Co-reporter:Ning Li, Ze Liu, Xinyun Wang, Meng Zhang
Materials Science and Engineering: A 2017 Volume 692(Volume 692) pp:
Publication Date(Web):24 April 2017
DOI:10.1016/j.msea.2017.03.062
Controlled activation of flow units and in-situ characterization of mechanical properties in metallic glasses are facing challenges thus far. Here, vibrational loading is introduced through nanoscale dynamic mechanical analysis technique to probe vibration-accelerated atomic level flow that plays a crucial role in the mechanical behavior of metallic glasses. The intriguing finding is that high vibrational frequency induces deep indentation depth, prominent pop-in events on load–depth curves and low storage modulus, exhibiting a vibration-facilitated activation of flow units in Pd40Cu30Ni10P20 metallic glass. Theoretical analysis revealed that vibration-moderated activation time-scale accelerate the activation of flow units and responsible for the above scenario.
Co-reporter:Di Ouyang, Ning Li, Wei Xing, Jianji Zhang, Lin Liu
Intermetallics 2017 Volume 90(Volume 90) pp:
Publication Date(Web):1 November 2017
DOI:10.1016/j.intermet.2017.07.010
•A crack-free Zr-based bulk metallic glass composite was successfully fabricated by selected laser melting.•The composite exhibited high strength of about 1500 MPa.•Both low thermal stress and high fractural toughness responsible for the crack-free BMG composite in selected laser melting.3D printing of crack-free bulk metallic glasses remains challenge due to the generation of huge thermal stress during the selective laser melting and their intrinsic brittleness. Herein, Zr55Cu30Ni5Al10 system was selected and 3D printed by selective laser melting technique. The results indicated that bulk metallic glassy composite comprises a large fraction (about 83%) of amorphous phase and minor fraction of intermetallic compounds with free of cracks were successfully fabricated. The 3D printed metallic glassy composite exhibited high strength over 1500 MPa. Experiment combined with finite-element-method simulation not only revealed the mechanism of crystallization at heat affected zones, but demonstrated that low thermal stress reduce the risk of micro-cracks generation and fracture toughness plays a crucial role in suppression the crack propagation during selective laser melting process.
Co-reporter:Ning Li, Haiping Yu, Zhu Xu, Zhisong Fan, Lin Liu
Materials Science and Engineering: A 2016 Volume 673() pp:222-232
Publication Date(Web):15 September 2016
DOI:10.1016/j.msea.2016.07.039
The identification of different deformation mechanisms in aluminum alloy under high-velocity electromagnetic forming and mechanical forming is a daunting task, due to the limitations in performing identical experimental conditions. Here, we present a special strategy to achieve electromagnetic and mechanical deformations with equivalent strain and strain rate. The intriguing finding is that the deformation mechanism of 5052 aluminum alloy is dominated by planar slip in mechanical deformation versus wavy slip in electromagnetic forming. The physical origin of the phenomenon is rationalized according to theoretical analysis coupled with finite-element-method simulation. The finite-element-method simulation presents planar and spatial force in the aluminum alloy during mechanical deformation and electromagnetic forming, respectively. The theoretical analysis reveals that under mechanical deformation with planar force, the destruction of short range cluster on the activate glide planes reduces the local resistance of dislocation motion and facilitates the planar slip. By contrast, the collective motion of dislocations in three dimensions caused by spatial force under electromagnetic forming facilitates the wavy slip that is represented by the dislocation cell structures. Our findings provide an effective method and fundamental understanding for unveiling various deformation mechanisms in aluminum alloy under electromagnetic and mechanical processing.
Co-reporter:Baiping Lu, Ning Li
Applied Surface Science 2015 Volume 326() pp:168-173
Publication Date(Web):30 January 2015
DOI:10.1016/j.apsusc.2014.11.138
Highlights
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The versatile aluminum alloy surfaces with various wettability have been fabricated simply.
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The mechanism is rationalized in terms of the Cassie–Baxter model by considering the surface energy gradient.
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The versatile metallic surfaces unfold application in antennas, lubricated surface and multi-transport of liquid microdroplets.
Co-reporter:Cong Yan, Ning Li, Huawen Jiang, Duzhen Wang, Lin Liu
Materials Science and Engineering: A 2015 Volume 638() pp:69-77
Publication Date(Web):25 June 2015
DOI:10.1016/j.msea.2015.04.058
The effect of electropulsing on the deformation behavior, texture and microstructure of 5A02 aluminum alloy was investigated through uniaxial tension, electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The Portevin-Le Chatelier (PLC) effect reflected as the serrated characteristic in stress–strain curves, became conspicuous firstly but then disappeared with further increase of electropulsing intensity. The texture analysis exhibited that the electropulsing causes an increase of Cube texture, accompanied with a reduction of S texture. Microstructure characterization revealed a transition of slipping mode from planar slip to wave slip with increasing electropulsing intensity. The temperature rise induced by electropulsing, together with the influence of solute atoms, was proposed to rationalize the present phenomena in detail.
Co-reporter:Zhu Xu, Ning Li, Huawen Jiang, Lin Liu
Materials Science and Engineering: A 2015 621() pp: 272-276
Publication Date(Web):
DOI:10.1016/j.msea.2014.10.085
Co-reporter:Ning Li, Xiaona Xu, Zhizhen Zheng, Lin Liu
Acta Materialia 2014 Volume 65() pp:400-411
Publication Date(Web):15 February 2014
DOI:10.1016/j.actamat.2013.11.009
Abstract
Vibrational loading was introduced as an innovative method to improve the thermoplastic formability of Zr35Ti30Be26.75Cu8.25 bulk metallic glass in a supercooled liquid state. The tensile strain, as a measure to characterize the formability, increased with increasing loading frequency, indicating a vibrational loading facilitated formability. The physical mechanism of this phenomenon was rationalized on the basis of both theoretical analysis and finite-element-method simulation. The theoretical analysis revealed that a more homogeneous distribution of flowing units with a smaller volume, together with a larger free volume concentration, existed in the specimen under relatively higher loading frequencies. The finite-element-method simulation combined with the free volume constitutive relation exhibited an increase in free volume concentration with increasing loading frequency, in agreement with theoretical analysis. Finally, compressive and hot-embossing tests under vibrational loading were carried out to further verify the applicability of this technique. The present results not only provide an effective method to facilitate the thermoplastic formability of bulk metallic glasses, especially in micro/nanoscale forming, but also offer a better understanding of the structural evolution of the metallic supercooled liquid under vibrational loading.
Co-reporter:Yuanyuan Xiong;Huawen Jiang
Acta Metallurgica Sinica (English Letters) 2014 Volume 27( Issue 2) pp:272-278
Publication Date(Web):2014 April
DOI:10.1007/s40195-014-0041-7
The microstructural evolution of AA7055 aluminum alloy under dynamic impact loading with the strain rate of 1.3 × 104 s−1 controlled by a split Hopkinson pressure bar was investigated, and compared with that under quasi-static mechanical loading in compression with strain rate of 1.0 × 10−3 s−1. The quasi-static-compressed sample exhibited equiaxed dislocation cells, which were different from the elongated and incomplete dislocation cells for the alloy undergoing dynamic compression. The high strain-rate compression also induced the formation of localized shear bands in which the recrystallizations characterized as fine equiaxed grains were observed. The microstructural evolutions under both quasi-static and dynamic compressions are rationalized in terms of the dislocation cell model combined with the dislocation kinetics, in addition to the adiabatic temperature rise in shear bands at high strain rate.
Co-reporter:J.J. He, N. Li, N. Tang, X.Y. Wang, C. Zhang, L. Liu
Intermetallics 2012 Volume 21(Issue 1) pp:50-55
Publication Date(Web):February 2012
DOI:10.1016/j.intermet.2011.10.001
A Zr-based bulk metallic glass (BMG) mould with microchannel structure has been hot-embossed on a silicon master mould with the desired reciprocal features. The cross section of the hot-embossed topography was observed by scanning electron microscopy (SEM), and the results revealed that there is no discernible gap at the interface between the silicon and the metallic glass. The simulations were performed using commercial software DEFORM 3D to reveal the micro-scale hot-embossing process. The theoretical forming pressure and the maximum filling length were calculated according to the Hagen–Poiseuille law. Both experimental and theoretical results demonstrated that the microchannel features can be accurately replicated under the hot-embossed conditions with a low flow stress. Finally, the microstructure of the hot-embossed microchannel part was characterized by transmission electron microscopy (TEM), and no detectable crystallization occurred, indicating that the Zr-based BMG remains amorphous after hot-embossing process.The cross section of the hot-embossed topography was observed by scanning electron microscopy (SEM), and the results revealed that there is no discernible gap at the interface between the silicon and the metallic glass, demonstrating that the microchannel features can be accurately replicated under the hot-embossed conditions with low forming stress.Highlights► We hot emboss a bulk metallic glass mould with micochannel structure. ► We examine the replication accuracy from theoretical and experimental aspects. ► We characterize the microstructure of the hot-embossed microchannel part.
