The effect of grain size of primary α phase on the bonding interface characteristic and shear strength of bond was investigated in the press bonding of Ti-6Al-4V alloy. The quantitative results show that the average ...The effect of grain size of primary α phase on the bonding interface characteristic and shear strength of bond was investigated in the press bonding of Ti-6Al-4V alloy. The quantitative results show that the average size of voids increases from 0.8 to 2.6 μm and the bonding ratio decreases from 90.9% to 77.8% with an increase in grain size of primary α phase from 8.2 to 16.4 μm. The shape of voids changes from the tiny round to the irregular strip. The highest shear strength of bond can be obtained in the Ti-6Al-4V alloy with a grain size of 8.2 μm. This is contributed to the higher ability of plastic flow and more short-paths for diffusion in the alloy with smaller grain size of primary α phase, which promote the void closure process and the formation of α/β grains across bonding interface.展开更多
Laser cladding deposited Ti-6Al-4V titanium alloy universally shows more complex microstructures,each of which has significant effect on mechanical properties. Of particular α/β interface phase has been observed in ...Laser cladding deposited Ti-6Al-4V titanium alloy universally shows more complex microstructures,each of which has significant effect on mechanical properties. Of particular α/β interface phase has been observed in this paper under certain conditions. It demonstrates that the influence of the α/β interface phase on the tensile properties is closely associated with dislocations and twin substructure through comparison experiments. The results show that the α/β interface phase hinders dislocation motion and decreases effective slip length. In addition, the twin substructure has been activated in the α/β interface phase during tensile process and has acted somehow like grain boundaries. Therefore, the strength and the work-hardening rate of the laser cladding deposited Ti-6Al-4V titanium alloy have been significantly improved due to the dynamic Hall-Petch effect. Besides, the α/β interface phase leads to more uniform dislocations distribution, which implies that relative lower local concentrated stress will be produced along the α/β interface phase or colony boundary after the same amount of plastic deformation. Moreover,the twinning-induced plasticity effects in the α/β interface phase further increase the plastic deformation capacity. These results in higher elongation for the laser cladding deposited Ti-6Al-4V titanium alloy.It can be concluded that the current work suggests an effective method to simultaneously improve the strength and plasticity of laser cladding deposited Ti-6Al-4V titanium alloy based on the α/β interface phase.展开更多
To better understand the strengthening mechanism of in-situ formed TiB reinforcements in dual-phase Ti6 Al4 V alloy,the interface characters and properties ofα-Ti/β-Ti/TiB system were thoroughly investigated with th...To better understand the strengthening mechanism of in-situ formed TiB reinforcements in dual-phase Ti6 Al4 V alloy,the interface characters and properties ofα-Ti/β-Ti/TiB system were thoroughly investigated with the combined use of high-resolution transmission electron microscopy(HRTEM),abinitio calculations,and indentation tests.The ab-initio calculations suggest that the highly coherent(100)_(TiB)/(121)_(β-Ti)phase boundary(PB)has fairly low interface energy of 0.082 J/m^(2)with an exceptionally high adhesion strength of 6.04 J/m^(2),owing to the formation of strong interfacial Ti–B ionic bonds.The semi-coherent(201)_(TiB)/(0001)_(α-Ti)interface shows a relatively higher interface energy of 1.442 J/m^(2)but still with a fairly high adhesion strength of 4.95 J/m^(2).With the obtained interfacial energetics,thermodynamics analyses were further carried out to explore the nucleation mechanism ofα-Ti in TiB reinforced Ti6Al4V composite.Superior to the heterogeneous nucleation at TiB/β-Ti interface,the homogeneous nucleation ofα-Ti within theβ-Ti phase can be more energy-preferred,due to its lower nucleation energy barrier and critical radius.Further indentation tests under various loads of different modes confirmed a remarkably enhanced load-bearing capacity of dual-phase Ti6Al4V alloys,under the critical significance of the strong interfacial bonding achieved by reinforcements of in-situ formed TiB.展开更多
The Richtmyer-Meshkov instability ofa ‘V＇ shaped air/helium gaseous interface subjected to a weak shock wave is experimentally studied. A soap film technique is adopted to create a ‘V＇ shaped interface with accura...The Richtmyer-Meshkov instability ofa ‘V＇ shaped air/helium gaseous interface subjected to a weak shock wave is experimentally studied. A soap film technique is adopted to create a ‘V＇ shaped interface with accurate initial conditions. Five kinds of ‘V＇ shaped interfaces with different vertex angles are formed to highlight the effects of initial conditions on the flow characteristics. The results show that a spike is generated after the shock impact, and grows constantly with time. As the vertex angle increases, vortices generated on the interface become less noticeable, and the spike develops less pronouncedly. The linear growth rate of interface width after compression phase is estimated by a linear model and a revised linear model, and the latter is proven to be more effective for the interface with high initial amplitudes. The linear growth rate of interface width is, for the first time in a heavy/light interface configuration, found to be a non-monotonous function of the initial perturbation amplitude-wavelength ratio.展开更多
In this paper,the interface states of the AlGaN/GaN metal–insulator–semiconductor(MIS)high electron mobility transistors(HEMTs)with an Al2 O3 gate dielectric are systematically evaluated.By frequency-dependent capac...In this paper,the interface states of the AlGaN/GaN metal–insulator–semiconductor(MIS)high electron mobility transistors(HEMTs)with an Al2 O3 gate dielectric are systematically evaluated.By frequency-dependent capacitance and conductance measurements,trap density and time constant at Al2 O3/AlGaN and AlGaN/GaN interface are determined.The experimental results reveal that the density of trap states and the activation energy at the Al2 O3/AlGaN interface are much higher than at the AlGaN/GaN interface.The photo-assisted capacitance-voltage measurements are performed to characterize the deep-level traps located near mid-gap at the Al2 O3/AlGaN interface,which indicates that a density of deep-level traps is lower than the density of the shallow-level states.展开更多
The effects of vanadium(V)on the microstructures and mechanical properties of the TiC cermet fusion welding interface were studied by adjusting the content of V in the self-developed flux-cored wires using metal inert...The effects of vanadium(V)on the microstructures and mechanical properties of the TiC cermet fusion welding interface were studied by adjusting the content of V in the self-developed flux-cored wires using metal inert gas arc(MIG)welding for surfacing on the TiC cermet.The results show that the increase in V content promotes the element diffusion between TiC cermet and weld metal.There are no de-fects observed in the interface,and the diffusion of elements refers to excellent metallurgical bonding.The shear strength of the fusion zone initially decreases and then increases with the increase in V content.The maximum shear strength of the TiC cermet/weld interface,reaching 552 MPa,occurred when the V content reached 0.65%.Meanwhile,the average hardness in the transition zone reached 488.2 HV0.2.展开更多
The methods for reducing interface aperture inconsistency are studied in NC orbital milling(NCOM)of CFRP/Ti6Al4V laminates with coarse pitch.Comparative experiments show burr,aperture inconsistency and error are typic...The methods for reducing interface aperture inconsistency are studied in NC orbital milling(NCOM)of CFRP/Ti6Al4V laminates with coarse pitch.Comparative experiments show burr,aperture inconsistency and error are typical interface defects.Meanwhile,aperture inconsistency and error are more serious than burr in NCOM with coarse pitch.As one of the major causes of interface defects,axial force and radial force are intensively studied.Based upon the machining principle of orbital milling(OM)and the actual hole-making condition in laminated structures,NCOM experiments with coarse pitch are conducted on CFRP/Ti6Al4V laminates under different cutting conditions.Then,the effects of interlayer clamping,minimal quantity lubrication(MQL),twice milling instead of reaming,and interlayer speed change on interface aperture are analyzed.Research shows that interlayer clamping,interlayer speed change and MQL can effectively reduce out-of-tolerance of interface aperture.When making holes of different diameters with one cutter,axial feed has a greater effect on interface aperture precision than tangential feed.When making holes of the same diameter with different cutters,small diameter cutter will reduce interface aperture precision in a single processing.But the method of“twice milling instead of reaming”can improve the aperture precision effectively.展开更多
This paper focuses on the direct current-alternating current （DC-AC） interfaced microsource based H∞ robust control strategies in microgrids. It presents detail of a DC-AC interfaced microsource model which is conn...This paper focuses on the direct current-alternating current （DC-AC） interfaced microsource based H∞ robust control strategies in microgrids. It presents detail of a DC-AC interfaced microsource model which is connected to the power grid through a controllable switch. A double loop current-regulated voltage control scheme for the DC-AC interface is designed. In the case of the load disturbance and the model uncertainties, the inner voltage and current loop are produced based on the H∞ robust control strategies. The outer power loop uses the droop characteristic controller. Finally, the scheme is simulated using the Matlab/Simulink. The simulation results demonstrate that DC-AC interfaced microsource system can supply high quality power. Also, the proposed control scheme can make the system switch smoothly between the isolated mode and grid-connected mode. 更多展开更多
基金Project(2014M562447) supported by the China Postdoctoral Science FoundationProject(51275416) supported by the National Natural Science Foundation of China+1 种基金Project(BP201503) supported by the Research Fund of the State Key Laboratory of Solidification Processing(NWPU)China
文摘The effect of grain size of primary α phase on the bonding interface characteristic and shear strength of bond was investigated in the press bonding of Ti-6Al-4V alloy. The quantitative results show that the average size of voids increases from 0.8 to 2.6 μm and the bonding ratio decreases from 90.9% to 77.8% with an increase in grain size of primary α phase from 8.2 to 16.4 μm. The shape of voids changes from the tiny round to the irregular strip. The highest shear strength of bond can be obtained in the Ti-6Al-4V alloy with a grain size of 8.2 μm. This is contributed to the higher ability of plastic flow and more short-paths for diffusion in the alloy with smaller grain size of primary α phase, which promote the void closure process and the formation of α/β grains across bonding interface.
基金supported by the National Key Research And Development Plan, China (No. 2016YFB1100100)the Research Fund of the State Key Laboratory of Solidification Processing (NWPU), China (No. KP201611)the National Natural Science Foundation of China (No. 51475380)
文摘Laser cladding deposited Ti-6Al-4V titanium alloy universally shows more complex microstructures,each of which has significant effect on mechanical properties. Of particular α/β interface phase has been observed in this paper under certain conditions. It demonstrates that the influence of the α/β interface phase on the tensile properties is closely associated with dislocations and twin substructure through comparison experiments. The results show that the α/β interface phase hinders dislocation motion and decreases effective slip length. In addition, the twin substructure has been activated in the α/β interface phase during tensile process and has acted somehow like grain boundaries. Therefore, the strength and the work-hardening rate of the laser cladding deposited Ti-6Al-4V titanium alloy have been significantly improved due to the dynamic Hall-Petch effect. Besides, the α/β interface phase leads to more uniform dislocations distribution, which implies that relative lower local concentrated stress will be produced along the α/β interface phase or colony boundary after the same amount of plastic deformation. Moreover,the twinning-induced plasticity effects in the α/β interface phase further increase the plastic deformation capacity. These results in higher elongation for the laser cladding deposited Ti-6Al-4V titanium alloy.It can be concluded that the current work suggests an effective method to simultaneously improve the strength and plasticity of laser cladding deposited Ti-6Al-4V titanium alloy based on the α/β interface phase.
基金financially supported by National Key R&D Program of China(No.2021YFB3701203)the National Natural Science Foundation of China(NSFC)under the Grant Nos.52171137,51731009,and 52071116+2 种基金Heilongjiang Postdoctoral Fund(No.LBHZ20058)Heilongjiang Provincial Natural Science Foundation of China(No.TD2020E001)Key-Area Research and Development Program of Guang Dong Province(No.2019B010942001)。
文摘To better understand the strengthening mechanism of in-situ formed TiB reinforcements in dual-phase Ti6 Al4 V alloy,the interface characters and properties ofα-Ti/β-Ti/TiB system were thoroughly investigated with the combined use of high-resolution transmission electron microscopy(HRTEM),abinitio calculations,and indentation tests.The ab-initio calculations suggest that the highly coherent(100)_(TiB)/(121)_(β-Ti)phase boundary(PB)has fairly low interface energy of 0.082 J/m^(2)with an exceptionally high adhesion strength of 6.04 J/m^(2),owing to the formation of strong interfacial Ti–B ionic bonds.The semi-coherent(201)_(TiB)/(0001)_(α-Ti)interface shows a relatively higher interface energy of 1.442 J/m^(2)but still with a fairly high adhesion strength of 4.95 J/m^(2).With the obtained interfacial energetics,thermodynamics analyses were further carried out to explore the nucleation mechanism ofα-Ti in TiB reinforced Ti6Al4V composite.Superior to the heterogeneous nucleation at TiB/β-Ti interface,the homogeneous nucleation ofα-Ti within theβ-Ti phase can be more energy-preferred,due to its lower nucleation energy barrier and critical radius.Further indentation tests under various loads of different modes confirmed a remarkably enhanced load-bearing capacity of dual-phase Ti6Al4V alloys,under the critical significance of the strong interfacial bonding achieved by reinforcements of in-situ formed TiB.
基金supported by the National Natural Science Foundation of China(U1530103,11302219,and 11272308)
文摘The Richtmyer-Meshkov instability ofa ‘V＇ shaped air/helium gaseous interface subjected to a weak shock wave is experimentally studied. A soap film technique is adopted to create a ‘V＇ shaped interface with accurate initial conditions. Five kinds of ‘V＇ shaped interfaces with different vertex angles are formed to highlight the effects of initial conditions on the flow characteristics. The results show that a spike is generated after the shock impact, and grows constantly with time. As the vertex angle increases, vortices generated on the interface become less noticeable, and the spike develops less pronouncedly. The linear growth rate of interface width after compression phase is estimated by a linear model and a revised linear model, and the latter is proven to be more effective for the interface with high initial amplitudes. The linear growth rate of interface width is, for the first time in a heavy/light interface configuration, found to be a non-monotonous function of the initial perturbation amplitude-wavelength ratio.
基金Project supported by the Key Program of National Natural Science Foundation of China(Grant Nos.61334002 and 61634005)the National Natural Science Foundation of China(Grant Nos.61604114 and 61704124)
文摘In this paper,the interface states of the AlGaN/GaN metal–insulator–semiconductor(MIS)high electron mobility transistors(HEMTs)with an Al2 O3 gate dielectric are systematically evaluated.By frequency-dependent capacitance and conductance measurements,trap density and time constant at Al2 O3/AlGaN and AlGaN/GaN interface are determined.The experimental results reveal that the density of trap states and the activation energy at the Al2 O3/AlGaN interface are much higher than at the AlGaN/GaN interface.The photo-assisted capacitance-voltage measurements are performed to characterize the deep-level traps located near mid-gap at the Al2 O3/AlGaN interface,which indicates that a density of deep-level traps is lower than the density of the shallow-level states.
基金supported by Henan Province Key Research and Development and Promotion Project(Grant No.201ZP20220010).
文摘The effects of vanadium(V)on the microstructures and mechanical properties of the TiC cermet fusion welding interface were studied by adjusting the content of V in the self-developed flux-cored wires using metal inert gas arc(MIG)welding for surfacing on the TiC cermet.The results show that the increase in V content promotes the element diffusion between TiC cermet and weld metal.There are no de-fects observed in the interface,and the diffusion of elements refers to excellent metallurgical bonding.The shear strength of the fusion zone initially decreases and then increases with the increase in V content.The maximum shear strength of the TiC cermet/weld interface,reaching 552 MPa,occurred when the V content reached 0.65%.Meanwhile,the average hardness in the transition zone reached 488.2 HV0.2.
基金Natural Science Research in Jiangsu Province(No.17KJB460008)the 333 Project Research Funding Project in Jiangsu Province(No.BRA2018310)the Innovation Project of Jiangsu Province.
文摘The methods for reducing interface aperture inconsistency are studied in NC orbital milling(NCOM)of CFRP/Ti6Al4V laminates with coarse pitch.Comparative experiments show burr,aperture inconsistency and error are typical interface defects.Meanwhile,aperture inconsistency and error are more serious than burr in NCOM with coarse pitch.As one of the major causes of interface defects,axial force and radial force are intensively studied.Based upon the machining principle of orbital milling(OM)and the actual hole-making condition in laminated structures,NCOM experiments with coarse pitch are conducted on CFRP/Ti6Al4V laminates under different cutting conditions.Then,the effects of interlayer clamping,minimal quantity lubrication(MQL),twice milling instead of reaming,and interlayer speed change on interface aperture are analyzed.Research shows that interlayer clamping,interlayer speed change and MQL can effectively reduce out-of-tolerance of interface aperture.When making holes of different diameters with one cutter,axial feed has a greater effect on interface aperture precision than tangential feed.When making holes of the same diameter with different cutters,small diameter cutter will reduce interface aperture precision in a single processing.But the method of“twice milling instead of reaming”can improve the aperture precision effectively.
基金supported by National Natural Science Foundation of China(No. 51177142)China Postdoctoral Science Foundation(Nos.2012T50019 and 20110490210)Hebei Provincial Natural Science Foundation of China(No.F2012203063)
文摘This paper focuses on the direct current-alternating current （DC-AC） interfaced microsource based H∞ robust control strategies in microgrids. It presents detail of a DC-AC interfaced microsource model which is connected to the power grid through a controllable switch. A double loop current-regulated voltage control scheme for the DC-AC interface is designed. In the case of the load disturbance and the model uncertainties, the inner voltage and current loop are produced based on the H∞ robust control strategies. The outer power loop uses the droop characteristic controller. Finally, the scheme is simulated using the Matlab/Simulink. The simulation results demonstrate that DC-AC interfaced microsource system can supply high quality power. Also, the proposed control scheme can make the system switch smoothly between the isolated mode and grid-connected mode. 更多
