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ISSN 1005-0302
CN 21-1315/TG
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      28 January 1994, Volume 10 Issue 1 Previous Issue    Next Issue
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    Mechanical Behaviour and Structure Instability of Al_3Ti Alloy
    D.G.Morris(Institute of Structural Metallurgy, University of Neuchatel, Avenue de Bellevaux 51, Neuchatel, Switzerland)
    J. Mater. Sci. Technol., 1994, 10 (1): 1-14. 
    Abstract   HTML   PDF (6906KB)
    Trialuminide alloys of elements such as Ti. Nb or Zr are of particular interest as materials for high temperature usage because their density is very low and specific strength and elastic rnoduli are then very high. This report concentrates on recent work on Al3Ti alloys which have been alloyed with ternary elements such that the higher symmetry ordered cubic structure is obtained, leading to somewhat easier operation of deformation mechan isms and hence improved ductility and toughness.Fine details of the crystal structure of cubic trialuminides are considered here and it is shown that the materials generally possess some remnant tetragonal chemical ordering which can affect their me chanical behaviour. In addition the compositional range over which a stable single phase is retained is shown to be extremely small, such that in most cases the materials examined show some form of microstructural instability. These instabilities affect the mechanical behaviour of the materials, for exarnple producing general strengthening. leading to precipitation hardening du ring hig h temperature testing, and causing age hardening instabilities during high temperature static or dynamic testing.Such structural instabifity feads to significant modifications at superdislocations, affecting both the dislocation cores and their associated APB's. Failure for these cubic materials still occurs at very small plastic strains and seems to be determined by difficulties of superdislocation creation near a propagating crack rather than by problems of suitable dislocation configuration and mobility. Possible ways to enhance ductility and toughness by alloying and microstructural modification will be discussed.
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    Three Dimensional Simulation of Upset Forging by Using Variational Upper Bound Method
    Jiang QIN(School of Mechanical Engineering, University of Bath, Claverton Down, Bath BA27AY, UK)
    J. Mater. Sci. Technol., 1994, 10 (1): 15-22. 
    Abstract   HTML   PDF (1420KB)
    The variation principle is discussed and Rayleigh-Ritz method is proposed for construction of veloci ty field. A kinematically admissible velocity field based on polynomials was appIied to the determina tion of forging load and deformed buIge profile during upset forging of blocks. Simulation of upsetforging of rectangular blocks under various friction condjtions was performed. Comparison of the computed results with experiments and FEM shows good agreement. It is shown that this techniquecan be used for 3D simulation of metal forming process.
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    On the Formability of Some Metastable Alloy Phases
    Bo TANG; Deshan KANG; Pei QING; Weiming ZHANG and Nianyi CHEN(Shanghai Institute of Metallurgy, Chinese Academy of Sciences, Shanghai, 200050, China)
    J. Mater. Sci. Technol., 1994, 10 (1): 23-26. 
    Abstract   HTML   PDF (330KB)
    Pattern recognition and neural network methods have been used to investigate the formability of metastable alloy phases, It has been found that some chemi cal bond parameters Such as valence electron number, electronegativity and metallic radii of cor-nponent elements are the dominating fac tors affecting metastable alloy phase formation. Some semi-empirical rules found in this way may be useful for the construction of expert system for materials design.
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    Recovery Stress in a Ni-Ti-Nb Shape Memory Alloy with Wide Transformation Hysteresis
    Wei CAI;Chunsheng ZHANG and Liancheng ZHAO(Harbin Institute of Technology, Harbin, 150006, China)
    J. Mater. Sci. Technol., 1994, 10 (1): 27-30. 
    Abstract   HTML   PDF (1131KB)
    The effect of deformation on recovery stress of Ni144.7Ti46.3Nb9 alloy has been studjed using tensile test at various temperatures and TEM observation. It ls shown that the recovery stress increases with jncreasing total strain ET and reaches a maximum value (max) as ET= 9% but the maximum recov erV strain of the alloy is only about 4.6%. This is different from that of Ti-Ni binary alloy in which is obtained usually at maximum recovery strain and the reason of the difference is dis Cussed. Deformation temperature Td has a little effect on recovery stress when Td is less than Ms However, recovery stress decreases sharply when Td is higher than M, and lowers approximately down to zero near Msσ
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    Catastrophe Theory Models for Stress-dependent Behaviour in a NiTi Shape Memory Alloy
    Bruce Friedman(Sunrise Enterprises, 1023 Hanson Street, Annapolis, Maryland 21403, USA)
    J. Mater. Sci. Technol., 1994, 10 (1): 31-33. 
    Abstract   HTML   PDF (240KB)
    The measurements by Huibin XU et al of the stress-dependence ot hysteresis in a NiTi shape memo ry alloy are modeled by catastrophe theory. The cusp catastrophe is used with the strain as the behaviour variable and the control parameters being functions of the stress and the temperature. A two constant model is found to be preferred to a four constant model.
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    A Biomimetic Model of Fiber-reinforced Composite Materials
    Shihong LI; Ronghui ZHANG; Shaoyun FU; Xin CHEN and Benlian ZHOU(Institute of Metal Research, Academia Sinica, Shenyang, 110015, China)Qiyun ZENG(Institute of Applied Ecology, Academia Sinica, Shenyang, 110015, China)
    J. Mater. Sci. Technol., 1994, 10 (1): 34-38. 
    Abstract   HTML   PDF (1295KB)
    In thjs paper. bamboo fiber has been. on micro scale. investigated as a helical. multi-layered hollow cylinder, the stiffness featu res of bamboo bast fiber were compared with those of a multifilament yarn in traditional fiber-reinforced composite materials, Moreover. a biomimetic model of the reinforce ment of fiber-reinforced composite materials was proposed by imitating the fine structure of bamboo bast fiber. The results show that the comprehensive stiffness properties of the cornplicated fine struc ture of bamboo fiber is superior over those of traditional fiber-reinforced composites.
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    Environmental Embrittlement in A_3B-type Intermetallic Alloys
    Xiaojing WAN; Jiahong ZHU; Kailiang JING; Weijie CHEN and Yue WU(Institute of Metallurgy and Materials Science, Shanghai University of Technology, Shanghai, 200072, China)
    J. Mater. Sci. Technol., 1994, 10 (1): 39-53. 
    Abstract   HTML   PDF (7955KB)
    Environmental embrittlement in A3B-type intermetallics based on Ni3Al and Fe3Al has been studied in this paper. For the Ni3Al doped with 120 wt ppm B and Ni,(Al,Cr.Zr) doped with 80 wt ppm B,their elongation and ultimate tensile strength decreased in the sequence:of vacuum > air >hydrogen. while for Ni,(Al,Mn) doped with 400 wt ppm B no envifonmental degradation was ob served, although a -Ni3(Al,Mn) alloy without B showed a decrease in ductility when tested in air in stead of oxygen. It is supposed that boron and hydrogen compete for the occupation of interstitial sites near grain boundaries. If boron content is sufficiently low, hydrogen embrittlement occurs ;however, if its content is sufficiently high. boron addition is capable of eliminating envjronmental ef fect in Ni3Al-based alloysi As to the micromechanism of hydrogen embrittlement in Ni3Al+B. S EM in situ observations showed that both grain boundary decohesion and a high stress concentration con tributed to hydrogen-assisted jntergranu lar cracking in this alloy. For the Fe3Al and Fe3 (Al.Cr) alloys.their mechanical properties depended strongly on grain size / grain shape and testing environment. A strain rate effect on ductiIity and fracture strength was also observed in the Fe3Al and Fe,(Al,Cr)+B aIloys. Preoxidation increased the ductility of the Fe,(Al,Cr)+B alloy. All these results can be rationalized from a hypothesis that surface reaction is the controlling process in embrittling Fe3Al-based alloys.
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    Damage from Particle Impact for Structural Ceramics
    Zhongzhe JIN and Yiwang BAO(China Building Materials Academy, Beijing, 100024, China)
    J. Mater. Sci. Technol., 1994, 10 (1): 54-58. 
    Abstract   HTML   PDF (333KB)
    In this study, the relationship between the maximum impact force and velocity of partjcle has been derived on the basis of elastic theory and energy principle. Critical impact force and critical speed which cause initial damage is anaIVsed and its analytical expression is presented. The impact force for six dlfferent materials was measu red at the same condition to investigate the v8riation of impact pararneter with material properties. The authors provide a simple test method and experimental de vice to imitate the impact of moving particle, A series of experiments on ceramics and gIass were car ried out to study the dependence of residual strength on the impulse.
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    Development of Fundamental Research of SiC_w / Al Composites in HIT Part Ⅱ: Mechanical Behaviour of Squeeze-cast SiC_w / Al Composites
    Jun LIU; Dezun WANG and Congkai YAO(Dept. of Metals and Technology, Harbin Institute of Technology, Harbin, 150001, China)
    J. Mater. Sci. Technol., 1994, 10 (1): 59-66. 
    Abstract   HTML   PDF (4777KB)
    Studies on the mechanical behaviour of squeeze-cast SiCw / Al composites have been revjewed. The results show that SiCw / Al composites exhibit improved mechan ical properties and cyclic hard ening. The reasons leading to the above results are discussed. Localized deformation near SiC whiskers plays an important role in the initiation of microcracks in the composites, and the fracture of the composites is caused by the abrupt linking of microcracks
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    Activity Interaction Coefficients of Si in Cu-Ti-Si Melts at 1550℃
    Xiangxin XUE; Yinchang CHE and Hegui DU(Department of Metallurgy, Northeastern University, Shenyang, 110006, China)
    J. Mater. Sci. Technol., 1994, 10 (1): 67-70. 
    Abstract   HTML   PDF (388KB)
    Activitibs of Si in binary Cu-Si and ternary Cu-Ti-Si melts were measured at 1 550℃ by using a method of chemical equilIbrium between gas and liquid. The activity interaction coefficients of Si in the melts have been determined from the experimental data (lny = -5.69. s = 6.69. P2: = -26.22. E; =-43.96) and activity interaction coefficients of Ti in binary Cu-Ti melt at 1550℃ has been estimated from Sommer's data based on the regular solution model (lny =-1 .10. : = 2.95.p:=-2.10).
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    Ionization Potentials and Electron Affinities of Cu_n Atomic Clusters
    Senyying LIU; Rongze HU and Chongyu WANG(Central Iron and Steel Research Institute, Beijing, 100081, China)
    J. Mater. Sci. Technol., 1994, 10 (1): 71-74. 
    Abstract   HTML   PDF (419KB)
    Ionization potentials and electron affinities of Cux (n = 2-7) atomic clusters with the optimal geom etries have been calculated by use of SC F-Xa-SW method and Slater's transition state theory. Theo retical calcuIations show that the ionization potentiaIs and electron affinities of Cu. (n = 2-7) atom ic clusters have a sharp even / odd alternation with increasing their sizes, which are related to the electronic structure of Cun atomic clusters. The theoretical results are consistent with the related ex perimental ones.
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    Natural Passivity of Amorphous Fe_(40)Ni_(40)P_(14)B_6 and Fe_(54.6)Ni_(38)Si_(4.1)B_(2.3)V_1 Alloys
    Erdong LU and Pengshou XU(Hefei National Synchrotron Radiation Lab., University of Science and Technology of China, Hefei, 230026, China)Mingrong JI;Maosheng MA and Xianming LIU(Structure Research Lab., University of Science and Technology of China, Hefe
    J. Mater. Sci. Technol., 1994, 10 (1): 75-78. 
    Abstract   HTML   PDF (370KB)
    The natural passive films forrned on Fe_(40)Ni_(40)P_(14)B_6 and Fe_(54.6)Ni_(38)Si_(4.1)B_(2.3)V_1 amorphous alloys long-term exposed in air have been studied by X-ray photoelectron spectroscopy (XPS) and Auger electron (including Ar+ ion depth profiling) spectroscopy (AES). The following aspects have been investigated: (1) chemical states of the elements in the films. binding energies and the chemical shifts measured by XPSf (2) structure and composition of the films fand (3) thickness of the passive films determined by AES depth profiling and XPS analysis.
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ISSN: 1005-0302
CN: 21-1315/TG
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