ISSN 0412-1961
CN 21-1139/TG
Started in 1956

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    A THREE-DIMENSIONAL CELLULAR AUTOMATON SIMULATION FOR DENDRITIC GROWTH
    JIANG Hongxiang ZHAO Jiuzhou
    Acta Metall Sin, 2011, 47 (9): 1099-1104.  DOI: 10.3724/SP.J.1037.2011.00050
    Abstract   PDF (1975KB) ( 1360 )
    Perhaps dendrite is the most observed solidification microstructure of many metallic materials. The dendritic morphologies show a dominating effect on the performance of casting products. A lot of work has been carried out to investigate the formation mechanism of dendritic microstructure. It is found that the development of dendritic microstructures is a complicated process controlled by the interplay of many factors such as thermal and solute transfer, capillary $etc$. Cellular automaton (CA) can simulate the solidification process with a high computational efficiency, thus, attracts great attentions. In recent years, progress has been made on the two dimensional CA models for the solidification microstructure formation. But up to date researches on three dimensional CA model are very limited. A combined cellular automaton-finite difference (CA-FD) model for the three dimensional simulation of dendritic growth was developed in this paper. Simulations were performed to investigate the dendritic growth in an undercooled Al-Cu alloy as well as in a directionally solidified Al-Cu alloy. The numerical results showed clearly the development of the free dendrite in the undercooled melt and the microstructure evolution in the directionally solidified alloy and agreed well with the theoretical predictions and the experimental results.
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    PREPARATION OF NANO-SIZED SiC REINFORCED NiTi SHAPE MEMORY COMPOSITES AND THEIR MECHANICAL PROPERTIES AND DAMPING BEHAVIOR
    JIANG Hongjie KE Changbo CAO Shanshan MA Xiao ZHANG Xinping
    Acta Metall Sin, 2011, 47 (9): 1105-1111.  DOI: 10.3724/SP.J.1037.2011.00281
    Abstract   PDF (1671KB) ( 1000 )
    NiTi shape memory alloys have attracted significant attention for applications in various fields in the past decades. Although porous NiTi alloys exhibit lower density compared with the dense ones, they are inevitably lower in strength, storage modulus and damping capacity. Therefore, it is imperative to study and improve the compressive performance and storage modulus in porous NiTi alloys. In this study, the nano-sized SiC particle reinforced NiTi shape memory alloy based composites (SiC/NiTi) have been successfully fabricated by means of a step powder-sintering method, which show unique characteristics of lightweight, high strength and stable superelasticity. The fabricated SiC/NiTi composites possess almost the same equivalent strength compared with dense NiTi alloys. On the other hand, they are in the nature of higher strength, including compressive strength and equivalent compressive strength, than porous NiTi alloys. Furthermore, the strength increases with increasing contents of SiC particles. It has been indicated that the addition of SiC particles has a slight influence on the phase composition of the SiC/NiTi composites, while the martensitic phase transformation temperatures of the composites keep unchanged compared with the NiTi alloy without SiC reinforcement. Meanwhile, the fabricated composites inherit the high damping performance of the NiTi matrix, and thus exhibit a high storage modulus.
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    EFFECT OF THERMAL PROCESSING ON THE CORROSION RESISTANCE OF ZIRCONIUM ALLOY N18 IN LiOH AQUEOUS AT 360 ℃/18.6 MPa
    ZHANG Xin YAO Meiyi LI Shilu ZHOU Bangxin
    Acta Metall Sin, 2011, 47 (9): 1112-1116.  DOI: 10.3724/SP.J.1037.2011.00238
    Abstract   PDF (2653KB) ( 933 )
    The effect of thermal processing on corrosion behavior of N18 alloy has been investigated by autoclave tests in 0.01 mol/L LiOH aqueous solution at 360 ℃ and l8.6 MPa, and the microstructures of these specimens were examined by TEM and SEM. The results show that the corrosion resistance of specimens is improved obviously by $\beta$ phase quenching before cold rolling and annealing due to nano second phase particles (SPPs) precipitated dispersively, but when the intermediate annealing temperature increased to 740 ℃ before cold rolling and annealing, the corrosion resistance is lowered greatly due to SPPs coarsened to several hundred nanometers, where the corrosion rate accelerates markedly after the corrosion transition at 150 d exposure. The existence of β-Zr phase in the microstructures of specimens treated at 780 and 800 ℃ for 2 h in dual phase region is harmful to the corrosion resistance, but the corrosion resistance returns to a better level after the decomposition of β-Zr phase during the following processes of cold rolling and annealing at 580 ℃ to obtain fine SPPs.
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    EFFECT OF DEFORMATION TEMPERATURE ON TENSILE DEFORMATION MECHANISM OF Fe-23Mn-2Al-0.2C TWIP STEEL
    QIN Xiaomei CHEN Liqing DI Hongshuang DENG Wei
    Acta Metall Sin, 2011, 47 (9): 1117-1122.  DOI: 10.3724/SP.J.1037.2011.00217
    Abstract   PDF (3304KB) ( 1183 )
    Twinning-induced plasticity (TWIP) steel can be classified into three types, Fe-Mn-Al-Si, Fe-Mn-C and Fe-Mn-Al-C steels. Owing to their high strength, superior plasticity and good formability, they have potential applications in automobile manufacturing industry as a new generation of steels. In order to reveal the dependence of deformation mechanism on temperature for Fe-23Mn-2Al-0.2C TWIP steel, microstructural observation, stacking fault energy calculation and tensile deformation experiments were performed at a temperature range from -60 ℃ to 600 ℃. With increasing the deformation temperature, the strength and elongation to failure of this steel firstly decrease, then increase and finally decrease. And their peak values appear at 300 ℃ during high temperature deformation. As deformation temperature increased from -60 ℃ to 600℃, the stacking fault energy of the steel increases and the deformation mechanism is changed from twining to slipping. Deformation twins with high density appear at lower deformation temperatures, however, they will gradually decrease with increasing temperature. When the sample was deformed at 600 ℃, only dislocations and dislocation cells appear. High-density deformation twins formed during low-temperature deformation result in the high tensile strength and elongation to failure in this steel.
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    COUPLING EFFECT ON RHEOLOGY AND MICROSTRUCTURE OF SEMI-SOLID SCN-5H2O MODEL ALLOY
    WANG Hongyan LIN Xin WANG Lilin MA Liang YANG Donghui HUANG Weidong
    Acta Metall Sin, 2011, 47 (9): 1123-1128.  DOI: 10.3724/SP.J.1037.2011.00252
    Abstract   PDF (1953KB) ( 683 )
    The most important characteristic of semi-solid processing is that the solidification microstructure changes markedly from dendritic growth under traditional conditions to non-dendritic or globular growth, which results in apparent viscosity greatly reduction. In another hand, semi-solid slurry shows admirable fluidity compared with traditional processing slurry. With the intensive development of semi-solid meta1 processing technology, the interaction between melt flow and solidification microstructure becomes gradually one of the important fundamental research fields in materials science. In the previous work, it is very difficult to measure apparent viscosity and observe microstructure of semi-solid simultaneity using opaque metal materials. Conclusions of rheological behavior and microstructure evolution in semi-solid processing can be drawn qualitatively. Because of the metal materials not transparency and the researches on microstructure only after quenching, it is difficult to measure rheological behavior and observe dynamic microstructure evolution simultaneously. Therefore, it is also hard to grasp the coupling effect on rheology and microstructure of semi-solid alloy, which has affected the understanding and controlling accurately on solid forming process. In present paper, the coupling effect of shear rate and the processing (continuous cooling and remelted) processes on the rheology and microstructure of semi-solid SCN-5H2O (molar fraction, %) transparent model alloys were investigated using rotating viscometer. It is found that the increase of shear rate will lead the apparent viscosity of the semi-solid alloy to present a transient shear-thickening and steady shear-thinning behavior, correspondingly, the size of non-dendritic microstructure decreases and the distribution of aggregate becomes more disperse with increasing the shear rate, while, the shape factor of the non-dendritic microstructure changes little; a larger particle size and slightly lower shape factor for non-dendritic microstructure were obtained in the semi-solid alloy slurry made by re-melted process on comparison with that by continuous cooling process, meanwhile, the aggregation of the aggregates becomes stronger, which also results in that the apparent viscosity of the semi-solid alloy slurry made by re-melted process is larger than that by continuous cooling process.
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    THERMAL FATIGUE BEHAVIORS OF THREE CAST NICKEL BASE SUPERALLOYS
    XIAO Xuan XU Hui QIN Xuezhi GUO Yongan GUO Jianting ZHOU Lanzhang
    Acta Metall Sin, 2011, 47 (9): 1129-1134.  DOI: 10.3724/SP.J.1037.2011.00066
    Abstract   PDF (4636KB) ( 1084 )
    Thermal fatigue (TF) behaviors of three Ni-based cast superalloys were investigated in the temperature ranges of 850, 900 and 950℃ to 20℃, respectively. OM and SEM were used to observe the microstructures and TF cracks of the tested specimens. The results demonstrated that the main style of crack initiation is the formation, gathering and interconnecting of oxidation cavities induced by thermal stress. Carbides, $\gamma$+$\gamma^{\prime}$ eutectics and grain boundaries can promote the initiation and propagation of TF cracks. The three alloys showed different mechanisms of TF crack propagation due to the distinct chemical compositions and microstructures. The TF cracks of equiaxial IN738 alloy propagate intergranularly, while those of the directional solidification (DS) DZ444 alloy propagate along interdendritical regions. The paths of TF crack propagation of DZ445 transfer from interdendrite to crystallographic orientation with increasing temperatures, i.e. (111)<110>, which is the easy slip system of face centered cubic alloy. The interaction of high-temperature oxidation and thermal stress is the main fractural mechanism in TF process. Some microstructural evolution at 950℃ accelerates the reduction of the TF property of three alloys.
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    A UNIFIED ANALYTICAL MODEL FOR THE PRIMARY SOLIDIFICATION PATH IN TERNARY ALLOYS
    ZHAO Guangwei LI Xinzhong XU Daming FU Hengzhi DU Yong HE Yuehui
    Acta Metall Sin, 2011, 47 (9): 1135-1140.  DOI: 10.3724/SP.J.1037.2011.00195
    Abstract   PDF (1216KB) ( 772 )
    Accurate prediction for the solidification path of a multicomponent alloy and the amounts of the secondary phases presented under a given solidification condition is critical in understanding and controlling the performances of the solidified alloy materials/parts. The degree of freedom of a single-phase solidification in multicomponent alloys is at least more than one, whilch brings some difficulty in accurate predicting of the solidification path. A new analytical model for predicting a single-phase solidification paths in ternary alloys was developed based on a previously proposed unified microsegregation model for dendrite solidification of binary alloys. The present unified analytical model can not only include the three limiting solidification conditions of equilibrium, nonequilibrium and paraequilibrium solidification, but also take into account of any solid diffusion coefficient, dendrite geometrical morphologies and solidification rates, etc. The algorithms for calculating the solidification paths of ternary alloys was closely coupled with a commercial software package/database of Thermo-Calc via its TQ6-interface in order to directly access to the thermodynamic data. The availability of the proposed analytical model for predicting the primary solidification paths of ternary alloys were demonstrated by the sample computations on Al-1.0Cu-6.3Mg, Al-1.49Si-0.64Mg and Al-1.49Si-2.90Mg alloys under different solidification conditions of solid back diffusion. It was found that the solidification conditions affect the solidification paths significantly. For an alloy, especially with a nominal composition far away from the ternary eutectic point, different solid back diffusion conditions and solidification rate can result in different amounts and even different kinds of secondary phase.
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    PROPERTIES OF Ti3XC2(X=Al, Si) WITH PLASMA SPRAYED ZrO2 THERMAL BARRIER COATING
    LIU Jing SHENG Hongfei ZHANG Baoshan PENG Liangming
    Acta Metall Sin, 2011, 47 (9): 1141-1146.  DOI: 10.3724/SP.J.1037.2011.00266
    Abstract   PDF (2343KB) ( 778 )
    There has been a great interest in the synthesis and characterization of Ti3AlC2 and Ti3SiC2 lamellar ceramics due to their striking combination of merits of both metals and ceramics, such as good high-temperature strength, excellent oxidation resistance. In this study, dense and high purity polycrystalline Ti3AlC2 and Ti3SiC2 lamellar ceramics were prepared from Ti, Al(Si) and C powders by reactive hot pressing in vacuum at 1450 ℃ for 1.5 h under 30 MPa. Their phase constitution, mechanical characterization and thermal properties were investigated. In addition, plasma-sprayed monolayer ZrO2 thermal barrier coatings free of metallic transition layer were prepared on the two ceramic substrates. The purity of the Ti3AlC2 and Ti3SiC2 were 91.5% and 90.3%, and the main impurity was TiC. The flexural strength and fracture toughness were 536 MPa, 7.8 MPa·m1/2 and 457 MPa, 6.8 MPa·m1/2 for Ti3AlC2 and Ti3SiC2, respectively. They took a respective average value of 8.77×10-6 and 9.14×10-6/℃ for the coefficient of thermal expansion (CTE) without remarkable temperature dependence between 25 and 1000℃. Furthermore, the coatings contributed to a more than 60\% decrease in the high temperature thermal conductivity compared to the two matrices. In general, Ti3AlC2 and ZrO2-coated Ti3AlC2 displayed superior comprehensive properties to Ti3SiC2 and ZrO2-coated Ti3SiC2. The temperature differences between the outside surface and the coating/matrix interfaces created by the thermal barrier coating were calculated to be 341 and 358 ℃ for Ti3AlC2 and Ti3SiC2 substrate, respectively.
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    PHOTOELECTROCHEMICAL STUDY ON SEMICONDUCTOR PROPERTIES OF Ni-BASED ALLOYS OXIDE FILMS FORMED IN 288℃ HIGH TEMPERATURE WATER
    ZHANG Shenghan TAN Yu LIANG Kexin
    Acta Metall Sin, 2011, 47 (9): 1147-1152.  DOI: 10.3724/SP.J.1037.2011.00270
    Abstract   PDF (1240KB) ( 783 )
    The oxide films formed on Ni-based alloys in high temperature water with semiconductor properties were investigated by photoelectrochemical responses. Two Ni-based alloys (Incoloy800HT and Inconel600) were corroded at 288℃ for 100 h in water, and four contributions from the photocurrent are obtained by photoelectrochemical responses. Band gap energy of 2.3 eV is attributed to the presence of nickel hydroxide or nickel-ferrite oxide. Band gap energy of 2.9 and 3.5 eV are attributed to Cr2O3 and band gap energy in the range of 4.1-4.3 eV is attributed to the spinel phase FexNi1-xCr2O4. In the photoelectrochemical responses in function of the applied potential tests, the oxide films on Incoloy800HT alloy indicate n type semiconductor in the potential range from -400 mV\linebreak to +400 mV, and the oxide films on Inconel600 alloy indicate n/p type semiconductor. In addition, the dephasing angle of the photoelectrochemical responses has a 180$^{\circ}$ evolution at the potential where the semiconductor of oxide film turns from n to p type.
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    ANALYSIS OF CRACK FORMATION AT INNER SURFACE OF 1Cr13 THICK WALL TUBE APPLIED IN NUCLEAR REACTOR
    SU Guoyue ZHANG Zhen
    Acta Metall Sin, 2011, 47 (9): 1153-1154.  DOI: 10.3724/SP.J.1037.2011.00204
    Abstract   PDF (625KB) ( 714 )
    Tempering brittleness is an important reason for microcrack formation and cracking in thick wall tube made by steel 1Cr13 which is applied in reactor driving mechanism. This article analysed the quenching effect caused by hot rolling followed by air cooling, tempering brittleness caused by annealing followed by slow cooling, and influence of rolling on the cracking direction. Improper heat treatment condition derives martensite transformation and tempering brittleness, which make the steel cracking when rapidly cold rolling. Tangential tensile stress caused by squashing the tube during rolling is the reason for the formation of longitudinal crack.
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    COMPONENT SELECTION AND TECHNOLOGICAL OPTIMIZATION OF THICK WALL 1Cr13 TUBE USED AS CONTROL POLES IN NUCLEAR POWER STATION DRIVING MACHINES
    DU Xiangyuan SU Guoyue
    Acta Metall Sin, 2011, 47 (9): 1155-1158.  DOI: 10.3724/SP.J.1037.2011.00209
    Abstract   PDF (870KB) ( 809 )
    The control poles for driving machine in the built and building nuclear power station are made of thick wall 1Cr13 tubes which all depend on overseas importation. With the fast development of domestic nuclear power stations and the need with coming export, as one of the key parts of driving machines, the 1Cr13 tubes used as control poles should be finished in our country. By optimizing the contents of C, Ni, Cr, H, O and N etc., and adjusting the technology of cold rolling, the cracking problem of 1Cr13 tube as control poles during machining is avoided and favorable surface quality is also obtained. The mechanical properties of  finished tubes reach the technical request after proper heat--treatment.
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    STOCHASTIC PROCESS-BASED MODELING METHOD FOR PITTING CORRSION OF Ni-BASED ALLOY 690
    ZHOU Binghai ZHAI Ziqing
    Acta Metall Sin, 2011, 47 (9): 1159-1166.  DOI: 10.3724/SP.J.1037.2011.00039
    Abstract   PDF (1287KB) ( 982 )
    Pitting corrosion is one of the most serious modes of localized corrosions that can cause deteriorations of Ni-based alloy 690 steam generator tubes. Because the initiation and propagation of pitting are subject to interactions of different factors, it is a stochastic process. It is almost impossible to draw any deterministic models for formations of the processes. To efficiently model the formation process of pitting, firstly, experimental schemes of pitting formations were designed. Based on stochastic theory, combined experimental data and analyzing results, a modeling method was presented with stochastic processes. Namely, non-homogeneous Poisson process (NHPP) was used to model the pitting initiation process and non-stationary Gamma model was used to set up pitting propagation model. A systemic method was built for pitting corrosion failure of the Ni-based alloy 690 tubes, including experimental method, modeling method and simulation method. Finally, the stochastic degradation failure of the Ni-based alloy 690 tubes was simulated. The probability distribution of the lifespan of the Ni-based alloy 690 tubes was obtained under different working environments. The results showed that the proposed modeling method is valid to analyze the initiation and propagation of pitting of the tubes according to different combinations of modeling parameters. It is important for the lifespan prediction and development of relevant maintenance plans of the tubes.
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    SIMULATION AND OPTIMIZATION OF THERMAL FIELD DURING CONTINUOUS CONSTRAINED RHEO-ROLLING OF AZ31 ALLOY
    GUAN Renguo ZHANG Qiusheng DAI Chunguang ZHAO Zhanyong LIU Chunming
    Acta Metall Sin, 2011, 47 (9): 1167-1173. 
    Abstract   PDF (2014KB) ( 754 )
    Semisolid metal processing (SSP) is recognized as a new near-shape forming technology, which combines the merits of both the liquid and the solid metal processing. Compared with the traditional rolling process, this technology has the features of low energy consumption, low cost equipment and high yield. Perhaps inevitably, a problem is the solid and liquid phases tend to separate with each other during rheo-rolling process, especially when the semisolid slurry has a low solid fraction. This problem causes macrosegregation and reduces the quality of the strip. Using rectangular groove roller may solve this problem. In this paper, numerical simulation method and experiment were combined for simulation and optimization of thermal field during continuous constrained rheo-rolling of AZ31 alloy. The results show that on the sloping plate surface, alloy temperature decreases gradually from the casting mouth to the exit with a linear pattern, the alloy temperature near the sloping plate surface is lower than that on the above surface, when the casting temperature is higher than 690℃, the melt temperature at the exit of the plate is higher than the liquidus of AZ31 alloy, which will cause product fracture. In the backward slip zone, semisolid metal deformation mainly happens, alloy temperature decreases gradually from the entrance to the exit of the roll gap, semisolid zone length increases with the casting temperature, isothermal lines have twice buckling, the buckling direction on the surface of the alloy is toward the exit of the roll gap, while the buckling direction in the center is toward the entrance of the roll gap, and their bending degree increases gradually from neutral flow plane to the entrance of the roll gap. In the forward slip zone, solid metal deformation mainly takes place, isothermal lines have once buckling, and the buckling direction is toward the exit of the gap. Under the current experimental conditions, the proper casting temperature between 670 and 690℃ is suggested.
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    CORROSION BEHAVIOR OF Mg-Zn-Y-Zr ALLOYS IN NaCl SOLUTION
    ZHANG Yacong WANG Jincheng LU Wenquan
    Acta Metall Sin, 2011, 47 (9): 1174-1180.  DOI: 10.3724/SP.J.1037.2011.00036
    Abstract   PDF (4793KB) ( 777 )
    In recent years, Mg-Zn-Y-Zr alloys have attracted significant interest due to the high strength at room and elevated temperature. Current researches mainly focus on the microstructures and mechanical properties of Mg-Zn-Y-Zr alloys, however, the corrosion behaviors of Mg-Zn-Y-Zr alloys have been seldom studied. In the present paper, the mass loss corrosion and electrochemical corrosion behavior of three Mg-Zn-Y-Zr alloys with Zn contents of 4.3% (mass fraction), 6% and 8.6% in 5% (mass fraction) NaCl solution were studied, respectively. The morphology, microstructure and phase composition of these alloys after different immersion time were observed. The results showed that the type of second phase and the content of Zn in these alloys significantly affect their corrosion resistance performance and the Mg-Zn-Y-Zr alloy with 4.3% Zn exhibited better corrosion resistance. With the increase of Zn content, the W phase with stronger effect of galvanic corrosion formed at grain boundaries and the content of Zn in α-Mg matrix also increased, which resulted in the worse corrosion performance. Experimental results also showed that the corrosion process of Mg-4.3Zn-0.7Y-0.6Zr alloy can be divided into three stages: galvanic corrosion, Zr-rich zone-Zr--poor zone corrosion and pitting corrosion.
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    BENDING FATIGUE DAMAGE MODELS OF STEEL HONEYCOMB SANDWICH PANELS
    ZOU Guangping LU Jie CAO Yang LIU Baojun
    Acta Metall Sin, 2011, 47 (9): 1181-1187.  DOI: 10.3724/SP.J.1037.2011.00253
    Abstract   PDF (1243KB) ( 798 )
    The four-point bending fatigue behaviors of steel honeycomb sandwich panels were investigated in this paper. The fatigue tests results were presented in fatigue life (S-N) diagrams. The results show that with a load ratio of R=0.20, the fatigue properties of specimens are significantly influenced by honeycomb cell orientations. The L-direction appears more suitable for cyclic loading than W-direction, and the fatigue strengths reach 1369 and 859 N, respectively. Based on the equivalent shear modulus degradation theory, the life prediction and damage evolution models were developed. Obviously, the lives of damage initiation for L-direction specimens are 86%-90% of the total number of cycles, while 73% at high load and reduce to 48% at low load for W-direction specimens. When the cores orientations were not concerned, the second order polynomial model and exponential model can be adopted to describe the damage evolution trends at high and low load levels, respectively. While the prediction models exhibit strong material dependent.
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    QUANTITATIVE RELATIONSHIPS BETWEEN MICROSTRUCTURE PARAMETERS AND MECHANICAL PROPERTIES OF ULTRAFINE CEMENTED CARBIDES
    ZHAO Shixian SONG Xiaoyan LIU Xuemei WEI Chongbin WANG Haibin GAO Yang
    Acta Metall Sin, 2011, 47 (9): 1188-1194.  DOI: 10.3724/SP.J.1037.2011.00262
    Abstract   PDF (1009KB) ( 810 )
    The microstructures of ultrafine WC-Co cemented carbides were characterized and analyzed by stereological methods. The quantitative relationships between the mechanical properties and microstructure parameters, such as the mean grain size dWC, mean free path LCo and contiguity CWC-WC, were obtained. The calculated results of mechanical properties agree well with the experimental measurements. With the equivalent contiguity, the Vickers hardness of ultrafine cemented carbides has linear relationships with dWC-1/2 and LCo-1/2 and the fracture toughness KIC has deterministic relationships with dWC-1/2 and LCo-1/2, respectively. With certain Co content and mean grain size, the transverse rupture strength decreases with the increase of contiguity. Especially when the contiguity is above 0.5, the strength decreases obviously. The present results may be used as criteria to optimize the microstructure and to improve mechanical properties of ultrafine cemented carbides.
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    CORROSION BEHAVIORS OF Ni-Cr-Mo CORROSION RESISTENCE ALLOYS IN CaCl2-CaF2 MOLTEN SALT
    PENG Haijian JIN Jun LI Defu HU Jie
    Acta Metall Sin, 2011, 47 (9): 1195-1199.  DOI: 10.3724/SP.J.1037.2011.00108
    Abstract   PDF (3415KB) ( 1226 )
    The corrosion behaviors of Hastelloy C276 alloy and Hastelloy N alloy in 80%CaCl2+20%CaF2 (mass fraction) molten salt were investigated by XRD, OM, SEM and EDS. The results show that intergranular corrosion takes place in the two alloys, and the form of intergranular corrosion is a type of selective corrosion, i.e., the desolutions of Cr and Mo occur along the grain boundary. The corrosion rates of the two alloys decelerate with the increases of corrosion time because of the hindering effect of corrosion products on the element diffusion, and the relationship of mass loss ($C$) and corrosion time (t) can be described by formula of C=Ktn.
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    HYDROGEN ABSORPTION AND DESORPTION PERFORMANCES OF THE SECOND PHASES IN ZIRCONIUM ALLOY WITH Nb
    WANG Jinhong WANG Rongshan WENG Likui ZHANG Yanwei GENG Jianqiao
    Acta Metall Sin, 2011, 47 (9): 1200-1204.  DOI: 10.3724/SP.J.1037.2011.00103
    Abstract   PDF (808KB) ( 732 )
    Referring to the compositions of the second phases in zirconium alloys, (Zr, Nb)2Fe, Zr(Nb, Fe)2 and $\beta$--Nb were prepared. Chemical composition analysis results indicated that the compositions of the experimental alloys are the same as those of the second phases in zirconium alloys. XRD analysis indicated that the structures of Zr(Nb, Fe)2 and β-Nb alloys are the same as the second phases in zirconium alloys. The pressure-composition-temperature (P-C-T) curves and kinetic curves of hydrogen absorption and desorption were obtained. Experimental results showed that the reversible hydrogen absorption and desorption abilities (Hrev) decrease in the sequence of Zr(Nb, Fe)2, (Zr, Nb)2Fe, β-Nb and Zr.
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    SMALL PUNCH TESTING OF THE EFFECT OF IRRADIATION ON MECHANICAL PROPERTY OF RPV STEEL
    ZHONG Weihua TONG Zhenfeng ZHANG Changyi QIAO Jiansheng YANG Wen
    Acta Metall Sin, 2011, 47 (9): 1205-1209.  DOI: 10.3724/SP.J.1037.2011.00214
    Abstract   PDF (2403KB) ( 755 )
    The small punch (SP) test on mechanical properties of the reactor pressure vessel (RPV) steel (A508-3) before and after irradiation was performed at -150 to 20℃, and then the relation between the tested results and standard test results was analyzed based on the empirical method. SEM analysis on the fractograph was carried out to study the mechanism of fracture under different temperatures. The impact property extracted from SP test on the irradiated specimen was compared with the standard impact test data, the result shows that the SP tested fracture energy can be a good value to character the irradiation hardening and embrittlement of the RPV steel. The tensile values which extracted from the SP test show the irradiation embrittlement effect as well.
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    IN SITU OBSERVATION OF MnS INCLUSION BEHAVIOR IN RESULFURIZED FREE-CUTTING STEEL DURING HEATING
    SHAO Xiaojing WANG Xinhua JIANG Min WANG Wanjun HUANG Fuxiang JI Yunqing
    Acta Metall Sin, 2011, 47 (9): 1210-1215.  DOI: 10.3724/SP.J.1037.2011.00183
    Abstract   PDF (2775KB) ( 1083 )
    MnS is a common type of non-metallic inclusions in steel, which is of good deformability during rolling. As elongated MnS inclusions in rolling direction often cause poor mechanical property of steel. However, MnS is indispensable in resulfurized free-cutting steel. In order to improve mechanical property, especially cutting property of free-cutting steel, the good control of shape and size of MnS is important. In this study, confocal scanning laser microscope was used firstly to observe the morphology evolution of large-sized slender MnS during heating. The effect of heating rate was also considered. The results indicated that for morphology evolution of MnS, the shrink occurred in longitudinal direction, whereas expansion and contraction happened in radial direction, which finally caused the split of slender MnS. When samples were heated at the rate between 0.5-2℃/s, the split degree of MnS decreased with the increase of heating rate. When the heating rate was in the range of 6-10℃/s, the splitting behavior of MnS could not occur.
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    HIGH TEMPERATURE OXIDATION BEHAVIOURS OF THREE ZIRCONIUM ALLOYS
    QIU Jun ZHAO Wenjin Thomas Guilbert Jean-Luc Bechade
    Acta Metall Sin, 2011, 47 (9): 1216-1220.  DOI: 10.3724/SP.J.1037.2011.00211
    Abstract   PDF (2309KB) ( 789 )
    Isothermal oxidation behaviors of Zr-alloys Zr-A and Zr-B cladding tubes in flowing oxygen were measured and compared to Zr-4 cladding tube over a wide temperature range from 700 ℃ to 1200 ℃. The results show that the kinetics oxidation curves of all the alloys basically obey the parabolic rate law at the temperature range from 700 ℃ to 1200 ℃. In 700 ℃ oxidation of alloy Zr-B, a rate transition occurrs at about 1200 s. The rate transitions in 800 ℃ curves of alloys Zr-A and Zr-B occurr at about 600 s. The oxidation kinetics curves are changed for all the alloys at 1000 ℃, which is resulted from the crack in the oxide layer due to the ZrO2 phase transformation from a monoclinic structure to a tetragonal structure. At the temperature above 1100 ℃, the oxidation kinetics curves of all the alloys obey the parabolic rate law, and no kinetics changes were observed. The results also show that the alloy composition has a negligible effect on the oxidation resistance at the temperature above 1100 ℃. The parabolic rate constant Kp of the oxidation reaction was get through calculating weight gain due to oxidation.
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    SIMULATION AND EXPERIMENTAL STUDY OF PREPARATION OF FUNCTIONALLY GRADIENT MATERIALS BY MIG WELDING UNDER MAGNETIC FIELD\par
    WANG Chao ZHANG Haiou WANG Guilan
    Acta Metall Sin, 2011, 47 (9): 1221-1226.  DOI: 10.3724/SP.J.1037.2010.00640
    Abstract   PDF (2341KB) ( 747 )
    A preparation method of functionally gradient materials (FGM) by metal inert-gas (MIG) welding under magnetic field was proposed in this paper. Three dimensional finite element models of magnetic field, welding gun and metal specimen were built. Maxwell vortex field and instantaneous field were applied to simulate the preparation process with permanent magnetic field, alternating magnetic field and without magnetic field, and the simulation model was verified by the experiment. Simulation and experimental results show that in permanent magnetic field, the stirring of molten pool is weak, the FGM can not be prepared; under alternating magnetic field, the axial oscillating magnetic force and lateral extrusion magnetic force mix round the molten pool effectively, FGM can be prepared by MIG. Without magnetic field, the gradient of Al content in formed FGM is not obvious. Experimental results accord with simulation ones commendably.
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