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Densification and microstructure of carbon/carbon composites prepared by chemical vapor infiltration using ethanol as precursor

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Science China(Technological Sciences) 2010年第8期53卷 2232-2238页

作者： LI Wei,ZHANG ShouYang ,YAN xiaFeng,LI HeJun&LI KeZhi State Key Laboratory of Solidification Processing,northwestern polytechnical university,xi’an 710072,China 1. State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi’an 710072 China

Chemical vapor infiltration of carbon fiber felts with uniform initial bulk density of 0.47 g·cm-3 was investigated at the ethanol partial pressures of 5-20 kPa,as well as the temperatures of 1050,1100,1150 and 1200°***,diluted by nitrogen,was employed as the precursor of pyrolytic *** light microscopy(PLM),scanning electron microscopy and X-ray diffraction were adopted to study the texture of pyrolytic carbon deposited at various temperatures.A change from medium-to high-textured pyrolytic carbon was observed in the sample infiltrated at 1050°***,homogeneous high-textured pyrolytic carbons were deposited at the temperatures of 1100,1150 and 1200°*** angles of 19°-21° were determined for different regions in the samples densified at the temperatures ranging from 1100 to 1200°*** electron microscopy of the fracture surface after bending test indicated that the prepared carbon/carbon composite samples exhibited a pseudo-plastic fracture *** addition,fracture behavior of the carbon/carbon samples was obviously effected by their infiltration *** fracture mode of C/C composites was transformed from shearing failure to tensile breakage with increasing infiltration temperature. Results of this study show that ethanol is a promising carbon source to synthesize carbon/carbon composites with homogeneously high-textured pyrolytic carbon over a wide range of temperatures(from 1100 to 1200°C).

关键词： C/C composites ethanol ICVI high-textured pyrolytic carbon

Surface Nitridation of Molybdenum by Laser-promoted Reaction

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Chinese Journal of Lasers 1997年第2期B6卷 161-168页

作者： WU Jiada WU Changzheng ZHONG xiaoxia SONG Zhoumo LI Fuming(Department of Physics, Fundan university, Shanghai 200433)(Deprtment of Applied Physics, northwestern polytechnical university, xi'an 710072, China) Fudan Univ Shanghai China

Experimental results are reported about the surface nitridation of molyly denum by repeated pulsed laser irradiation on molyboenum foils in pure nitrogen atmosphere. In this laser treatment, the laser irradiation activates nitrogen and melts Mo surface, initating a nitridation reaction in liquid phase. The obtained nitride layers were analyzed and characterized by scanning electron micrography, Auger electron spectroscopy and X -ray diffraction. It is found that the nitride layers contain γ-Mo2N phase and have microstructure much denser than that of the original material. Surface heating and melting and transicnt shock waves induced by laser pulses could account for the microstructure densification of the nitride layers.

关键词： laser-promoted reaction laser heating and melting surface nitridation

THE CAPP SYSTEM IN CIMS ENVIRONMENT

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Chinese Journal of Aeronautics 1995年第2期8卷 125-132页

作者： Fan Qijin Huang Naikang Zhang Zhenming(Faculty 1003,northwestern polytechnical university,xi’an,China,710072)

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ＴＨＥＣＡＰＰＳＹＳＴＥＭＩＮＣＩＭＳＥＮＶＩＲＯＮＭＥＮＴＴＨＥＣＡＰＰＳＹＳＴＥＭＩＮＣＩＭＳＥＮＶＩＲＯＮＭＥＮＴ￥ＦａｎＱｉｊｉｎ；ＨｕａｎｇＮａｉｋａｎｇ；ＺｈａｎｇＺｈｅｎｍｉｎｇ（Ｆａｃｕｌｔｙ１００３，ＮｏｒｔｈｗｅｓｔｅｒｎＰｏｌｙ...

关键词： computer aided design computer aided manufacturing tools

SOLUTION OF 2D SHALLOW WATER EQUATIONS BY GENUINELY MULTIDIMENSIONAL SEMI-DISCRETE CENTRAL SCHEME

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Journal of Hydrodynamics 2006年第4期18卷 436-442页

作者： CHEN Jian-zhong, SHI Zhong-ke College of Automation Northwestern Polytechnical University Xi＇an 710072 China

A numerical two-dimensional shallow water method was based on method for solving the equations was presented. This the third-order genuinely multidimensional semi-discrete central scheme for spatial discretization and the optimal third-order Strong Stability Preserving （SSP） Runge-Kutta method for time integration. The third-order compact Central Weighted Essentially Non-Oscillatory （CWENO） reconstruction was adopted to guarantee the non-oscillatory behavior of the presented scheme and improve the resolution. Two kinds of source terms were considered in this work. They were evaluated using different approaches. The resulting scheme does not require Riemann solvers or characteristic decomposition, hence it retains all the attractive features of central schemes such as simplicity and high resolution. To evaluate the performance of the presented scheme, several numerical examples were tested. The results demonstrate that our method is efficient, stable and robust.

关键词： 2D shallow water equations semi-discrete central scheme Central Weighted Essentially Non-Oscil]atory (CWENO) reconstruction

EXPERIMENTAL STUDY ON THE STALL FLOW FOR DIFFERENT GEOMETRIC PARAMETERS OF CASCADE

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Chinese Journal of Aeronautics 1994年第2期7卷 102-109页

作者： Zhu Junqiang Liu Zhiwei Ma Cunbao(Faculty 704, northwestern polytechnical university, xi’an, China, 710072)

AbstractWith the help of the hot-film probe and a three-hole probe containing fast responsetransducers in association with a digital data acquisition and processing system, the flowmeasurements during stall on an isolated rotor are obtained. The relation between thenumber and speed of stall cells and the circumferential stalled region and the maingeometric parameters of cascade is described. The experimental results indicate thatfirstly, the rate of circumferential variation for acrodynamic parametero of allow passingthe cascade becomes smoother as the stagger angle is increased or the solidity decreasedand secondly, there is complex mass transport between the stalled and unstalled parts ofthe flow. It is confirmed by the latter that the fluid must cross from one side of the cell tothe other in the tangential direction.

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Atomic-scale computer simulation for ternary alloy Ni-Cr-Al during early precipitation process

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Progress in Natural Science:Materials International 2005年第7期15卷 656-660页

作者： CHU Zheng , CHEN Zheng, WANG Yongxin, LU Yanli and LI Yongsheng (State Key Laboratory of Solidification Processing, northwestern polytechnical university, xi’an 710072, China) State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi'' an 710072 China

The aging behaviors of Ni-Cr-Al ternary alloy are studied at temperature 873 K based on the mean-field theory, and the early precipitation process is simulated at atomic-scale with microscopic phase-field model. The precipitation mechanism of the low supersaturated alloy Ni-12.2at. %Cr-7.8at. %Al is non-classical nucleation and growth, the L12 structure (Ni3Al) and D022 structure (Ni3Cr) phases precipitate simultaneously, a part of D022 phase transmits to Ll2 structure phase, and other part retains its previous structure. For high supersaturated alloy, congruent ordering appears first, then followed by spinodal decomposition, the nonstoicheometric ordered phases are produced in this process, which occurs before clustering. The precipitation mechanism of Ni-8at. %Cr-18at. % Al alloy is similar to Ni-10at. %Cr-12at. %AI alloy, but the ordering process of the former is ahead of the latter.

关键词： microscope phase-field model Ni-Cr-Al precipitation ordering parameter simulation.

CCT-DIAGRAMS OF Si-Mn-Mo BAINITIC STEELS

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Acta Metallurgica Sinica(English Letters) 1993年第5期6卷 273-277页

作者： LIU xiao ZHANG Mingxing CHEN Daming ZHOU Lubin KANG Mokuang northwestern polytechnical university,xi’an,China LIU xiao Faculty No.401,northwestern polytechnical university,xi’an 710072,China

CCT-diagrams of Si-Mn-Mo bainitic steels have been *** Mo 0.25%,the high-temperature transformation of the steel shifts large to the right,and the bainitic trans- formation region becomes a“flat topped C-curve”at cooling rate in wide *** in the steel may cause shift of the bainitic transformation region towards the right,and of the pro-eutectoid ferritic transformation region towards the *** may delay the high temper- ature transformation more violently than the bainitic transformation.

关键词： meta-bainite bainitic steel CCT-curve

Microscopic phase field study of the antisite defect of Ni_3 Al in binary Ni-Al alloys

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Science China(Physics,Mechanics & Astronomy) 2010年第11期53卷 2047-2053页

作者： ZHANG Jing ,CHEN Zheng,LU YanLi,ZHANG MingYi & WANG Yongxin State Key Laboratory of Solidification Processing School of Material Science and Engineering,northwestern polytechnical university,xi’an 710072,China 1. State Key Laboratory of Solidification Processing School of Material Science and Engineering Northwestern Polytechnical University Xi’an 710072 China

The temporal evolution feature of a microscopic phase field model is utilized to study the antisite defects of L1 2-Ni 3 Al;this is quite different from other physicist’ *** are mainly two points in ***,antisite defects Ni Al and Al Ni ,which are caused by the deviation from the stoichiometric Ni 3 Al,coexist in the Ni 3 Al *** surplus Ni atom in the Ni-rich side is prone to substitute Al thus producing the antisite defect Ni Al that maintains the stability of the L1 2 *** other case,the surplus Al atom in the Al-rich side is accommodated by a Ni sublattice consequently giving rise to antisite defect Al Ni .The calculated equilibrium occupancy probability of Ni Al is much higher than that of Al Ni .This point is generally in line with other theoretical and experimental ***,both Ni Al and Al Ni have a strong negative correlation to time step during the disorder-order *** the initial value of Ni Al and Al Ni on each site of the matrix is right at the concentration that we set,we can observe the decrease process of Ni Al and Al Ni from the initial disordered high anti-structure state to their respective equilibrium state,*** the result of the ordering process further coarsening.

关键词： antisite defect L1 2 -Ni 3 Al temporal evolution microscopic phase field model

MICROSTRUCTURE AND MORPHOLOGY OF HIGH MANGANESE NON-MAGNETIC STEEL

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Acta Metallurgica Sinica(English Letters) 1990年第3期3卷 158-163页

作者： YANG Yanqing MA Shiliang QIN xiongpu KANG Mokuang northwestern polytechnical university,xi’an,China YANG Yanqing,Graduate student,Dept.of Materials Science and Engineering,northwestern polytechnical university,xi’an 710072,China

Two types of lath structures and kinked ε martensite were observed in the high manganese non-magnetic *** the short non-continuous lath formed by quenching and the long thin straight lath induced by plastic deformation are composed of ε martensite and fcc twin. The transformation mechanism was *** crystallographic analysis indicates that the e martensite at both sides of the fcc twin boundary is of kinked morphology owing to the orientation of their matrices differing from each *** kinked region is hcp twin.

关键词： εmartensite fcc twin lath structure kink