Minor Dy element was added into a Mg?4Y?3Nd?0.4Zr alloy,and its effects on the microstructure and the mechanicalproperties at elevated temperatures were investigated.Scanning electron microscope(SEM)and transmission e...Minor Dy element was added into a Mg?4Y?3Nd?0.4Zr alloy,and its effects on the microstructure and the mechanicalproperties at elevated temperatures were investigated.Scanning electron microscope(SEM)and transmission electron microscope(TEM)were used to observe the microstructures.The results indicated that the as-cast eutectic and isolated cuboid-shaped Mg?REphases were Mg5RE and Mg3RE17,respectively,and distributed mainly along grain boundaries.After a solution treatment,theeutectic Mg5RE phases were dissolved into the matrix,whereas the Mg3RE17compound still remained.After peak aging,fineMg?RE phases were precipitated homogeneously within the matrix of the alloys containing Dy.Dy addition can result in asignificant improvement in the tensile strength at both room and elevated temperatures,and a slight decrease in the elongation.展开更多
Determining whether the high-latitude Bering land bridge(BLB)was ecologically suitable for the migration of mesothermal plants is significant for Holarctic phytogeographic inferences.Paleobotanical studies provide a c...Determining whether the high-latitude Bering land bridge(BLB)was ecologically suitable for the migration of mesothermal plants is significant for Holarctic phytogeographic inferences.Paleobotanical studies provide a critical source of data on the latitudinal positions of different plant lineages at different times,permitting assessment of the efficacy of the BLB for migration.Here we report exceptionally preserved fossils of Firmiana and Tilia endochrysea from the middle Miocene of South Korea.This represents a new reliable record of Firmiana and the first discovery of the T.endochrysea lineage in the fossil record of Asia.The occurrence of these fossils in South Korea indicates that the two lineages had a distribution that extended much farther north during the middle Miocene,but they were still geographically remote from the BLB.In light of the broader fossil record of Asia,our study shows that,in the middle Miocene,some mesothermal plants apparently inhabited the territory adjacent to the BLB and thus they were possibly capable of utilizing the BLB as a migratory corridor.Some other mesothermal plants,such as Firmiana and the T.endochrysea lineages,however,are restricted to more southern regions relative to the BLB based on current fossil evidence.These lineages may have been ecologically unable to traverse the BLB,which raises questions about the efficacy of the BLB as a universal exchange route for mesothermal plants between Asia and North America during the middle Miocene.展开更多
Eurya has an excellent fossil record in Europe, but it has only a few fossil occurrences in East Asia though this vast area houses the highest modern diversity of the genus. In this study, three-dimensionally preserve...Eurya has an excellent fossil record in Europe, but it has only a few fossil occurrences in East Asia though this vast area houses the highest modern diversity of the genus. In this study, three-dimensionally preserved fossil seeds of Eurya stigrnosa （Ludwig） Mai from the late Pliocene of northwestern Yunnan, southwestern China are described. The seeds are compressed and flattened, slightly campylotropous, and nearly circular to slightly angular in shape. The surface of the seeds is sculptured by a distinctive foveolate pattern, consisting of funnel-shaped and finely pitted cells. Each seed valve contains a reniform or horseshoe-shaped embryo cavity, a characteristic condyle structure and an internal raphe. These fossil seeds represent one of the few fossil records of Eurya in East Asia. This new finding therefore largely extends the distributional ranges of Eurya during Neogene. Fossil records summarized here show that Eurya persisted in Europe until the early Pleistocene, but disappeared thereafter. The genus might have first appeared in East Asia no later than the late Oligocene, and dispersed widely in regions such as Japan, Nepal, and southwestern China.展开更多
The palaeodiversity of flowering plants in Yunnan has been extensively interpreted from both a molecular and fossil perspective. However, for cryptogamic plants such as ferns, the palaeodiversity remains poorly known....The palaeodiversity of flowering plants in Yunnan has been extensively interpreted from both a molecular and fossil perspective. However, for cryptogamic plants such as ferns, the palaeodiversity remains poorly known. In this study, we describe a new ferny fossil taxon, Drynaria lanpingensis sp. nov. Huang,Su et Zhou(Polypodiaceae), from the late Pliocene of northwestern Yunnan based on fragmentary frond and pinna with in situ spores. The frond is pinnatifid and the pinnae are entirely margined. The sori are arranged in one row on each side of the primary vein. The spores have a semicircular to bean-shaped equatorial view and a tuberculate surface. Taken together with previously described fossils, there are now representatives of three known fossil taxa of Drynaria from the late Pliocene of western Yunnan.These finds suggest that Drynaria diversity was considerable in the region at that time. As Drynaria is a shade-tolerant plant, growing preferably in wet conditions in the understory of forests, its extensive existence may indicate forest vegetation and humid climates in western Yunnan during the late Pliocene.This is in line with results from floristic investigations and palaeoclimatic reconstructions based on fossil floras.展开更多
Surface uplift at the southeastern margin of the Tibetan Plateau has been widely studied,but more palaeoaltimetry data are required to better understand the elevation history of this geologically complex region.In thi...Surface uplift at the southeastern margin of the Tibetan Plateau has been widely studied,but more palaeoaltimetry data are required to better understand the elevation history of this geologically complex region.In this study,fossil leaves of Abies(Pinaceae),a cool-temperate element,recovered from the latest Miocene-Pliocene Yangyi Formation of the southern Baoshan Basin,were used as a proxy to estimate the local palaeoelevation.Based on the regional modern altitude range(2100-4280 m)of the genus as well as regional temperature discrepancy(1.5℃)between the past and present,the palaeoelevation of the study area was calculated to be>2360 m above sea level as compared to 1670 m at present.Our result suggests that the southern Baoshan Basin experienced pronounced uplift prior to the time of fossil deposition,probably as a result of crustal shortening and thickening of the northern Baoshan Terrane during the Eocene-Oligocene.We infer that surface growth in areas south of the Dali Basin may have been greater than previously interpreted,and that a widespread plateau or plateau patches higher than 2000 m probably extended southwards into at least the Baoshan Basin by the latest Miocene-Pliocene.We also infer that the elevation of the southern Baoshan Basin has decreased by at least 690 m since then,in contrast to most other scenarios in which the elevation of the southeastern margin of the Tibetan Plateau has increased or remained close to modern levels since the late Miocene.The major cause of the inferred altitude decline is likely tectonic deformation.As a transtensional graben basin,the Baoshan Basin has experienced pull-apart and base-fall movement since the late Miocene,which would reduce the altitude of its southern part located on the hanging wall.Surface erosion associated with the increased summer rainfall might also have played a role especially in reducing the local relief,although its contribution can be limited.Our study provides one of the few palaeoelevation estimates from areas south of the Dali Basin and an example of past elevation loss at the southeastern margin of the Tibetan Plateau,thus shedding important light on the landscape evolution of this region.展开更多
The distinctive intrinsic heat treatment(IHT)originating from cyclic reheating in the laser-directed energy deposition(LDED) has attracted growing attention in recent years.In this investigation,simulations and experi...The distinctive intrinsic heat treatment(IHT)originating from cyclic reheating in the laser-directed energy deposition(LDED) has attracted growing attention in recent years.In this investigation,simulations and experimental characterizations were performed to examine the impact of IHT on the micros true ture and mechanical properties of LDED-fabricated CrCoNi medium-entropy alloy(MEA).The results show that the intensity of the IHT is proportional to the utilized laser energy density(LED).As the LED increased,significant dynamic recrystallization and grain refinement occurred within the alloy due to the enhanced intensity of IHT.However,the high LED leads to severe hot cracking within the as-built MEA,resulting in inferior ductility.By decreasing LED,the hot cracking was effectively eliminated.Meanwhile,low LED weakened the intensity of IHT and consequently inhibited kinetic conditions of dynamic recrystallization,resulting in a heterogeneous grain structure characterized by multi-scale-sized grains.This structure provides significant hetero-deformation-induced hardening during plastic deformation,enabling the alloy to have a sustainable work-hardening capacity.We expect that this work will have implications in taking full advantage of the unique IHT of the LDED process to fabricate ME As with excellent metallurgical quality and mechanical performance.展开更多
Wildfire bears a close relationship with vegetation as its fuel source.The southeastern margin of the Tibetan Plateau witnesses frequent wildfires among various types of vegetation,whereas such wide in-teractions betw...Wildfire bears a close relationship with vegetation as its fuel source.The southeastern margin of the Tibetan Plateau witnesses frequent wildfires among various types of vegetation,whereas such wide in-teractions between wildfire and vegetation remain poorly studied from geological times.In this study,we reported a local fire using sedimentary macroscopic charcoals from the latest Miocene to early Pliocene of the Baoshan Basin in this region,and then inferred the local vegetation at the time of the fire event based chiefly on the coexistent fruit and seed fossil assemblage.Our taxonomic results show that the charcoal assemblage is probably dominated by broadleaved plants and the fruit and seed fossil assemblage is apparently dominated by Salix(Salicaceae)followed by Sambucus(Adoxaceae),suggesting a deciduous broadleaved forest in which the fire likely occurred.Under a seasonally dry climate associated with the Asian monsoon,this type of vegetation might be prone to natural fire,because in the wet rainy season the plants grew well to accumulate biofuel and in the dry season abundant ground litter resulting from leaf decay would be desiccated to become highly flammable.Due to the fire-tolerant habit of Salix as the dominant plant,the forest might be in return adapted to the fire event or even more fires that potentially followed.All these may suggest a close relationship between the fire event and the reconstructed vegetation.Our finding documents a new type of wildfire—vegetation interaction,namely the interaction between wildfire and deciduous broadleaved forest,from the geological past at the southeastern margin of the Tibetan Plateau.It therefore sheds new light on the wildfire history coupling vegetation change in the region.展开更多
Even in their bulk forms,complex alloys like high-entropy alloys(HEAs)exhibit favorable activity and stability as electrocatalysts for the oxygen evolution reaction(OER).However,the underlying reasons are not yet full...Even in their bulk forms,complex alloys like high-entropy alloys(HEAs)exhibit favorable activity and stability as electrocatalysts for the oxygen evolution reaction(OER).However,the underlying reasons are not yet fully understood.In a family of Mo-doped CrFeCoNi-based HEAs,we have identified three crucial factors that govern their performance:(i)homogeneous solid solution phase of HEAs helps to maintain high-valence states of metals;(ii)surface reconstruction results in a hybrid material comprising amorphous domains and percolated crystalline structures;(iii)diversity of active intermediate species(M–O,M–OOH,and,notably,the abundance of superoxideμ–OO),which display stronger adsorption capacity on the reconstructed surface.These results are revealing due to their resemblance to findings in other families of electrocatalysts for OER,as well as their unique features specific to HEAs.In line with these factors,a CrFeCoNiMo0.2 bulk integrated electrode displays a low overpotential of 215 mV,rapid kinetics,and long-term stability of over 90 d.Bulk HEAs hold great potential for industrial applications.展开更多
The use of resistance spot welding（RSW）technology for joining Ti40Zr25Ni3Cu12Be20 metallic glass was investigated.The microstructure obtained from the welded BMG sample was studied.Joint without precipitates was pre...The use of resistance spot welding（RSW）technology for joining Ti40Zr25Ni3Cu12Be20 metallic glass was investigated.The microstructure obtained from the welded BMG sample was studied.Joint without precipitates was prepared with welding current of 5.0 kA for 2cycles.A fully coupled thermal-electrical-mechanical finite element model（FEM） was developed to complement the experimental study.The simulated results agree well with the measurements.The effects of key process parameters such as welding current and welding time on the evolvement and microstructure of the weldment were determined and discussed.Moreover,the critical cooling rate for preserving the amorphous state in the weld fusion zone is determined to be approximately 1×10^3 K·s^-1.展开更多
Here,bulk CoCrFeMnNi high-entropy alloy was prepared via laser melting deposition,and its microstructure and mechanical properties at room and cryogenic temperature were investigated by a series of microstructural cha...Here,bulk CoCrFeMnNi high-entropy alloy was prepared via laser melting deposition,and its microstructure and mechanical properties at room and cryogenic temperature were investigated by a series of microstructural character-izations and mechanical tests.The results showed that the as-built samples possessed a single fcc phase and highly dense microstructures.Compared to the mechanical prop-erties at room temperature,tensile properties,microhard-ness and wear resistance of the as-built samples showed a signiflcant enhancement at cryogenic temperature,which was attributed to the deformation mechanism converting from dislocation slipping to deformation twinning at cryogenic temperature.The formation of deformation nanotwins signiflcantly improved the deformation resis-tance in cryogenic conditions,and the sliding wear in the liquid nitrogen could decrease the oxygen concentration,suppress the generation of oxide particles and thus enhance the wear resistance.展开更多
The effect of electropulsing treatment（EPT）on the microstructure of a Ti-based bulk metallic glass（BMG）has been studied.The maximum current density applied during EPT can exert a crucial role on tuning the microst...The effect of electropulsing treatment（EPT）on the microstructure of a Ti-based bulk metallic glass（BMG）has been studied.The maximum current density applied during EPT can exert a crucial role on tuning the microstructure of the BMG.When the maximum current density is no more than 2 720A/mm^2,the samples retains amorphous nature,whereas,beyond that,crystalline phases precipitate from the glassy matrix.During EPT,the maximum temperature within the samples EPTed at the maximum current densities larger than 2 720A/mm^2 is higher than the crystallization temperature of the BMG,leading to the crystallization event.展开更多
The morphology of double oxide film defects and their influence on the tensile mechanical properties of a commercial Cu-Al （C95800） alloy were investigated in this study. Plane castings were produced with two types ...The morphology of double oxide film defects and their influence on the tensile mechanical properties of a commercial Cu-Al （C95800） alloy were investigated in this study. Plane castings were produced with two types of pouting systems, and their tensile properties were measured and then analyzed by means of Weibull statistics method. The fracture surfaces of the tensile specimens were examined using scanning electron microscopy equipped with energy-dispersive spectroscopy. A large amount of double oxide film defects were observed on the tensile fractured specimens of the topfilled plane castings, and their chemical composition is identified to be Al2O3. Weibull statistics analyses showed that the double oxide film defects significantly reduce mechanical properties of the castings investigated. Furthermore, the ultimate tensile strength is more obviously deteriorated by double oxide film defects than elongation.展开更多
High-entropy alloys(HEAs)exhibit unique microstructural features and properties in nanoscale and atomic scale because of their multi-element alloy system.The nanoscratching behaviors of three HEAs with different phase...High-entropy alloys(HEAs)exhibit unique microstructural features and properties in nanoscale and atomic scale because of their multi-element alloy system.The nanoscratching behaviors of three HEAs with different phase constituents,relative to the microstructure and mechanical properties of the HEAs,were investigated.Three typical phase constituents were selected:face-centered cubic(FCC)structure,body-centered cubic(BCC)structure,and a dual-phase structure containing both FCC and BCC phases.Despite the fact that the FCC alloy has the highest ductility and strain hardening capability,it exhibited inferior scratch resistance due to the over-softening of hardness.Due to the brittle failure mode,the BCC alloy hardly exhibited desirable scratch resistance despite its highest hardness.By contrast,the nanostructured dual-phase alloy exhibited the best scratch resistance because of its good combination of strength and ductility,as well as the ductile failure mode.This research suggests that the HEA with structure comprising nanoscale hard and soft phases is desirable for nanoscratch resistance,and possesses appropriate hardness for industrial applications.展开更多
Mciro-arc oxidation（MAO）was used to coat porous films on the surface of a Zr-based bulk metallic glass sample.The compressive test results indicated that,compared with the as-cast sample,the MAO treated one exhibite...Mciro-arc oxidation（MAO）was used to coat porous films on the surface of a Zr-based bulk metallic glass sample.The compressive test results indicated that,compared with the as-cast sample,the MAO treated one exhibited higher deformation capacity,associated with multiple shear bands with higher density on the side surface and well-developed vein patterns with smaller size on the fractured surface.The pore in the MAOed film and the matrix/coating interface initiated the shear bands and impeded the rapid propagation of shear bands,thus favoring the enhanced plasticity of the MAO treated sample.The obtained results demonstrated that MAO can be considered as an effective method to finely tune the mechanical performance of monolithic bulk metallic glasses.展开更多
基金Project(GB09209)supported by the Science and Technology Bureau of Heilongjiang Province,China
文摘Minor Dy element was added into a Mg?4Y?3Nd?0.4Zr alloy,and its effects on the microstructure and the mechanicalproperties at elevated temperatures were investigated.Scanning electron microscope(SEM)and transmission electron microscope(TEM)were used to observe the microstructures.The results indicated that the as-cast eutectic and isolated cuboid-shaped Mg?REphases were Mg5RE and Mg3RE17,respectively,and distributed mainly along grain boundaries.After a solution treatment,theeutectic Mg5RE phases were dissolved into the matrix,whereas the Mg3RE17compound still remained.After peak aging,fineMg?RE phases were precipitated homogeneously within the matrix of the alloys containing Dy.Dy addition can result in asignificant improvement in the tensile strength at both room and elevated temperatures,and a slight decrease in the elongation.
基金supported by the National Natural Science Foundation of China(No.31900194)the Foundation of the State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences(No.183112)+1 种基金the Yunnan Province Natural Science Foundation(No.2019FB061)the“Light of West China”Program,CAS,and the Youth Innovation Promotion Association,CAS(No.2017439).
文摘Determining whether the high-latitude Bering land bridge(BLB)was ecologically suitable for the migration of mesothermal plants is significant for Holarctic phytogeographic inferences.Paleobotanical studies provide a critical source of data on the latitudinal positions of different plant lineages at different times,permitting assessment of the efficacy of the BLB for migration.Here we report exceptionally preserved fossils of Firmiana and Tilia endochrysea from the middle Miocene of South Korea.This represents a new reliable record of Firmiana and the first discovery of the T.endochrysea lineage in the fossil record of Asia.The occurrence of these fossils in South Korea indicates that the two lineages had a distribution that extended much farther north during the middle Miocene,but they were still geographically remote from the BLB.In light of the broader fossil record of Asia,our study shows that,in the middle Miocene,some mesothermal plants apparently inhabited the territory adjacent to the BLB and thus they were possibly capable of utilizing the BLB as a migratory corridor.Some other mesothermal plants,such as Firmiana and the T.endochrysea lineages,however,are restricted to more southern regions relative to the BLB based on current fossil evidence.These lineages may have been ecologically unable to traverse the BLB,which raises questions about the efficacy of the BLB as a universal exchange route for mesothermal plants between Asia and North America during the middle Miocene.
基金Acknowledgments We thank Lin-Bo Jia from Kunming Institute of Botany, Chinese Academy of Sciences, for help with fossil collection and the editor and two anonymous reviewers for improving the manuscript. Fossil examinations with the 3D Super Depth Digital Microscope and SEM were performed in the Central Lab of Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences and examination of the extant seeds with the SEM was performed in the Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences. Extant seeds of Eurya were provided by the Herbarium of Kunming Institute of Botany, Chinese Academy of Sciences. This study was supported by the National Natural Science Foundation of China （No. U1502231, 31300187）. This study is a contribution to NECLIME （Neogene Climate of Eurasia）.
文摘Eurya has an excellent fossil record in Europe, but it has only a few fossil occurrences in East Asia though this vast area houses the highest modern diversity of the genus. In this study, three-dimensionally preserved fossil seeds of Eurya stigrnosa （Ludwig） Mai from the late Pliocene of northwestern Yunnan, southwestern China are described. The seeds are compressed and flattened, slightly campylotropous, and nearly circular to slightly angular in shape. The surface of the seeds is sculptured by a distinctive foveolate pattern, consisting of funnel-shaped and finely pitted cells. Each seed valve contains a reniform or horseshoe-shaped embryo cavity, a characteristic condyle structure and an internal raphe. These fossil seeds represent one of the few fossil records of Eurya in East Asia. This new finding therefore largely extends the distributional ranges of Eurya during Neogene. Fossil records summarized here show that Eurya persisted in Europe until the early Pleistocene, but disappeared thereafter. The genus might have first appeared in East Asia no later than the late Oligocene, and dispersed widely in regions such as Japan, Nepal, and southwestern China.
基金supported by the National Natural Science Foundation of China (31300187,U1502231)the Major Program of National Science Foundation of China (31590823)
文摘The palaeodiversity of flowering plants in Yunnan has been extensively interpreted from both a molecular and fossil perspective. However, for cryptogamic plants such as ferns, the palaeodiversity remains poorly known. In this study, we describe a new ferny fossil taxon, Drynaria lanpingensis sp. nov. Huang,Su et Zhou(Polypodiaceae), from the late Pliocene of northwestern Yunnan based on fragmentary frond and pinna with in situ spores. The frond is pinnatifid and the pinnae are entirely margined. The sori are arranged in one row on each side of the primary vein. The spores have a semicircular to bean-shaped equatorial view and a tuberculate surface. Taken together with previously described fossils, there are now representatives of three known fossil taxa of Drynaria from the late Pliocene of western Yunnan.These finds suggest that Drynaria diversity was considerable in the region at that time. As Drynaria is a shade-tolerant plant, growing preferably in wet conditions in the understory of forests, its extensive existence may indicate forest vegetation and humid climates in western Yunnan during the late Pliocene.This is in line with results from floristic investigations and palaeoclimatic reconstructions based on fossil floras.
基金supported by the National Natural Science Foundation of China(41972023,42272026)the Natural Science Foundation of Yunnan Province(202301AT070374,202201AT070131)+1 种基金the Ten Thousand Talent Plans for Young Top-notch Talents of Yunnan Province(YNWR-QNBJ-2019-261)the West Light Foundation of the Chinese Academy of Sciences to Y.-J.Huang,and the Foundation of the State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology,CAS(213106)。
文摘Surface uplift at the southeastern margin of the Tibetan Plateau has been widely studied,but more palaeoaltimetry data are required to better understand the elevation history of this geologically complex region.In this study,fossil leaves of Abies(Pinaceae),a cool-temperate element,recovered from the latest Miocene-Pliocene Yangyi Formation of the southern Baoshan Basin,were used as a proxy to estimate the local palaeoelevation.Based on the regional modern altitude range(2100-4280 m)of the genus as well as regional temperature discrepancy(1.5℃)between the past and present,the palaeoelevation of the study area was calculated to be>2360 m above sea level as compared to 1670 m at present.Our result suggests that the southern Baoshan Basin experienced pronounced uplift prior to the time of fossil deposition,probably as a result of crustal shortening and thickening of the northern Baoshan Terrane during the Eocene-Oligocene.We infer that surface growth in areas south of the Dali Basin may have been greater than previously interpreted,and that a widespread plateau or plateau patches higher than 2000 m probably extended southwards into at least the Baoshan Basin by the latest Miocene-Pliocene.We also infer that the elevation of the southern Baoshan Basin has decreased by at least 690 m since then,in contrast to most other scenarios in which the elevation of the southeastern margin of the Tibetan Plateau has increased or remained close to modern levels since the late Miocene.The major cause of the inferred altitude decline is likely tectonic deformation.As a transtensional graben basin,the Baoshan Basin has experienced pull-apart and base-fall movement since the late Miocene,which would reduce the altitude of its southern part located on the hanging wall.Surface erosion associated with the increased summer rainfall might also have played a role especially in reducing the local relief,although its contribution can be limited.Our study provides one of the few palaeoelevation estimates from areas south of the Dali Basin and an example of past elevation loss at the southeastern margin of the Tibetan Plateau,thus shedding important light on the landscape evolution of this region.
基金financially supported by the funding from Guangdong Province Basic and Applied Research Key Projects (No.2020B0301030001)National Key R&D Programme,Ministry of Science and Technology of China (Nos. 2018YFB1105200 and 2019YFA0209904)the National Natural Science Foundation of China (Nos.52371106 and 52371025)。
文摘The distinctive intrinsic heat treatment(IHT)originating from cyclic reheating in the laser-directed energy deposition(LDED) has attracted growing attention in recent years.In this investigation,simulations and experimental characterizations were performed to examine the impact of IHT on the micros true ture and mechanical properties of LDED-fabricated CrCoNi medium-entropy alloy(MEA).The results show that the intensity of the IHT is proportional to the utilized laser energy density(LED).As the LED increased,significant dynamic recrystallization and grain refinement occurred within the alloy due to the enhanced intensity of IHT.However,the high LED leads to severe hot cracking within the as-built MEA,resulting in inferior ductility.By decreasing LED,the hot cracking was effectively eliminated.Meanwhile,low LED weakened the intensity of IHT and consequently inhibited kinetic conditions of dynamic recrystallization,resulting in a heterogeneous grain structure characterized by multi-scale-sized grains.This structure provides significant hetero-deformation-induced hardening during plastic deformation,enabling the alloy to have a sustainable work-hardening capacity.We expect that this work will have implications in taking full advantage of the unique IHT of the LDED process to fabricate ME As with excellent metallurgical quality and mechanical performance.
基金supported by the National Natural Science Foundation of China(No.41972023)the Natural Science Foundation of Yunnan Province(No.202301AT070374)+1 种基金the Ten-thousand Talents Program of Yunnan Province(No.YNWR-QNBJ-2019-261)the West Light Foundation of the Chinese Academy of Sciences to Y.-J.Huang.
文摘Wildfire bears a close relationship with vegetation as its fuel source.The southeastern margin of the Tibetan Plateau witnesses frequent wildfires among various types of vegetation,whereas such wide in-teractions between wildfire and vegetation remain poorly studied from geological times.In this study,we reported a local fire using sedimentary macroscopic charcoals from the latest Miocene to early Pliocene of the Baoshan Basin in this region,and then inferred the local vegetation at the time of the fire event based chiefly on the coexistent fruit and seed fossil assemblage.Our taxonomic results show that the charcoal assemblage is probably dominated by broadleaved plants and the fruit and seed fossil assemblage is apparently dominated by Salix(Salicaceae)followed by Sambucus(Adoxaceae),suggesting a deciduous broadleaved forest in which the fire likely occurred.Under a seasonally dry climate associated with the Asian monsoon,this type of vegetation might be prone to natural fire,because in the wet rainy season the plants grew well to accumulate biofuel and in the dry season abundant ground litter resulting from leaf decay would be desiccated to become highly flammable.Due to the fire-tolerant habit of Salix as the dominant plant,the forest might be in return adapted to the fire event or even more fires that potentially followed.All these may suggest a close relationship between the fire event and the reconstructed vegetation.Our finding documents a new type of wildfire—vegetation interaction,namely the interaction between wildfire and deciduous broadleaved forest,from the geological past at the southeastern margin of the Tibetan Plateau.It therefore sheds new light on the wildfire history coupling vegetation change in the region.
基金work was supported by the National Thousand a Young Talents Program of China,the Fundamental Research Funds for the Central Universities(2018KFYXKJC009)the National Natural Science Foundation of China(51871076)the NSFC of Hubei(Grant 2021CFB420).
文摘Even in their bulk forms,complex alloys like high-entropy alloys(HEAs)exhibit favorable activity and stability as electrocatalysts for the oxygen evolution reaction(OER).However,the underlying reasons are not yet fully understood.In a family of Mo-doped CrFeCoNi-based HEAs,we have identified three crucial factors that govern their performance:(i)homogeneous solid solution phase of HEAs helps to maintain high-valence states of metals;(ii)surface reconstruction results in a hybrid material comprising amorphous domains and percolated crystalline structures;(iii)diversity of active intermediate species(M–O,M–OOH,and,notably,the abundance of superoxideμ–OO),which display stronger adsorption capacity on the reconstructed surface.These results are revealing due to their resemblance to findings in other families of electrocatalysts for OER,as well as their unique features specific to HEAs.In line with these factors,a CrFeCoNiMo0.2 bulk integrated electrode displays a low overpotential of 215 mV,rapid kinetics,and long-term stability of over 90 d.Bulk HEAs hold great potential for industrial applications.
基金financially supported by the National Natural Science Foundation of China (No.50904021)the Naural Science Foundation of the Education Department of Anhui Province (No.KJ2014A023)the Scientific Research Starting Foundation of Anhui Polytechnic University (No.2012YQQ006)
文摘The use of resistance spot welding（RSW）technology for joining Ti40Zr25Ni3Cu12Be20 metallic glass was investigated.The microstructure obtained from the welded BMG sample was studied.Joint without precipitates was prepared with welding current of 5.0 kA for 2cycles.A fully coupled thermal-electrical-mechanical finite element model（FEM） was developed to complement the experimental study.The simulated results agree well with the measurements.The effects of key process parameters such as welding current and welding time on the evolvement and microstructure of the weldment were determined and discussed.Moreover,the critical cooling rate for preserving the amorphous state in the weld fusion zone is determined to be approximately 1×10^3 K·s^-1.
基金the National Natural Science Foundation of China(Nos.52171154,52071118,51871076 and 51827801)the National Key Research and Development Program of China(No.2018YFB1105200)。
文摘Here,bulk CoCrFeMnNi high-entropy alloy was prepared via laser melting deposition,and its microstructure and mechanical properties at room and cryogenic temperature were investigated by a series of microstructural character-izations and mechanical tests.The results showed that the as-built samples possessed a single fcc phase and highly dense microstructures.Compared to the mechanical prop-erties at room temperature,tensile properties,microhard-ness and wear resistance of the as-built samples showed a signiflcant enhancement at cryogenic temperature,which was attributed to the deformation mechanism converting from dislocation slipping to deformation twinning at cryogenic temperature.The formation of deformation nanotwins signiflcantly improved the deformation resis-tance in cryogenic conditions,and the sliding wear in the liquid nitrogen could decrease the oxygen concentration,suppress the generation of oxide particles and thus enhance the wear resistance.
基金Item Sponsored by National Natural Science Foundation of China(51371065)Postdoctoral Science-Research Developmental Foundation of Heilongjiang Province of China(LBH-Q12073)
文摘The effect of electropulsing treatment（EPT）on the microstructure of a Ti-based bulk metallic glass（BMG）has been studied.The maximum current density applied during EPT can exert a crucial role on tuning the microstructure of the BMG.When the maximum current density is no more than 2 720A/mm^2,the samples retains amorphous nature,whereas,beyond that,crystalline phases precipitate from the glassy matrix.During EPT,the maximum temperature within the samples EPTed at the maximum current densities larger than 2 720A/mm^2 is higher than the crystallization temperature of the BMG,leading to the crystallization event.
文摘The morphology of double oxide film defects and their influence on the tensile mechanical properties of a commercial Cu-Al （C95800） alloy were investigated in this study. Plane castings were produced with two types of pouting systems, and their tensile properties were measured and then analyzed by means of Weibull statistics method. The fracture surfaces of the tensile specimens were examined using scanning electron microscopy equipped with energy-dispersive spectroscopy. A large amount of double oxide film defects were observed on the tensile fractured specimens of the topfilled plane castings, and their chemical composition is identified to be Al2O3. Weibull statistics analyses showed that the double oxide film defects significantly reduce mechanical properties of the castings investigated. Furthermore, the ultimate tensile strength is more obviously deteriorated by double oxide film defects than elongation.
基金The authors are grateful for the financial supports from the Defense Industrial Technology Development Program(No.JCKY2018407C008)the National Natural Science Foundation of China(NSFC)(Grant Nos.51304061 and 51474092)the NCST Science Fund for Distinguished Young Scholars(No.JQ201702).
文摘High-entropy alloys(HEAs)exhibit unique microstructural features and properties in nanoscale and atomic scale because of their multi-element alloy system.The nanoscratching behaviors of three HEAs with different phase constituents,relative to the microstructure and mechanical properties of the HEAs,were investigated.Three typical phase constituents were selected:face-centered cubic(FCC)structure,body-centered cubic(BCC)structure,and a dual-phase structure containing both FCC and BCC phases.Despite the fact that the FCC alloy has the highest ductility and strain hardening capability,it exhibited inferior scratch resistance due to the over-softening of hardness.Due to the brittle failure mode,the BCC alloy hardly exhibited desirable scratch resistance despite its highest hardness.By contrast,the nanostructured dual-phase alloy exhibited the best scratch resistance because of its good combination of strength and ductility,as well as the ductile failure mode.This research suggests that the HEA with structure comprising nanoscale hard and soft phases is desirable for nanoscratch resistance,and possesses appropriate hardness for industrial applications.
基金the financial support from the National Natural Science Foundation of China(Grant Nos.51371065,51671070,51671067,51671071)the Opening Funding of AWJ-16-Z02 in the State Key Laboratory of Advanced Welding and Joining,China
文摘Mciro-arc oxidation（MAO）was used to coat porous films on the surface of a Zr-based bulk metallic glass sample.The compressive test results indicated that,compared with the as-cast sample,the MAO treated one exhibited higher deformation capacity,associated with multiple shear bands with higher density on the side surface and well-developed vein patterns with smaller size on the fractured surface.The pore in the MAOed film and the matrix/coating interface initiated the shear bands and impeded the rapid propagation of shear bands,thus favoring the enhanced plasticity of the MAO treated sample.The obtained results demonstrated that MAO can be considered as an effective method to finely tune the mechanical performance of monolithic bulk metallic glasses.
