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

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    CERTAIN BASIC SUBJECTS ON CLEAN STEEL
    XU Kuangdi
    Acta Metall Sin, 2009, 45 (3): 257-269. 
    Abstract   PDF (2844KB) ( 2444 )

    Clean steel is a general designation of certain types of steel with higher cleanness upgraded gradually by steel factories with promotion of process and equipment step by step according to the customer demands on product quality. The requirements for cleanness of typical steel and the possible lowest level of impurity in commercial steel since last half century were introduced. The total oxygen content in steel is extremely important for its cleanness. Relevant theories of changes and decreases of total oxygen content during refining and solidification processes used by major steel factories at home and abroad were enumerated. Decreasing the inclusion amount and controlling its shape are also key tasks for clean steel production. The influences of deoxidization products, re--oxidation of deoxidizer as well as top slag composition and refractory materials on the cleanness were mentioned separately, inclusion control in stainless steel series 430 and optimum stirring intensity in refining process were introduced, the theory foundation of inclusion transformation in aluminum--killed steel treated by calcium was briefly outlined, the metallurgical principles of ultra--low phosphorus steel and ultra--low sulphur steel productions were emphasized, ultra--low sulphur and sulphide shape control which are required by anti--HIC of linepipe steel was introduced, the possible ways of removing other impurities from steel were also discussed.

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    FORMATION OF REVERSED AUSTENITE AND ITS EFFECT ON CRYOGENIC TOUGHNESS OF 9Ni STEEL DURING TWO--PHASE REGION HEAT TREATMENT
    YANG Yuehui CAI Qingwu WU Huibin WANG Hua
    Acta Metall Sin, 2009, 45 (3): 270-274. 
    Abstract   PDF (1099KB) ( 1781 )

    The changes of amount, distribution and stability of reversed austenite and their effects on the cryogenic toughness of 9Ni steel treated by two--phase region heat treatment were studied with XRD and EBSD. It is found that the cryogenic toughness of the 9Ni steel treated by two--phase region heat treatment is more excellent than that of the one treated by quenching and tempering (QT). When temperature of two--phase region is 650 ℃, the most excellent impact toughness is observed and the impact energy at -196 ℃ reaches to 177 J, at the same time the amount of reversed austenite increases to 10.15%, which indicates that the amount of austenitic has important effect on the cryogenic toughness of 9Ni steel. Results of EBSD show that most of the reversed austenite in the steel treated by QT distribute along the grain boundary, but in the steel treated by two--phase region heat treatment the austenites distribute uniformly along all kinds of boundaries, especially also along the lath martensite boundary in the grain, so the cryogenic toughness can be also improved even the amount of austenitic is lower than that in the steel treated by QT process. The stability analysis of reversed austenite shows that the optimized stability can not be observed under the conditions provided in this work.

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    MICROSTRUCTURE AND MECHANICAL PROPERTY OF COLD DRAWN HIGH STRENGTH 00Cr18Ni10N STAINLESS STEEL WIRE
    HUANG Wenke KONG Fanya
    Acta Metall Sin, 2009, 45 (3): 275-279. 
    Abstract   PDF (872KB) ( 1376 )

    00Cr18Ni10N (mass fraction, %) stainless steel wires with different reductions of area were obtained through cold drawing. Tensile test, magnetic test and microstructure observation show that at the initial stage of deformation (ε≦40%), slipping and twinning are the main deformation mechanism, more amounts of twin lamella and dislocation cell microstruture appear, and the tensile strength changes from 600 to 1200 MPa. At the large deformation stage (ε>40%), strain induced martensites begin to take a part of deformation, the microstructure exhibits a fibrous band--like character, its substructure consists of dislocation cell and broken deformation twin with irregular shape, and the tensile strength is above 1200 MPa.

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    MORPHOLOGY AND SUBSTRUCTURE OF JUJUBE--STONE--LIKE MARTENSITE IN ULTRAHIGH CARBON STEEL
    ZHANG Zhanling LIU Yongning YU Guang ZHU Jiewu HE Tao
    Acta Metall Sin, 2009, 45 (3): 280-284. 
    Abstract   PDF (908KB) ( 1310 )

    In the martensitic transformation of an ultrahigh carbon steel (UHCS) containing 1.58%C, a kind of jujube-stone-like martensite has been observed in addition to lath and twinning martensites. The substructure of the jujube-stone-like martensite is high density dislocation with 1013/cm2 and no twin has been found. Theoretical analysis based on a disc-like martensite grain shows that the strain energy is not relative to the critical thickness of the disc (2t0*) but relative to the critical diameter of the disc (2r0*), and the critical nucleation energy ΔG* is inversely related to the square of the critical aspect ratio, t0*/r0*, of martensitic grains. When t0*/r0*<1, martensitic nucleus is disc shape, t0*/r0*>1, the nucleus is jujube--stone--like and t0*/r0*>>1, the nucleus is rod shape.

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    EFFECT OF STRAIN RATE ON STRAIN INDUCED α'--MARTENSITE TRANSFORMATION AND MECHANICAL RESPONSE OF AUSTENITIC STAINLESS STEELS
    LIU Wei LI Zhibin WANG Xiang ZOU Hua WANG Lixin
    Acta Metall Sin, 2009, 45 (3): 285-291. 
    Abstract   PDF (1259KB) ( 1538 )

    Tensile tests of cold rolled and annealed EN1.4318 (AISI301L) and EN1.4301 (AISI304) stainless steel sheet samples with 2 mm in thickness were performed at the strain rates of 5×10-4 s-1 (slow strain rate) and 2×10-2 s-1 (fast strain rate). The mechanism and volume fraction of strain induced α'--martensite transformation were investigated by using TEM, SEM and XRD. The amount of strain induced α'--martensite in EN1.4318 is much higher than that in EN1.4301 when both steels are deformed at the same strain rate. Adiabatic heating caused by the fast strain obviously decreases the α'--martensite transformation rate and work hardening rate in cold rolled EN1.4318 steel. The amount of α'--martensite and transformation rate for both steels are reduced during uniform deformation compared with those at slow strain rate, this behavior is more significant in cold rolled steels than that in annealed ones. For the more stable EN1.4301 with low saturated amount of α'--martensite (<0.3, volume fraction), rapidly plastic instability and tremendous reduction of uniform elongation are due to the small hardening effect at fast strain. In contrast, for EN1.4318 with low stacking fault energy and rather high saturated amount of α'--martensite, the tensile strength is significant decreased with increasing saturated amount of α'--martensite when deformation at fast strain. The strain rate sensitivity of EN1.4318 is much higher than that of EN1.4301.

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    INFLUENCE OF SUPER--FINE SUBSTRUCTURE ON TOUGHNESS OF LOW--ALLOYING ULTRA--HIGH STRENGTH STRUCTURE STEEL
    WANG Liuding DING Fucai WANG Baimin ZHU Ming ZHONG Yingliang LIANG Jinkui
    Acta Metall Sin, 2009, 45 (3): 292-296. 
    Abstract   PDF (1275KB) ( 1343 )

    A series of low--alloying ultra--high strength structure steels (LUHSSS) which contain Si, Mn as the alloying elements are developed through controlling the transformation temperature, cooling rate and tempering parameters. The observations on the microstructure by means of TEM, SEM and AFM show that LUHSSS are composed of very fine and close ferrite (F) lathes and retained austenite (AR) of thin film shape with high stability, and no blocky AR and cementite are observed in steels. The discontinuous F lathes consist of several shear units and their thickness range is 75---100 nm. During low temperature tempering, the dislocations in the shear units move and finally form a number of homogeneous cell substructures with the diameter less than 17 nm. Under the condition of ultra--high strength (σb>1400 MPa), the multi--scale, multi--level and double--phase of microstructure significantly increase the impact absorption energy (AKV≈200 J). Furthermore, the mechanism of toughness improvement caused by cell substructures is analyzed.

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    HIGH TEMPERATURE WEAR BEHAVIOR OF NiAl--Cr(Mo)--Ho--Hf EUTECTIC ALLOY
    WANG Zhensheng GUO Jianting ZHOU Lanzhang SHENG Liyuan HU Zhuangqi
    Acta Metall Sin, 2009, 45 (3): 297-301. 
    Abstract   PDF (990KB) ( 1118 )

    The wear behaviors of NiAl--28Cr--5.6Mo--0.25Ho--0.15Hf eutectic alloy against SiC ceramic under dry sliding from 600 to 1000 ℃ were investigated on a pin--on--disc test rig. The results show that the eutectic alloy exhibits excellent self--lubricating properties in the temperature range of 700---900 ℃, which is attributed to the formation of 1---3 μm thick glass--ceramic lubricant film. During wear testing the lubricant film was partially transferred to the SiC counterface, which avoided the direct tribo--contact between the alloy and SiC ceramic. At temperatures above 900 ℃ or below 700 ℃ the friction coefficient and wear rate are higher, owing to the adhesion between matrix and film weakening or no film forming.

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    STRUCTURE EVOLUTION OF DIRECTIONALLY SOLIDIFIED Ti--43Al--3Si ALLOY I. Microstructure Evolution in the Transition Region
    FAN Jianglei LI Xinzhong GUO Jingjie SU Yanqing FU Hengzhi
    Acta Metall Sin, 2009, 45 (3): 302-307. 
    Abstract   PDF (1379KB) ( 1305 )

    Ti--43Al--3Si (atomic fraction, %) alloys, seeding material used in preparation of TiAl base alloy, were prepared by directional solidification with growth rate range of 3---100 μm/s. The influences of growth rate on interfacial morphology and microstructure evolution in transition region were studied. Cellular growth appears in a wide range of growth rate of 3---60 μm/s, and the cellular spacing decreases with increase of growth rate. When growth rate is 90 μm/s, a dendritic growth is observed. During the initial solidification, a thermal transition region can be observed clearly. The distribution of Ti5Si3 phase along transition region and relevance of microstructures between the transition region and directional solidification region have obvious effects on the seeding. When the growth rate is lower than 10 μm/s, a good distribution of Ti5Si3 phase and a good relevance appear, which is favourable in seeding for the present alloy.

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    STRUCTURE EVOLUTION OF DIRECTIONALLY SOLIDIFIED Ti--43Al--3Si ALLOY II. Microstructure Evolution in the Steady--State Growth Region
    LI Xinzhong FAN Jianglei GUO Jingjie SU Yanqing FU Hengzhi
    Acta Metall Sin, 2009, 45 (3): 308-313. 
    Abstract   PDF (1444KB) ( 1162 )

    Microstructure evolutions in the steady--state growth region of directionally solidified Ti--43Al--3Si (atomic fraction, %) alloy were studied at growth rates of 3---100 μm/s. There are four main phase transitions during directional solidification: L→Ti5Si3, L→α+Ti5Si3, α→α2(Ti3Al)+γ(TiAl) and α2γ+Ti5Si3, especially, the eutectic reaction of α and Ti5Si3 is the typical solidification behavior. When the growth rate exceeds 20 μm/s, another phase transition of L→γ+Ti5Si3 also happens. With increase of growth rate, the steady--state growth microstructure changes from coarse cells to fine cells, to cellular dendrites and then to dendrites. The Ti5Si3 phase stabilizing $\alpha$ phase distributes in the α matrix at a low growth rate, and in the solidified γ matrix at a relatively high growth rate, which is unfavorable in seeding. When the growth rate is 10 μm/s, the distance needed to reach steady--state region becomes shorter, which is favourable in seeding for the present alloy.

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    EVOLUTION OF MICROSTRUCTURE OF SEMISOLID METAL SLURRY IN ULTRASOUND FIELD
    ZHAO Junwen WU Shusen WAN Li CHEN Qihua AN Ping
    Acta Metall Sin, 2009, 45 (3): 314-319. 
    Abstract   PDF (1156KB) ( 1081 )

    The microstructural evolution of semisolid ZL101 hypoeutectic Al--Si alloy solidified in ultrasound field was investigated. The results indicate that the morphology of primary particles is related closely to the temperature of the applied ultrasound field. The primary grains grow into globular shape when ultrasound is applied from 640 to 585 ℃ (nearly solidified temperature) When the ultrasound is applied from 610 (solid fraction 0.1) to 598 ℃ (applied 120 s), the originally formed dendrites are granulated. When the ultrasound is applied at 600 ℃ (solid fraction 0.25) and holding temperature for 120 s (about 595 ℃), a mixture structure consisted of dendrite and granulated grains is formed. The evolution mechanism of semisolid microstructure under ultrasound field was discussed.

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    EFFECT OF HEAT TREATMENT ON FATIGUE BEHAVIOR OF 25Cr2NiMo1V STEEL
    ZHU Mingliang XUAN Fuzhen ZHU Kuilong WANG Guozhen JIA Tianyao
    Acta Metall Sin, 2009, 45 (3): 320-325. 
    Abstract   PDF (1215KB) ( 1323 )

    The specimens of commercial 25Cr2NiMo1V steel were treated at 955 ℃ quenching +665 ℃ tempering (HP) and 900 ℃ quenching +625 ℃ tempering (LP), respectively. Fatigue threshold and fatigue crack propagation rate tests were conducted in HP and LP specimens. The results show that in threshold regime, the HP specimen has larger fatigue threshold and lower fatigue crack growth rates than the LP specimen. The fatigue behavior is related to crack closure and the surface roughness is a main factor for crack closure. HP specimen has a larger crack closure ability than LP specimen due to the densified bainites and larger prior austenite grain size. HP specimen has more tempering martensites which do not play an important role in preventing crack growth. In Paris regime, no clear difference between fatigue behaviors of HP and LP specimens is observed.

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    EFFECT OF DYNAMIC STRAIN AGING ON FATIGUE--CREEP BEHAVIOR OF 316L AUSTENITIC STAINLESS STEEL
    JIANG Huifeng CHEN Xuedong FAN Zhichao DONG Jie JIANG Heng LU Shouxiang
    Acta Metall Sin, 2009, 45 (3): 326-330. 
    Abstract   PDF (803KB) ( 1405 )

    The fatigue--creep behaviors of hot rolled and dynamic strain aging pre--treated 316L austenitic stainless steels were investigated under different loading conditions at 550 ℃. Under stress control mode, the macroscopic manifestation of dynamic strain aging is the abrupt displacement jumps during cyclic deformation. By comparing with the hot rolled treatment the dynamic strain aging pre--treatment makes the cyclic strain amplitude decrease and the cycle number at the first abrupt displacement jump postpone, i.e., the material strength is enhanced and fatigue--creep life is effectively prolonged.

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    MODIFICATION OF ZENER'S TWO--PARAMETER IN THE SUPERELEMENT MODEL FOR Fe--Σ Xi--C ALLOY SYSTEMS
    PENG Ningqi TANG Guangbo LIU Zhengdong WU Xiuyue
    Acta Metall Sin, 2009, 45 (3): 331-337. 
    Abstract   PDF (1101KB) ( 1264 )

    On the basis of experimental value of Ae3, a modified superelement model has been developed by the modification of Zener's two--parameter for substitutional elements, such as Si, Mn, Ni, Co, Mo, Al, Cu and Cr, according to Aaronson's method of superelement model, in which the interactions between alloying elements have been taken into account. The prediction accuracy of the modified model has been greatly improved in comparison with the existing superelement models. The standard deviations between the Ae3 value calculated by the modified superelement model and measured Ae3, and Thermo--Calc calculated Ae3, are 10.8 and 2.35 ℃, respectively. The standard deviation between the experimental Ae1 and the Ae1 calculated by the superelement model with new Zener's two--parameter is 6.8 ℃. In accordance with the thermodynamics calculation approach of the transformation from austenite to martensite, the martensite start temperature, Ms, has also been calculated with the modified parameters, and the standard deviation between the experimental and calculated Ms values is 25.3 ℃.

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    CORROSION BEHAVIOR OF THE HOT--DIP GALVANIZED STEEL SHEET UNDER ADHESION OF AN ALKALINE MUD IN HOT--HUMID ENVIRONMENTS
    ZHANG Hong QI Huibin DU Cuiwei LI Xiaogang
    Acta Metall Sin, 2009, 45 (3): 338-344. 
    Abstract   PDF (1460KB) ( 1354 )

    The corroded behavior of the hot--dip galvanized (HDG) steel sheet used in automobile under mud adhesion was investigated by the hot and humid corrosion test. The corrosion products were observed and analyzed by means of SEM and XRD. The results show that the corrosion process of the HDG steel sheet with the mud adhesion could be divided into two steps, i.e., the formation of white rust due to corrosion of the zinc coating and the formation of red--black rust due to corrosion of the steel substrate. The content of γ--FeOOH in the corrosion products of the substrate is higher than others and the aggregation of Cl- ions in the mud accelerates the failure of the protection of the rust layer. The corrosion mass--loss increases continually with time but the corrosion mass--loss rate decreases correspondingly. The corrosion mass--loss rate at the higher temperature increases suddenly after a period of exposing time because the high temperature accelerates the interface reactions. In the corrosion process, there is a jump in the corrosion potential from a lower to a higher value, corresponding to the corrosion process of the zinc coating and the steel substrate, respectively. The potential jump will become earlier with temperature increasing.

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    PREPARATION AND CHARACTERISTICS OF HIGH TEMPERATURE PROTON CONDUCTOR Ba3Ca1.18Nb1.82O9-δ
    WANG Dong LIU Chunming WANG Changzhen
    Acta Metall Sin, 2009, 45 (3): 345-350. 
    Abstract   PDF (1167KB) ( 1219 )

    Ba3Ca1.18Nb1.82O9-δ powders with different particle sizes were synthesized by high temperature sintering (1400 ℃/10 h) of the mixed powders of BaCO3, CaCO3 and Nb2O5 milled for different times. Laser paticle size analysis, DSC--TG and SEM results show that the proper milling time can make particle refine, decrease the synthesis temperature, and increase the density of sample. EIS result shows that the temperature dependences of total conductivities of the sintered samples prepared by 6 and 10 h milling conform to the Arrhenius equation in the measured temperature range of 300---800 ℃, and the activation energies are 0.84 and 0.68 eV, respectively. Raising the density of Ba3Ca1.18Nb1.82O9-δ sample is an effective way to decrease the activity energy and increase the total conductivity at low and intermediate temperatures (300---600 ℃).

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    MAGNETIC--FIELD--CONTROLLED SHAPE MEMORY EFFECT AND SUPERELASTICITY OF Ni53.2Mn22.6Ga24.2 SINGLE CRYSTAL
    Acta Metall Sin, 2009, 45 (3): 351-355. 
    Abstract   PDF (835KB) ( 1171 )

    A two--step complete thermoelastic martensitic transformation, martensitic transformation and intermartensitic transformation, in Ni53.2Mn22.6Ga24.2 single crystal was proved. The transformation characteristics of the alloy under the separate and complex actions of temperature, magnetic field and stress were studied. The results show that the martensitic and intermartensitic transformations exhibit the same transition character, and this alloy exhibits a magnetic--field--controlled shape memory effect. Moreover, the stress--strain measurements of the single crystal under the magnetic field indicate that the magnetic field not only has an effect on the stress needed for reorientation of the variants during the martensitic transformation, but also makes the initial irreversible transition become reversible. The magnetically controlled superelastic characteristic of the Ni53.2Mn22.6Ga24.2 single crystal predicts the possibility of utilizing the alloy as magnetically controlled element.

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    THERMOMECHANICAL MODELING OF SOLIDIFICATION PROCESS OF SQUEEZE CASTING I. Mathematic Model and Solution Methodology
    HAN Zhiqiang ZHU Wei LIU Baicheng
    Acta Metall Sin, 2009, 45 (3): 356-362. 
    Abstract   PDF (1042KB) ( 1257 )

    A coupled thermomechanical finite element model has been developed to simulate the temperature, stress and shape developments during the solidification process of squeeze casting. The model includes the effect of latent heat and volume shrinkage due to solidification, the mutual dependence of interfacial heat transfer and casting deformation, and the mechanical behavior of the solidified shell under the punch pressure. The stress model features a thermo--elasto--viscoplastic constitutive equation that accounts for the response of the solidified shell as well as a special treatment given to the liquid and mushy zones. A contact algorithm was employed for the casting/die interface, and an iterative algorithm was employed to simulate the movement of the punch. The model can be used to investigate the effects of die design and process parameters (die temperature, punch pressure, etc.) on the quality of castings.

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    THERMOMECHANICAL MODELING OF SOLIDIFICATION PROCESS OF SQUEEZE CASTING II. Numerical Simulation and Experimental Validation
    ZHU Wei HAN Zhiqiang LIU Baicheng
    Acta Metall Sin, 2009, 45 (3): 363-368. 
    Abstract   PDF (1150KB) ( 1267 )

    Based on the thermomechanical model and solution methodology described in Part I, a finite element program for simulating the solidification process of squeeze casting was developed. By using the program and a constitutive relationship based on Gleeble test data, the solidification processes of A356 aluminum alloy under different process parameters were simulated. Squeeze casting experiments were carried out for validating the developed model and program. It is shown that the results of numerical simulation are in good agreement with the experimental results.

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    INTERFACE REACTION BETWEEN CERAMIC MOULDS AND Ti46Al1B AS--CAST VALVES
    MA Yingche WANG Weidong CHEN Bo GAO Ming LIU Kui LI Yiyi
    Acta Metall Sin, 2009, 45 (3): 369-373. 
    Abstract   PDF (1130KB) ( 968 )

    Al2O3 and Y2O3 were used as surface materials of shell mould to centrifugal--cast Ti46Al1B (atomic fraction, %) valves, the interface reaction between shell and alloy and its mechanism were analyzed by SEM and XRD, and oxygen increment in the castings was measured by gas analysis. The results show that the reaction layer thicknesses of Y2O3 and Al2O3 shells are about 90 and 170 μm, respectively, indicating Y2O3 shell has better thermodynamic stability and smaller increment of oxygen in casting than Al2O3 shell, which is accordant with thermodynamic calculation. So the Y2O3 mould is fitter for casting Ti46Al1B valves than Al2O3 mould.

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    RAPID SOLIDIFICATION WELDING OF ULTRA--THIN Zr55Cu50Al12Ni3 AMORPHOUS FOILS
    ZHAI Qiuya XU Jinfeng ZHANG Xing YANG Jinshan GUO Xuefeng
    Acta Metall Sin, 2009, 45 (3): 374-377. 
    Abstract   PDF (869KB) ( 1246 )

    The rapid solidification welding of Zr55Cu30Al12Ni3 amorphous foils with the thickness of 25---35 μm was conducted using a micro--type capacitor discharge welder. XRD analysis shows that the joint presents still amorphous structure under the rapid solidification welding conditions. The joint cooling rate calculated is high up to 106 K/s, which is much higher than that of critical cooling rate of amorphous Zr base alloy, and effectively suppresses the crystallization of joint zone. The micro joints with the size of 60---90 μm in diameter are produced and there are no welding defects such as porosity and inclusions within the joints. The joint shear strength is up to 1141 MPa. Contributing to higher electrical resistivity, the welding energy for welding metal glass foils is lower than that of crystallized metal foils remarkably.

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    HIGH TEMPERATURE OXIDATION BEHAVIOR OF A (MCrAlY+AlSiY) COMPOSITE COATING
    PENG Xin JIANG Sumeng DUAN Xuhai GONG Jun SUN Chao
    Acta Metall Sin, 2009, 45 (3): 378-384. 
    Abstract   PDF (1592KB) ( 1529 )

    A composite coating (MCrAlY+AlSiY) was prepared on a Ni--based superalloy K465 by arc ion plating technique. The oxidation behaviors of the composite coating and the reference coating NiCoCrAlYSiB were investigated. The results show that the outer layer of composite coating consists of β--(Ni, Co)Al and dispersed σ--NiCoCr and Cr3Si, and the inner layer of composite coating consists of Cr--rich phases and minor β--(Ni, Co)Al after vacuum annealing at 1050 ℃. Because of the excessive consumption of Al, the spinels and NiO are formed on the surface of the reference coating. For the composite coating, the protective alumina scale is continuous and dense. The enhanced oxidation resistance of the composite coating is related to the gradient distributions of Al--enriched outer layer and Cr--enriched inner layer.

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