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2004 Vol. 30, No. 10

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Diagnosis methods and criterions for mechanical failure modes, causes and mechanisms
Zhong Qunpeng, Song Guangxiong, Zhang Zheng, Luo Hon
2004, 30(10): 913-918.
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Mechanical failure modes, causes and mechanisms were described, based on four kinds of failure information including fracture, cracking, related failure marks and certain parameters. Mechanical failure modes, causes, main causing conditions and identifying principles were summarized and listed, "multi phase" information system was provided with single phase analysis and synthetic analysis, which provide reasoning rules and principal methods for mechanical failure analysis. Main criterions for discriminating fatigue failure mode, stress corrosion cracking(SCC) and relevant failure modes were also concerned, which offer signposts for recognizing 2nd level failure modes.
Failure process of thermal barrier coatings under thermal and mechanical loading
Xu Huibin, Gong Shengkai, Chen Liqiang, Zhang Chunxia
2004, 30(10): 919-924.
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High temperature behaviors of thermal barrier coatings prepared by electron beam physical vapor deposition were investigated under mechanical loading. The change in microstructure and the formation of microcrack were studied by means of impedance spectroscopy (IS) and acoustic emission (AE) methods. The impedance value is very sensitive to the microcrack in the thermally grown oxidation (TGO) layer in the low frequency range. The formation and the propagation of the microcracks can be monitored by comparing the change of impedance value combining with acoustic emission. It has been found that the failure mode was quite different for TBC samples tested with or without mechanical loading. When TBCs were tested during high temperature creep, the microcracks formed in the equiaxial crystalline area between TGO layer and columnar structure of YSZ top coat, instead of in TGO layer during thermal cyclic testing without mechanical loading. However, cracks initialized in the diffusion layer between substrate and bond coat when TBCs were tested with low cycle fatigue at high temperature.
Formation and mechanical properties of Cu-Zr-Ti bulk glassy alloys
Zhang Tao, Men Hua, Ti Yunjie
2004, 30(10): 925-929.
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Cu-base bulk glassy alloys with high glass-forming ability were fabricated in Cu-Zr-Ti ternary system by copper mold casting. The critical diameter for glass formation was 5 mm for Cu60Zr40-xTix(x=7.5%, 10%, 12.5%) alloys, 4 mm for Cu60Zr25Ti15 alloy and 3 mm for Cu60Zr40-xTix(x=15%, 17.5%, 22.5%, 25%) alloys. The glassy alloys exhibited distinct glass transition together with supercooled liquid region in the range of 38~65 K. The Young’s modulus, compressive fracture strength, plastic strain and Vickers hardness of the bulk glassy alloys are in the range of 80~114 GPa, 1 730~1 865 MPa, 0.3%~1.5% and Hv 693~Hv 824, respectively, and increase with increasing Ti content in the alloys. The finding of the Cu-based bulk glassy alloys with high glass-forming ability, high fracture strength and distinct plastic strain indicates a possibility for subsequent development of glassy alloys with new compositions which can be used for structural materials.
Analysis of the residual thermal stresses of SiC joint with Ti/Ag/Ti interlayer by FEM
Mao Yangwu, Zhang Jianjun, Li Shujie
2004, 30(10): 930-933.
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With regard to the joining of ceramic to ceramic using metallic interlayers or the joining of ceramic to metal, the mismatch of thermal expansion coefficient between the ceramic and the metallic materials generates residual thermal stresses during joining and cooling. The stresses may cause microcracks leading to low weld strength and even failure of joining. The residual thermal stresses of SiC joint with Ti/Ag/Ti interlayer were analysized by finite element method(FEM). The results indicate that the residual thermal stresses mainly distribute in the area near the welding seam. The area close to the outer surface and near the welding seam is the weakest area of the joint, where cracks are likely to be initiated. The fracture position of the joint indicated by the FEM analysis is in accordance with the result of experiment.
Factors effecting on the wicking of epoxy resin in capillaries of unidirectional fibre bundles
Zhang Zuoguang, Li Min, Sun Zhijie, Chen Liang
2004, 30(10): 934-938.
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Understanding the wetting behavior of resin in fiber assemblies is critical for predicting and improving the fabrication performance of composites. According to capillary rise method, the wicking flow in unidirectional fiber bundles was characterized through measuring the mass gain in fibers at different time. The effects of many factors on the wicking performance of epoxy resin in unidirectional fiber bundles were investigated, such as the volume fraction of fibers, the type of fibers, the temperature of resins and the sizing on fibers. The experimental data suggest that the wicking velocity of resins could be increased with increasing fiber volume fraction, with enhancing temperature and by removing the sizing on S-2 glass fibers.
Array materials of one-dimensional oxides prepared by MOCVD method
Zhang Yue, Yuan Hongtao, Cheng Jin, Song Qiang
2004, 30(10): 939-943.
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The structure and the new features of a new-type atmospheric metal organic chemical vapor deposition (MOCVD) system were introduced. The atmospheric MOCVD method was introduced to prepare array materials of oxides by the example of preparing array material of ZnO nanorods. The preparing process of oxide array materials was discussed in detail. SEM experiments showed that all these tropistic growing materials of one-dimensional oxides grew in a certain direction perpendicular to the substrates and well aligned. These one-dimensional materials are characterized of no crystal boundaries, few crystal defects, little superficial area and special tips. How to make all kinds of array materials of one-element metal oxides (such as VOx, FeOx, TiO2, etc.) and doped multi-element metal oxides (such as ZnAlO,ZnMgO, etc.) was introduced.
Improvement of soft magnetic properties of FeCo core alloy by vacuum and field annealing
Bi Xiaofang, Zhang Shanqing, Zhu Fangzhen, Xu Huibin
2004, 30(10): 944-948.
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Microstructures and soft magnetic properties of FeCo alloy were investigated in an attempt to improve its soft magnetic properties. Microstructural dependence of the magnetic properties was studied by vacuum annealing at various temperatures. Magnetic field annealing was performed to study the dependence of the coerecivity on the magnetic filed applied during annealing. The field annealing effect was observed only for the alloys after recrystallization, and was increased with increasing the applied field within the range of 2.0×104A/m(250Oe). Coercivity of the FeCo alloys was decreased to 72A/m(0~9Oe) after annealing with a magnetic field of 1.76×104A/m(220Oe) at 850℃. The microscopic mechanism of the field annealing effect was also discussed in terms of magnetostrictive characterizations.
Effect of thermal treatment on thermal diffusivity of nanostructured zirconia coating
Zhou Chungen, Wang Na, Gong Shengkai, Xu Huibin
2004, 30(10): 949-952.
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Yttria partially stabilized nanostructured zirconia coatings were prepared by atmospheric plasma spraying (APS). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were applied to analyze the nanostructured coatings and that after heat-treatment. Thermal conductivity were also measured by laser pulsed diffraction method. It was found that the as-sprayed zirconia coating had an average grain size of 67nm, and mainly composed of metastable tetragonal phase, together with some monoclinic phase and tetragonal phase. The thermal diffusivity of the as-sprayed nanostructured zirconia coating was 2.15×10-3~2.75×10-3cm2/s between room temperature and 800℃, but 2.65×10-3~3.25×10-3cm2/s for the coating after heat treatment at 1050℃ for 34 hours.
High-temperature relaxation of TiNiFe shape memory alloy
Liu Fushun, Han Dong, Zheng Lei, Xu Huibin
2004, 30(10): 953-957.
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For the shape memory alloy pipe connector, the stress relaxation’s stability has more influence on the pipe connector in the working environment. So the particular study on the stress relaxation’s stability of the aero shape memory alloy pipe connectors in the working environment has vital practical significance. The stress relaxation and stability of TiNiFe and TiNiNb shape memory alloys were investigated under different temperature. The examination was experimentalized on American 880 type 100KN-MTS, through which stress relaxation curves of the TiNiNb and TiNiFe shape memory alloys were gained. It is indicated that at high temperature both alloys are of good stability. At 300℃, TiNiNb alloy performed a better stability to resist the stress relaxation than TiNiFe alloy; but TiNiFe alloy can endure higher load than TiNiNb alloy. Temperature has great influence on the high-temperature stability of shape memory alloy, but the degree of influence on the different stages of the stress relaxation is different.
Effect of Cr on ZrO2/Ni thermal barrier coatings interface cohesion
Shang Jiaxiang, Wang Fuhe, Xu Huibin
2004, 30(10): 958-961.
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The thermal barrier coatings (TBC) are widely used in aeronautics and astronautics industry. The cohesion between the coatings and substrate is a vital effect in determining the TBC lifetime. The interface cohesion must strong enough in order to have longer lifetime. Based on density functional theory the first-principles discrete variational (DV) method was used to study the thermal barrier coating. The energy and electronic structure of the Cr-doped interface of TBCs (ZrO2Ni) were investigated. Result shows that after adding Cr on the interface, the system’s energy is reduced. The segregation energy of Cr is 6.03 eV. This means the system is more stable when Cr atom segregates on interface than that of clean system. Further analysis shows that the interface’s charge-density is increased after adding Cr, this is propitious to bond on the direction of spanning the interface, thereby the bonds between the substrate Ni and ZrO2 are enhanced; the bonds between atoms neighboring to Cr atom in plane are also enhanced.
Rapid solidification laser processing and forming of advanced aeronautical metallic materials
Wang Huaming, Zhang Lingyun, Li An, Cai Lianxu, Tang Haibo
2004, 30(10): 962-967.
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Research progress on rapid solidification laser surface modifications of advanced metallic materials, rapid solidification laser cladding for high-temperature wear and corrosion resistant multifunctional intermetallic coatings, and rapid solidification laser additive manufacturing for high performance metallic components was reported. The main contents include laser surface alloying and laser cladding surface modification of titanium alloys, liquid/solid interface structure and growth mechanisms of typical faceted phase under non-equilibrium rapid solidification conditions, laser rapid forming/manufacturing of high performance titanium and nickel-base alloys, laser constrained melting/forming of refractory metals and intermetallic alloys, and directionally solidified columnar grained titanium alloys.
Magnetostrictive properties and AC electrical properties of activated carbon black filled polypropylene composites
Zhan Maosheng, Ding Naixiu
2004, 30(10): 968-971.
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Carbon black was activated and then filled into polypropylene to prepare composites, of which the alternating current (AC) electrical properties and the magnetostrictive properties were measured. It is shown that there are both conductive properties and magnetostrictive properties in the composites. The variation of AC electrical properties as a function of frequency shows that the conduction network of carbon black has been formed in the composites. Three phenomena could be observed during the course of the magnetostriction measurement. The first is that a relative large magnetostriction value of 115ppm is obtained. The second is that the magnetostriction is strongly dependent on the applied magnetic field and time interval. And the third is that obvious hysteresis effect appears,which is seldom found for material of TbxDy1-xFe2-y considered as typical magnetostrictive material.
Effects of Zr addition on structure and properties of Mg-Zr alloy
Kong Zhigang, Liu Hongbo, Zhang Hu
2004, 30(10): 972-975.
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Grain refining mechanisms of magnesium-zirconium alloys were investigated. Mg-Zr alloys were prepared and a mixture gas containing SF6 was used for protection during melting and casting. The microstructure and properties of Mg-Zr alloys and the effects of strain, frequency, temperature as well as the addition of Zr on the damping capacity were studied. The damping capacity was validated with vibration attenuation experiment. The results show that zirconium is a potent grain refiner for magnesium alloys. The average grain size can be reduced to 30μm for Mg-0.45%Zr(mass fraction) alloy and the mechanical properties of Mg-Zr alloys can be dramatically improved with increasing zirconium content. It is also found that the damping capacity has almost no connection with frequency, but increases with strain, the loss factor reaches 5.3×10-2 at a strain amplitude of 1×10-4. The value of transfer ratio of Mg-Zr base is 1.88 and obviously less than that of ZM6 alloy base and LY12 alloy base.
Microstructures and properties of a Mg-Li-Al-Zn wrought alloy
Chen Bin, Feng Linping, Zhong Hao, Zhou Tietao, Liu Peiying
2004, 30(10): 976-979.
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A novel β base Mg-Li-Al-Zn wrought alloy was designed according as the Mg-Li binary phase diagram and effect of Al, Zn on the alloys. The microstructure and alloy phases changes of the alloy on the states of casting, forging, rolling and rolling-annealing were systematically investigated by optical microscope and X-Ray. The results show that the microstructure of as rolling-annealing is satisfying. The results from tensile test show that the alloy at the state after rolling and consequent heating at 220℃ with holding time of 2 hour has either the highest fracture strength or the highest ratio of the yield strength to fracture strength, meanwhile the plasticity is quite acceptable.
Self-reaction in-situ synthesis of TiC/FeNiCr composite coating in centrifugal field
Xi Wenjun, Zhu Weili, Duan Huiping, Zhang Tao
2004, 30(10): 980-983.
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A TiC-FeNiCr composite materials coating on the substrate of a low carbon steel was successfully prepared using centrifugal-thermit process with raw materials Fe2O3, CrO3, NiO, Al, Ti and C powders. The microstructure of the coating were investigated using scanning electron microscope (SEM) and X-ray diffraction (XRD). The microhardness and wear-ability of the coating were measured. The results shows that the coating is composed of austenite phase and the reinforced phase TiC. The coating is metallurgical bonded to the carbon steel substrate. The TiC grain takes the shape of a polygon or petal and it’s size is lager than that of the austenite phase. The microhardness of the composite coating is about Hv 500~Hv 800, and it has good wear resistance under dry sliding wear test condition.
Transient liquid phase bonding of TiAl and Inconel 718
Duan Huiping, Luo Jun, Zhang Tao, Mustafa Kocak
2004, 30(10): 984-988.
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Ti foil combined with Cu or Ni foils was used as insert metals to join TiAl intermetallic and Inconel 718 employing transient liquid phase (TLP) bonding technique. The effect of dwell time at bonding temperature on the interfacial structures of the joints was investigated. Results showed that defect-free joints was fabricated, but the liquid formation processes and mechanism of Ti-Cu and Ti-Ni insert metals were quite different. Some sublayers were found in the joined zone because the alloyed elements which diffused from Inconel 718 alloy segregated at the interface between Inconel 718 alloy and joined zone. Morphologies and hardness profiles of the joined zones showed that the joint produced using Ti-Ni insert metals could isothermally solidify much faster than that produced using Ti-Cu insert metals under the experimental conditions.
Effect of ball blasting on the service properties of NiCoCrAlY coating of the alloy IC6 vane
Li Shusuo, Zhou Chungen, Gong Shengkai, Song Jinxia, Han Yafang
2004, 30(10): 989-992.
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NiCoCrAlY overlay coating was deposited on the vane made of alloy IC6 by arc physics vapour deposit(PVD). In order to improve the surface roughness of the vane, a ball blasting treatment was operated. It shows that the surface roughness obviously got improved, the original average value of the roughness is 2.04 μm, but the value is only 1.02 μm after treatment. After 22 cycles in the thermal shock experiment, the bonding between coating and matrix is still fine in spite of ball blasting treatment or not, but the treatment can furtherly improve the oxidation resistance.
Manufacturing of GF/PP warp-knitting fabrics reinforced polypropylene composite materials
Duan Yuexin, Zuo Lu, Zhang Yadong, Liang Zhiyong
2004, 30(10): 993-997.
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Continuous glass fiber reinforced polypropylene (GF/PP) composite material were manufactured with a new kind of warp-knitting fabrics in two different forms by thermoforming. The microstructure of impregnation quality of the composite material was observed with the scanning electronic microscope (SEM) and substantiated by the results of void content measuring. The fabric structure effects on impregnation quality were investigated. The composite mechanical properties influencing factors and change tendency were also discussed. The two different fabric forms were compared. The results show that it is feasible to manufacture thermoplastic composite materials with warp-knitting fabrics; different knitting forms lead to different impregnation quality which directly influences composite mechanical properties.
Electrochemical characteristics of titanium alloy in engine oil and NaCl solution
Liu Jianhua, Shang Haibo, Wu Hao, Li Songmei
2004, 30(10): 998-1002.
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The electrochemical characteristics of a new titanium alloy Ti-6Al-1.5Cr-2Zr in 3# kerosene and 928 lubricating oil with high resistance were studied by using potentiodynamic polarization. The electrochemical properties including the laws of polarization, open-circuit potential, linear polarization resistance and variation of corrosion current were investigated. The corrosion behaviors of titanium alloy were investigated by using immersion method in 3# kerosene and 928 lubricating oil. No visible corrosion appeared in the oil medium. The electrochemical characteristics of the alloy in 3.5% NaCl solution were also studied to compare that in the oil medium. The open-circuit potential was -0.18V, passivation potential was 0.23V, passivation current density was 0.31×10-4A/cm2 in 3.5%NaCl solution and the passivation area potential was in the range of 0.27~1.24V in 3.5% NaCl solution.
High temperature oxidation resistance of nickel multiple plating containing SiO2,ZrO2 particles
Du Yanbin, Zhu Liqun, Liu Huicong, Bai Zhenquan
2004, 30(10): 1003-1007.
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Nickel multiple plating containing 11.3％(atoms％)SiO2 or 5.31％(atoms％)ZrO2 particles on copper alloy base was obtained by composite electrodeposition method. Through high-temperature oxidation and thermal cycling test at 800℃ and 900℃, the high-temperature oxidation performance of samples prepared previouly and adhension between composite coating and copper base were studied too. The results show that after being tested for 40 hour at high temperature, the anti-oxidation ability of two composite nickel-plated films both reaches the anti-oxidation level according to HB 5258-83, and the composite coating containing SiO2 particles has better oxidation resistance than that containing ZrO2 particles. The adhension between the composite coating containing SiO2 particles and the copper base is well after thermal cycling test for 55 times.
Preferred orientation of electrolytic copper foil
Zhang Shichao, Jiang Tao, Bai Zhiming
2004, 30(10): 1008-1012.
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Preferred orientation of copper foil which was electrodeposited under different conditions in electrolyte solution containing thioureas,glue additives was studied by X-ray diffraction(XRD), all-purpose material testing machine．The results showed that the copper foil which was electrodeposited in electrolyte solution containing thioureas has the character of preferential orientation (220),the extent of the texture was influenced by the thickness and current density．the peak of TC(220) was 93.2%．The kind of additives has influence on the texture．The foil produced in electrolyte solution containing glue has no evidently character of preferential orientation．The tensile strength and elongation paralleling the surface of the foil are at the same level in different orientation.
Effect of sulfate-reduced bacteria on corrosion and electrochemical behaviors of LY6 Al alloy
Li Songmei, Liu Jianhua, Liang Xin, Jia Xiaoli
2004, 30(10): 1013-1016.
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The open circuit potential, potentiodynamic scanning polarization and electrochemical impedance spectroscopy (EIS) were employed to analyze the corrosion behaviors of LY6 Al alloy in solutions with and without sulfate reduced bacteria(SRB).It was showed that SRB accelerated the corrosion rate of LY6 Al alloy, and the corrosion rate of dynamic test sample was larger than that of static test sample. The open circuit potential shifted negatively with the time. The shifted values were 0.26V(SCE)and 0.16V (SCE) in solution with and without SRB,respectively. The range of apparent pitting potential obtained from anodic polarization was -0.6~0.2V(SCE). It was found that polarization resistance decreased with the time based on EIS results.
Influence of salt spray corrosion on the performance of NiCoCrAlY coatings
Xiang Min, Zhang Qi, Luo Junhua
2004, 30(10): 1017-1020.
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The NiCoCrAlY coatings prepared by electron beam physical vapor deposition (EB-PVD) was studied by a salt-spray-test. The influence of salt spray corrosion on the microstructure and high-temperature cyclic oxidation behavior of NiCoCrAlY coating was investigated. Results show that the alumina formed on the corroded NiCoCrAlY coating is roughness, cracked and incontinuous and many pits was formed on the surface of the coating after the salt-spray test. The Al2O3 films formed within the pit are rougher, which suggests the congregation of stresses and spallation of the oxide film during the cyclic oxidation. These changes will reduce the protection ability of the coatings during high-temperature oxidation and shorten the lifetime of cyclic oxidation of NiCoCrAlY coatings.
Self-assembly structure of CeO2 nanoparticles: synthesis, characterization and catalytic property
Zhang Yahui, Qi Xingyi, Guo Lin, Zhang Qi
2004, 30(10): 1021-1024.
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A new approach to synthesis of self-assembly CeO2 nanoparticles by using microemulsion method was investigated. The structure of the product was characterized by the methods of X-ray diffraction (XRD), transmission electron microscopy (TEM), and extended X-ray absorption fine structure (EXAFS). XRD result indicates the face-center cubic(FCC) structure of the produced CeO2 nanoparticles. EXAFS shows that the oxygen coordination number around Ce in CeO2 nanoparticles decrease compared with the bulk CeO2, and the bond-length of Ce-O in CeO2 nanoparticles is obviously longer than that of bulk materials. The catalytic property of CeO2 on the decomposition of H2O2 was investdigated, and the results demonstrate that CeO2 nanoparticles have much stronger catalytic activity than bulk CeO2.
Catalytic removal of nitrogen oxides for the lean-burn automobile exhaust
Zhu Tianle, Hao Jiming, Fu Lixin, Li Junhua
2004, 30(10): 1025-1028.
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Al2O3, Ag/Al2O3, Sn/Al2O3, Ga/Al2O3, Co/Al2O3 and Pt/Al2O3 catalysts were prepared by the sol-gel mixture method and the activities of NO reduction by C3H6 over the catalysts were compared in the presence of oxygen. The Ag/Al2O3 displayed the highest NO reduction activity among catalysts studied. The effects of reaction conditions on NO reduction by C3H6 and CH3OH over Ag/Al2O3 were also investigated. The results showed that the presence of H2O resulted in a decrease in the NO reduction activity and the inhibition effect was reversible. In the presence of SO2 the activity of NO reduction by CH3OH significantly increased while that of NO reduction by C3H6 decreased.

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