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Yoshihito Kawamura - One of the best experts on this subject based on the ideXlab platform.

  • elastic properties of an mg zn Y alloY single crYstal with a long period stacking ordered structure
    Acta Materialia, 2013
    Co-Authors: Masakazu Tane, Koji Hagihara, Y Nagai, Hajime Kimizuka, Yoshihito Kawamura
    Abstract:

    Abstract The elastic properties of an Mg85Zn6Y9 (at.%) alloY single crYstal with a long-period stacking-ordered (LPSO) structure, sYnchronized with periodic enrichment of Zn and Y atoms, were investigated, the properties having remained unclear because of the difficultY in growing large single crYstals. DirectionallY solidified (DS) Mg85Zn6Y9 alloY polYcrYstals consisting of a single phase of the 18R-tYpe LPSO structure were prepared using the Bridgman technique. For the DS polYcrYstals, a complete set of elastic constants was measured with resonant ultrasound spectroscopY combined with electromagnetic acoustic resonance, in which the texture formed bY the directional solidification was taken into account. BY analYzing the elastic stiffness of DS polYcrYstals on the basis of a newlY developed inverse Voigt–Reuss–Hill approximation, the elastic stiffness components of the single-crYstalline LPSO phase were determined. It was revealed that the Young’s modulus of the LPSO phase along 〈0 0 0 1〉 in the hexagonal expression was clearlY higher than that along 〈 1 1 2 ¯ 0 〉 , and the Young’s modulus and shear modulus were clearlY higher than those of pure magnesium. These findings were validated bY first-principles calculations based on densitY functional theorY. AnalYses bY first-principles calculations and micromechanics modeling indicated that the long periodicitY of the 18R-tYpe stacking structure hardlY enhanced the elastic modulus, whereas the Zn/Y-enriched atomic laYers, containing stable short-range ordered clusters, exhibited a high elastic modulus, which contributed to the enhancement of the elastic modulus of the LPSO phase in the Mg–Zn–Y alloY.

  • crYstallographic classification of kink bands in an extruded mg zn Y alloY using intragranular misorientation axis analYsis
    Acta Materialia, 2013
    Co-Authors: Michiaki Yamasaki, Shinichi Inoue, Jason Paul Hadorn, Koji Hagihara, Yoshihito Kawamura
    Abstract:

    Abstract Within extruded Mg89Zn4Y7 (at.%) alloYs containing a long period stacking ordered (LPSO) phase a unique deformation mode referred to as “kink deformation” is found to occur within the LPSO phase grains, forming kink bands that are each represented bY an arraY of geometricallY necessarY dislocations. Intragranular misorientation axis (IGMA) analYsis suggests that this kink deformation results in lattice rotation predominatelY about the 〈 1 1 ¯ 0 0 〉 , 〈 0 1 ¯ 1 0 〉 , 〈 0001 〉 , and 〈 1 2 ¯ 1 0 〉 axes of the 18R-tYpe LPSO structure. IGMA analYsis is based on slip-induced lattice rotation and determination of its rotation axis (TaYlor axis). Therefore, it is possible to determine the dominant slip mode in a grain that is deformed bY matching the TaYlor axis for a given slip sYstem to its experimentallY obtained IGMA distribution. In this studY the strong preference of 〈 1 1 ¯ 0 0 〉 and 〈 0 1 ¯ 1 0 〉 TaYlor axes suggests that kinking occurs through a basal 〈a〉 slip mode. The 〈0 0 0 1〉 TaYlor axes suggest that kink bands form through a prismatic 〈a〉 slip mode. These axes are categorized as “principal rotation” axes, which result from one Burgers vector of dislocations. Kink bands with a 〈 1 2 ¯ 1 0 〉 TaYlor axis are produced through combination of basal 〈a〉 slip variants. This axis is categorized as a “combination-tYpe rotation” axis, which results from more than one Burgers vector of dislocations. It is concluded that IGMA analYsis can be effectivelY used to studY and geometricallY classifY kink bands.

  • application of mixture rule to finite element analYsis for forging of cast mg zn Y alloYs with long period stacking ordered structure
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012
    Co-Authors: Ryo Matsumoto, Michiaki Yamasaki, Masaaki Otsu, Tsuyoshi Mayama, Hiroshi Utsunomiya, Yoshihito Kawamura
    Abstract:

    Abstract To establish forging process for high strength Mg–Zn–Y alloYs with a long period stacking ordered (LPSO) structure, the flow stresses of Mg–Zn–Y alloYs with different volume fractions of LPSO phase were measured bY the upsettabilitY test. Since mixture rule for the flow stress was satisfied in Mg–Zn–Y two-phase (α-Mg and LPSO) alloYs, the flow stresses of α-Mg and LPSO single phase alloYs were estimated from the flow stresses of Mg–Zn–Y alloYs with different volume fractions of LPSO phase. To examine the validitY of the mixture rule, the finite element analYsis for tensile test and forging of as-cast Mg–Zn–Y alloY was carried out using the estimated flow stresses of α-Mg and LPSO single phase alloYs on the basis of mixture rule of the properties of Mg–Zn–Y alloY. The calculated load-stroke curves in tensile test and forging agreed well with the experimental ones, and the deformation behaviour of Mg–Zn–Y alloY was discussed.

  • polYtYpes of long period stacking structures sYnchronized with chemical order in a dilute mg zn Y alloY
    Philosophical Magazine Letters, 2011
    Co-Authors: Eiji Abe, Michiaki Yamasaki, Akira Ono, Takaomi Itoi, Yoshihito Kawamura
    Abstract:

    A series of structural polYtYpes formed in an Mg–1 at.%Zn–2 at.%Y alloY has been identified, which are reasonablY viewed as long-period stacking derivatives of the hexagonal-close-packed Mg structure with alternate AB stacking of the close-packed atomic laYers. Atomic-resolution Z-contrast imaging clearlY revealed that the structures are long-period chemical-ordered as well as stacking-ordered; unique chemical order along the stacking direction occurs as being sYnchronized with a local faulted stacking of AB′C′A, where B′ and C′ laYers are commonlY enriched bY Zn/Y atoms.

  • polYtYpes of long period stacking structures sYnchronized with chemical order in a dilute mg zn Y alloY
    arXiv: Materials Science, 2011
    Co-Authors: Eiji Abe, Michiaki Yamasaki, Akira Ono, Takaomi Itoi, Yoshihito Kawamura
    Abstract:

    A series of structural polYtYpes formed in an Mg-1at.%Zn-2at.%Y alloY has been identified, which are reasonablY viewed as long-period stacking derivatives of the hcp Mg structure with alternate AB stacking of the close-packed atomic laYers. Atomic-resolution Z-contrast imaging clearlY revealed that the structures are long-period chemical-ordered as well as stacking-ordered; unique chemical order along the stacking direction occurs as being sYnchronized with a local faulted stacking of AB'C'A, where B' and C' laYers are commonlY enriched bY Zn/Y atoms.

Enhou Han - One of the best experts on this subject based on the ideXlab platform.

  • microstructure and texture optimization bY static recrYstallization originating from 10 12 extension twins in a mg gd Y alloY
    Journal of Materials Science & Technology, 2020
    Co-Authors: Runkun Chen, Enhou Han
    Abstract:

    Abstract During the deformation of Mg alloYs, {10–12} extension twin often contributes to the formation of basal texture but rarelY assists the nucleation of recrYstallization, i.e., effective grain refinement, therefore it seems to make against the improvement of formabilitY and mechanical properties. In this work, {10–12} extension twin has been creativelY utilized as a preference nucleation site for static recrYstallization (SRX), achieving grain refinement and orientation randomization in a Mg-Gd-Y alloY using multi-directional impact forging (MDIF) and subsequent annealing treatment. Effect of {10–12} extension twin on SRX behavior has been investigated bY annealing treatment at 450 °C using quasi-in-situ optical microscopY (OM) and quasi-in-situ electron back-scattering diffraction (EBSD). The microstructural evolution during annealing shows that several SRX gains can nucleate from the grain boundarY of untwinned grains, but theY onlY have few influences on the final microstructure due to their limited volume faction and sluggish growth. In contrast, a large number of SRX gains can initiate from {10–12} extension twin and grow up without the confine of twin boundaries. FinallY, theY consume their parent grains and make the main contribution to grain refinement. This should be attributed to those pinned {10–12} twin boundarY, bY interacting with various dislocation slips during the MDIF process, which can operate like grain boundarY, store enough strain energY, and promote the nucleation of SRX during annealing. On the other hand, SRX grains usuallY keep initial random orientation and further randomize the forging texture during annealing treatment.

  • reasonable utilization of 10 12 twin for optimizing microstructure and improving mechanical propertY in a mg gd Y alloY
    Materials & Design, 2020
    Co-Authors: Ruiyi Chen, Enhou Han
    Abstract:

    Abstract During the deformation of Mg alloYs, {10-12} extension twin, as one of the most active deformation mechanisms, contributed much to the formation of basal texture, Yet little to dYnamic recrYstallization (DRX) grains, i.e., effective grain refinement. In this work, {10-12} extension twin had been creativelY utilized to achieve grain refinement and propertY improvement in a Mg-Gd-Y alloY bY multi-directional impact forging (MDIF). FirstlY, flourishing {10-12} extension twins divided the parent grain into manY fine independent regions (~10 μm). Meanwhile, a large number of twin boundaries were pinning mainlY bY interaction with neighboring dislocations in twin or matrix. SecondlY, those pinned twin boundaries can effectivelY accumulate dislocation slips and promote the formation of extensive low angle grain boundaries (LAGBs). These high densities of LAGBs can further subdivide the independent regions provided bY extension twins into micro-regions (~5 μm). ThirdlY, those fine micro-regions developed to be DRX after a dYnamic recoverY. FinallY, we obtained a Yield isotropY high-strength Mg alloY with an ultimate tensile strength of 354 MPa after MDIF of 110 passes. This work proposed a brand new insight to prepare wrought Mg alloY with fine grain, Yet without strong texture, which is beneficial to better formabilitY and mechanical propertY isotropY.

  • the effect of twinning on dYnamic recrYstallization behavior of mg gd Y alloY during hot compression
    Journal of Alloys and Compounds, 2019
    Co-Authors: Rongfeng Chen, Enhou Han
    Abstract:

    Abstract The effects of twinning on the dYnamic recrYstallization (DRX) of the Mg-6.58Gd-5.7Y-0.55Zr alloY were investigated through uniaxial compression tests at 400 °C and 450 °C with an initial strain rate of 0.001–0.1 s −1 and were characterized through optical microscopY (OM), scanning electron microscopY (SEM), electron back-scattering diffraction (EBSD) and transmission electron microscopY (TEM). At a relativelY high strain rate, extension twins can mainlY be activated during the initial stage of hot compression, and the subsequent DRX is closelY related to the twin-twin and twin-dislocation interactions. The intersected twin boundaries of the extension twins from multiple twin variants maY provide effective DRX sites and promote microstructure refinement. However, extension twins from a single twin variant pair maY quicklY grow, soon swallowing the matrix and decreasing the DRX efficiencY.

  • suppressing effect of heat treatment on the portevin le chatelier phenomenon of mg 4 li 6 zn 1 2 Y alloY
    Journal of Materials Science & Technology, 2016
    Co-Authors: Bi Wang, Enhou Han, Liyuan Sheng
    Abstract:

    Microstructural evolution and Portevin–Le Chatelier (PLC) phenomenon of the as-extruded Mg–4%Li–6%Zn–1.2%Y alloY before and after heat treatment have been investigated. It has been demonstrated that for the as-extruded and solid solution treated (T4) samples, the PLC phenomenon could be obviouslY observed on tensile stress–strain curves. Moreover, the PLC phenomenon in T4 samples was more salient than that in the as-extruded condition, suggesting that the occurrence of PLC phenomenon was closelY related to the super-saturation degree of solute atoms in the matrix. Since most of solute atoms were consumed for the formation of MgZn precipitates (β1′ and a little of β2′) during the subsequent ageing treatment (T6), the PLC phenomenon of T6 samples was eliminated. Meanwhile, due to the pinning effect of the formed MgZn precipitates on mobile dislocations, the tensile strength of T6 samples was relativelY higher than those of the other two conditions.

  • effect of temperature on the mechanical abnormitY of the quasicrYstal reinforced mg 4 li 6 zn 1 2 Y alloY
    Journal of Magnesium and Alloys, 2015
    Co-Authors: Enhou Han, L Wang
    Abstract:

    Abstract The serrated phenomena of the quasicrYstalline phase reinforced Mg–4%Li–6%Zn–1.2%Y alloY after the extrusion, solid solution treatment and aged treatment have been investigated at different temperatures. The result shows that when the temperature is above 100 °C, the serrated phenomenon becomes weak and all the serrated amplitudes are lower than 1 MPa. Among them, the serrated amplitude of samples in aged condition is the lowest and the value is onlY 0.1–0.2 MPa. The underneath mechanism for the lower plastic instabilitY at higher temperature (≥100 °C) can be ascribed to the weak pining effect of solute atoms on the movement of dislocation and release of the pile-up dislocations.

Michiaki Yamasaki - One of the best experts on this subject based on the ideXlab platform.

  • crYstallographic classification of kink bands in an extruded mg zn Y alloY using intragranular misorientation axis analYsis
    Acta Materialia, 2013
    Co-Authors: Michiaki Yamasaki, Shinichi Inoue, Jason Paul Hadorn, Koji Hagihara, Yoshihito Kawamura
    Abstract:

    Abstract Within extruded Mg89Zn4Y7 (at.%) alloYs containing a long period stacking ordered (LPSO) phase a unique deformation mode referred to as “kink deformation” is found to occur within the LPSO phase grains, forming kink bands that are each represented bY an arraY of geometricallY necessarY dislocations. Intragranular misorientation axis (IGMA) analYsis suggests that this kink deformation results in lattice rotation predominatelY about the 〈 1 1 ¯ 0 0 〉 , 〈 0 1 ¯ 1 0 〉 , 〈 0001 〉 , and 〈 1 2 ¯ 1 0 〉 axes of the 18R-tYpe LPSO structure. IGMA analYsis is based on slip-induced lattice rotation and determination of its rotation axis (TaYlor axis). Therefore, it is possible to determine the dominant slip mode in a grain that is deformed bY matching the TaYlor axis for a given slip sYstem to its experimentallY obtained IGMA distribution. In this studY the strong preference of 〈 1 1 ¯ 0 0 〉 and 〈 0 1 ¯ 1 0 〉 TaYlor axes suggests that kinking occurs through a basal 〈a〉 slip mode. The 〈0 0 0 1〉 TaYlor axes suggest that kink bands form through a prismatic 〈a〉 slip mode. These axes are categorized as “principal rotation” axes, which result from one Burgers vector of dislocations. Kink bands with a 〈 1 2 ¯ 1 0 〉 TaYlor axis are produced through combination of basal 〈a〉 slip variants. This axis is categorized as a “combination-tYpe rotation” axis, which results from more than one Burgers vector of dislocations. It is concluded that IGMA analYsis can be effectivelY used to studY and geometricallY classifY kink bands.

  • microstructure and mechanical properties of mgznY alloY sheet prepared bY hot rolling
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013
    Co-Authors: Takaomi Itoi, Michiaki Yamasaki, Toshiharu Inazawa, Y Kawamura, Mitsuji Hirohashi
    Abstract:

    Abstract In this studY, the microstructure and mechanical properties of MgZnY alloY sheets were investigated. Tensile tests at room temperature were performed along the rolling direction of Mg 98 Zn 1 Y 1 -, Mg 96 Zn 2 Y 2 -, and Mg 94 Zn 3 Y 3 - alloY sheets and their annealed states (773 K for 0.6 ks). These alloY sheets exhibited Yield strengths of 261, 317, and 380 MPa, and elongations of 12, 10, and 6%, respectivelY. The Yield strength of a MgZnY alloY sheet with Zn and Y contents greater than 2 at% was higher than 300 MPa. The microstructure observations suggested that the alloY sheet strength mainlY resulted from (i) the formation of basal texture in the long period stacking ordered (LPSO) phase and (ii) the uniform dispersion of a fine Mg 3 Zn 3 Y 2 phase. In the annealed state, the Yield strength tended to decrease, while the elongation tended to increase. Large elongations of 20% or more were achieved in the Mg 98 Zn 1 Y 1 - and Mg 96 Zn 2 Y 2 -alloY annealed sheets. The cold workabilitY of the MgZnY alloY sheets and an AZ31-O sheet were evaluated, using a V-bending test at room temperature. Both Mg 98 Zn 1 Y 1 - and Mg 96 Zn 2 Y 2 - annealed sheets could be bent without cracking with a minimum bending radius per thickness of 3.3, which was less than that of the AZ31-O sheet. Texture randomization occurred in the MgZnY alloY annealed sheets owing to re-crYstallization of the Mg phase, which was confirmed bY electron backscattering diffraction (EBSD) analYsis. Large elongations and good cold workabilitY of the MgZnY annealed sheets are presumablY attributed to an increase in the randomness of the Mg phase owing to re-crYstallization. These results suggested that a Mg alloY sheet of high Yield strength or good cold workabilitY could be prepared bY controlling the alloY composition and its microstructure in the MgZnY alloY sYstem.

  • application of mixture rule to finite element analYsis for forging of cast mg zn Y alloYs with long period stacking ordered structure
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012
    Co-Authors: Ryo Matsumoto, Michiaki Yamasaki, Masaaki Otsu, Tsuyoshi Mayama, Hiroshi Utsunomiya, Yoshihito Kawamura
    Abstract:

    Abstract To establish forging process for high strength Mg–Zn–Y alloYs with a long period stacking ordered (LPSO) structure, the flow stresses of Mg–Zn–Y alloYs with different volume fractions of LPSO phase were measured bY the upsettabilitY test. Since mixture rule for the flow stress was satisfied in Mg–Zn–Y two-phase (α-Mg and LPSO) alloYs, the flow stresses of α-Mg and LPSO single phase alloYs were estimated from the flow stresses of Mg–Zn–Y alloYs with different volume fractions of LPSO phase. To examine the validitY of the mixture rule, the finite element analYsis for tensile test and forging of as-cast Mg–Zn–Y alloY was carried out using the estimated flow stresses of α-Mg and LPSO single phase alloYs on the basis of mixture rule of the properties of Mg–Zn–Y alloY. The calculated load-stroke curves in tensile test and forging agreed well with the experimental ones, and the deformation behaviour of Mg–Zn–Y alloY was discussed.

  • polYtYpes of long period stacking structures sYnchronized with chemical order in a dilute mg zn Y alloY
    Philosophical Magazine Letters, 2011
    Co-Authors: Eiji Abe, Michiaki Yamasaki, Akira Ono, Takaomi Itoi, Yoshihito Kawamura
    Abstract:

    A series of structural polYtYpes formed in an Mg–1 at.%Zn–2 at.%Y alloY has been identified, which are reasonablY viewed as long-period stacking derivatives of the hexagonal-close-packed Mg structure with alternate AB stacking of the close-packed atomic laYers. Atomic-resolution Z-contrast imaging clearlY revealed that the structures are long-period chemical-ordered as well as stacking-ordered; unique chemical order along the stacking direction occurs as being sYnchronized with a local faulted stacking of AB′C′A, where B′ and C′ laYers are commonlY enriched bY Zn/Y atoms.

  • polYtYpes of long period stacking structures sYnchronized with chemical order in a dilute mg zn Y alloY
    arXiv: Materials Science, 2011
    Co-Authors: Eiji Abe, Michiaki Yamasaki, Akira Ono, Takaomi Itoi, Yoshihito Kawamura
    Abstract:

    A series of structural polYtYpes formed in an Mg-1at.%Zn-2at.%Y alloY has been identified, which are reasonablY viewed as long-period stacking derivatives of the hcp Mg structure with alternate AB stacking of the close-packed atomic laYers. Atomic-resolution Z-contrast imaging clearlY revealed that the structures are long-period chemical-ordered as well as stacking-ordered; unique chemical order along the stacking direction occurs as being sYnchronized with a local faulted stacking of AB'C'A, where B' and C' laYers are commonlY enriched bY Zn/Y atoms.

Toshiji Mukai - One of the best experts on this subject based on the ideXlab platform.

  • Effect of Solidification Cooling Rate on Microstructure and Mechanical Properties of an Extruded Mg-Zn-Y AlloY
    MDPI AG, 2018
    Co-Authors: Alok Singh, Hidetoshi Somekawa, Yoshiaki Osawa, Toshiji Mukai
    Abstract:

    The Effect of the solidification conditions and subsequent extrusion of a Mg-3.0Zn-0.5Y (at. %) alloY containing quasicrYstalline icosahedral (i-) phase was studied. Solidification was carried out bY three methods using a chill casting mold, a conventional steel mold and a water-cooled mold. SubsequentlY, castings were extruded in the temperature range of 235–270 ∘ C at an extrusion ratio of 25:1. The solidification molds showed different characteristics. The water-cooled mold was most effective in cooling through the walls, but least effective at the center of the mold. The conventional cast mold was the most effective in cooling at the mold center. All the castings had an interdendritic eutectic structure of the i-phase, and a supersaturation of the matrix in zinc. As a result, all the extrusions had similar grain size close to 1 μ m and verY fine nano-size precipitation. Yield strengths in tension were in the range of 376 and 404 MPa, and from 300 to 330 MPa in compression. All elongations to fracture were about 13%. It is concluded that supersaturation of the matrix during solidification is the main factor, resulting in the dYnamic precipitation of verY fine precipitates and fine grain size during extrusion

  • increasing volume fraction of precipitates and strength of a mg zn Y alloY bY pre ageing deformation
    mt13, 2013
    Co-Authors: Julian M Rosalie, Hidetoshi Somekawa, Alok Singh, Toshiji Mukai
    Abstract:

    Pre-ageing deformation was applied to a Mg-Zn-Y alloY to refine the size of s′1 precipitates. Reductions in the precipitate length and diameter were accompanied bY a substantial increase in the volume fraction of the s′1 precipitates from 0.5% (no prestrain) to 2.3% (5% pre-strain). This contrasted with Mg-Zn alloYs, in which the precipitate volume fraction in the peak aged condition was not affected bY pre-ageing strain. The increase in precipitate volume fraction contributed significantlY to an increase in the Yield strength from 217 MPa (no pre-strain) to 286 MPa (5% pre-strain). Precipitate strengthening via Orowan looping was the most significant contributor to the overall strength of the alloY.

  • effect of precipitation on strength and ductilitY in a mg zn Y alloY
    Journal of Alloys and Compounds, 2013
    Co-Authors: Julian M Rosalie, Hidetoshi Somekawa, Alok Singh, Toshiji Mukai
    Abstract:

    Abstract The effect of pre-ageing deformation on the size and distribution of β 1 ′ precipitates and subsequentlY on the resulting strength and ductilitY have been measured in a Mg-3.0at.%Zn-0.5at.%Y alloY. The alloY was extruded and then subjected to a T8 heat treatment comprised of a solution-treatment, cold-work and artificial ageing. Extrusion was used to introduce texture, ensuring that deformation occurred via slip rather than twinning. Samples were subjected to controlled uniaxial deformation and then isothermallY aged to peak hardness. Precipitate length, diameter and number densitY were measured and evaluated in terms of the strength and ductilitY of the alloY. The nucleation of the β 1 ′ precipitates in peak-aged condition without pre-ageing deformation (i.e. T6 treatment) was poor, with onlY 0.5% volume fraction, compared to approximatelY 3.5% in T6 treated binarY Mg-3.0at.%Zn alloY. The microstructure of the Mg–Zn–Y alloY was less refined, with larger diameter precipitates and lower β 1 ′ number densities than a binarY Mg-3.0at.%Zn alloY. Deformation to 5% plastic strain increased the volume fraction of β 1 ′ precipitates to approximatelY 2.3% and refined the β 1 ′ precipitate length and diameter. The combination of these effects increased the Yield strength after isothermal ageing from 217 MPa (0% cold-work) to 287 MPa (5% cold-work). The Yield stress increased linearlY with reciprocal interparticle spacing on the basal and prismatic planes and the alloY showed similar strengthening against basal slip to Mg–Zn. The elongation increased linearlY with particle spacing. The ductilitY of Mg–Zn–Y alloYs was similar to that of Mg-Zn for equivalentlY spaced particles.

  • evaluating the effect of pre ageing deformation on β precipitate size and distribution in mg zn Y alloYs
    Magnesium Technology, 2012
    Co-Authors: Julian M Rosalie, Hidetoshi Somekawa, Alok Singh, Toshiji Mukai
    Abstract:

    The effect of pre-ageing deformation on the precipitate diameter and length distribution in Mg-Zn(-Y) alloYs was examined. Extrusion and pre-ageing deformation were used to introduce dislocations while precluding twin formation. Dislocations provided nucleation sites for rod-like ²′1 precipitates, resulting in a refinement of the precipitate size distribution. In the binarY alloY 5% strain reduced the average precipitate length from approximatelY 450nm to 60nm, and average diameter from 14 to 9 nm. Substantial reductions in precipitate size were also observed in the Mg-Zn(-Y) alloY. The average interparticle spacing of the rod-like precipitates was measured bY DelaunaY triangulation. The precipitate distribution was found to be significantlY inhomogeneous, with measured interparticle spacings approximatelY 32% greater than predicted. For 5% pre-ageing deformation the Yield strength of the binarY alloY approached 95% of the ultimate tensile strength.

  • High temperature processing of Mg–Zn–Y alloYs containing quasicrYstal phase for high strength
    Materials Science and Engineering: A, 2011
    Co-Authors: Alok Singh, Hidetoshi Somekawa, Toshiji Mukai
    Abstract:

    Abstract A process to obtain high strength in a Mg–Zn–Y alloY containing quasicrYstalline phase is described. The process involves solutionizing at a high temperature, precipitation of the quasicrYstal phase during extrusion, followed bY ageing. Tensile Yield strengths of over 350 MPa are obtained with grain sizes of 14–20 μm.

X L - One of the best experts on this subject based on the ideXlab platform.

  • unravelling the local ring like atomic pattern of twin boundarY in an mg zn Y alloY
    Philosophical Magazine, 2019
    Co-Authors: X H Shao, Shucheng Zheng, Q Q Jin, Zhengjun Peng, Yu Zhou, B Zhang, Qiang Chen, X L
    Abstract:

    Understanding the interactions between deformation twins and plate-like phases in magnesium alloYs is one of the keY issues to tailor the microstructure of magnesium alloYs for better mechanical pr...

  • new polYtYpes of lpso structures in an mg co Y alloY
    Philosophical Magazine, 2017
    Co-Authors: Q Q Jin, X H Shao, Z Z Peng, X L
    Abstract:

    AbstractThe magnesium alloYs containing long-period stacking ordered (LPSO) structures exhibit excellent mechanical properties. Each LPSO structure is known to contain either AB′C′A or AB′C building block and feature its own stacking sequences. BY atomic-scale high-angle annular dark field scanning transmission electron microscopY, we find the co-existence of AB′C′A and AB′C building block in a single LPSO structure of the as-cast Mg92Co2Y6 (at.%) alloY, leading to the formation of six new polYtYpes of the LPSO structures determined as 29H, 51R, 60H, 72R, 102R and 192R. The lattice parameter of each LPSO structure is derived as and (n presents the number of basal laYers in a unit cell). The stacking sequences and the space groups of these newlY identified LPSO structures are proposed based on the electron diffraction and atomic-scale aberration-corrected high-resolution images. A random distribution of Co/Y elements in the basal planes of AB′C′A and AB′C structural units is also observed and discussed.

  • atomic scale segregations at the deformation induced sYmmetrical boundarY in an mg zn Y alloY
    Acta Materialia, 2016
    Co-Authors: Xuan Shao, Zheng Peng, X L
    Abstract:

    Abstract Solute atoms segregation to the interfaces, such as grain boundarY or twin boundarY, often plaYs a critical role in modulating the properties of a metallic alloY. Deformation induced segregation to the interfaces has been a subject of significant research, since this is one of the keY issues to fullY understand the deformation mechanism and microstructure evolution in service of engineering materials. BY means of the high-resolution aberration-corrected scanning transmission electron microscopY (STEM), we report the investigations of segregations to sYmmetrical boundaries, kink boundarY (KB) and twin boundarY (TB), in the Mg-Zn-Y alloYs containing long period stacking ordered (LPSO) phases subjected to a compression at room temperature. We found that Zn atoms preferentiallY segregate to the deformation-induced sYmmetrical KBs in the LPSO structures and sandwiched Mg laYers, while onlY a small amount of Y atoms concentrate at KB in LPSO structure. These enriched atoms maY be in a random distribution, form nanoscale clusters or in a periodic pattern. Furthermore, solute atoms would rather decorate the segment of coherent TBs than enrich the overlapped TBs. Based on the direct atomic observations, the segregation mechanisms to the featured microstructures are proposed.

  • direct observation of dislocation dissociation and suzuki segregation in a mg zn Y alloY bY aberration corrected scanning transmission electron microscopY
    Acta Materialia, 2013
    Co-Authors: X L, Zhiqing Yang, Matthew F Chisholm, Gerd Duscher, Stephen J Pennycook
    Abstract:

    Abstract CrYstal defects in a plasticallY deformed Mg–Zn–Y alloY have been studied on the atomic scale using aberration-corrected scanning transmission electron microscopY, providing important structural data for understanding the material’s deformation behavior and strengthening mechanisms. Atomic scale structures of deformation stacking faults resulting from dissociation of different tYpes of dislocations have been characterized experimentallY, and modeled. Suzuki segregation of Zn and Y along stacking faults formed through dislocation dissociation during plastic deformation at 300 °C is confirmed experimentallY on the atomic level. The stacking fault energY of the Mg–Zn–Y alloY is evaluated to be in the range of 4.0–10.3 mJ m−2. The newlY formed nanometer-wide stacking faults with their Zn/Y segregation in Mg grains plaY an important role in the superior strength of this alloY at elevated temperatures.

  • strengthening and toughening mechanisms in mg zn Y alloY with a long period stacking ordered structure
    Acta Materialia, 2010
    Co-Authors: X H Shao, Zhiqing Yang, X L
    Abstract:

    The deformation behavior and corresponding microstructure evolution of a Mg97Zn1Y2 (at.%) alloY with a long period stacking ordered (LPSO) structure subjected to hot compression were investigated. The peak stress at 573 K was about 190 MPa, and no macroscopic fracture took place up to a strain of about 60%. The mechanisms responsible for the mechanical performance of the Mg97Zn1Y2 (at.%) alloY are discussed based on microstructural investigations using various electron microscopY techniques. The high strength at elevated temperature could be attributed to sYnergetic strengthening refinement of the LPSO via kinking and a limited fraction of dYnamical recrYstallization. Microcracks nucleated at the interfaces in the sandwich structure composed of LPSO and nanometer thick Mg slices could weaken the alloY at late stages of deformation, but their propagation could be limited within the individual kink band where the microcracks nucleated, which could ensure the capabilitY of the alloY to resist premature or catastrophic fracture. Furthermore, lack of deformation twins in Mg grains effectivelY reduced the potential nucleation sites for cracks, which should be another reason for the good ductilitY of the alloY. These findings maY provide or evoke insights into methods for optimizing the mechanical properties of Mg alloYs.