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NUMERICAL SIMULATION OF CHANNEL SEGREGATION IN Al-4.5wt-%Cu ALLOY

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Acta Metallurgica Sinica(English Letters) 1991年第8期4卷 108-114页

作者： YU Qiuping ZHOU Yaohe northwestern polytechnical university,xi’an,China northwestern polytechnical Univ Xi'an China

Equations for numerical simulation of channel segregation based on a model of continuum ap- proach to porous medium were *** order to solve the non-linear computation prob- lem caused by the interactions between unknown variables in the equations,the trial-and-er- ror method is *** computation results showed that the radial back-flow due to natural convection in mushy zone indeed exists in A1-4.5wt-%Cu alloy ingot under the condition of low cooling rate,and that the numerical simulation of channel segregation is applicable due to the coincidence of calculated concentration with the experimental values.

关键词： channel segregation numerical simulation back-flow mushy zone

RECALESCENCES AND SOLIDIFICATION MICROSTRUCTURE OF HIGHLY UNDERCOOLED Ni_(68)B_(21)Si_(11) ALLOY

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Acta Metallurgica Sinica(English Letters) 1993年第2期6卷 111-116页

作者： LI Delin YANG Gencang ZHOU Yaohe northwestern polytechnical university,xi’an,China Faculty No.403,northwestern polytechnical university,xi’an 710072,China northwestern polytechnical Univ Xian China

One,two and three recalescence events in the solidification of highly undercooled Ni_68B_21Si_11 alloy melt and the conditions of undercooling together with the effect on solidification morphologies were *** solidification morphologies of the undercooled alloy may be examined in the light of two aspects,i.e,growth of either Ni_3B,Ni_6Si_2B and Ni_2B ternary eutectic or dendrite cluster with Ni_3B as leading *** the degree of undercooling below 200 or over 310 K,the alloy solidifies to accompany one recalescence only, and the crystals grow according to the first mode of *** undercooling at other temperatures,two or three events of recalescence may occur and the dendrite cluster may so- lidify.

关键词： recalescence event undercooling X-ray analysis

DENUCLEATION AND HIGH UNDERCOOLING OF Ni-32.5%Sn EUTECTIC ALLOY

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Acta Metallurgica Sinica(English Letters) 1991年第8期4卷 115-120页

作者： WEI Bingbo YANG Gencang ZHOU Yaohe northwestern polytechnical university,xi’an,China northwestern polytechnical Univ Xi'an China

Undercoolings up to 397 K(0.283 T_E)have been obtained for Ni-32.5% Sn eutectic alloy melted by superheating-cooling cycles and denucleating with inorganic *** predomi- nant dissipation of heat for highly undercooled alloy melt is through *** approxi- mate method is consequently derived to calculate its mean specific heat from measured cooling *** the aid of high speed cinematography,it is revealed that the surface or interface heterogeneous nucleation takes place in preference to homogeneous nucleation even though the undercooling has exceeded 0.2 T_E.

关键词： undercooling rapid solidification nucleation eutectic alloy specific

Phenomenological Anisotropic Study of Surface Finish in Pack Rolling

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Journal of Materials Science & Technology 2003年第2期19卷 133-136页

作者： Zhufeng YUEDepartment of Engineering Mechanics, northwestern polytechnical university, xi’an 710072, China Dept. of Eng. Mech. Northwestern Polytech. Univ. Xi'an 710072 China

A phenomenological anisotropic model has been presented for the surface roughness modeling of pack rolling. The model is an assembly of grains in different orientations and sizes. The grain size is assumed to be in log-normal distribution. To model the macro anisotropic mechanical behavior of the grains induced by the slip deformation, the grains are assumed as isolated anisotropic units. The units have different mechanic behavior, and depend on the crystallographic orientations and the external loading as well as the interaction of the adjunctive grains. In the paper, the material properties of the grains are assumed as uniform distributions. The roughness of the contact surfaces depends on the distribution types and the scatters of the distributions. It is found that the initial roughness of the contact surfaces has a little influence on the surface roughness when the rolling deformation is large. The comparison between the phenomenological model and crystallographic model shows that the phenomenological model can also give out a reasonable result, while it only takes much less CPU time. The agreement between the single sheet model and the pack rolling model shows that in a certain degree the pack rolling model can be replaced by the single sheet model to decrease the CPU time.

关键词： Phenomenological anisotropic model Pack rolling Surface roughness Statistic distribution Initial roughness Single sheet model Crystallographic model

Non-uniform Stress Field and Stress Concentration Induced by Grain Boundary and Triple Junction of Tricrystal

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Journal of Materials Science & Technology 2003年第4期19卷 303-308页

作者： Jiansong WAN and Zhufeng YUEDepartment of Engineering Mechanics, northwestern polytechnical university, xi’an 710072, China Dept. of Eng. Mech. Northwestern Polytech. Univ. Xi'an 710072 China

The stress characteristics in the anisotropic bicrystal and tricrystal specimens were analyzed using the anisotropic elastic model, orthotropic Hill's model and rate-dependent crystallographic model. The finite element analysis results show that non-uniform stresses are induced by the grain boundary. For bicrystal specimens in different crystallographic orientations, there exist stress concentrations and high stress gradients nearby the boundaries. The activation and slipping of the slip systems are dependent on the crystallographic orientations of the grains and also on the relative crystallographic orientations of the two adjoining grains. For the tricrystal specimens, there is not always any stress concentrations in the triple junction, and the concentration degree depends on the relative crystallographic orientations of the three grains. Different from the bicrystal specimens, there may be or no stress concentration in the vicinity of grain boundaries for the tricrystal specimens, which depends on the relative crystallographic orientations of the three grains. The stress concentration near to the grain boundaries and triple junction can be high enough for the local plastic deformation, damage and voiding or cracking even when the whole specimen is still under the elastic state. It can be further concluded that homogeneous assumption for polycrystalline materials is not suitable to study the detailed meso- or micro-mechanisms for damaging and fracturing.

关键词： Crystallographic plasticity Bicrystal specimens Tricrystal specimens Stress characteristics Hill's modei Anisotropy Finite element analysis

CHARACTERISTICS OF CRITICAL STATE OF TENSILE INSTABILITY

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中国有色金属学会会刊：英文版 1996年第3期6卷 58-62页

作者： Zhou Weixian(Department of Aeronautical Manufacturing Engineering, northwestern polytechnical university, xi’an 710072) northwestern POLYTECH UNIV DEPT AERONAUT MFG ENGNXIAN 710072PEOPLES R CHINA

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ＣＨＡＲＡＣＴＥＲＩＳＴＩＣＳＯＦＣＲＩＴＩＣＡＬＳＴＡＴＥＯＦＴＥＮＳＩＬＥＩＮＳＴＡＢＩＬＩＴＹ￥ＺｈｏｕＷｅｉｘｉａｎ（ＤｅｐａｒｔｍｅｎｔｏｆＡｅｒｏｎａｕｔｉｃａｌＭａｎｕｆａｃｔｕｒｉｎｇＥｎｇｉｎｅｅｒｉｎｇ，ＮｏｒｔｈｗｅｓｔｅｒｎＰ...

关键词： tensile instability critical state deformation characteristic

HOT DEFORMATION OF CAST Pr-Fe-B MAGNETS

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Acta Metallurgica Sinica(English Letters) 1992年第11期5卷 357-363页

作者： CHEN Zhongmin SHI Zhengxing WANG Leyi FU Hengzhi northwestern polytechnical university,xi’an,China northwestern polytechnical Univ Xi'an China

The hot deformation process of cast Pr_(19)Fe_(74.5)B_5Cu_(1.5) magnets were *** is found that the easy-axes are aligned parallel to the compressive strain direction in vari- ous hot deformation *** hot deformation,the crushing of Pr_2Fe_(14)B matrix grains and the relative slip and rotation between the grains take place and the Pr-rich melt is squeezed out of the magnet,leading to a fine,dense and well-aligned microstruc- ture in the fully-deformed *** properties of B_r=990 mT,_iH_c=880 kA/m and(BH)_m=191 kJ/m^3are *** increase of coercivity is attributed to the fine Pr_2Fe_(14)B grains and the thin Pr-rich phase layer continuously distributed at the grain *** increasing remanence is resulted primarily from the develop- ment of the easy-axis alignment as well as from the densification of the Pr_2Fe_(14)B matrix. The easy-axis alignment is developed by the relative slip and rotation of the crushed Pr_2Fe_(14)B grains.A full and slow hot deformation is necessary for the good easy-axis alighnment and high magnetic properties.

关键词： Pr-Fe-B magnet hot deformation microstructure magnetic property

CLEAVAGE RUPTURE OF Ti ALLOY TC11 UNDER FATIGUE-CREEP INTERACTION

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Acta Metallurgica Sinica(English Letters) 1992年第5期5卷 341-344页

作者： ZHOU Yu ZHO U Yigang YU Hanqing northwestern polytechnical university,xi’an,China northwestern polytechnical Univ Xi'an China

The cleavage rupture behaviour of the Ti alloy TC11 with various microstructures,i.e., equiaxed,duplex and interweaving,has been studied under fatigue-creep interaction at 520℃.It was found to be not only related to the rate of creep void initiating,but also control- led by the creep strain accumulation on holding under tension test and stress state at *** seem to be combinably offected by both value of critic void initiating strain and parameter,V_(GC),of critic void growth.

关键词： fatigue-creep interaction cleavage rupture void initiation void growth Ti alloy TC11

Effect of Notches and Environment on Cyclic Life of Alumina

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Journal of Materials Science & Technology 1995年第6期11卷 452-454页

作者： Fenghui WANG Minxu LU Jianfeng WE and xiulin ZHENG (northwestern polytechnical university, xi’an, 710072, China) northwestern Ploytechnical Univ Xi'an China

Four-point bending cyclic fatigue testing has been performed for alumina specimens with two kinds of notch radius in corrosive environments. Cyclic life is found to be dependent on notch radius and environments, the tests also show that the fatigue notch factor Kf is roughly equal to the theoretical notch factor Kt, the fatigue strength and fatigue limit σc are reduced in environment in the sequence: formamide-room air-distilled water

关键词： Alumina