To improve the strength, toughness, heat-resistance and deformability of magnesium alloy, the microstructure and mechanical properties of ZK60 alloy strengthened by Mg-Zn-Nd spherical quasi-crystal phase (I-phase) par...To improve the strength, toughness, heat-resistance and deformability of magnesium alloy, the microstructure and mechanical properties of ZK60 alloy strengthened by Mg-Zn-Nd spherical quasi-crystal phase (I-phase) particles were investigated. Mg40Zn55Nd5 (I-phase) particles in addition to α-Mg, MgZn phase and MgZn2 phases can be obtained in ZK60-based composites under normal casting condition by the addition of quasi-crystal containing Mg-Zn-Nd master alloy. The experimental results show that the introduction of Mg-Zn-Nd spherical quasi-crystal phase into ZK60 alloy makes a great contribution to the refinement of the matrix microstructures and the improvement of mechanical properties. While adding Mg-Zn-Nd spherical quasi-crystal master alloy of 4.0wt.%, the ultimate tensile strength and yield strength of ZK60-based composite at ambient temperature reach their peak values of 256.7 MPa and 150.4 MPa, which were about 17.8% and 24.1% higher respectively than those of the ZK60 alloy. The improved mechanical properties are mainly attributed to the pinning effect of the quasi-crystal particles (I-phase) at the grain boundaries. This research results provide a new way for strengthening and toughening of magnesium alloys as well as a new application of Mg-based spherical quasi-crystals.展开更多
Using the complex variable function method and the technique of conformal mapping, the anti-plane shear problem of an elliptic hole with asymmetric colfinear cracks in a one-dimensional hexagonal quasi-crystal is solv...Using the complex variable function method and the technique of conformal mapping, the anti-plane shear problem of an elliptic hole with asymmetric colfinear cracks in a one-dimensional hexagonal quasi-crystal is solved, and the exact analytic solutions of the stress intensity factors （SIFs） for mode Ⅲ problem are obtained. Under the limiting conditions, the present results reduce to the Griffith crack and many new results obtained as well, such as the circular hole with asymmetric collinear cracks, the elliptic hole with a straight crack, the mode T crack, the cross crack and so on. As far as the phonon field is concerned, these results, which play an important role in many practical and theoretical applications, are shown to be in good agreement with the classical results.展开更多
Effects of spherical quasi-crystal contained in Mg-Zn-Y-Mn master alloy on the microstructure and as-cast mechanical properties of ZA155 high zinc magnesium alloy have been investigated by means of optical microscopy,...Effects of spherical quasi-crystal contained in Mg-Zn-Y-Mn master alloy on the microstructure and as-cast mechanical properties of ZA155 high zinc magnesium alloy have been investigated by means of optical microscopy,XRD,SEM,EDS,tensile test,impact test and hardness test.Experimental results show that the addition of spherical quasi-crystal contained in the Mg-Zn-Y-Mn master alloy into the ZA155 high zinc magnesium alloy resulted in grain refinement of the matrix,changing the morphologies of φ-Al2Mg5Zn2 phase and τ-Mg32(Al,Zn)49 phase from continuous net-like structures to discontinuous strip-like structure and blocky one,respectively.In the present research,the best comprehensive mechanical properties of reinforced ZA155 high zinc magnesium alloy has been obtained when 5.0wt% spherical quasi-crystal was introduced from the Mg-Zn-Y-Mn master alloy into the target alloy system.In such case,the room-temperature tensile strength reached 207 MPa,about 23% higher than that of the base alloy;the impact toughness peaked at 5.5 J/cm2,about 40% higher than that of the base alloy;and the elevated-temperature tensile strength reached 203 MPa,indicating improved heat resistance.展开更多
The interface crack problems in the two-dimensional(2D)decagonal quasicrystal(QC)coating are theoretically and numerically investigated with a displacement discontinuity method.The 2D general solution is obtained base...The interface crack problems in the two-dimensional(2D)decagonal quasicrystal(QC)coating are theoretically and numerically investigated with a displacement discontinuity method.The 2D general solution is obtained based on the potential theory.An analogy method is proposed based on the relationship between the general solutions for 2D decagonal and one-dimensional(1D)hexagonal QCs.According to the analogy method,the fundamental solutions of concentrated point phonon displacement discontinuities are obtained on the interface.By using the superposition principle,the hypersingular boundary integral-differential equations in terms of displacement discontinuities are determined for a line interface crack.Further,Green’s functions are found for uniform displacement discontinuities on a line element.The oscillatory singularity near a crack tip is eliminated by adopting the Gaussian distribution to approximate the delta function.The stress intensity factors(SIFs)with ordinary singularity and the energy release rate(ERR)are derived.Finally,a boundary element method is put forward to investigate the effects of different factors on the fracture.展开更多
Mg-Zn-Y-based quasi-crystal （QC） alloys were fabricated by pouring melts into different cooling media. The effects of different cooling rates on the QC morphology, size, volume fraction and micro-hardness were studi...Mg-Zn-Y-based quasi-crystal （QC） alloys were fabricated by pouring melts into different cooling media. The effects of different cooling rates on the QC morphology, size, volume fraction and micro-hardness were studied. Multi-component Mg-Zn-Y-based QC alloys were synthesized based on amorphous design principle. QC morphology transformation and its influencing factors were analyzed. Micro/nano spherical quasi-crystals （QCs） were fabricated through a wedge-shaped copper mould and their forming mechanism were discussed by atoms cluster theory, optimum cooling rate theory and the known crucial criteria. The results of research show that with the cooling rate reduced, the solidified morphology of QC phase changes from near-spherical, micro petals （1 to 2 um） to big petals （20 um） and finally grows up to bulk pentagon or hexagon （200 to 400 um）. Multi-component micro-spherical QCs possess higher value of micro-hardness than petal-like QCs with the same components, and also higher than ternary micro-Mg-Zn-Y QCs. The fine master alloys containing micro-QCs （0.4 um） and nano-QCs （about 300 nm and 40 nm） have been fabricated correspondingly on the middle and the tip of wedge-shaped castings. A morphology evolution schematic diagram of Mg-Zn-Y-based QCs is included in this paper.展开更多
Quaternary Mg-Zn-Y-Ce quasi-crystal-containing alloys were fabricated using a metal mold casting route. The microstructures of Mg-Zn-Y-Ce alloys and the distribution of the major elements were analyzed. The difference...Quaternary Mg-Zn-Y-Ce quasi-crystal-containing alloys were fabricated using a metal mold casting route. The microstructures of Mg-Zn-Y-Ce alloys and the distribution of the major elements were analyzed. The differences in morphology and micro-hardness between quaternary Mg-Zn-Y-Ce quasi-crystals and ternary Mg- Zn-Y quasi-crystals were discussed. The result showed that the micro-hardness of Mg-Zn-Y-Ce quasi-crystals reached peak value when the content of Ce was 0.8at.%. Subsequently, various contents of Mg-Zn-Y-0.8Ce alloys were used to strengthen AZ91 magnesium alloys. The microstructural modification and mechanical properties of reinforced AZ91 alloys with and without solution, as well as their aging treatments, were also studied. Further research showed that aging-treated AZ91-10wt.%(Mg-Zn-Y-0.8at.%Ce) alloys exhibited excellent mechanical properties: their Brinell hardness, tensile strength, and elongation were HV91, 252 MPa, and 4.1%, respectively. Through this study, the range of application of AZ91 alloys can further be extended.展开更多
There seems to be a one to one correspondence between the phases of atomic and molecular matter（AMOM） and vortex matter（VM） in superfluids and superconductors. Crystals, liquids, and glasses have been experimental...There seems to be a one to one correspondence between the phases of atomic and molecular matter（AMOM） and vortex matter（VM） in superfluids and superconductors. Crystals, liquids, and glasses have been experimentally observed in both AMOM and VM. Here, we propose a vortex quasi-crystal state which can be stabilized due to boundary and surface energy effects for samples of special shapes and sizes. For finite sized pentagonal samples, it is proposed that a phase transition between a vortex crystal and a vortex quasi-crystal occurs as a function of magnetic field and temperature as the sample size is reduced.展开更多
By means of optical microscope （OM）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM） analyses, the microstructures of as-cast and heat-treated Mg--4Zn-IY ...By means of optical microscope （OM）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM） analyses, the microstructures of as-cast and heat-treated Mg--4Zn-IY （wt%） alloy containing quasi-crystal phase were studied. The microstructure of the as-cast alloy consists of a-Mg solid solution grains, intermetallic particles and eutectic phases （W-phase and 1-phase）, and huge grains with seri- ous dendritic segregation are clearly observed. After heat treatment, phase transformation and dissolution occur in the alloy and many phases remain. When the alloy was treated above 410 ~C, the eutectic phases transform into spherical shape as the I-phase turns to W-phase. After heat treatment for long time, the alloy is over burnt and the W-phase decomposes to Mg-Y binary phase.展开更多
Guided waves in the multilayered one-dimensional quasi-crystal plates are,respectively,investigated in the context of the Bak and elasto-hydrodynamic models.Dispersion curves and phonon and phason displacements are ca...Guided waves in the multilayered one-dimensional quasi-crystal plates are,respectively,investigated in the context of the Bak and elasto-hydrodynamic models.Dispersion curves and phonon and phason displacements are calculated using the Legendre polynomial method.Wave characteristics in the context of these two models are analyzed in detail.Results show that the phonon-phason coupling effects on the first two layers are the same at low frequencies;but,they are more significant on the first layer than those on the second layer at high frequencies.These obtained results lay the theoretical basis of guided-wave nondestructive test on multilayered quasi-crystal plates.展开更多
We demonstrated a two-dimensional quasi-crystal dendritic structure model with negative permeability.The microwave transmission and reflection properties of periodic and quasi-crystal dendritic structure mediums with ...We demonstrated a two-dimensional quasi-crystal dendritic structure model with negative permeability.The microwave transmission and reflection properties of periodic and quasi-crystal dendritic structure mediums with varied angle incidence were measured.The results showed that the resonant peaks of quasi-crystal negative permeability samples and left-handed samples had tiny shift with the altering of incident angle.Because of the influence of coupling between quasi-crystal dendritic cells,the resonance of the entire material was enhanced or weakened.The quasi-crystal dendritic structure model will provide an easy method to design isotropic left-handed materials(LHMs).展开更多
基金supported by the National Science Foundation of China(No.50571073)the Natural Science Foundation of Shanxi province(No.2009011028-3)
文摘To improve the strength, toughness, heat-resistance and deformability of magnesium alloy, the microstructure and mechanical properties of ZK60 alloy strengthened by Mg-Zn-Nd spherical quasi-crystal phase (I-phase) particles were investigated. Mg40Zn55Nd5 (I-phase) particles in addition to α-Mg, MgZn phase and MgZn2 phases can be obtained in ZK60-based composites under normal casting condition by the addition of quasi-crystal containing Mg-Zn-Nd master alloy. The experimental results show that the introduction of Mg-Zn-Nd spherical quasi-crystal phase into ZK60 alloy makes a great contribution to the refinement of the matrix microstructures and the improvement of mechanical properties. While adding Mg-Zn-Nd spherical quasi-crystal master alloy of 4.0wt.%, the ultimate tensile strength and yield strength of ZK60-based composite at ambient temperature reach their peak values of 256.7 MPa and 150.4 MPa, which were about 17.8% and 24.1% higher respectively than those of the ZK60 alloy. The improved mechanical properties are mainly attributed to the pinning effect of the quasi-crystal particles (I-phase) at the grain boundaries. This research results provide a new way for strengthening and toughening of magnesium alloys as well as a new application of Mg-based spherical quasi-crystals.
基金supported by the National Natural Science Foundation of China (Grant No 10761005)the Inner Mongolia Natural Science Foundation of China (Grant No 200607010104)
文摘Using the complex variable function method and the technique of conformal mapping, the anti-plane shear problem of an elliptic hole with asymmetric colfinear cracks in a one-dimensional hexagonal quasi-crystal is solved, and the exact analytic solutions of the stress intensity factors （SIFs） for mode Ⅲ problem are obtained. Under the limiting conditions, the present results reduce to the Griffith crack and many new results obtained as well, such as the circular hole with asymmetric collinear cracks, the elliptic hole with a straight crack, the mode T crack, the cross crack and so on. As far as the phonon field is concerned, these results, which play an important role in many practical and theoretical applications, are shown to be in good agreement with the classical results.
基金supported by both the National Natural Science Foundation of China (No. 50571073)the Natural Science Foundation of Shanxi Province (No. 2009011028-3,20051052)
文摘Effects of spherical quasi-crystal contained in Mg-Zn-Y-Mn master alloy on the microstructure and as-cast mechanical properties of ZA155 high zinc magnesium alloy have been investigated by means of optical microscopy,XRD,SEM,EDS,tensile test,impact test and hardness test.Experimental results show that the addition of spherical quasi-crystal contained in the Mg-Zn-Y-Mn master alloy into the ZA155 high zinc magnesium alloy resulted in grain refinement of the matrix,changing the morphologies of φ-Al2Mg5Zn2 phase and τ-Mg32(Al,Zn)49 phase from continuous net-like structures to discontinuous strip-like structure and blocky one,respectively.In the present research,the best comprehensive mechanical properties of reinforced ZA155 high zinc magnesium alloy has been obtained when 5.0wt% spherical quasi-crystal was introduced from the Mg-Zn-Y-Mn master alloy into the target alloy system.In such case,the room-temperature tensile strength reached 207 MPa,about 23% higher than that of the base alloy;the impact toughness peaked at 5.5 J/cm2,about 40% higher than that of the base alloy;and the elevated-temperature tensile strength reached 203 MPa,indicating improved heat resistance.
基金the National Natural Science Foundation of China (Nos. 11572289,1171407,11702252,and 11902293)the China Postdoctoral Science Foundation (No. 2019M652563)。
文摘The interface crack problems in the two-dimensional(2D)decagonal quasicrystal(QC)coating are theoretically and numerically investigated with a displacement discontinuity method.The 2D general solution is obtained based on the potential theory.An analogy method is proposed based on the relationship between the general solutions for 2D decagonal and one-dimensional(1D)hexagonal QCs.According to the analogy method,the fundamental solutions of concentrated point phonon displacement discontinuities are obtained on the interface.By using the superposition principle,the hypersingular boundary integral-differential equations in terms of displacement discontinuities are determined for a line interface crack.Further,Green’s functions are found for uniform displacement discontinuities on a line element.The oscillatory singularity near a crack tip is eliminated by adopting the Gaussian distribution to approximate the delta function.The stress intensity factors(SIFs)with ordinary singularity and the energy release rate(ERR)are derived.Finally,a boundary element method is put forward to investigate the effects of different factors on the fracture.
基金supported by Natural Science Foundation of Hebei Province, China (E2010000057, E2010000121, E2012202017)International S & T Cooperation Program of China (2010DFA51850)
文摘Mg-Zn-Y-based quasi-crystal （QC） alloys were fabricated by pouring melts into different cooling media. The effects of different cooling rates on the QC morphology, size, volume fraction and micro-hardness were studied. Multi-component Mg-Zn-Y-based QC alloys were synthesized based on amorphous design principle. QC morphology transformation and its influencing factors were analyzed. Micro/nano spherical quasi-crystals （QCs） were fabricated through a wedge-shaped copper mould and their forming mechanism were discussed by atoms cluster theory, optimum cooling rate theory and the known crucial criteria. The results of research show that with the cooling rate reduced, the solidified morphology of QC phase changes from near-spherical, micro petals （1 to 2 um） to big petals （20 um） and finally grows up to bulk pentagon or hexagon （200 to 400 um）. Multi-component micro-spherical QCs possess higher value of micro-hardness than petal-like QCs with the same components, and also higher than ternary micro-Mg-Zn-Y QCs. The fine master alloys containing micro-QCs （0.4 um） and nano-QCs （about 300 nm and 40 nm） have been fabricated correspondingly on the middle and the tip of wedge-shaped castings. A morphology evolution schematic diagram of Mg-Zn-Y-based QCs is included in this paper.
基金supported by the Hebei Provincial Natural Science Foundation of China(No. E2010000057)the International S & T Cooperation Program of China (No. 2010DFA51850)
文摘Quaternary Mg-Zn-Y-Ce quasi-crystal-containing alloys were fabricated using a metal mold casting route. The microstructures of Mg-Zn-Y-Ce alloys and the distribution of the major elements were analyzed. The differences in morphology and micro-hardness between quaternary Mg-Zn-Y-Ce quasi-crystals and ternary Mg- Zn-Y quasi-crystals were discussed. The result showed that the micro-hardness of Mg-Zn-Y-Ce quasi-crystals reached peak value when the content of Ce was 0.8at.%. Subsequently, various contents of Mg-Zn-Y-0.8Ce alloys were used to strengthen AZ91 magnesium alloys. The microstructural modification and mechanical properties of reinforced AZ91 alloys with and without solution, as well as their aging treatments, were also studied. Further research showed that aging-treated AZ91-10wt.%(Mg-Zn-Y-0.8at.%Ce) alloys exhibited excellent mechanical properties: their Brinell hardness, tensile strength, and elongation were HV91, 252 MPa, and 4.1%, respectively. Through this study, the range of application of AZ91 alloys can further be extended.
基金supported by the National Natural Science Foundation of China(Grant Nos.11274009,11434011,and 111522436)the National Key Basic Research Program of China(Grant No.2013CB922000)+1 种基金the Research Funds of Renmin University of China(Grant Nos.10XNL016 and 16XNLQ03)the Program of State Key Laboratory of Quantum Optics and Quantum Optics Devices(Grant No.KF201404)
文摘There seems to be a one to one correspondence between the phases of atomic and molecular matter（AMOM） and vortex matter（VM） in superfluids and superconductors. Crystals, liquids, and glasses have been experimentally observed in both AMOM and VM. Here, we propose a vortex quasi-crystal state which can be stabilized due to boundary and surface energy effects for samples of special shapes and sizes. For finite sized pentagonal samples, it is proposed that a phase transition between a vortex crystal and a vortex quasi-crystal occurs as a function of magnetic field and temperature as the sample size is reduced.
基金financially supported by the National Natural Science Foundation of China(Nos.50835002 and 51105102)
文摘By means of optical microscope （OM）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM） analyses, the microstructures of as-cast and heat-treated Mg--4Zn-IY （wt%） alloy containing quasi-crystal phase were studied. The microstructure of the as-cast alloy consists of a-Mg solid solution grains, intermetallic particles and eutectic phases （W-phase and 1-phase）, and huge grains with seri- ous dendritic segregation are clearly observed. After heat treatment, phase transformation and dissolution occur in the alloy and many phases remain. When the alloy was treated above 410 ~C, the eutectic phases transform into spherical shape as the I-phase turns to W-phase. After heat treatment for long time, the alloy is over burnt and the W-phase decomposes to Mg-Y binary phase.
基金The authors gratefully acknowledge the support by the National Natural Science Foundation of China(No.U1804134 and No.51975189)the Program for Innovative Research Team of Henan Polytechnic University(No.T2017-3)the Key Scientific and Technological Project of Henan Province(Nos.192102210189 and 182102210314).
文摘Guided waves in the multilayered one-dimensional quasi-crystal plates are,respectively,investigated in the context of the Bak and elasto-hydrodynamic models.Dispersion curves and phonon and phason displacements are calculated using the Legendre polynomial method.Wave characteristics in the context of these two models are analyzed in detail.Results show that the phonon-phason coupling effects on the first two layers are the same at low frequencies;but,they are more significant on the first layer than those on the second layer at high frequencies.These obtained results lay the theoretical basis of guided-wave nondestructive test on multilayered quasi-crystal plates.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 50632030 and 50025207)National Basic Research Program of China (Grant No. 2004CB719805)NPU Foundation for Fundamental Research (Grant No. WO18101)
文摘We demonstrated a two-dimensional quasi-crystal dendritic structure model with negative permeability.The microwave transmission and reflection properties of periodic and quasi-crystal dendritic structure mediums with varied angle incidence were measured.The results showed that the resonant peaks of quasi-crystal negative permeability samples and left-handed samples had tiny shift with the altering of incident angle.Because of the influence of coupling between quasi-crystal dendritic cells,the resonance of the entire material was enhanced or weakened.The quasi-crystal dendritic structure model will provide an easy method to design isotropic left-handed materials(LHMs).
