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Effect of surface nanocrystallization on the corrosion behavior of Zircaloy-4

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Science china(Technological Sciences) 2009年第8期52卷 2227-2231页

作者： ZHU YuTao1,2.& ZHANG XiYan1,2.3 1 College of Materials Science and engineering, Chongqing university, Chongqing 400045, {2. 2.national engineering research center for magnesium alloys, Chongqing university, Chongqing 400044, {2. 3 School of Physical Science and engineering Technology, Guangxi university, Nanning 530004, {2. 1. College of Materials Science and engineering Chongqing University Chongqing 400045 China 2. national engineering {2. center for magnesium alloys Chongqing University Chongqing 400044 China 3. School of Physical Science and engineering Technology Guangxi University Nanning 530004 China

The contrastive corrosion experiments between surface nanocrystallined Zircaloy-4 and coarse-grained Zircaloy-4 under the condition of 673 K/10.3 MPa in pure water are carried out, and the microstructure of oxide films has been studied. The results indicate that the growth rate of oxide films formed on the nanocrystalline Zircaloy-4 is lower than that of oxide films formed on the coarse-grained Zircaloy-4. Simultaneously, the oxide/metal interface of the former is more regular and glossy than that of the latter. For nanocrystalline Zircaloy-4, the low oxygen diffusion rate through the oxide/metal interface can hinder the reaction of oxygen ion with metal ion. Furthermore, more tetragonal ZrO2.are observed in the oxide films, which can delay the martensite phase transition from tetragonal to monoclinic phase in oxide films.

关键词： nanocrystalline Zircaloy oxide film microstructure

Thermal-stress Simulation of Direct-chill Casting of AZ31 magnesium Alloy Billets

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Journal of Wuhan university of Technology(Materials Science) 2009年第3期24卷 376-382页

作者：胡红军 College of Materials Science and engineering Chongqing University national engineering {2. center for magnesium alloys Chongqing University College of Material Science and engineering Chongqing University of Technology

Two-dimensional （2.） transient coupled finite element model was developed to compute the temperature and stress field in cast billets, so as to predict the defects of the I-type billets made from AZ31 magnesium alloy and find the causes and solutions for surface cracks and shrinkages during direct-chill （DC） casting process. Method of equivalent specific heat was used in the heat conduction equation. The boundary and initial conditions used for primary and secondary cooling were elucidated on the basis of the heat transfer during the solidification of the billet. The temperature and the thermal-stress fields were simulated with the thermal-structural coupled module of ANSYS software. The influences of casting parameters on the distributions of temperature and stress were studied, which helped optimize the parameters （at pouring temperature of 680 ℃, casting speed of 2.min/s, heat-transfer coefficient of the second cooling equals to 5 000 W/m^2.℃^-1）. The simulation results of thermal stress and strain fields reveal the formation mechanism of some casting defects, which is favourable for optimizing the casting parameters and obtain high quality billets. Some measures of controlling processes were taken to prevent the defects for direct-chill casting billets.

关键词： magnesium alloy direct-chill casting temperature and stress fields numerical simulation solidification model

Effects of scandium addition on microstructure and mechanical properties of ZK60 alloy

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Progress in Natural Science:Materials International 2011年第1期21卷 59-65页

作者： Fu-sheng PAN~(1,2.,Ting-ting LIU~(1,2.,Xi-yan ZHANG~(1,2.,Ai-tao TANG~(1,2.,Wei-qing WANG~(1,2. 1.national engineering {2. center for magnesium alloys,Chongqing university,Chongqing 400045,china 2.College of Materials Science and engineering,Chongqing university,Chongqing 400045,china [a] national engineering {2. center for magnesium alloys Chongqing University Chongqing 400045 China [b] College of Materials Science and engineering Chongqing University Chongqing 400045 China

The effects of Sc addition on the microstructure and mechanical properties of the ZK60 wrought magnesium alloy were investigated by using optical microscope,scanning electron microscopy,X-ray diffraction and tensile *** experimental results show that a minor Sc addition to ZK60 alloy has an obvious effect on the refinement of the microstructure of the ZK60 alloy. During hot extrusion,incomplete dynamic recrystallization occurs in all the alloys,and the recrystallized grains become much finer with increasing Sc *** tensile strengths of ZK60 evidently increase with the addition of Sc,but the elongations decrease. The ZK60 alloy with 0.6%(mass fraction) Sc addition is found to have the tensile strength of about 350 MPa and the yield strength of about 2.0 *** T6 heat treatment,the tensile strength of the alloy containing 0.6%Sc remains almost ***, the yield strength of the alloy increases up to 352.MPa,and the ratio of the tensile strength to the yield strength is close to 1.

关键词： wrought magnesium alloy scandium microstructure mechanical properties

Phase Evolution during Carbothermic Reduction Process of Ilmenite for TiC_xN_(1-x) Composite Powders

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稀有金属材料与工程 2011年第S3期40卷 281-285页

作者： Tang Aitao1,2. Chen Min1, Wang Jian1,2. Liu Chuanpu1, Pan Fusheng1,2. Wang Weiqing1 1 College of Materials Science and engineering, Chongqing university,Chongqing 400045, {2. 2.national engineering research center for magnesium alloys, Chongqing university, Chongqing 400044, {2. Chongqing Univ Coll Mat Sci & Engn Chongqing 400045 Peoples R China Chongqing Univ Natl Engn Res Ctr Magnesium Alloys Chongqing 400044 Peoples R China

As cutting materials and wear-resistant materials, the composites reinforced by Ti(C,N) have very high performances. The super-high cost of these composites, however, limits apparently their wider application to industry due to use of very expensive Ti(C,N) powders. Therefore, it is very necessary to develop a new process technology with low fabrication cost. In the present work, ilmenite (FeTiO3), which is very cheap and very rich in china, was used to fabricate the Ti(C,N) powder directly. The phase evolution during carbothermic reduction process of ilmenite was investigated by XRD, TG-DSC and thermodynamic calculation. The ilmenite and graphite were mixed by high energy ball milling and then sintered in pure flowing nitrogen atmosphere. The experimental results showed that a new phase, Ti4O7, appeared at 900 ℃ and disappeared at 1100 ℃ while sintered in pure flowing nitrogen atmosphere. The phase evolution during carbothermic reduction process of ilmenite was found to be continuous as FeTiO3→Ti4O7→T3O5→TiCN. XRD results showed that the composite powders produced in the present reaction were composed of α-Fe and TiC1-xNx. The thermodynamic calculation results were agreeable with experimental results.

关键词： ilmenite TiCxN1-x composite powders thermodynamic calculation carbothermic reduction

Grain refinement of Mg-Li-Al cast alloys by adding typical master alloys

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Progress in Natural Science:Materials International 2011年第3期21卷 236-239页

作者： Bin JIANG~(1,2.,Qing-shan YANG~2.Ming-xing ZHANG~3,Dong QIU~3,Rui-hong LI~2.Fu-sheng PAN~(1,2. 1.national engineering {2. center for magnesium alloys,Chongqing university,Chongqing 400044,china 2.College of Materials Science and engineering,Chongqing university,Chongqing 400044,china 3.Division of Materials,School of Mechanical and Mining engineering, The university of Queensland,St Lucia,QLD 4072.Australia [a] national engineering {2. center for magnesium alloys Chongqing University Chongqing 400044 China [b] College of Materials Science and engineering Chongqing University Chongqing 400044 China [c] Division of Materials School of Mechanical and Mining Engineering The University of Queensland St Lucia QLD 4072 Australia

Commercial Al-3Ti-1C and Al-5Ti-1B master alloys were added in order to refine the grains of Mg-Li-Al *** effects of their addition levels on grain refinement of Mg-Li-Al cast alloy were investigated and the mechanism of the grain refinement was *** results showed that the addition of Al-3Ti-1C master alloy reduced the grain size of LA141 cast alloy from 900μm to 400μm,while the addition of Al-5Ti-1B master alloy reduced the grain size of LA51 cast alloy from 500μm to 2.0μ*** grain refining mechanism was the heterogeneity nucleation of TiC and TiB2.because of less than 10%mismatches of TiC/β-Li and TiB2.α-Mg.

关键词： magnesium lithium alloy master alloy grain refinement

Effects of Multiple Plastic Deformations on Microstruc-ture and Mechanical Properties of 7A04-T6

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稀有金属材料与工程 2011年第S3期40卷 69-72页

作者： Zhang Zhimin1,2. Yu Jianmin1, Wang Qiang2. Zhang Xing 2.1 engineering research {2. of magnesium-base Material Processing Technology, Ministry of Education, Taiyuan 030051, china 2.North university of china, Taiyuan 030051, china Minist Educ Engn Res Ctr Magnesium Base Mat Proc Technol Taiyuan 030051 Peoples R China N Univ china Taiyuan 030051 Peoples R China

The influences of multiple plastic deformations on microstructure and mechanical properties of 7A04-T6 alloy by isothermal compression experiments in different passes deformation on the 6300 kN extrusion press. The experimental results showed that the strength and elongation of 7A04-T6 alloy were increased firstly and then decreased as the deformation pass increases at above 400 ℃. The grains of 7A04-T6 alloy was refined firstly and then grow, the grain was become refinement after four deformations under this experimental conditions. The second phase η (MgZn2. in the matrix would precipitate after solution, precipitation strengthening taking place. It is obvious that the number of second phase which dissolve into the matrix will increase as the deformation pass increasing. So the tensile strength reached the highest after four deformations, is 590.9 MPa, yield strength is 532.5 MPa, and elongation is 12.4%. After four deformations of 7A04-T6 alloy, tensile fracture surface of samples was composed of the deep and uniform dimples, belonging to ductile fracture. Therefore, 7A04-T6 alloy has better comprehensive mechanical properties after four deformations.

关键词： 7A04 high-strength aluminum alloy multiple deformations T6 heat treatment

Influence of Solution Treatment on Impact Toughness and Microstructure of Cobalt-free Maraging Steel

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稀有金属材料与工程 2011年第S3期40卷 114-117页

作者： Yu Jianmin1, Li Baocheng1, Zhang Baohong2. Yang Weiyu2.1North university of china, Taiyuan 030051, china 2.3} research center of magnesium-base Material Processing Technology, Ministry of Education, Taiyuan 030051, china N Univ china Coll Mat Sci & Engn Taiyuan 030051 Peoples R China Minist Educ Engn Res Ctr Magnesium Base Mat Proc Technol Taiyuan 030051 Peoples R China

The influence of different solution temperature on microstructure and impact toughness of cobalt-free maraging steel 00Ni14Cr3Mo3Ti was investigated by SEM and X-Ray *** experimental results showed that with the solution temperature variation, the martensite morphology has not changed, is still lath *** Laves phase hindered the dislocation movement after 750 ℃ solution heat treatment, which result in a very low impact absorbed energy, the impact fracture has no obvious plastic deformation, with bad *** the solution temperature increased, the undissolved phase gradually dissolved, the impact absorbed energy increased *** the Laves phase dissolved when reach to 900 ℃, the impact absorbed energy reaches the maximum, is 61 *** morphology change from brittle fracture into toughness transgranular fracture with deep dimple. When solution temperature is above 900 ℃, with the solution temperature further increase, austenite grain size increases *** grain diameter of austenite is about 70 μm after 1050 ℃ solution treatment, the density of precipitates on the grain boundary of maraging steel is increase substantially, deformation compatibility deteriorate, which result in the impact absorbed energy decreased *** type becomes transgranular and quasi-cleavage mixed fracture with the characteristics of the river patterns from ductile transgranular fracture.

关键词： cobalt-free maraging steel solution treatment impact toughness separation

Solid reaction mechanism of CaHPO_4·2._2. + CaCO_3 with and without yttria

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Rare Metals 2009年第1期28卷 77-81页

作者： WANG Yong GAO Jiacheng HU Jinzhu ZHANG Yan College of Materials Science and engineering Chongqing University Chongqing 400045 China national engineering {2. center for magnesium alloys Chongqing University Chongqing 400045 China College of Materials Science and engineering Southwest University Chongqing 400700 China

The effect of yttria on the solid reaction mechanism of a CaHPO4·2.2. ＋ CaCO3 system at different temperatures was experimentally stud-ied. The samples with and without yttria were subjected to thermogravimetric/differential scanning calorimetry measurement. The samples were heat treated at the temperatures corresponding to the peaks on the DSC spectra, and the resulted phase compositions were identified by X-ray diffraction. The transformation mechanism was deduced by comparing the phases obtained at different temperatures. The results show that the transformations at below 1073 K are not affected by yttria, but all those at above 1073 K are completely altered. The formation tem-perature of hydroxyapatite decreases by 134 K, and the decomposition temperature increases by 38 K. The polymorphous transformation of Ca3（PO4）2.from β phase to α phase increases by 47 K. The thermodynamic properties of the transformations at above 1073 K are also modi-fied by the addition of yttria; that is, the endothermal peaks are substituted by exothermal peaks.

关键词： bioceramics solid reaction mechanism X-ray diffraction thermal analysis yttria

Effect of Sr on microstructure and aging behavior of Mg-14Li alloys

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Progress in Natural Science:Materials International 2012年第2期22卷 160-168页

作者： Bin Jiang a,b,c,Ying Zeng b,Hengmei Yin a,b,Ruihong Li a,b,Fusheng Pan a,b a national engineering {2. center for magnesium alloys,Chongqing university,Chongqing 400030,china b College of Materials Science and engineering,Chongqing university,Chongqing 400030,china c New Materials center,Chongqing Academy of Science and Technology,Chongqing 40112.,china [a] national engineering {2. center for magnesium alloys Chongqing University Chongqing 400030 China [b] College of Materials Science and engineering Chongqing University Chongqing 400030 China [c] New Materials center Chongqing Academy of Science and Technology Chongqing 401123 China

The as-cast and as-extruded Mg-14 wt%Li-xSr(x=0.14,0.19,0.39 wt%)alloys were,respectively,prepared through a simple alloying process and hot *** effects of Sr addition on microstructure and aging behavior of the Mg-14 wt%Li-xSr alloys were *** results indicated that b(Li)and Mg2.r were the two primary phases in the microstructures of both as-cast and as-extruded Mg-14 wt%Li-xSr ***,with the increase of Sr content from 0.14 wt%to 0.39 wt%,the grain sizes of the as-cast and as-extruded Mg-14 wt%Li-xSr alloys markedly decreased from 5000 mm and 38 mm to 330 mm and 2. mm respectively,while no obvious changes of the micro-hardness and microstructure of the as-extruded alloys were observed during the aging treatment.

关键词： magnesium-lithium alloys Microstructure Grain refinement Aging behavior