Papers by Author: Xin Pei Ma

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Authors: Lu Lu Wang, Guang Xin Li, Xin Pei Ma, Feng Jiang, Jun Sun
Abstract: The mechanical properties of two high manganese steels with manganese contents (15% and 25%) were investigated during tensile tests at room temperature. The results indicated that the strengths of steels were a little low and the elongations were improved greatly with increasing the manganese content. Stress fluctuations were found during tensile tests of the Fe-15Mn steels, and as the strain increased the range of stress fluctuations became wider. The strain hardening exponent n of samples changed with strain in a parabola model. The microstructures before and after deformation were investigated and the results showed that phase transformation of γ (fcc) →ε (hcp) and γ (fcc) →ε (hcp) →α (bcc) induced plasticity occurred in the Fe-15Mn steels. However, in the Fe-25Mn steels, at the beginning stage of the deformation, phase transformation induced plasticity played an important role, and with the increase of deformation, the main mechanism was twinning induced plasticity.
Authors: Xin Pei Ma, Guang Xin Li, Zhi Hao Jin, Ji Hua Chen, Mao Ju Yang, Yun Jie Han
Abstract: Glass-ceramics are especially useful for the dental restorations because of their good biocompatibility, chemical stability, aesthetic, mechanical strength and wear resistance. The aim of this work was to obtain one mica glass-ceramic, which can be easily used for rapid machining into all-ceramic tooth with computer assisted design/computer assisted manufacture (CAD/CAM) devices. In the study, on the base of low melting machinable fluorosilicic mica glass ceramics, the effects of CeO2 and Fe2O3 in SiO2-B2O3-K2O-Na2O-Li2O-Al2O3-MgO-F system on color were studied. By orthogonal experimental design, the effects of crystallized parameters on the color, three point flexural strength and machinability of the glass ceramics were obtained, and the samples were analyzed by differential thermal analysis(DTA), X-ray diffraction (XRD) and scanning electron microscopy(SEM), respectively. Experimental results showed that the glass-ceramics with color close to the tooth can be obtained by adjusting the percentage of CeO2 and Fe2O3, and the glass-ceramics crystallized at 680°C for 2h have excellent mechanical properties and machinability.
Authors: Xin Pei Ma, Guang Xin Li, Jian Feng Yang, Zhi Hao Jin
Abstract: Machinable mica glass ceramics with more ZnO and B2O3 showed the phase separation by spinodal decomposition. the size of two phases formed by phase separation is in micron meter order. The nucleation and growth of crystal is performed through the diffusion of atoms. Another kind of materials with no ZnO and B2O3 addition behaves different mechanism of phase separation in terms of nucleation and growth. Many fine particles are obtained after the phase separation , the size of which is less than 100nm in diameter. Subsequently nucleation and growth in the crystallization is accomplished by aggregation and unification of the granular phase precipitation. The mechanism of the aggregation and unification nucleation-growth is different from one controlled by atom diffusion in nature. The different mechanisms in crystal nucleation and growth, caused by the composition changing.
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