the lake sediment samples indicating that there were similarities among the populations of microorganisms in all the lake sediments.The DGGE profiles of Lake Xuanwu and Lake Mochou were similar and about 20 types of micro-organisms were identified in the sediment samples of both lakes.These results suggest that the sediment samples of these two city lakes(Xuanwu,Mochou)have similar microbial communities.However,the DGGE profiles of sediment samples in Lake Taihu were significantly different from these two lakes.Furthermore,the DGGE profiles of sediment samples in different locations in Lake Taihu were also different,suggesting that the microbial communities in Lake Taihu are more diversified than those in Lake Xuanwu and Lake Mochou.The differences in microbial diversity may be caused by the different environmental conditions,such as redox potential,pH,and the concentrations of organic matters.Seven major bands of 16S rDNA genes fragments from the DGGE profiles of sediment samples were further reamplified and sequenced.The results of sequencing analysis indicate that five sequences shared 99%-100%homology with known sequences(Bacillus and Brevibacillus,uncultured bacteria),while the other two sequences shared 93%-96%homology with known sequences(Acinetobacter,and Bacillus).The study shows that the PCR-DGGE technique combined with sequence analysis is a feasible and efficient method for the determination of microbial communities in sediment samples.
文摘Marine streptomycetes are rich sources of natural products with novel structures and interesting biological activities,and genome mining of marine streptomycetes facilitates rapid discovery of their useful products.In this study,a marine-derived Streptomyces sp.M10 was revealed to share a 99.02%16S rDNA sequence identity with that of Streptomyces marokkonensis Ap1T,and was thus named S.marokkonensis M10.To further evaluate its biosynthetic potential,the 7,207,169 bps of S.marokkonensis M10 genome was sequenced.Genomic sequence analysis for potential secondary metaboliteassociated gene clusters led to the identification of at least three polyketide synthases(PKSs),six non-ribosomal peptide synthases(NRPSs),one hybrid NRPS-PKS,two lantibiotic and five terpene biosynthetic gene clusters.One type I PKS gene cluster was revealed to share high nucleotide similarity with the candicidin/FR008 gene cluster,indicating the capacity of this microorganism to produce polyene macrolides.This assumption was further verified by isolation of two polyene family compounds PF1 and PF2,which have the characteristic UV adsorption at 269,278,290 nm(PF1)and 363,386 and 408 nm(PF2),respectively.S.marokkonensis M10 is therefore a new source of polyene metabolites.Further studies on S.marokkonensis M10 will provide more insights into natural product biosynthesis potential of related streptomycetes.This is also the first report to describe the genome sequence of S.marokkonensis-related strain.