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

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    Orginal Article
    AGE-HARDENING RESPONSE FOR Mg96.17Zn3.15Y0.5Zr0.18 SOLID SOLUTION ALLOY UNDER HIGH PRESSURE
    Zhibin FAN, Xiaoping LIN, Yun DONG, Jie YE, Chan LI, Bo LI
    Acta Metall Sin, 2016, 52 (12): 1491-1496.  DOI: 10.11900/0412.1961.2016.00098
    Abstract   HTML   PDF (2566KB) ( 930 )

    Rare-earth (RE) element addition can remarkably improve the mechanical properties of magnesium alloys through solid solution and age-hardening. Increasing the solubility in the Mg matrix and enhancing the precipitation density are effective measures to improve ageing strengthening of magnesium alloys. In this work, solid solution treatment at 600~800 ℃ under 4 GPa, and then isothermal ageing at 200 ℃ for Mg96.17Zn3.15Y0.5Zr0.18 alloy was carried out. The microstructures of the high pressure solution treatment Mg96.17Zn3.15Y0.5Zr0.18 alloy before and after ageing were investigated by TEM, HRTEM, SEM and XRD, and age-hardening curves of Mg96.17Zn3.15Y0.5Zr0.18 alloy after solution treatment under the high pressure of 4 GPa have been tested. The results show that, as the rise of the solution treatment temperature, I-Mg3Zn6Y and W-Mg3Zn3Y2 continually dissolved into the Mg matrix, and the solubility of Zn in the Mg matrix drastically improved after solution treatment under the high pressure of 4 GPa. The solubility of Zn in the Mg matrix reached up to 6.60% (mass fraction) after solution treatment at 700~800 ℃ under the high pressure of 4 GPa than 2.11% after solution treatment at 400 ℃ under the atmosphere, and the supersaturated solid solution α-Mg has been attained. After ageing treatment at 200 ℃, the peak hardness of Mg96.17Zn3.15Y0.5Zr0.18 alloy after solution treatment under the high pressure of 4 GPa could been reached in short ageing time, the peak hardness of the Mg96.17Zn3.15Y0.5Zr0.18 alloy after solution treatment at 800 ℃ under 4 GPa was 105 HV, which was increased by 30% than 81 HV of the alloy after solution treatment at 400 ℃ under the atmosphere. HRTEM analysis results indicated that the high precipitation density was found in the Mg96.17Zn3.15Y0.5Zr0.18 alloy after solution treatment under the high pressure of 4 GPa, and some of precipitation were particle quasicrystal I-Mg3Zn6Y phases.

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    EFFECT OF PREAGED STRETCH AFTER QUENCHED ON THE PROPERTIES AND MICROSTRUCTURE OF A NATURALLY AGED Al-Li ALLOY
    Xianfeng ZHANG,Guoai LI,Zheng LU,Juan YU,Min HAO
    Acta Metall Sin, 2016, 52 (12): 1497-1502.  DOI: 10.11900/0412.1961.2016.00207
    Abstract   HTML   PDF (3362KB) ( 726 )

    Al-Cu-Li-X alloy has attractive applications in the aerospace and aeronautic industry due to its excellent combination of mechanical properties and corrosion resisting properties. However, the microstructural complexity, especially the type and distribution of precipitates have effects on the properties. Besides changing the chemical compositions of alloy, the preaged stretch after quenched and aging process is the main method to control the type and distribution of precipitates. In this work, the effect of preaged stretch after quenched on tensile properties, corrosion property, aging response and microstructure of a naturally aged Al-Li alloy were studied by DSC, TEM, tensile test and corrosion test. The results show that the yield strength increases gradually at the stretch range from 0 to 6%, ultimate tensile strength decreases with the increase of stretch from 0 to 3%, and then become stable when stretch over 3%. Accompany with the increasing stretch, the corrosion type of alloy changes from intergranular corrosion to point corrosion. The T34 state of alloy has the least corrosion depth, about 0.03 mm. The aging response character of alloy is changed by preaged stretch. Compared with T4 state, the endothermic peak near 100 ℃ move to higher temperature, and two exothermic peaks near 180 ℃ and 260 ℃ move to lower temperature in T3x state, respectively. Preaged stretch after quenched restrains the precipitation of δ’ phase in grain and grain boundary with increasing the density of dislocation in grains. The variations of δ’ phase and dislocation affect the tensile and corrosion properties of alloy.

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    RESERCH ON QUENCH SENSITIVITY AND MICROSTRUCTURE ANALYSIS OF 7050 ALUMINUM ALLOY
    Shuzhou WU,Youping YI,Shiquan HUANG,Jun LI,Chen LI
    Acta Metall Sin, 2016, 52 (12): 1503-1509.  DOI: 10.11900/0412.1961.2016.00050
    Abstract   HTML   PDF (4956KB) ( 1064 )

    7050 aluminum alloy is an important structural material widely used in aerospace industry with a high quench sensitivity. In this work, the time-temperature-transformation (TTT) curves of 7050 aluminum alloy were determined by interrupted quench method. The microstructure evolution and phase transformation kinetics during solid solution, isothermal quenching, ageing treatment were studied by TEM and JMA equation.The results show that the nose temperature of TTT curves is about 330 ℃, with the quench sensitivity range of 300~380 ℃. The quenching sensitivity of high temperature range of 400~450 ℃ is lower than that of low temperature range of 210~270 ℃. The laminar equilibrium η phases characterized with nucleus of Al3Zr particles and several needle-shaped S phases are the main precipitations of the supersaturated solid solution decomposes during isothermal holding process. With the increase of holding time, the volume fraction of precipitated phases rises quickly, which coarsen the grain boundary continuously and broaden precipitation free zone (PFZ). While holding far away from the nose temperature, the speed of precipitation slow down and the degree of continuity and coarsening of grain boundary decrease. The values of n in JMA equation vary from 0.50 to 0.65, indicating that the precipitations are mainly laminar precipitated phases and supplementarily needle-shaped phases.

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    SOLID FEEDING MECHANISM AND ITS APPLICA-TION ON CASTINGS WITH LARGE HEIGHT-TO-DIAMETER RATIO
    Longfei CHEN,Yikun LUAN,Dianzhong LI,Yiyi LI
    Acta Metall Sin, 2016, 52 (12): 1510-1516.  DOI: 10.11900/0412.1961.2016.00075
    Abstract   HTML   PDF (2750KB) ( 859 )

    Shrinkage porosity is one of major defects in castings, which seriously influences the quality of the castings. In general, the common method to eliminate this defect is to increase the liquid feeding ability of the casting through setting a riser in the corresponding position. However, for the casting with large height-to-diameter ratio, narrow and long feeding channel increases the flow resistance of the liquid metal in the late stage of the solidification. It is difficult to achieve a long-range liquid feeding, and the effect of the feeding is very little. Therefore, the penetrated shrinkage porosity in axis is frequently produced in the continuous casting ingots with large height-to-diameter ratio and large cross-section. As the liquid feeding mechanism has no effect on this problem, the solid feeding mechanism is proposed. First, the solid feeding mechanic is clarified by analyzing the effect of the hydrostatic tense stresses on the pore formation and the solid deformation. In addition, the ability of the solid feeding is determined by the value of the fracture of liquids, the content of the gas solute in liquid metal and yield strength of the solid. Then on the basis of this mechanism, reducing the temperature gradient in the radial direction of the casting is proposed to enhance the solid feeding ability. Finally, a verification experiment was conducted, and the results proved the function of the solid feeding on eliminating the shrinkage porosity defects.

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    ALLOYING ELEMENT SEGREGATION EFFECT IN A MULTI-PHASE STRENGTHENED MARAGING STAINLESS STEEL
    Jialong TIAN,Yongcan LI,Wei WANG,Wei YAN,Yiyin SHAN,Zhouhua JIANG,Ke YANG
    Acta Metall Sin, 2016, 52 (12): 1517-1526.  DOI: 10.11900/0412.1961.2016.00234
    Abstract   HTML   PDF (8366KB) ( 952 )

    Maraging stainless steels are the most widely used high strength stainless steels because of their excellent combination of high strength, superior corrosion resistance and good weldability. The typical heat treatment of maraging stainless steel consists of solution treatment and the following aging treatment. Aging treatment is the important process since it affects the steel's final properties and then determines its application prospect. Thus, understanding well the segregation behavior of alloying elements during the aging treatment plays a key role in developing the new maraging stainless steel with superior properties. In this work, segregation of alloying elements as well as its effect on mechanical properties and corrosion resistance of a multi-phase strengthened maraging stainless steel was studied by HRTEM and APT analyses. It was found that three precipitating species including Mo-rich R′ phase, η phase and Cr-rich α′ phase were identified in the steel. A unique core-shell structure with membrane-like R′ phase formed on the surface of η phase was identified however α′ phase distributed in the matrix separately. The core-shell structure enabled the maraging stainless steel a superior over-aging resistance and since aging time has reached 40 h, the characteristics of precipitations change little even aging time prolongs to 100 h. The corrosion test results indicated that the occurrence of α′ phase resulted in the formation of Cr-depleted zone and deteriorated the corrosion resistance seriously. In conclusion, the segregation behavior of alloying elements in maraging stainless steel has a significant effect on both mechanical property and corrosion resistance although some underlying mechanisms still haven't been understood well.

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    AN ULTRAFINE GRAINED DUPLEX Mn12Ni2MoTi(Al) STEEL FABRICATED BY COLD ROLLINGAND ANNEALING
    Yanqi YIN,Cuilan WU,Pan XIE,Kai ZHU,Songli TIAN,Mei HAN,Jianghua CHEN
    Acta Metall Sin, 2016, 52 (12): 1527-1535.  DOI: 10.11900/0412.1961.2016.00044
    Abstract   HTML   PDF (6019KB) ( 867 )

    For decades, transformation induced plasticity (TRIP) assisted steels with high tensile strength and exceptional ductility at room temperature have attracted a great deal of attentions. Their applications are often limited due to the low yield strength. In this work, an ultrafine grained (UFG) duplex Mn12Ni2MoTi(Al) TRIP steel with high yield strength and good ductility is fabricated by cold rolling and subsequent annealing at 710~745 ℃. The microstructure and mechanical properties of the steels with different heat treatment conditions are investigated by means of XRD, SEM, TEM, hardness and tensile tests. It is found that after annealing at 710~745 ℃, the deformation microstructure of the cold-rolled samples has transformed into a sub-micron UFG duplex microstructure consisting of austenite, ferrite and dispersed second-phase precipitations. The second-phase precipitations formed during annealing are rich in Ti, Mo and Si, and play an important role in preventing the ultrafine grains from coarsening, which results in high yield strength and good thermal stability. After annealing at 710 ℃ for 24 h, the average grain size of the UFG steel is still less than 500 nm. The elongation of the UFG duplex steel is increasing with the increment of the volume fraction of austenite in the UFG duplex steel at room temperature. The volume fraction of austenite in the UFG duplex steel at room temperature first increases and then decreases with the annealing temperature and time increasing, and reaches the maximum value when annealing at 745 ℃ for 0.5 h. The yield strength and total elongation of the UFG steel can be as large as 900 MPa and 23%, respectively, which are about double those of the quenched martensitic sample.

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    EFFECT OF MICROSTRUCTURAL EVOLUTION ON THE PITTING CORROSION OF COLD DRAWING PEARLITIC STEELS
    Yue HE,Song XIANG,Wei SHI,Jianmin LIU,Yu LIANG,Chaoyi CHEN
    Acta Metall Sin, 2016, 52 (12): 1536-1544.  DOI: 10.11900/0412.1961.2016.00186
    Abstract   HTML   PDF (11797KB) ( 704 )

    Heavily cold drawing pearlitic steel wires are widely used for aerospace, tire cord, suspension bridge cable, and architecture due to the high strength with acceptable level of ductility. For marine steel wires, which are widely applied in the marine and offshore structures enduring the effect of stress and corrosion, the corrosion performance is significant. Corrosion is a primary cause of structural deterioration for marine and offshore structures, which results in structural failure, leakage, product loss, environmental pollution and the loss of life. Numerous studies have been devoted to the microstructure evolution or cementite dissolution induced by cold drawing. With respect to the effect of microstructure evolution on the performance of pearlitic steel, the views were mainly focused on the mechanical performance, and only a little attention was paid to the effect of microstructure evolution on the corrosion behavior of pearlitic steel. Hence, it is still unclear whether and how the cold drawing influences the corrosion resistance of pearlitic steel. In this work, the effect of microstructure evolution on the pitting corrosion of pearlitic steel was investigated. The electrochemical measurements were carried out by electrochemical impedance spectroscopy and potentiodynamic measurement. Meanwhile, the corrosion morphology after immersion for 5 d was observed by standard visual techniques. The results indicate that corrosion resistance of cross section decreases with increasing the strain of cold drawing, while the corrosion resistance of longitudinal section decreases in the first stage of cold drawing (strain ε ≤1.2) but increases in the second step of cold drawing (ε =1.6). By characterizing the distribution of pits in the evolutionary microstructure induced by cold drawing, the grain boundary, the pearlite colony boundary and the phase boundary where the pits are inclined to initiate and propagation, are sensitive to pitting. Thus, the decrease of corrosion resistance of cross section and longitudinal section in the first stage of cold drawing (ε ≤1.2) is due to the multiplication of interface, which increases the pitting sensibility of microstructure. Electron backscattered scattering detection was used to quantify the content of <110> texture of pearlitic steels with different strains. The result showed that the improvement of corrosion resistance of the longitudinal section in the second stage of cold drawing (ε =1.6) is due to the variation of misorientation angle distribution caused by the formation of <110> texture.

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    EVALUATING SERVICE TEMPERATURE FIELD OF HIGH PRESSURE TURBINE BLADES MADE OF DIRECTIONALLY SOLIDIFIED DZ125 SUPERALLOY BASED ON MICRO-STRUCTURAL EVOLUTION
    Yadong CHEN, Yunrong ZHENG, Qiang FENG
    Acta Metall Sin, 2016, 52 (12): 1545-1556.  DOI: 10.11900/0412.1961.2016.00170
    Abstract   HTML   PDF (9498KB) ( 726 )

    To get the actual service temperature distribution of turbine blades in aeroengines is very important for the design and maintenance. However, the acquisition of service temperature distribution has always been a challenge due to the complex and severe working condition of turbine blades. In this work, one turbine blade made of directionally solidified DZ125 superalloy was investigated after the service in air for 900 h. The microstructural evolution of DZ125 superalloy after thermal exposure at 900~1100 ℃ without the stress in different time period was also investigated, for comparison. According to microstructural degradation behaviors in the dendritic region, interdendritic region, carbides and grain boundary of DZ125 superalloy before and after service, the volume fraction of γ’ precipitates in the dendritic region was determined as the quantitative characterization parameter. A method to evaluate the service temperature of turbine blades was developed, based on the quantitative characterization of microstructural evolution, such as the relationship between the thermally exposured temperature and volume fraction of γ’ precipitates. The equivalent average service temperature (Tave) and the equivalent maximum service temperature (Tmax) were proposed based on the assumption of the constant temperature during service and the nearly service condition with variable temperature of blades, respectively. The results indicate that the service temperature was higher in the middle of the blade, and became lower at the locations closer to the tip or the root. For each cross-section, the service temperatures of the serviced blade in the descending order were leading edge, pressure side, trailing edge and suction side. The highest service temperature of 1050~1100 ℃ appeared at the leading edge in the middle of the blade. The distribution trend of Tave agreed well with that of Tmax, but Tmax was higher than Tave in some locations of the blade. This work suggests that the evaluation results of Tmax were more reasonable than those of Tave. This method would be helpful to establish the assessment method of the service-induced microstructural damage in turbine blades made of directionally solidified superalloys.

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    CORROSION BEHAVIOR OF A NEW NICKEL BASE ALLOY IN SUPERCRITICAL WATERCONTAINING DIVERSE IONS
    Meiqiong OU,Yang LIU,Xiangdong ZHA,Yingche MA,Leming CHENG,Kui LIU
    Acta Metall Sin, 2016, 52 (12): 1557-1564.  DOI: 10.11900/0412.1961.2016.00113
    Abstract   HTML   PDF (4107KB) ( 487 )

    The productivity of municipal sewage sludge is difficult to treat by traditional methods. Supercritical water oxidation (SCWO) is an attractive municipal sewage sludge treatment technology. However, the process of SCWO must be carried out in a reactor which will resist not only high temperature (above 374.15 ℃) and high pressure (above 22.1 MPa) conditions but also a corrosive environment. Thus, the material used in the equipment is referred to be a key factor that restricts the application of the SCWO technology. Many materials have been selected for corrosion test under corrosive environments with SCWO, including austenitic stainless steel, nickel base alloys, titanium alloys and zirconium alloys. At present, in order to treat rich phosphorous sewage sludge, a new corrosion resistant nickel base alloy X-1# alloy has been developed to apply to the reactor of SCWO process. X-1# alloy has excellent corrosion-resistance and oxidation-resistance properties in supercritical water containing PO43-, Cl- and SO42-. The corrosion behaviors of X-1# alloy exposed to 550 ℃, 23 MPa supercritical water containing PO43-, Cl- and SO42- were investigated in this research. The exposed time was 72, 159, 248, 429 and 537 h. Morphologies, microstructures and chemical composition of oxide films in X-1# alloy and deposit sediment in reaction were studied using grazing incidence XRD, XPS and SEM equipped with EDS. The XRD, EDS and XPS analysis of X-1# alloy was performed to identify the composition of oxide layers, which were identified as NiCr2O4, Cr2O3, NiO, Ni3(PO4)2, CrPO4 and Na3PO4. In addition, it was founded that continuous and uniform oxide films were formed in supercritical water. The oxide film was a duplex-layer structure, the loose outer layer was NiO, Ni(OH)2 and phosphates, including Ni3(PO4)2, CrPO4 and Na3PO4, while the compact inner layer consisted of NiCr2O4 and Cr2O3. X-1# alloy showed a high corrosion rate in the initial stage and the corrosion rate decreased obviously after exposed to 248 h, the reason of which was that the compact inner layer of oxide films had good stability and benefited to the corrosion behavior of X-1# alloy. In order to explain the corrosion behavior of X-1# alloy, the oxide films growth mechanical, metal ions and oxygen ions dissolution mechanism and phosphates precipitation mechanism will be discussed in this research.

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    INVESTIGATION ON THE CORROSIVE ANISOTROPY OF Zr-Sn-Fe-Cr-(Nb) ALLOYS IN 500 ℃ SUPER-HEATED STEAM
    Jun ZHANG,Meiyi YAO,Xuankai FENG,Zhigang WANG,Jiao HUANG,Xun DAI,Jinlong ZHANG,Bangxin ZHOU
    Acta Metall Sin, 2016, 52 (12): 1565-1571.  DOI: 10.11900/0412.1961.2016.00043
    Abstract   HTML   PDF (5857KB) ( 575 )

    Zirconium alloys are widely used as nuclear fuel cladding in water reactors because of their low cross-section for thermal neutron absorption, reasonable mechanical properties and adequate corrosion resistance in high temperature water. Zirconium alloys have a prominent anisotropic characteristic because of the hexagonal close-packed crystal structure. The anisotropic growth of oxide layers is related to corrosion conditions and chemical composition of zirconium alloys. The corrosive anisotropy of Zr-0.72Sn-0.32Fe-0.14Cr and Zr-0.85Sn-0.16Nb-0.37Fe-0.18Cr coarse-grained specimens was investigated in a superheated steam at 500 ℃ and 10.3 MPa by autoclave tests. EBSD, SEM and TEM were used to investigate the microstructures of the alloys and the relationship between the oxide thickness and the grain orientation of the metal matrix. Results showed that the structures of second phase particles (SPPs) can be affected by Nb: the face-centered cubic Zr(Fe, Cr)2 precipitates were mainly detected in Zr-0.72Sn-0.32Fe-0.14Cr alloy, while the face-centered cubic and hexagonal close packed Zr(Nb, Fe, Cr)2 precipitates were observed in the Zr-0.85Sn-0.16Nb-0.37Fe-0.18Cr alloy. No nodular corrosion appeared on the two alloys for 500 h exposure. There was no big difference between the thickness of oxide layers and the grain orientations, i.e. no corrosive anisotropy of the two alloys was presented.

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    EFFECTS OF DEUTERIUM CONTENT ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Zr-4 ALLOY
    Cheng ZHANG,Xiping SONG,Jingru LIU,Yun YANG,Li YOU
    Acta Metall Sin, 2016, 52 (12): 1572-1578.  DOI: 10.11900/0412.1961.2016.00193
    Abstract   HTML   PDF (13380KB) ( 329 )

    Zirconium alloy has been employed widely in nuclear industry, yet the absorption of deuterium in zircaloy is considered to play a critical role in mechanical properties especially in high temperature under a loss of coolant accident (LOCA) and application for deuterium storage. However, little is known about the microstructure evolution of zircaloy during deuterium absorption. In this work, deuterium was charged into the sample at 900oC and different pressures, and the effects of deuterium content on microstructure and mechanical properties of Zr-4 alloy have been studied by means of OM, BSE, SEM, XRD, and hardness and compressive tests. The results showed that the amount of deuteride increased with the increase of deuterium content from 1.35% to 2.21%, accompanying with the morphology variations from intragranular deuteride needles to intergranular deuteride blocks, which formed an interlinked deuteride configuration and grew into equiaxed α-Zr grains. Deuteride layer was observed on the surface of sample at higher deuterium content with the micro-crack appeared within it. The mostly deuteride was δ-deuteride, and ε-deuteride was observed on sample surface with high deuterium content. There existed a hardness gradient from surface to center. With the increase of deuterium content, the hardness increased and hardness gradient became evident. With increasing deuterium content, the compressive yield strength of samples in creased slightly, but the compressive ultimate strength decreased greatly from 1176 MPa (1.35%) to 856 MPa (2.21%). The deceasing of compressive ultimate strength was probably related to the formation of micro-crack. The cracks nucleated and propagated within the intergranular deuteride blocks, which leads to the degradation of compressive ultimate strength.

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    MICROSTRUCTURES AND MECHANICAL PROPERTIES OF TiAl/Ti3Al MULTI-LAYERED COMPOSITE
    Zaoyu SHEN,Limin HE,Guanghong HUANG,Rende MU,Jinwang GU,Weizhong LIU
    Acta Metall Sin, 2016, 52 (12): 1579-1585.  DOI: 10.11900/0412.1961.2016.00091
    Abstract   HTML   PDF (6025KB) ( 901 )

    In recent years, intermetallic compounds have received a lot of considerable attentions for high temperature applications in modern aircraft manufacturers, high temperature engine components, shape memory devices and power generation industry. Among these materials, Ti-Al intermetallic compounds are fascinating materials owing to their low density, high stiffness and good creep properties. However, the structure of the metallic bonding in these intermetallics is the important reason for their insufficient ductility at room temperature. In this work, large-sized TiAl/Ti3Al multi-layered composite thin sheet with uniform chemical composition was prepared by electron beam physical vapor deposition (EB-PVD) technology. The composite and microstructure of multi-layered composite were analyzed by XRD and SEM. The results indicated that the prepared material with visible lamellar structure was composed of α2-Ti3Al and γ-TiAl phases. The densification process of composite was carried out by hot isostatic pressing. The multi-layered material was evaluated with static tensile test before and after hot isostatic pressing. The multi-layered composite after hot isostatic pressing had a higher tensile strength and a good characteristic of tensile elongation. Based on the tensile fracture morphology, the microscopic deformation mechanisms and fracture mechanism were investigated. After hot isostatic pressing, the fracture mechanism transforms to a mixed mode which consists of intergranular fracture and cleavage fracture.

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    STUDY ON ADSORPTION AND DISSOCIATION OF WATER MOLECULE ON Au, Cu AND THEIR ALLOYS' SURFACES BY DFT CALCULATIONS
    Zongyou JIANG,Zongyan ZHAO
    Acta Metall Sin, 2016, 52 (12): 1586-1594.  DOI: 10.11900/0412.1961.2016.00203
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    In order to reduce the amount and cost of gold catalyst in practical application, it is an effective technical strategy to construct binary metal alloy with gold and transition metals. In this work, the adsorption behaviors and dissociation reaction path of water on the different surfaces of Au, Cu, and AuCu binary alloy were studied by using DFT calculations. Based on the calculations, the corresponding catalytic performance of each model was further analyzed. The calculated results showed that the catalytic activity of the considered four surface models is on the following order: Au(111) < AuCu(111)-Cu < AuCu(111)-Au < Cu(111), if using the active energy as comparison standard. The underlying reason of this phenomenon is closely related with the adsorption behavior: the molecular adsorptions of water on Cu(111) and AuCu(111)-Au surfaces have relatively small adsorption energies; while at the same time, the dissociation adsorptions of water on these two surfaces have relatively large adsorption energies. Based on the electron transfer and bonding electronic structure, it could be found that the more electrons transfer between surface and water or H+OH groups, the more strong interaction between catalyst and adsorbate. Furthermore, the overlapping or hybridization between the d states of metal atoms on the surface and the 1b1 states of water or lb1-like states of H+OH groups also determines this interaction. Therefore, using AuCu binary alloy to replace Au as catalyst or co-catalyst reduces cost, and enhances the catalytic activity.

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    STUDY ON PREPARATION AND PROPERTIES OF AMORPHOUS Al2O3 THIN FILMS BY RADIO FREQUENCY MAGNETRON SPUTTERING FROM POWDER TARGET
    Fayu WU,Jianwei LI,Yi QI,Wutong DING,Ziming FAN,Yanwen ZHOU
    Acta Metall Sin, 2016, 52 (12): 1595-1600.  DOI: 10.11900/0412.1961.2016.00139
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    Al2O3 thin films are widely applied in mechanic, optic and electronic fields due to their excellent properties. Among many deposition techniques, magnetron sputtering is regarded as one of the most practical approaches for preparing Al2O3 films. In sputtering process, the use of powder targets could offer the advantages of easily variable and controllable composition and low cost. However, it is not yet known well enough how to determine sputtering parameters, microstructure and properties of Al2O3 films from powder targets. In this work, Amorphous Al2O3 films were prepared by radio frequency magnetron sputtering process in which high pure Al2O3 powder was used as the target material. The effects and mechanism of the sputtering parameters on the microstructures, surface morphology and optical properties of amorphous Al2O3 films were analyzed by XRD, AFM, surface profile, UV-Vis spectroscopy and so on. Considering used as the packaging material, the antimicrobial performance of amorphous Al2O3 films was also studied. The experimental results showed that: increasing the oxygen flow, decreasing the sputtering power and shortening the sputtering time could make the particle size and roughness of amorphous Al2O3 films lower while depressing the deposition rate of amorphous Al2O3 films. Moreover, the increase of the oxygen flow and decrease of the sputtering time would widen the band gap which the maximum was up to 4.21 eV, and heighten the transmittance of the visible light which was beyond 90%. The antibacterial rate of amorphous Al2O3 films under the natural light after 24 h was up to 98.6%, which reflected the photocatalytic characteristics of the antimicrobial mechanism.

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    STUDY ON ATOMIC-SCALE STRENGTHENING MECHANISM OF TRANSITION-METAL NITRIDE MNx (M=Ti, Zr, Hf) FILMS WITHIN WIDE COMPOSITION RANGES
    Kechang HAN,Yiqi LIU,Guoqiang LIN,Chuang DONG,Kaiping TAI,Xin JIANG
    Acta Metall Sin, 2016, 52 (12): 1601-1609.  DOI: 10.11900/0412.1961.2016.00078
    Abstract   HTML   PDF (1966KB) ( 858 )

    Transition-metal nitrides have long attracted considerable attention among researchers and ubiquitous applications in various fields due to their renowned mechanical properties. However almost all the discussions of the strengthening mechanism were on conventional meso scale. For further understanding on the atomic scale strengthening mechanism of transition-metal nitrides, three groups of MNx (M=Ti, Zr, Hf) films with different nitrogen contents were synthesized on the Si substrates by magnetic filtering arc ion plating. The morphologies and thickness of the as-deposited films were characterized by FESEM, the microstructures and the residual stresses were characterized by XRD, the XPS and Nano Indenter were used to measure the chemical states and hardness (also the elastic modulus) of as-deposited films, respectively. The results show that all three groups MNx films perform the B1-NaCl single-phase structure within the large composition ranges. The preferred orientation, thickness, grain size and residual stress of the MNx films with different nitrogen contents were not changed so much. While the nanohardness and elastic modulus of MNx both first increased and then decreased with the rise of nitrogen content, and the peak values all existed when x near to 0.82. The strengthening mechanism was discussed and the decisive factor of composition dependent hardness enhancement was found from the atomic-scale chemical bonding states and electronic structure in this work, rather than the conventional meso-scale factors, such as preferred orientation, grain size and residual stress.

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    INFLUENCE OF SUBSTRATE MECHANICAL PROPER-TIES ON DEPOSITION BEHAVIOUR OF 316L STAINLESS STEEL POWDER
    Guanglu MA, Xinyu CUI, Yanfang SHEN, CINCA Nuria, M. GUILEMANY Josep, Tianying XIONG
    Acta Metall Sin, 2016, 52 (12): 1610-1618.  DOI: 10.11900/0412.1961.2016.00154
    Abstract   HTML   PDF (2842KB) ( 662 )

    Nowadays the theory of critical velocity of particles in cold spray has been already accepted generally. In the familiar semi-empirical formulas of the theory, only the properties and conditions of particles have been considered but there is no consideration of substrate. Yet most researches for effect of substrates' properties implied hardness of substrate was the most essential. However, little attention has been devoted to influence of other mechanical properties (e.g. Young's modulus and Poisson's ratio) and their cooperation on the deposition behavior. In order to study the effect systematically, 316L stainless steel particles were deposited by wipe test on six different substrates with a widely range of mechanical properties including Young's modulus, hardness and Poisson's ratio. They are pure Al, pure Cu, 7075T6 Al alloy, mild steel, Inconel625 and Ti6Al4V. The specimens have been investigated from morphology, cross-section and deposition efficiency. It is found that not only hardness but also Young's modulus and Poisson's ratio can affect deformation and deposition of bonded particles through playing a role in energy partition and bonding mechanism. In the case, the deformation of deposited particles is dependent on energy accepted by the particles, while the deposition efficiency is related to the bonding mechanism and energy accepted by substrate. According to the deformation level of the deposited particles, there are two kinds of substrate materials. On the one hand, bonding between particles with little deformation and their substrates is mainly dependent on mechanical interlock, in which both hardness and Young′s modulus of the substrates are lower than that of the particle. Then a parameter, Epara, has been calculated to predict the tendency of deposition efficiency for the situations. AZ91 alloy has been employed as substrate material in confirmatory experiment. Its result indicates that Epara is available for tendency prediction of the deposition efficiency of spherical-like deposited particle. On the other hand, the bonding mechanism of deposited particle with obviously flattening is more complex. In this situation, either hardness or Young′s modulus of the substrates is higher than that of the particle. The more area of fresh metal contacts on the interface, the higher deposition efficiency is.

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