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CN 21-1315/TG
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      28 March 1989, Volume 5 Issue 2 Previous Issue    Next Issue
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    Steady State Creep Rate Equation of Inconel 718 Superalloy
    HAN Yafang M. C. Chaturvedi Institute of Aeronautical Materials, Beijing, Chi na. Department of Mechanical Engineering, University of Manitoba, Canada.
    J. Mater. Sci. Technol., 1989, 5 (2): 79-84. 
    Abstract   HTML   PDF (535KB)
    The steady state creep rate equdtion of a nickel base superalloy Inconel 718, strengthened by coherent ordered disc-shaped bct γ~(11) phase and coherent spherical fcc γ~1 phase precipitates, has been established in the stress and temperature ranges of 620-840 MN m~(-2) and 853-943K, respecti- vely. Constant stress tensile creep tests were used to medsure the values of steady state creep rate, ε_s, and the consecutive stress reduction method was used to measure the back stress during creep deformation. The values of effective stress exponent, n_e, were detemined from the slopes of the lgε_s vs. lg(σ_a-σ_0)/G plots. The effect of grain size, d, on steady state creep rdte has been also studied in this investigation, and the grain size sensitive exponents m were detemined from the slopes of lgε_s vs. lg(b/d) plots. The creep rate equations of Inconel 718, in the above stress and temperature ranges, have been proposed to be ε_s=1.6×10~(-5)(D_1Gb/KT) (b/d )~(0.19)[(σ_a-σ_0)/G]~(1.35) in diffusional creep region, and ε_s =75(D_1Gb/KT) (b/d)~(-0.42)[(σ_a-σ_0)/G]~(5.5) in dislocation power law creep region.
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    The Morphology of Rolling Contact Fatigue Fracture of Hardened Steels
    WANG Xu;ZHANG Shouhua;CUI Peiyong Beijing University of Science and Technology, Beijing, China. Central Iron and Steel Research Institute, Beijing, China.
    J. Mater. Sci. Technol., 1989, 5 (2): 85-89. 
    Abstract   HTML   PDF (1771KB)
    Rolling Contact Fatigue(RCF) is a cumulative damage phenomenon when metals are subjected to repeated contact stresses. The fomation of pitting on the contact surface is the result of the rolling contact fatigue. The morphologies of rolling contact fatigue fracture of the har- dened steels (86CrHoV7, 42CrMo) show that strong resemblance in fractuye mechanisms exists between rolling contact fatigue and uni-axial fatigue. Since fatigue striations are hardly observed in hardened steels under uni-axial fatigue, it is interesting to note that the state of stress in rolling contact fatigue is more favor- able to ductile fractures than in uni-axial fatigue.
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    Influence of Carbon Content and Solidification Condition on Incipient Melting of DS Superalloy MAR-M200+2Hf
    ZHENG Yunrong;WANG Luobao;LI Chenggong Institute of Aeronautical Naterials, Beijing, China. To whom correspondence should be addressed.
    J. Mater. Sci. Technol., 1989, 5 (2): 90-95. 
    Abstract   HTML   PDF (1161KB)
    Hf lowers the incipient melting temperature of superalloy. As carbon content in Hf-bearing alloy decreases, the incipient melting temperature drops furthey. PD ingots have stronger tendency to incipient melting than HRS ones. Even though in PD ingot, the sensitivities at both ends of the ingot are quite different. The melting of Ni_5Hf phase may be considered as one of the main factors affecting incipient melting. The more Ni_5Hf the alloy contains, the more serious the incipient melting becomes. The results of differential thermal analysis (DTA) have proved that the peak of 1135-1160℃ corresponds to the melting range or Ni_5Hf. By means of a pretreatment at 1150℃, 8h, Ni_5Hf phase can be eliminated in two ways: the reaction Ni_5Hf+γ(C)→MC_(2)+γ and solid solution, and therefore the final solid solution treatment can be carried out at 1260℃. This brings about a high homogenized structure and further increases the stress rupture properties of the alloy at 1040℃, 140 MPa.
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    An Improvement on Adhesion of Sputtered TiC Coating to Steel Substrate
    QI Zhenzhong;YAO Weiguo;WANG Yuqi;LIU Ling;JIA Junhui Institute of Solid State Physics, Academia Sinica, Hefei, China.
    J. Mater. Sci. Technol., 1989, 5 (2): 96-100. 
    Abstract   HTML   PDF (663KB)
    Introducing N_2 during sputtering and pre-oxidation of substrate were investigated to improve the adhesion of sputtered TiC coating to steel substrate. The results show that yeactive gas N_2 increases the adhesion of TiC coating to steel because of a graded interface existing between coating and substrate. The interaction of discharge plasma with the surface of substrate was discussed. Pre-oxidation of substrate is effective for improving the adhesion due to the fomation of FeTi0_3 which appeared as an inteylayer between coating and pre-oxidized substrate.
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    Unusual W-shaped Galvanic Cell Model of ISCC of α-brass in Neutral Mattsson's Solution
    WU Shaobin;R. J. Arsenault;I. R. Kramer Metallurgical Materials Laboratory, University of Maryland, USA.
    J. Mater. Sci. Technol., 1989, 5 (2): 101-112. 
    Abstract   HTML   PDF (2239KB)
    Intergranular stress corrosion cracking (ISCC) of α-brass in neutral Mattsson's solution was found to be controlled by an unusual "W"-shaped galvanic cell whose cathode is the grain boundary oxide film (G.B.0. film) and surface film and the anode is fresh metal at the cracked tip on both sides of the G.B.0. film. Redox reactions involved in the cell have been proposed here. According to this mdel, initidtion of ISCC is caused by the rupturing of surface film along grain boundaries, thus forming a galvanic cell. Propagation of ISCC resulted from alternate advances of G.B.0. film and dissolution on both sides of G.B.0. film caused by the effect of electrochemical reaction. This work developed an effective approach to investigate the embrittlement process at the tip of the crack, by increasing the length of the embrittlement region through constant strain test and distinguishing the morphology and the nature of the corrosion products by optical microscopy and scanning electron microscopy (SEH).
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    Phase Equilibria in Zn-Al-Cu-Si System at 285℃
    ZHU Yaohua Tongji Univeysity, Shanghai, China.
    J. Mater. Sci. Technol., 1989, 5 (2): 113-118. 
    Abstract   HTML   PDF (1980KB)
    As a part of the systematic investigation on phase relationships of Zn-Al based alloys containing Cu and/or Si, the equilibrium phase transformations of the quaternary Zn-Al-Cu-Si system at 285℃ were investigated by using X-ray diffracti on, scanning electron microscopy and electron probe microanalysis techniques. A five-phase of (α+β+εT'+σ) and a four- phase of (β+ε+η+σ) were detected separately coexisting in the Zn-Al-Cu-Si system at 285℃. Then the 285℃ isothermal section of Zn-Al-Cu-Si system (with 0.1% -Si content) was established, and an equilibrium reaction was determined at 286℃ as the following pattern, β+T'=α+ε
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    Fusion Equation of Metals
    HONC Yongyan Zhejiang Institute of Technology, Hangzhou, China.
    J. Mater. Sci. Technol., 1989, 5 (2): 119-122. 
    Abstract   HTML   PDF (270KB)
    An expression of initial slope of melting curve of pure metals was obtained as follows: (dT_m/dP)_o=T_(mo)/c, where c=1.09 (N_(at))~(5/3)z~(-1/3), the unit of c is GPa, N_(at) is the atomic concentra- tion (in 10~(28) m~(-3)), z is the valence, T_(mo) is the melting temperature (in k) of metal under one atmosphere. The calculated results for thirty-one metals agree well with experiments. It has also been proved that by using the free electron model of melting, the fusion equation of metals is Simon equation (T_m/T_(mo))q=1+(p/d). Two parameters q and d, which have to fit with experiments in Simon's empirical equation, now can be predicted theoretically, e.g. for Mg, giving q=1.56, d=7.88GPa, the calculated melting curve in a fairly wide pressure range (0~60GPa) is shown to be close to the experimental one.
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    Intergranular Fatigue Cracking Behaviour in Aluminium
    LIU Wei;WANG Zhongguang;XIA Yuebo Institute of Matal Research, Academia Sinica, Shenyang, China.
    J. Mater. Sci. Technol., 1989, 5 (2): 123-129. 
    Abstract   HTML   PDF (2384KB)
    In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequently so as to study the grain boundary (GB) cracking behaviour by the surface observation. The results show that crack initiation at GB was a process controlled by multi-factors, such as boundary structure, GB-slip interaction, GB sliding and so on. If these factors are varied so that the incompati- bility at a GB increased, the possibility of cyacking at the boundary will be raised. Some inteygranular cracking phenomena are not able to be explained by the GB stepping mechanism.
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    The Acoustic Emission Effects of Martensite Transformation in Alloys Cr12MoV and Fe-33Ni-4Ti-10Co
    JIAO Chengge;ZHANG Baoqi;WU Gaohui;YAO Zhongkai Harbin Institute of Technology, Harbin, China. Daqing Petroleum College, Anda, China.
    J. Mater. Sci. Technol., 1989, 5 (2): 130-134. 
    Abstract   HTML   PDF (619KB)
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    Some Observations of Flow Localization and Shear Cracking in Pearlite during Deformation
    XU Yongbo Institute of Metal Research, Academia Sinica, Shenyang, China.
    J. Mater. Sci. Technol., 1989, 5 (2): 135-137. 
    Abstract   HTML   PDF (920KB)
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    Laboratory of Solid State Microstructures(LSSMS)
    No Author
    J. Mater. Sci. Technol., 1989, 5 (2): 138-139. 
    Abstract   HTML   PDF (654KB)
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    Preliminary Announcement for the Second International Conference on HSLA Steels
    J. Mater. Sci. Technol., 1989, 5 (2): 140-141. 
    Abstract   HTML   PDF (114KB)
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    metals news
    No Author
    J. Mater. Sci. Technol., 1989, 5 (2): 142-146. 
    Abstract   HTML   PDF (545KB)
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