Papers by Author: Li Ma

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Authors: Li Ma, Ting Zhang, Xiao Li, Zhao Hui Hu
Abstract: Large-scale Ni-based super-alloy sheet has been prepared by electron beam physical vapor deposition (EB-PVD). Microstructure and the dislocation structures in the γ-γ′ double phase alloy under different temperature after tensile strain are studied with Transmission electron microscopy (TEM). The results show that the dislocation glide in single slip system and shearing mechanics, the dislocation climb with part shearing, absolute dislocation climb and cross slip, dislocation round are a course of the interacting degree between dislocation and γ′ phase gradually weakened under the tensile temperature from room temperature to high temperature, so as to decrease materials strength and increase plasticity.
251
Authors: Hai Bo Wang, Li Ma, Wei Cai
Abstract: The microstructure evolution of sputtered polycrystalline Ni54.75Mn13.25Fe7Ga25 ferromagnetic shape memory thin film annealed under different conditions is studied. Microstructure of different annealed films was studied using Transmission Electron Microscope (TEM) and corresponding selected area electron diffraction (SAED) patterns. The result shows that in the microstructure of as-deposited Ni54.75Mn13.25Fe7Ga25 free-standing film, after annealed at 1073 K for different time, the crystalline grain grows up with the increase of the annealing time. By analysis of the SAED patterns, the structure of the thin films change from face-centered cubic austenite to orthorhombic structure martensite compared between the film annealed at 1073 K for 10 mins, 1hr, 4 hrs, and 24 hrs respectively. It indicated that the heat treatment is an effective method of crystallizing behavior for the thin film.
1745
Authors: Hai Bo Wang, Hao Xiong, Li Ma, Wei Cai
Abstract: The Ni54.75Mn13.25Fe7Ga25 (at.%) ferromagnetic shape memory thin film was deposited onto silicon substrates using radio-frequency magnetron sputtering. The martensitic transformation, crystallographic structure, microstructure and magnetic-field induced strain were investigated by means of Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), Transmission Electron Microscope (TEM) and metal strain gauges. The results show that the martensite transformation temperature Ms is 296.6 K, the film with typical self-accommodated morphology is orthorhombic structure at room temperature. The field-induced strain of 52 ppm is obtained in this shape memory thin film.
408
Authors: Xiao Li, Bai Yang Lou, Xiao Dong He, Li Ma
Abstract: High silicon electrical steel prepared by EB-PVD was subjected to high temperature rapid thermal annealing and subsequent pack rolling. The phase composition and Fe configurations were characterized by X-ray diffraction and Mössbauer spectroscopy. The results show that the as-deposited, as-annealed and as-rolled samples mainly consist of DO3 ordering phase and the as-deposited electrical steel is composed of six kinds of Fe sites corresponding to 333.8KOe, 319KOe, 302 KOe, 284 KOe, 249 KOe, 196 KOe, respectively, while the Fe site corresponding to 196 KOe hasn’t been found in the other two samples. Moreover, the other two samples show a larger Fe site occupancy corresponding to 284 KOe.
352
Authors: Yi Jie Zhao, Li Ma, Xiao Dong He
Abstract: By using electron beam physical vapor deposition (EB-PVD) technology, Ti-Al thin sheet with dimension of 450mm×450mm×0.2mm was prepared and the microstructure of Ti-Al deposit was investigated by means of scanning electron microscopy (SEM), atom force microscopy (AFM) and X-ray diffraction (XRD), and then the effect on deposit by re-evaporation of Al was explored by calculating the ratio of re-evaporating capacity with depositing capacity of Al on the substrate. The results indicate that there existed equiaxed crystal and columnar crystal along the cross-sectional may resulted from the transformation latent heats released during the transition course of atoms from gaseous state to solid state, and the variation of target-substrate distance would take effect on the phase composition due to the changing of atoms collision probability and radiant heat quantity absorbed by substrate. The effect on deposit by re-evaporation of Al could be neglected because the re-evaporating capacity of Al was far below that of the depositing capacity.
302
Authors: Gu Ping Wang, Li Ma
Abstract: TiAl based micro-laminated sheet was deposited by electron beam physical vapor deposition (EB-PVD) with dual-target in this work, and then the microstructure and phase analysis of as-deposited samples were studied by SEM, XRD and TEM. The results show that the difference of melting points between Ti and Al led to the distinctive structure: the Ti-Al layers were mainly constituted of equiaxed grains and Ti layers were constituted of column grains. Because of the deviation of saturated vapor pressure between Ti and Al element, the component showed a gradient change periodically along the normal direction of Ti-Al layers and results in several sub-layers. The Ti layers, Ti-Al layers and interfacial layers were constituted of α phase, γ+α2 phase and α2 phase respectively.
422
Authors: Li Ma, Lu Ju He, Hai Bo Wang, Gu Ping Wang
Abstract: The residual stress and the effect of microstructure parameters on failure performance of Ti/TiAl micro-laminated sheet were studied by Correlative theory and FE method. The results showed that the fracture work increases gradually with the increasing of layer number or thickness ratio. However, the rising extent reduced gradually and when the two parameters exceeded a certain value, the fracture work would not be changed. The value of residual stress reached its maximum at the centre and reached its minimum at the edge of micro-laminated sheet. Residual stress in Ti layers and Ti-Al layers was compressive stress and tension stress respectively. With increasing of layer number or thickness ratio, compressive stress would rise gradually and compressive stress would reduce gradually.
1137
Authors: Li Ma, Zhao Hui Hu
Abstract: Large-sized Ti/Ti-Al micro laminated thin sheet with thickness of 0.12mm was prepared by high-power electron beam physical vapor deposition technology, and then tensile tests of specimen after hot-pressing densification were carried out at room and high temperature, and tensile specimen was examined the fractured surfaces by SEM and OM. It was found that the tensile specimen under room temperature presents a compound quasi-cleavage and intergranular fracture, and a certain plastic deformation of Ti toughening layer was detected during fracture process. Tensile fractured surfaces under high temperature present the feature of compound dimple models and quasi-cleavage, furthermore, the size and the quantity of dimple exhibited an enhancing trend with test temperature increased. Results show that the cracks will stagger along the inter-laminar interface or the layer due to which micro-laminate expresses a good characteristic of delayed fracture. The toughening mechanisms are that the crack deflection and micro-bridge connection caused by the toughening layers increases crack propagation resistance.
308
Authors: Li Ma, Lu Ju He, Hai Bo Wang
Abstract: The heat convection was the main heat exchange in the autoclave by which composite pressure vessel was cured. To determine the heat convection coefficient, the combination of theoretical calculation and temperature test is absolutely necessary. In the theoretical calculation, the determination of the heat convection coefficient is considered as an inversion problem of thermal conduction. By adjusting convection coefficient value in the finite element calculation, optimization method was employed to obtain a good agreement between calculated temperature and measured temperature. In the temperature test, the metallic liner of pressure vessel was used as test component to record temperature data which was compared with the calculated temperature. The results present the equivalent thermal boundary condition for the simulation of curing process of pressure vessel.
915
Authors: Li Ma, Hai Bo Wang, Zhao Hui Hu
Abstract: A microlaminate consisting of Ti and α2-Ti3Al+γ-TiAl has been synthesized using electron beam physical vapor deposition technique. The microstructure and various properties have been explored. It is demonstrated that the nano-hardness and elastic modulus of Ti layer and Ti-Al layer are of gradient distribution according to the distance to the interface layer which may be results from the pile-up effect and the stress concentration at interface. The presence of Ti layers will lead to the cracks stagger along the inter-laminar interface or the layer due to which micro laminate expresses a good characteristic of delayed fracture. The toughening mechanisms are that the crack deflection and micro-bridge connection caused by the toughening layers increases crack propagation resistance.
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