We propose a scheme for generating squeezed light by using a double-cavity optomechanical system driven by a blue detuned laser in one cavity and by a red detuned laser in the other. This ...double-cavity system is shown to effectively mimic an interaction that is similar to the one for a downconverter, which is known to be a source of strong squeezing for light fields. There are however distinctions, as the phonons which lead to such an interaction can contribute to the quantum noise. We show that squeezing of the output fields, of the order of 10 dB, can be achieved even for an effective mechanical mode occupation number of about 4, which for the chosen parameters corresponds to 10 mK. Our results are generic and applicable to a wide class of electromechanical and optomechanical systems involving the interaction of two electromagnetic modes and one mechanical mode.
This study presents the effects of Zr addition on microstructure, phase composition, and superelasticity of Ti-24Nb-xZr (at.%, x = 0, 2, 6) alloys fabricated by spark plasma sintering (SPS). The ...obtained microstructures were studied using X-ray diffraction and electron microscopy, and the mechanical properties and shape memory properties were evaluated through both compressive testing and cyclic compression experiments. The results show the addition of Zr is beneficial to the formation of the α’’ phase and β-Ti grain refinement. The sintered Ti-24Nb-6Zr shows better compressive yield strength (1457 MPa), ultimate strength (2458 MPa), and strain (45.31%). Cycle compression tests reveals that the Ti-24Nb-6Zr alloy demonstrates stable recoverable strain of 4.11% and remarkable recovery strain rate of 98.1% in the second cycle, and a maximum 7.8% recovery strain and good recovery strain rate of 82.4% in the fifth cycle. In contrast, the sintered Ti-24Nb alloy exhibits recoverable strain of 4.58%, a recovery strain rate of 96.6% in the third cycle, and only 48.8% recovery strain rate in the fifth cycle. The transmission electron microscopy results indicate that the formation of microcracks and dislocations during the cycle compression results in significant recovery strain reduction for the Ti-24Nb alloy. The results provide guidelines to design high-performance Ti-24Nb-based alloys with excellent shape memory properties for structural applications.
•Our results provide guidelines to design high-performance Ti-24Nb-based alloys.•The Zr addition is effective to enhance strength and ductility of Ti-24Nb-based alloys.•The formation of microcracks and dislocations result in poor cycle stability of superelasticity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
13.
Shear band fracture in metallic glass: Sample size effect Qu, R.T.; Wang, S.G.; Wang, X.D. ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
01/2019, Volume:
739
Journal Article
Peer reviewed
Previous studies have revealed that the shear band propagation of metallic glasses can be strongly influenced by decreasing the sample size, leading to the dramatically enhanced plasticity. Here we ...show that the sample size also affects the shear band fracture behavior. When reducing the sample size, the compressive shear band fracture mode is changed from the typical instant fracture with vein patterns into a gradual fracture mode without the formation of vein pattern. This can be explained by the marked reduction of energy dissipation density during shear band sliding in small samples and thus the enhanced shear band stability against the instable fracture.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We report on the formation of ultrafine-grained (Ti69.71Nb23.72Zr4.83Ta1.74)100−xSix (at.%, x=0, 2 and 5) alloys designed by d-electron alloy design theory and fabricated by spark plasma sintering of ...nanocomposite powder precursor. The designed and fabricated alloys exhibit a high yield and fracture strength of 1296MPa and 3263MPa along with an ultra-large fracture strain of 65% under compression. Meanwhile, they display low elastic modulus of 37–48GPa. The high-performance titanium alloys without toxic elements show high potential for application as biomaterials.
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•Biomedical TiNbZrTaSi alloys were designed by d-electron alloy design theory.•The new ductile TiNbZrTaSi bulk alloys were fabricated by spark plasma sintering.•The ultrafine-grained composite structure contains β-Ti matrix and S2 phase.•The bulk alloys exhibit superplasticity, high strength and low modulus.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•The effect of confinement on the plastic deformation of MG was systematically studied.•The external confinement can significantly improve the stability of shear banding.•The kinetic and energy ...dissipation equations for the confined MG were derived.•The mechanisms of confinement effect in various confined MG systems were summarized.
While metallic glasses (MGs) usually fracture catastrophically under uniaxial loading, external confinement like coating has been proved quite effective for improving the plasticity. The positive effect of confinement was mainly attributed to the lateral confining stress on the interface between sample and confinement, which impedes the excess propagation of shear bands and promotes their multiplication. Here we show that, even though there is no contact between the MG and the confinement, the brittle fracture can be effectively suppressed. Three dimensional (3D) high resolution X-ray tomography observations successfully captured the shear-band cracking evolution and confirmed that the external confinement caused the change of shear-band fracture mode. Analysis on the thermodynamics and kinetics of shear banding in the confined MG shows that the confinement extremely reduces the shear velocity, contributes to the shear band arrest, and largely lowers the energy release rate, leading to the increase of the shear stability and the resistance to instant fracture. Finally, the mechanisms of confinement effect on the plastic deformation in various confined MG systems were summarized. These results suggest new understandings on the effect of confinement for the fracture of MG composites or coated MG structures, and on the mechanisms of shear-band cracking and fracture in different MG loading systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
a- Ti-based composite was fabricated by SPS and crystallization of amorphous phase. a- The strength and ductility are superior to counterpart nanostructured composites. a- Theoretical base of ...fabricating crystallized phase-containing alloy was elucidated. a- Nucleation and growth mechanism of crystalline phase were elucidated. a- The results provide a way to fabricate crystallized phase-containing composites. Ductile ultrafine-grained Ti66Nb13Cu8Ni6.8Al6.2 composites with in situ precipitated b-Ti(Nb) phase were fabricated by spark plasma sintering and crystallization of amorphous phase. Microstructure analysis indicates that hard b-Ti(Nb) forms the matrix and soft (Cu, Ni)-Ti2 acts as the reinforced phase, but the two phase regions have different scale, morphology and distribution. Fracture strength and fracture strain of the composites reach as high as 2415MPa and 32.6%, respectively. Theoretical bases of fabricating the ultrafine-grained composites, and nucleation and growth mechanism of crystalline phase during the crystallization process were elucidated. The results obtained provide a promising method for fabricating large-sized crystallized phase-containing bulk composites with excellent mechanical property by powder metallurgy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The different mechanical properties for the consolidated and crystallized (Ti69.7Nb23.7Zr4.9Ta1.7)100−xFex (x=0, 2, 6, and 10) alloys are attributed to the different crystallized phases and ...microstructures induced by the different nuclei growth mechanisms of as-milled nanocrystalline/amorphous alloy powders. Display omitted
► With the increased Fe content, the GFA of as-milled TiNbZrTaFe alloy increases gradually. ► The crystallization mechanism of as-milled alloy powders is different. ► Fe alloying addition affect the mechanical property of the crystallized alloys. ► The results provide a way for fabricating biomedical material by powder metallurgy.
(Ti69.7Nb23.7Zr4.9Ta1.7)100−xFex (x=0, 2, 6, and 10) nanocrystalline, nanocomposite and metallic glass powders were synthesized by mechanical alloying. The glass-forming ability (GFA) and crystallization behavior of the synthesized alloy powders are investigated by X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. With the increased Fe content, the synthesized alloy powders after the steady state milling transform from full nanocrystalline structure for x=0 to nanocomposite structure containing amorphous matrix surrounding nanocrystals for x=2 and 6 and to full amorphous structure for x=10, and thus has the increased enthalpy of crystallization and the increased GFA. The non-isothermal crystallization kinetics is analyzed by the modified Johnson–Mehl–Avrami (JMA) equation. The values of the Avrami exponent imply that the crystallization of (Ti69.7Nb23.7Zr4.9Ta1.7)100−xFex nanocomposite/metallic glass powders with x=6 and 10 is governed by diffusion-controlled three and two-dimensional growth, respectively. Moreover, the crystallized bulk alloys consolidated from the synthesized alloy powders have different crystallized phases, microstructures and mechanical properties. The increased GFA with the increased Fe content could be explained by the total number of intermetallics present in the milled powders, appropriate atomic-size mismatch and large negative heat of mixing among constituent elements.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We report a novel microstructure evolution and corresponding mechanical behavior of bimodal eutectic (Ti63.5Fe26.5Co10)82Nb12.2Al5.8 alloys processed by semi-solid sintering (SSS) of the as-milled ...alloy powders with various glass contents resulted from various milling times. Results show that the as-milled alloy powders have more homogeneous element distribution and higher content of glassy phase with increased milling time. Correspondingly, although the SSSed bulk alloys possess the same constituted phases of the bcc β-Ti, bcc B2 Ti(Fe, Co) and fcc Ti2(Co, Fe), their eutectic structures containing bcc β-Ti and bcc B2 Ti(Fe, Co) evolve from irregular eutectic, to partial coarse eutectic, to fine cellular eutectic matrix, and finally to typical nano and ultrafine lamellar eutectic matrix. Interestingly, it is the first time to report that the lamellar eutectic matrix has an bimodal structure consisting of interleaving nano- and ultrafine-grained B2 Ti(Fe, Co) and bcc β-Ti lamellae. Corresponding to the evolution of eutectic structure, the SSSed bulk alloys exhibit a gradual increase in yield strength and plastic strain. Especially, the SSSed bimodal eutectic alloy has ultra-high yield strength of 2050MPa and large plasticity of 19.7%, superior to those of equivalent counterparts. Theoretically, strengthening mechanism of the SSSed bimodal eutectic alloy can be mainly rationalized as ordering strengthening of B2 superstructured Ti(Fe, Co) and coherency strengthening between bcc β-Ti and bcc B2 Ti(Fe, Co) lamellae inside the lamellar eutectic matrix.
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In this paper, the effects of heat treatment processes on microstructure, residual stress and dimensional stability of 70vol.% SiCp/Al composites were investigated by using a field emission gun ...scanning electron microscope (SEM), the X-ray stress analyzer and the thermal cycling test method. The results showed that the matrix of the as-cast composite is in compression. After the solution-quenching (SQ), aging and thermal-cold cycling (TCC) treatment, the residual stress was reduced due to the plastic deformation of the matrix. With the increase in the numbers of the SQ treatment, the long rod Al(MnFe)3Si2 phase and the blocky CuAl2 phase decreased while the spheroidization of these intermetallics increased. The TCC treatment refined the size of these intermetallics. As the number of the TCC treatments is increased, the resistance to micro-plastic deformation of the composite was also enhanced. The composite, which experienced the three-step SQ and aging and 12 times TCC treatment, presented the optimum thermal stability. Its hysteresis strain achieved 0.26×10−5, and remained constant during the second and third cycling tests. The excellent dimensional stability shows a promising potential to be used as mirror materials for preparing mirror substrates in industry.
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•The morphology feature can predict the dimensional stability of the composite.•The solution-quenching treatment generates the macro-plastic deformation.•The aging and thermal-cold cycling treatment cause the micro-plastic deformation.•The net hysteresis strain can evaluate the thermal stability of the composite.•The hysteresis strain of the composite after heat treatment achieves 0.26×10−5.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Non-isothermal and isothermal crystallization kinetics of mechanically alloyed Ti65Nb23.33Zr5Ta1.67Si5 metallic glass (MG) powder and their effect on microstructure and mechanical property of ...spark-plasma-sintered and crystallized bulk counterparts were investigated by using Johnson–Mehl–Avrami–Kolmogorov equation. Results show the MG powder has two distinct crystallization steps, which precipitates bcc β-Ti and hexagonal (Ti, Zr)2Si phases successively. The larger apparent activation energy of the second crystallization step than that for the first one indicates the easier occurrence of precipitation for bcc β-Ti phase. Comparative analysis of crystallization kinetics indicates that regardless of non-isothermal and isothermal crystallization types, the first crystallization step is dominated by diffusion-controlled three- and two-dimensional growth of nuclei for the early and late crystallization stage, respectively, while the second one is governed by diffusion-controlled three-dimensional growth of nuclei in the whole crystallization process. Both nucleation rates of these two steps increase firstly and then reduce in the early and late crystallization stage, respectively. The processing technologies combined with crystallization kinetics decide different grain sizes and yield strengths for the sintered and crystallized bulk alloys. The results obtained provide a new insight into tailoring microstructure and mechanical property of bulk alloys by designing and optimizing processing technologies based on crystallization kinetics.
•The as-prepared TiNbZrTaSi MG powder has two distinct crystallization steps.•Ex1<Ex2 implies that its first crystallization step is easier to be occurred.•Non-isothermal and isothermal crystallization mechanisms are similar.•Sintering condition and crystallization mechanism affect structure of bulk alloys.•The results provide a new way tailoring structure and property of bulk alloys.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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