We produced a 316 L stainless steel with heterogeneous nanometer-thick lamellar structures by severe cold-rolling at room temperature,and conducted micro-scale tensile tests in different orientations to evaluate both ...We produced a 316 L stainless steel with heterogeneous nanometer-thick lamellar structures by severe cold-rolling at room temperature,and conducted micro-scale tensile tests in different orientations to evaluate both the inplane(parallel to the nano-lamellae)and out-of-plane(normal and 45inclined to the nano-lamellae)mechanical anisotropy.The parallel orientation demonstrates the greatest tensile strength while the inclined orientation exhibits the least strength.The tensile tests in normal and inclined directions also indicate significant transient elastic-plastic response due to the strain path change.Fractographic examination demonstrates that the specimen fails in the normal direction by premature micro-void nucleation and growth,which restricts its tensile strength;however,we identified zig-zag cracking associated with lamellar shear cracking in the inclined direction.展开更多
The perfect single crystal has ultra-high strength but is often accompanied by catastrophic failures after yielding.This study reveals that nano-lamellar TiAl single crystals alleviate the catastrophic failure due to ...The perfect single crystal has ultra-high strength but is often accompanied by catastrophic failures after yielding.This study reveals that nano-lamellar TiAl single crystals alleviate the catastrophic failure due to a post-yielding dislocation retraction through atomistic simulations and theoretical analyses.This dislocation retraction leads to a retained post-yielding strength of1.03 to 2.33 GPa(about 50%of the yielding strength).It is shown that this dislocation retraction is caused by local stress relaxation and interface-mediated image force.The local stress relaxation is due to successive dislocation nucleation in different slip systems,and the interface-mediated image force is caused by the heterogeneous interface.Based on dislocation theory,this study demonstrates that the size effect also plays a vital role in dislocation retraction.Theoretical modeling shows that the dislocation retraction occurs when the lamellar thickness is less than approximately 12 nm.Additionally,the post-yielding dislocation retraction is more pronounced at higher temperatures,making it more effective in alleviating catastrophic failures.These findings demonstrate a viable option for avoiding catastrophic failure of single crystals through nanoscale-lamellar design.展开更多
Accumulative roll bonded （ARB） Copper Niobium （Cu-Nb） nano-lamellar composite （NLC） panels were friction stir welded （FSWed） to evaluate the ability to join panels while retaining the nano-lamellar structure. ...Accumulative roll bonded （ARB） Copper Niobium （Cu-Nb） nano-lamellar composite （NLC） panels were friction stir welded （FSWed） to evaluate the ability to join panels while retaining the nano-lamellar structure. During a single pass of the friction stir welding （FSW） process, the nano-lamellar structure of the parent material （PM） was retained but was observed to fragment into equiaxed grains during the second pass. FSW has been modeled as a severe deformation process in which the material is subjected to an instantaneous high shear strain rate followed by extreme shear strains. The loss of the nano-lamellar layers was attributed to the increased strain and longer time at temperature resulting from the second pass of the FSW process. Kinematic modeling was used to predict the global average shear strain and shear strain rates experienced by the ARB material during the FSW process. The results of this study indicate that through careful selection of FSW parameters, the nano-lamellar structure and its associated higher strength can be maintained using FSW to join ARB NLC panels.展开更多
In order to provide ultraviolet barrier, antifungal and antibacterial properties, nano-zinc oxide (ZnO) was added to lamellar zirconium phosphate (ZrP). The phosphate was synthesized via reaction of zirconium oxychlor...In order to provide ultraviolet barrier, antifungal and antibacterial properties, nano-zinc oxide (ZnO) was added to lamellar zirconium phosphate (ZrP). The phosphate was synthesized via reaction of zirconium oxychloride octahydrate and phosphoric acid following its chemical modification with Jeffamine and nano-ZnO. Diffractometric, morphological, thermal, structural and relaxometric evaluations were conducted. Fourier transform infrared spectroscopy (FTIR) revealed increase of the area between 4000 - 3000 cm<sup>-1</sup> due to the formation of ionic specie PO? <sup>+</sup>NH<sub>3</sub>-[C-(H)(CH<sub>3</sub>)-CH<sub>2</sub>-O-(C-(H)(CH<sub>3</sub>)-CH<sub>2</sub>-O)<sub>8</sub>-(CH<sub>2</sub>-CH<sub>2</sub>-O-CH<sub>3</sub>)] and nano-ZnO particles. Wide-angle X-ray diffraction indicated that intercalation of Jeffamine was successful. Thermogravimetry confirmed that nano-ZnO particle forced the expulsion of Jeffamine outside ZrP galleries. Scanning electron microscopy evidenced the Jeffamine intercalation and sample heterogeneity. Hydrogen molecular relaxation indicated the increase of molecular rigidity owing to the formation of ionic specie and the addition of nano-ZnO particles. It was postulated that a multifunctional and miscellaneous material constituted by as prepared ZrP, some delaminated ZrP platelets and nano-ZnO particles was achieved. The material has potential for usage as filler in polymeric composites.展开更多
基金financial support from the National Key R&D Program of China(Grant No.2017YFA0204403)financial support by the National Natural Science Foundation of China(Grant No.51931010,51601196 and U1608257)+2 种基金the Liaoning Revitalization Talents Program(Grant No.XLYC1802026)the Key Research Program of Frontier Science,Chinese Academy of Sciencesthe financial support of the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX180408).
文摘We produced a 316 L stainless steel with heterogeneous nanometer-thick lamellar structures by severe cold-rolling at room temperature,and conducted micro-scale tensile tests in different orientations to evaluate both the inplane(parallel to the nano-lamellae)and out-of-plane(normal and 45inclined to the nano-lamellae)mechanical anisotropy.The parallel orientation demonstrates the greatest tensile strength while the inclined orientation exhibits the least strength.The tensile tests in normal and inclined directions also indicate significant transient elastic-plastic response due to the strain path change.Fractographic examination demonstrates that the specimen fails in the normal direction by premature micro-void nucleation and growth,which restricts its tensile strength;however,we identified zig-zag cracking associated with lamellar shear cracking in the inclined direction.
基金supported by the National Key Research and Development Program of China(Grant No.2019YFA0705400)the National Natural Science Foundation of China(Grant No.51535005)+2 种基金the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Grant No.MCMS-I-0419K01)the Fundamental Research Funds for the Central Universities(Grant Nos.NJ2020003,and NZ2020001)a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘The perfect single crystal has ultra-high strength but is often accompanied by catastrophic failures after yielding.This study reveals that nano-lamellar TiAl single crystals alleviate the catastrophic failure due to a post-yielding dislocation retraction through atomistic simulations and theoretical analyses.This dislocation retraction leads to a retained post-yielding strength of1.03 to 2.33 GPa(about 50%of the yielding strength).It is shown that this dislocation retraction is caused by local stress relaxation and interface-mediated image force.The local stress relaxation is due to successive dislocation nucleation in different slip systems,and the interface-mediated image force is caused by the heterogeneous interface.Based on dislocation theory,this study demonstrates that the size effect also plays a vital role in dislocation retraction.Theoretical modeling shows that the dislocation retraction occurs when the lamellar thickness is less than approximately 12 nm.Additionally,the post-yielding dislocation retraction is more pronounced at higher temperatures,making it more effective in alleviating catastrophic failures.These findings demonstrate a viable option for avoiding catastrophic failure of single crystals through nanoscale-lamellar design.
基金supported by the Los Alamos National Laboratory Directed Research and Development (LDRD) project 20130764ECR
文摘Accumulative roll bonded （ARB） Copper Niobium （Cu-Nb） nano-lamellar composite （NLC） panels were friction stir welded （FSWed） to evaluate the ability to join panels while retaining the nano-lamellar structure. During a single pass of the friction stir welding （FSW） process, the nano-lamellar structure of the parent material （PM） was retained but was observed to fragment into equiaxed grains during the second pass. FSW has been modeled as a severe deformation process in which the material is subjected to an instantaneous high shear strain rate followed by extreme shear strains. The loss of the nano-lamellar layers was attributed to the increased strain and longer time at temperature resulting from the second pass of the FSW process. Kinematic modeling was used to predict the global average shear strain and shear strain rates experienced by the ARB material during the FSW process. The results of this study indicate that through careful selection of FSW parameters, the nano-lamellar structure and its associated higher strength can be maintained using FSW to join ARB NLC panels.
文摘In order to provide ultraviolet barrier, antifungal and antibacterial properties, nano-zinc oxide (ZnO) was added to lamellar zirconium phosphate (ZrP). The phosphate was synthesized via reaction of zirconium oxychloride octahydrate and phosphoric acid following its chemical modification with Jeffamine and nano-ZnO. Diffractometric, morphological, thermal, structural and relaxometric evaluations were conducted. Fourier transform infrared spectroscopy (FTIR) revealed increase of the area between 4000 - 3000 cm<sup>-1</sup> due to the formation of ionic specie PO? <sup>+</sup>NH<sub>3</sub>-[C-(H)(CH<sub>3</sub>)-CH<sub>2</sub>-O-(C-(H)(CH<sub>3</sub>)-CH<sub>2</sub>-O)<sub>8</sub>-(CH<sub>2</sub>-CH<sub>2</sub>-O-CH<sub>3</sub>)] and nano-ZnO particles. Wide-angle X-ray diffraction indicated that intercalation of Jeffamine was successful. Thermogravimetry confirmed that nano-ZnO particle forced the expulsion of Jeffamine outside ZrP galleries. Scanning electron microscopy evidenced the Jeffamine intercalation and sample heterogeneity. Hydrogen molecular relaxation indicated the increase of molecular rigidity owing to the formation of ionic specie and the addition of nano-ZnO particles. It was postulated that a multifunctional and miscellaneous material constituted by as prepared ZrP, some delaminated ZrP platelets and nano-ZnO particles was achieved. The material has potential for usage as filler in polymeric composites.
