This study describes a new two-step process to cool the thermal vibration of microcantilevers. The process combines active mechanical feedback cooling and optical cavity cooling. A micro-Fabry-Perot ...interferometer, built in-house, is set atop a microcantilever to measure the vibration amplitude, the high optical power density of which induces cavity cooling in the optical cavity. Using a two-step cooling procedure, the equivalent temperature of the thermal vibration of a microcantilever is lowered from room temperature to the theoretical cooling limit of 0.063 K, a much lower temperature than that achieved via simple cavity cooling (18 K), and then by mechanical feedback cooling (0.135 K) obtained for the same type of microcantilevers in previous studies. This experimental demonstration showcases a new type of cooling process of the amplitude of thermal vibration for micro-mechanical resonators to a lower temperature and does not need additional cooling using a conventional cryogenic refrigerator.
Manipulating topological spin textures is a key for exploring unprecedented emergent electromagnetic phenomena. Whereas switching control of magnetic skyrmions, e.g., the transitions between a ...skyrmion-lattice phase and conventional magnetic orders, is intensively studied towards development of future memory device concepts, transitions among spin textures with different topological orders remain largely unexplored. Here we develop a series of chiral magnets MnSi
Ge
, serving as a platform for transitions among skyrmion- and hedgehog-lattice states. By neutron scattering, Lorentz transmission electron microscopy and high-field transport measurements, we observe three different topological spin textures with variation of the lattice constant controlled by Si/Ge substitution: two-dimensional skyrmion lattice in x = 0-0.25 and two distinct three-dimensional hedgehog lattices in x = 0.3-0.6 and x = 0.7-1. The emergence of various topological spin states in the chemical-pressure-controlled materials suggests a new route for direct manipulation of the spin-texture topology by facile mechanical methods.
The mechanical properties of Mg97Zn1Y2 extruded alloy, composed of Mg matrix phase and a long-period stacking ordered phase, the so-called LPSO phase, with a volume fraction of approximately 24%, ...were investigated using compression tests at room temperature. The microstructure was varied to a large degree by various heat treatments at high temperatures above 400°C, and the relationship between the microstructure and mechanical properties was clarified. The plastic behavior of the Mg/LPSO two-phase alloy was compared with that of Mg99.2Zn0.2Y0.6 alloy, composed almost Mg-solid-solution phase, and the strengthening mechanisms at work in the Mg97Zn1Y2 extruded alloy are discussed. The existence of the LPSO phase strongly enhanced the refinement of Mg matrix grains during extrusion, which led to a large increase in yield stress through the Hall–Petch relationship. In addition, the LPSO phases, which were aligned along the direction of extrusion in the Mg97Zn1Y2 extruded alloy, acted as hardening phases, being roughly coordinated with the short-fiber reinforcement mechanism.
Mg97Zn1Y1RE1 (RE=La, Ce, Nd and Sm, at. %) alloys were prepared by high-frequency induction melting in an Ar atmosphere. Rods were extruded at 623K and a ram speed of 2.5mm·s−1 using a circular die ...with an extrusion ratio of 10. The microstructure and mechanical properties of the extruded alloys were investigated. The Mg97Zn1Y1Nd1 and Mg97Zn1Y1Sm1 alloys consisted of only two phases: α-Mg and a Mg-RE intermetallic compound. The Mg97Zn1Y1La1 and Mg97Zn1Y1Ce1 alloys consisted of three phases: α-Mg, a Mg-RE intermetallic compound, and a Mg12ZnY phase with a long-period stacking ordered (LPSO) phase. Additionally, after extrusion, the three-phase Mg97Zn1Y1RE1 alloys, i.e., those with an LPSO phase, had a stratified microstructure and exhibited better mechanical properties than those without an LPSO. At room temperature, the yield strength and ultimate tensile strength of the three-phase Mg97Zn1Y1La1 and Mg97Zn1Y1Ce1 alloys were 381–384MPa and 427–429MPa, respectively, and yield strengths greater than 280MPa were observed at the elevated temperature of 523K.
It has recently been found that Mg97Zn1Y2 extruded alloy containing a long-period stacking ordered (LPSO) phase has superior mechanical properties. In this study, the high-temperature deformation ...mechanism of the Mg97Zn1Y2 extruded alloy was examined. Grain-boundary strengthening due to the refined Mg-matrix phase and fiber-like reinforcement due to the LPSO phase dominantly contribute to the strengthening of the alloy at room temperature, and they were confirmed to effectively act even at 200°C. As a result, the extremely high strength of the alloy is maintained up to 200°C, unlike other conventional Mg alloys. At 300°C, however, the yield stress of the Mg97Zn1Y2 alloy largely decreases, and the orientation and the grain size dependence of the yield stress become weak. Increases in the operation frequency of non-basal slip in the Mg-matrix grains weaken the grain-boundary strengthening effect. In addition, the effect of fiber-like reinforcement due to the LPSO phase is also weakened at 300°C because the window of microstructure suitable for inducing this effect becomes significantly narrow at this temperature.
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 〈0001〉 in the hexagonal expression was clearly higher than that along 〈112¯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.
The crystal structure of a long period stacking-ordered (LPSO) phase newly found in the Mg–Al–Gd ternary system has been investigated by scanning transmission and transmission electron microscopy. ...The LPSO phase in the Mg–Al–Gd system is found to form by stacking structural blocks, each of which consists of six close-packed atomic planes. In each of the structural blocks long-range ordering occurs for the constituent Mg, Al and Gd atoms, with enrichment of Gd atoms occurring in four consecutive planes of the six close-packed atomic planes. The ideal chemical composition of the structural block is determined to be Mg29Al3Gd4 (Mg–8.3 at.% Al–11.1 at.% Gd). However, the stacking of structural blocks is largely disordered. Strictly speaking, the technical term LPSO cannot be used to describe this phase because of the long-range ordering of the constituent atoms in each structural block. The crystal structure of the LPSO phase can thus be crystallographically described as one of the order–disorder structures, and either the C2/m, P3112 or P3212 space group is assigned when the simplest stacking of structural blocks is assumed.
Recent progress on welding in bulk metallic glasses (BMGs) has been reviewed. BMGs have been successfully welded to BMGs or crystalline metals by liquid phase welding using explosion, pulse–current ...and electron-beam methods, and by supercooled liquid phase welding using friction method. Successful welding of the liquid phase methods was due to the high glass-forming ability of the BMGs and the high concentration of welding energy in these methods. In contrast, the supercooled liquid phase welding was successful due to the thermally stable supercooled liquid state of the BMGs and the superplasticity and viscous flow of the supercooled liquid. The successful welding of BMGs to BMGs and crystalline materials is promising for the future development of BMGs as engineering materials.
We have identified a novel long-period stacking/order (LPSO) phase in a Mg-Ni-Y alloy, which provides novel LPSO structural features regarding both the stacking/order aspects; the 12R-type stacking ...sequence and the in-plane modulation of approximately 7×(12¯10)hcp with respect to the fundamental hexagonal-closed-packed Mg structure. The ideal 7 M model for the present 12R-type LPSO phase is constructed based on the ordered arrangements of the L12-type Ni6Y8 clusters embedded in the local ABCA stacking layers, resulting in the stoichiometry Mg77Ni9Y12 (Mg78.6Ni9.2Y12.2) that appears to be extremely close to the experimentally determined composition Mg78.4Ni9.0±0.2Y12.6±0.3 (at.%). This in turn suggests the robustness of the solute cluster with a specific ratio (Ni6Y8), emerging the pseudo-binary formation behaviors of the LPSO phase in the Mg ternary alloys.
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•A novel type of the long-period stacking/order structure has been determined.•Combined use of electron diffraction/microscopy and first principles calculations.•12R-type stacking sequence and the in-plane order of approximately 7×(12¯10)hcp.•Robust L12-Ni6Y8 cluster rules the LPSO phase formation as a pseudo-binary system.
In this study, the microstructure and mechanical properties of MgZnY alloy sheets were investigated. Tensile tests at room temperature were performed along the rolling direction of Mg98Zn1Y1-, ...Mg96Zn2Y2-, and Mg94Zn3Y3- alloy sheets and their annealed states (773K for 0.6ks). These alloy sheets exhibited yield strengths of 261, 317, and 380MPa, and elongations of 12, 10, and 6%, respectively. The yield strength of a MgZnY alloy sheet with Zn and Y contents greater than 2at% was higher than 300MPa. 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 Mg3Zn3Y2 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 Mg98Zn1Y1- and Mg96Zn2Y2 -alloy annealed sheets. The cold workability of the MgZnY alloy sheets and an AZ31-O sheet were evaluated, using a V-bending test at room temperature. Both Mg98Zn1Y1- and Mg96Zn2Y2- 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 MgZnY 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 MgZnY 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 MgZnY alloy system.
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