First-principles calculations were performed to investigate the structures and energetics of {101n} coherent twin boundaries(CTBs) and glide twin boundaries(GTBs) in hexagonal close-packed(hcp) Ti. The formation mecha...First-principles calculations were performed to investigate the structures and energetics of {101n} coherent twin boundaries(CTBs) and glide twin boundaries(GTBs) in hexagonal close-packed(hcp) Ti. The formation mechanism of GTBs and their correlation with twin growth were fundamentally explored. Results suggested that GTBs can form from the gliding of CTBs, through their interaction with basal stacking fault. The gliding eventually restored the CTB structures by forming a pair of single-layer twinning disconnections. The pile-up of twinning disconnections should be responsible for the wide steps at twin boundaries as observed in high-resolution transmission electron microscopy, which can further promote twin growth. Possible effects of various alloying elements on pinning twin boundaries were also evaluated, to guide the strengthening design of Ti alloys.展开更多
The aim of this study was to examine and quantify the growth of extension twins and the associated texture change in an extruded AM30 magnesium alloy during compression along the extrusion direction. Three stages of t...The aim of this study was to examine and quantify the growth of extension twins and the associated texture change in an extruded AM30 magnesium alloy during compression along the extrusion direction. Three stages of twin growth with increasing strain were observed due to twin-dislocation interactions, together with increasing texture volume fraction of {1210}〈0001〉 and {01- 10}〈0001〉 components. Stage I was characterized by a relatively slow and gradually accelerating growth. A steady-state twin growth was reached in stage II, where the twin width increased linearly with increasing strain. Stage III twin growth became decelerated, exhibiting a plateau-like character.展开更多
An in situ ultrahigh-strength ductile Al50Sc50 bulk alloy is produced by the copper mold casting method with a composite microstructure of micron-/submicron-sized grains and nanoscale twins. According to the microstru...An in situ ultrahigh-strength ductile Al50Sc50 bulk alloy is produced by the copper mold casting method with a composite microstructure of micron-/submicron-sized grains and nanoscale twins. According to the microstruc- rural investigations, hierarchical nanotwinned lamellar AISc bundles with embedded micron-/submicron-sized AI2Sc and AISc2 are observed. The as-cast alloy displays a unique act of ultrahigh strength of -1.85 GPa to- gether with pronounced work hardening and a large plasticity of -14%. Further microstructural investigations on deformed specimens indicate that abundant hierarchical nanotwinned lamellar AISc bundles are effective to dissipate localization of shear stress or block dislocations from spreading throughout the alloy and hinder the propagation of mierocracks formed by local stress transition.展开更多
Rice with polyembryony characterized bytwin seedlings is a good genetic tool for apomixisresearch.A study on the effect of five plantgrowth regulators(IAA,KT,GA,2,4-D and6-BAP)on rate of twin seedlings in 3 rice varie...Rice with polyembryony characterized bytwin seedlings is a good genetic tool for apomixisresearch.A study on the effect of five plantgrowth regulators(IAA,KT,GA,2,4-D and6-BAP)on rate of twin seedlings in 3 rice varie.ties with polyembryony(Shuang 3,Shuang 13and Lu 52)was conducted.The results showed展开更多
装备测试性工程技术起源于20世纪80年代,是先进测试技术与系统工程紧密结合的产物。该技术经过40余年的发展逐渐成熟,在测试性需求分析与分配、测试性建模与方案优化设计、机内测试(Built⁃In Test,BIT)与自动测试系统(Automatic Test Sy...装备测试性工程技术起源于20世纪80年代,是先进测试技术与系统工程紧密结合的产物。该技术经过40余年的发展逐渐成熟,在测试性需求分析与分配、测试性建模与方案优化设计、机内测试(Built⁃In Test,BIT)与自动测试系统(Automatic Test System,ATS)设计、测试性试验与评估等方面形成了较完善的理论体系,并在各型装备中得到了普遍应用,取得了较大的军事和社会效益。今后测试性基础研究和应用探索究竟该如何开展,未来发展方向是怎样的,是亟需深入探讨的问题。在对测试性工程技术的产生背景与需求、概念与内涵、发展历程、关键技术现状与新进展进行剖析的基础上,指出了目前测试性工程技术研究存在的问题和今后研究突破的方向。展开更多
Martensites distributed along the austenite grain boundaries and twin boundaries have been examined in Fe-C,Fe-Ni-C and Fe-Cr-Mn-Mo-C alloys.The martensites may nucleate preferentially and grow easily along these boun...Martensites distributed along the austenite grain boundaries and twin boundaries have been examined in Fe-C,Fe-Ni-C and Fe-Cr-Mn-Mo-C alloys.The martensites may nucleate preferentially and grow easily along these boundaries.In the mixed martensites,the preferentially formed one is plate or butterfly martensite展开更多
The microstructure and mechanical properties of near-eutectic Al-12 Si alloys modified with 0-0.4% Nd（mass fraction） were investigated. The results indicate that a submicro- or nano-sized Al2 Nd phase is observed in...The microstructure and mechanical properties of near-eutectic Al-12 Si alloys modified with 0-0.4% Nd（mass fraction） were investigated. The results indicate that a submicro- or nano-sized Al2 Nd phase is observed in the modified alloy with 0.3% Nd. The morphology of the α（Al） phase is significantly refined in the Nd-modified alloys. The primary Si morphology simultaneously changes into a fine, particle-like morphology, and the morphology of eutectic Si becomes fine-fibrous instead of coarse-acicular. Relatively few growth twins are observed on the surface of the Si plate in the Al-12Si-0.3Nd alloy at the optimal modification level. The mechanical property test results confirm that the mechanical properties of the as-cast Al-12 Si alloys are enhanced after the Nd addition, with optimal ultimate tensile strength（UTS） of 252 MPa and elongation（EL） of 13% at an Nd content of 0.3%. The improved mechanical properties are attributed to the refined morphology of Si phase and the formation of the Al2 Nd phase.展开更多
基金the financial support from the National MCF Energy R&D Program of China (2018YFE0306100)the National Natural Science Foundation of China (51971249)the State Key Laboratory for Powder Metallurgy,Central South University,Changsha,China
文摘First-principles calculations were performed to investigate the structures and energetics of {101n} coherent twin boundaries(CTBs) and glide twin boundaries(GTBs) in hexagonal close-packed(hcp) Ti. The formation mechanism of GTBs and their correlation with twin growth were fundamentally explored. Results suggested that GTBs can form from the gliding of CTBs, through their interaction with basal stacking fault. The gliding eventually restored the CTB structures by forming a pair of single-layer twinning disconnections. The pile-up of twinning disconnections should be responsible for the wide steps at twin boundaries as observed in high-resolution transmission electron microscopy, which can further promote twin growth. Possible effects of various alloying elements on pinning twin boundaries were also evaluated, to guide the strengthening design of Ti alloys.
基金the Natural Sciences and Engineering Research Council of Canada(NSERC)AUTO21 Networks of Centres of Excellence of Canada for providing financial support
文摘The aim of this study was to examine and quantify the growth of extension twins and the associated texture change in an extruded AM30 magnesium alloy during compression along the extrusion direction. Three stages of twin growth with increasing strain were observed due to twin-dislocation interactions, together with increasing texture volume fraction of {1210}〈0001〉 and {01- 10}〈0001〉 components. Stage I was characterized by a relatively slow and gradually accelerating growth. A steady-state twin growth was reached in stage II, where the twin width increased linearly with increasing strain. Stage III twin growth became decelerated, exhibiting a plateau-like character.
基金Supported by the Scientific Research Foundation of Xi’an University of Technology under Grant No 101-451115007the National Basic Research Program of China under Grant No 2007CB613900+1 种基金the National Natural Science Foundation of China under Grant No 51174161the Pivot Innovation Team of Shaanxi Electric Materials and Infiltration Technique under Grant No 2012KCT-25
文摘An in situ ultrahigh-strength ductile Al50Sc50 bulk alloy is produced by the copper mold casting method with a composite microstructure of micron-/submicron-sized grains and nanoscale twins. According to the microstruc- rural investigations, hierarchical nanotwinned lamellar AISc bundles with embedded micron-/submicron-sized AI2Sc and AISc2 are observed. The as-cast alloy displays a unique act of ultrahigh strength of -1.85 GPa to- gether with pronounced work hardening and a large plasticity of -14%. Further microstructural investigations on deformed specimens indicate that abundant hierarchical nanotwinned lamellar AISc bundles are effective to dissipate localization of shear stress or block dislocations from spreading throughout the alloy and hinder the propagation of mierocracks formed by local stress transition.
文摘Rice with polyembryony characterized bytwin seedlings is a good genetic tool for apomixisresearch.A study on the effect of five plantgrowth regulators(IAA,KT,GA,2,4-D and6-BAP)on rate of twin seedlings in 3 rice varie.ties with polyembryony(Shuang 3,Shuang 13and Lu 52)was conducted.The results showed
文摘装备测试性工程技术起源于20世纪80年代,是先进测试技术与系统工程紧密结合的产物。该技术经过40余年的发展逐渐成熟,在测试性需求分析与分配、测试性建模与方案优化设计、机内测试(Built⁃In Test,BIT)与自动测试系统(Automatic Test System,ATS)设计、测试性试验与评估等方面形成了较完善的理论体系,并在各型装备中得到了普遍应用,取得了较大的军事和社会效益。今后测试性基础研究和应用探索究竟该如何开展,未来发展方向是怎样的,是亟需深入探讨的问题。在对测试性工程技术的产生背景与需求、概念与内涵、发展历程、关键技术现状与新进展进行剖析的基础上,指出了目前测试性工程技术研究存在的问题和今后研究突破的方向。
文摘Martensites distributed along the austenite grain boundaries and twin boundaries have been examined in Fe-C,Fe-Ni-C and Fe-Cr-Mn-Mo-C alloys.The martensites may nucleate preferentially and grow easily along these boundaries.In the mixed martensites,the preferentially formed one is plate or butterfly martensite
基金Projects(5140521651165032)supported by the National Natural Science Foundation of China+3 种基金Project(20151BAB216018)supported by the Natural Science Foundation of Jiangxi ProvinceChinaProject(GJJ14200)supported by the Education Commission Foundation of Jiangxi ProvinceChina
文摘The microstructure and mechanical properties of near-eutectic Al-12 Si alloys modified with 0-0.4% Nd（mass fraction） were investigated. The results indicate that a submicro- or nano-sized Al2 Nd phase is observed in the modified alloy with 0.3% Nd. The morphology of the α（Al） phase is significantly refined in the Nd-modified alloys. The primary Si morphology simultaneously changes into a fine, particle-like morphology, and the morphology of eutectic Si becomes fine-fibrous instead of coarse-acicular. Relatively few growth twins are observed on the surface of the Si plate in the Al-12Si-0.3Nd alloy at the optimal modification level. The mechanical property test results confirm that the mechanical properties of the as-cast Al-12 Si alloys are enhanced after the Nd addition, with optimal ultimate tensile strength（UTS） of 252 MPa and elongation（EL） of 13% at an Nd content of 0.3%. The improved mechanical properties are attributed to the refined morphology of Si phase and the formation of the Al2 Nd phase.
