Although a new-class of heat pumps based on mechanically flexible nanoporous materials holds great poten-tial for the utilization of sustainable refrigerants with a considerably high coefficient of performance(COP),re...Although a new-class of heat pumps based on mechanically flexible nanoporous materials holds great poten-tial for the utilization of sustainable refrigerants with a considerably high coefficient of performance(COP),reducing their system volume remains a challenge.In this study,we explored the potential of this innovative type of heat pump in terms of COP and system volume.To broaden the scope of material exploration,we devised a new thermodynamic heat pump system applicable to soft mesoporous materials,in addition to the conventional system that is suitable only for flexible microporous materials.Several key factors have been identified through the comparison of various nanoporous materials and refrigerants.Our systematic investigation reveals that the combination of mechanically softer nanoporous materials with ammonia refrigerants can achieve a high COP and a reduced system volume.展开更多
Quasi-equiatomic Co Cr Fe Mn Ni high entropy alloy(HEA)has been in-situ alloyed by selective laser melting(SLM)from a blend of Co Cr Fe Ni pre-alloyed powder and Mn elemental powder.The blended powder shows good print...Quasi-equiatomic Co Cr Fe Mn Ni high entropy alloy(HEA)has been in-situ alloyed by selective laser melting(SLM)from a blend of Co Cr Fe Ni pre-alloyed powder and Mn elemental powder.The blended powder shows good printability with various SLM parameters and the as-built HEA samples achieve a reliable forming quality.Despite the slight evaporation of Mn,energy dispersive spectrometer mapping and Xray diffraction results show that the as-built HEA has a homogeneous chemical distribution and presents a single face-centred-cubic(fcc)phase,indicating successful in-situ alloying.The study has verified the feasibility of using blended powder to prepare high-quality HEA by SLM.展开更多
Ultra-high strength Al alloy system was developed by cryorolling and the contribution of various strengthening mechanisms to the overall yield strength of the system was evaluated. Cryorolling of Al-4%Cu-3%TiB2 in sit...Ultra-high strength Al alloy system was developed by cryorolling and the contribution of various strengthening mechanisms to the overall yield strength of the system was evaluated. Cryorolling of Al-4%Cu-3%TiB2 in situ composite followed by short annealing at 175 ℃ and ageing at 125℃ resulted in an ultra-high yield strength of about 800 MPa with 9%total elongation. The strengthening contributions form solid solution strengthening, grain refinement, dislocation strengthening, precipitation hardening and dispersion strengthening were evaluated using standard equations. It was estimated that the maximum contribution was from grain refinement due to cryorolling followed by precipitation and dispersion strengthening.展开更多
Silicon composite of nano-capsule type is newly applied as an active anode material for lithium ion batteries.TiO2-encapsulated silicon powders were synthesized by a sol-gel reaction with titanium ethoxide.Silicon nan...Silicon composite of nano-capsule type is newly applied as an active anode material for lithium ion batteries.TiO2-encapsulated silicon powders were synthesized by a sol-gel reaction with titanium ethoxide.Silicon nanoparticles were successfully embedded into porous titanium oxide capsules that played as a buffer layer against drastic volume changes of silicon during the charge-discharge cycling,consequently leading to the retardation of the capacity fading of intrinsic silicon materials.The electrochemical and structural properties of silicon nanocomposites with different surface areas of encapsulating TiO2 layer were characterized by X-ray diffraction(XRD),nitrogen gas adsorption analysis by the Brunauer-Emmett-Teller(BET) equation,transmission electron microscopy(TEM),and galvanostatic charge-discharge experiments.展开更多
In this work, the morphology, phase composition, and corrosion properties of microarc oxidized (MAO) gas tungsten arc (GTA) weldments of AZ31 alloy were investigated. Autogenous gas tungsten arc welds were made as ful...In this work, the morphology, phase composition, and corrosion properties of microarc oxidized (MAO) gas tungsten arc (GTA) weldments of AZ31 alloy were investigated. Autogenous gas tungsten arc welds were made as full penetration bead-on-plate welding under the alternating-current mode. A uniform oxide layer was developed on the surface of the specimens with MAO treatment in silicate-based alkaline electrolytes for different oxidation times. The corrosion behavior of the samples was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy. The oxide film improved the corrosion resistance substantially compared to the uncoated specimens. The sample coated for 10 min exhibited better corrosion properties. The corrosion resistance of the coatings was concluded to strongly depend on the morphology, whereas the phase composition and thickness were concluded to only slightly affect the corrosion resistance.展开更多
In-situ alloying has the potential to combine the compositional flexibility of high entropy alloys(HEAs)and the advanced forming capability of laser powder bed fusion(LPBF).This study fundamentally investigated the el...In-situ alloying has the potential to combine the compositional flexibility of high entropy alloys(HEAs)and the advanced forming capability of laser powder bed fusion(LPBF).This study fundamentally investigated the elemental homogenisation and grain development in the in-situ alloying process of CoCrFeMnNi HEA,by analysing the basic units,i.e.,tracks and layers,and introducing Mn as an alloying element to the base Co Cr Fe Ni HEA.Different modelling methods were employed to predict meltpool dimensions,and the results indicated the dependence of the modelling on practical meltpool modes.Delimitation of elemental distribution was found in keyhole meltpools since an intensive flow was generated due to recoil pressure.The homogeneity of in-situ alloyed Mn in single tracks was insufficient whether operated in conduction mode or keyhole mode,which required remelting from adjacent tracks and following layers to promote homogenisation significantly.The preferred orientation in single tracks along scanning directions changed from<001>to<101>as the scanning speed increased,although the cross-sections were similar in size with identical linear energy density.Such preference can be inherited during the printing process and lead to different textures in three-layer samples.It was also observed that applying hatch spacing smaller than a half meltpool width could coarsen the grains in a layer.The results from this study provide structure-parameter correlations for future microstructural tailoring and manipulation.展开更多
文摘Although a new-class of heat pumps based on mechanically flexible nanoporous materials holds great poten-tial for the utilization of sustainable refrigerants with a considerably high coefficient of performance(COP),reducing their system volume remains a challenge.In this study,we explored the potential of this innovative type of heat pump in terms of COP and system volume.To broaden the scope of material exploration,we devised a new thermodynamic heat pump system applicable to soft mesoporous materials,in addition to the conventional system that is suitable only for flexible microporous materials.Several key factors have been identified through the comparison of various nanoporous materials and refrigerants.Our systematic investigation reveals that the combination of mechanically softer nanoporous materials with ammonia refrigerants can achieve a high COP and a reduced system volume.
基金supported financially by the Shenzhen ScienceandTechnologyInnovationCommission(Nos.ZDSYS201703031748354 and JCYJ20170817110358927)the Science and Technology Planning Project of Guangdong Province of China(No.2017B090911003)the Natural Science Foundation of Guangdong Province(No.2016A030313756)。
文摘Quasi-equiatomic Co Cr Fe Mn Ni high entropy alloy(HEA)has been in-situ alloyed by selective laser melting(SLM)from a blend of Co Cr Fe Ni pre-alloyed powder and Mn elemental powder.The blended powder shows good printability with various SLM parameters and the as-built HEA samples achieve a reliable forming quality.Despite the slight evaporation of Mn,energy dispersive spectrometer mapping and Xray diffraction results show that the as-built HEA has a homogeneous chemical distribution and presents a single face-centred-cubic(fcc)phase,indicating successful in-situ alloying.The study has verified the feasibility of using blended powder to prepare high-quality HEA by SLM.
基金the Department of Science & Technology (DST) for their financial support for carrying out this research through Fast Track Scheme (DST Sanction No: SR/FT/ET-005/2008)Technical Education Quality Improvement Programme (TEQIP)
文摘Ultra-high strength Al alloy system was developed by cryorolling and the contribution of various strengthening mechanisms to the overall yield strength of the system was evaluated. Cryorolling of Al-4%Cu-3%TiB2 in situ composite followed by short annealing at 175 ℃ and ageing at 125℃ resulted in an ultra-high yield strength of about 800 MPa with 9%total elongation. The strengthening contributions form solid solution strengthening, grain refinement, dislocation strengthening, precipitation hardening and dispersion strengthening were evaluated using standard equations. It was estimated that the maximum contribution was from grain refinement due to cryorolling followed by precipitation and dispersion strengthening.
文摘Silicon composite of nano-capsule type is newly applied as an active anode material for lithium ion batteries.TiO2-encapsulated silicon powders were synthesized by a sol-gel reaction with titanium ethoxide.Silicon nanoparticles were successfully embedded into porous titanium oxide capsules that played as a buffer layer against drastic volume changes of silicon during the charge-discharge cycling,consequently leading to the retardation of the capacity fading of intrinsic silicon materials.The electrochemical and structural properties of silicon nanocomposites with different surface areas of encapsulating TiO2 layer were characterized by X-ray diffraction(XRD),nitrogen gas adsorption analysis by the Brunauer-Emmett-Teller(BET) equation,transmission electron microscopy(TEM),and galvanostatic charge-discharge experiments.
基金the Department of Metallurgical and Materials Engineering,National Institute of Technology,Tiruchirapalli for providing the funds and facilities to conduct this research work
文摘In this work, the morphology, phase composition, and corrosion properties of microarc oxidized (MAO) gas tungsten arc (GTA) weldments of AZ31 alloy were investigated. Autogenous gas tungsten arc welds were made as full penetration bead-on-plate welding under the alternating-current mode. A uniform oxide layer was developed on the surface of the specimens with MAO treatment in silicate-based alkaline electrolytes for different oxidation times. The corrosion behavior of the samples was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy. The oxide film improved the corrosion resistance substantially compared to the uncoated specimens. The sample coated for 10 min exhibited better corrosion properties. The corrosion resistance of the coatings was concluded to strongly depend on the morphology, whereas the phase composition and thickness were concluded to only slightly affect the corrosion resistance.
基金financially supported by the Research and Development Program Project in Key Areas of Guangdong Province(No.2019B090907001)the Shenzhen Science and Technology Innovation Commission(Nos.JCYJ20180504165824643 and JSGG20210420091802007)the National Natural Science Foundation of China(Nos.51971108 and U19A2085)。
文摘In-situ alloying has the potential to combine the compositional flexibility of high entropy alloys(HEAs)and the advanced forming capability of laser powder bed fusion(LPBF).This study fundamentally investigated the elemental homogenisation and grain development in the in-situ alloying process of CoCrFeMnNi HEA,by analysing the basic units,i.e.,tracks and layers,and introducing Mn as an alloying element to the base Co Cr Fe Ni HEA.Different modelling methods were employed to predict meltpool dimensions,and the results indicated the dependence of the modelling on practical meltpool modes.Delimitation of elemental distribution was found in keyhole meltpools since an intensive flow was generated due to recoil pressure.The homogeneity of in-situ alloyed Mn in single tracks was insufficient whether operated in conduction mode or keyhole mode,which required remelting from adjacent tracks and following layers to promote homogenisation significantly.The preferred orientation in single tracks along scanning directions changed from<001>to<101>as the scanning speed increased,although the cross-sections were similar in size with identical linear energy density.Such preference can be inherited during the printing process and lead to different textures in three-layer samples.It was also observed that applying hatch spacing smaller than a half meltpool width could coarsen the grains in a layer.The results from this study provide structure-parameter correlations for future microstructural tailoring and manipulation.
