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Jiang G.,Tsinghua University | Li Y.,Key Laboratory for Advanced Materials Processing Technology | Li Y.,Tsinghua University
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

The documented experimental results of hydrogen solubility in different liquid metals were summarized according to the periodic table. It is found that the hydrogen solubility in liquid transition metals is much higher than in others and it changes regularly with the atomic number to form a V-shaped curve. It is supposed that the electron interaction between the hydrogen and metal atoms of the liquid is the major factor in determining hydrogen solubility in the liquid metal. Based on this consideration, a model was proposed for characterizing electron interaction and calculating the hydrogen solubility in various liquid metals according to the nearly free-electron theory. The calculated hydrogen solubility in liquid transition metals agrees well with the documented experimental results, and some undocumented results could be predicted. © 2010 The Minerals, Metals & Materials Society and ASM International. Source

Yang M.,Tsinghua University | Xiong S.-M.,Tsinghua University | Xiong S.-M.,Key Laboratory for Advanced Materials Processing Technology | Guo Z.,Tsinghua University
Acta Materialia

In solidification, dendritic morphology was observed to change accordingly if either the type or quantity of the additional element was modified. To gain insight into this phenomenon, the 3D dendrite morphology of different binary magnesium alloys, including MgAl, MgBa, MgCa and MgZn alloys was characterized using synchrotron X-ray tomography and electron backscattered diffraction. Results showed that for most Mg-based alloys, the dendrite exhibited a typical 18-branch morphology with preferred growth orientations along (1120) and (1123), whereas for MgZn alloys, the dendrite morphology would change from the 18-branch pattern to 12-branch if the Zn content increased, i.e. the so-called dendrite orientation transition (DOT) took place. This DOT behaviour of the Mg alloy dendrite was then successfully modelled using the 3D phase field method by changing the magnitude of related parameters in the specially formulated anisotropy function based on spherical harmonics. © 2016 Acta Materialia Inc. All rights reserved. Source

Du M.,Tsinghua University | Zhang H.W.,Tsinghua University | Zhang H.W.,Key Laboratory for Advanced Materials Processing Technology | Li Y.X.,Tsinghua University | Li Y.X.,Key Laboratory for Advanced Materials Processing Technology
Surface and Coatings Technology

A new method was explored for inner surface alloying on pores of lotus-type porous copper. Zinc was deposited on the inner surface of pores by electroless plating with thorough supersonic vibration. Then, the Cu substrate together with Zn coatings was transformed into a brass layer by annealing treatment. From images filmed by a digital single lens reflex camera and a field emission scanning electron microscopy, it can be observed that the appearance and microstructure of lotus-type porous copper surface and pore walls were changed after the sequential treatments. The statistical thickness of the alloy layer at the distance of 0.5. mm from pore openings increased with the electroless plating time increase, attaining a maximum of about 1.7. μm when the time exceeded 1.5. h. The alloy layer thickness at the sample height of 2.5. mm along the pore axial direction was determined as about 1.5. μm by the nano-indentation technique. Uniform coating and alloy layer can be achieved on the inner surface of 5. mm-long pores. The influence of annealing temperatures on phase compositions was studied by X-ray diffraction. © 2014 Elsevier B.V. Source

Ouyang A.,Tsinghua University | Ouyang A.,Key Laboratory for Advanced Materials Processing Technology | Liang J.,Tsinghua University | Liang J.,Key Laboratory for Advanced Materials Processing Technology
RSC Advances

Porous chitosan beads are widely used as adsorption media in environmental and biomedical areas. We present two simple methods to tailor the adsorption behavior of chitosan beads by dynamic adsorption and structural modification. Compressing the chitosan beads repeatedly in solutions containing dye molecules or nanoparticles leads to significant improvement in adsorption rate by enhancing internal molecular diffusion, compared with statically placed beads. We also create a hierarchical core-shell structure consisting of a single-walled carbon nanotube network uniformly wrapped around each chitosan bead, in which the outside nanotube network can block or slow down the diffusion of larger size nanoparticles without influencing adsorption of small sized molecules and nanoparticles. Our strategy involving dynamic adsorption and fabrication of hierarchical porous structures might be applied to many other porous materials to tailor their adsorption properties. © the Partner Organisations 2014. Source

Guo Z.,Tsinghua University | Guo Z.,Key Laboratory for Advanced Materials Processing Technology | Xiong S.M.,Tsinghua University | Xiong S.M.,Key Laboratory for Advanced Materials Processing Technology
Computer Physics Communications

An algorithm comprising adaptive mesh refinement (AMR) and parallel (Para-) computing capabilities was developed to efficiently solve the coupled phase field equations in 3-D. The AMR was achieved based on a gradient criterion and the point clustering algorithm introduced by Berger (1991). To reduce the time for mesh generation, a dynamic regridding approach was developed based on the magnitude of the maximum phase advancing velocity. Local data at each computing process was then constructed and parallel computation was realized based on the hierarchical grid structure created during the AMR. Numerical tests and simulations on single and multi-dendrite growth were performed and results show that the proposed algorithm could shorten the computing time for 3-D phase field simulation for about two orders of magnitude and enable one to gain much more insight in understanding the underlying physics during dendrite growth in solidification. © 2015 Elsevier B.V. All rights reserved. Source

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