铁酸镍基金属陶瓷的强化烧结与熔盐腐蚀行为

采用气氛烧结方法制备NiFe2O4基金属陶瓷材料,并进行960℃的铝电解腐蚀实验.通过分析烧结体的显微结构和物相组成、电解试样的表层形貌与成分以及电解质和阴极铝的杂质含量等,研究BaO、Yb2O3和CoO的添加以及金属相的组成对NiFe2O4基金属陶瓷烧结性能的影响;表征J该金属陶瓷强化烧结体作为铝电解惰性阳极的电解腐蚀性能;并对材料强化烧结机制和熔盐腐蚀行为进行探讨.结果表明烧结过程中,BaO和Yb2O3与该金属陶瓷中的陶瓷相反应生成新的物相,CoO与陶瓷相形成固溶体,并加快烧结致密化进程;以Cu-Ni取代纯Cu和纯Ni作为金属陶瓷的金属相,可提高材料的相对密度;NiFe2O4基金属陶瓷的高致密度可抑制电解过程中金属相的流失和陶瓷相的腐蚀,阳极表层也转变为致密的NiFe2O4相.     

铝电解用NiFe2O4-10NiO基金属陶瓷惰性阳极的耐腐蚀性能

制备铝电解用NiFe2O4-10NiO基金属陶瓷惰性阳极,并在实验室电解槽中考察其电解腐蚀性能。结果表明,电解过程中虽然惰性阳极在960°C熔盐电解质中表现出优异的耐腐蚀性能,但采用XRD、SEM/EDX和金相分析其物相组成和微观结构后发现,电解后阳极中的金属相发生了优先腐蚀,在阳极表面产生大量孔洞。NiFe2O4相中的 Fe 元素的优先溶解可能导致 NiFe2O4晶粒的不均匀腐蚀。溶解在电解液中的 Al2O3与阳极中的 NiO 或FeO 发生反应生成的 NiFe2O4-NiAl2O4-FeAl2O4相对 NiO 相的吞并以及体积膨胀,阳极表面形成致密的NiFe2O4-NiAl2O4-FeAl2O4保护层。因此,致密的NiFe2O4-NiAl2O4-FeAl2O4保护层可以阻挡阳极表面金属相的损失和陶瓷相的腐蚀。     

铁酸镍基金属陶瓷惰性阳极材料的研究进展

惰性阳极铝电解技术的发展主要基于经济和环境的考虑,对铝电解工业的长远发展具有重要意义,已成为铝电解工业进步的关键技术。合金惰性阳极具有易加工成形、良好的抗热震性和导电性,金属陶瓷惰性阳极兼顾陶瓷的高温热稳定性及金属的高导电性和高韧性,二者已成为惰性阳极的主要候选材料体系,并进行了工程化铝电解试验研究。近年来,惰性阳极的研究集中在合金阳极表面保护膜形成与溶解的动态平衡控制、金属陶瓷组成与结构优化、惰性阳极的电解腐蚀机制及抑制技术等方面。综述了铝电解用合金阳极和金属陶瓷惰性阳极的近期研究进展,从材料学的角度介绍铁酸镍基金属陶瓷的组成优化、烧结、电解腐蚀特性等方面的最新研究成果。     

17（Cu-10Ni）-（NiFe2O4-10NiO）基金属陶瓷在铝电解过程中的相演变（英文）

采用冷压气氛烧结制备17(Cu-10Ni)-(NiFe2O4-10NiO)金属陶瓷,并作为阳极在960°C下分别进行10和40h的铝电解试验。对电解前后金属陶瓷的显微结构、物相成分进行分析检测。对电解质及阴极金属中的杂质含量进行分析,研究阳极组成中Fe、Ni和Cu元素的腐蚀行为。研究发现:在电解过程中,在材料表面形成NiFe2O4相致密层,该致密层随电解时间的延长而增厚。在NiFe2O4相致密层形成与增厚过程中,出现NiFe2O4相吞噬NiO相和金属相氧化的现象,金属陶瓷中Cu元素优先腐蚀溶解。并着重讨论NiFe2O4相致密层形成与增厚过程中金属相的腐蚀形式及NiO相向NiFe2O4相的转变机制。     

Co添加对17Ni-(10NiO-NiFe_2O_4)金属陶瓷的致密化及力学性能的影响

为了改善17Ni-(10NiO-NiFe2O4)金属陶瓷惰性阳极中金属相的分布,在原料中添加不同含量的Co,以Co-Ni取代纯Ni作为金属相,采用真空烧结方法制备17(x Co-Ni)-(10NiO-NiF e2O4)金属陶瓷,并研究Co添加量对金属陶瓷物相组成、显微组织、致密度及力学性能的影响。结果表明:烧结样品主要由Co-Ni、Ni Fe2O4、Ni O组成,部分Co与陶瓷基体反应生成CoO与Fe2O3。添加适量Co可以改善金属相在陶瓷相的分布和形貌,使团聚孤立的金属相分布均匀,且部分球状金属相变为长条状金属相;同时,添加适量Co还可以促进烧结,提高试样的致密度。适量Co的添加还能降低晶粒尺寸,大幅提高金属陶瓷材料强度与韧性。当Co质量分数为金属相的20%时,金属陶瓷的综合性能最好,致密度、抗弯强度、断裂韧性及硬度分别达到96.87%、163.65 MPa、8.38 MPa/m1/2和820.81HV。     

铝电解用NiFe2O4-Cu金属陶瓷惰性阳极的制备

以高温固相合成法合成的NiFe2O4陶瓷粉体和金属Cu粉为原料, 采用冷压-烧结法制备了Cu含量在5%～20%之间的NiFe2O4-Cu金属陶瓷惰性阳极, 研究了烧结气氛和烧结温度对其物相组成、微观形貌和基本物理性能的影响. 结果表明 通过控制烧结气氛中氧分压在NiO和Cu2O的离解反应平衡氧分压之间, 可以制备出具有目标物相组成的NiFe2O4-Cu金属陶瓷; 烧结温度和保温时间对所得NiFe2O4-Cu金属陶瓷的相对密度有较大影响; NiFe2O4和Cu之间的不润湿性限制了NiFe2O4-Cu金属陶瓷烧结温度的提高和保温时间的延长, 在保证金属相分布均匀且不溢出的前提下, 所制备的NiFe2O4-Cu金属陶瓷的相对密度较小; 金属相Cu含量越高, NiFe2O4-Cu金属陶瓷最高烧结温度越低、最长保温时间越短, 从而相对密度越低、孔隙率越高; 除了尽量降低金属相含量外, 还可向NiFe2O4-Cu金属陶瓷中添加其他金属如Ni和Co等, 以改善陶瓷相与金属相之间的润湿性, 以提高烧结温度, 进而提高其相对密度和耐腐蚀性能.     

铣削刀片用纳米改性金属陶瓷的显微组织和力学性能

研究了铣削刀片用纳米改性金属陶瓷的显微组织与力学性能。SEM观察结果表明,铣削刀片用纳米改性金属陶瓷组织仍由陶瓷相和金属相组成,其中粗大的陶瓷相颗粒为芯/壳结构;Mo元素添加能有效细化金属陶瓷陶瓷基体组织。抗弯测试表明,随金属相含量增加,金属陶瓷的抗弯强度和断裂韧性增加,而硬度则降低;断口分析可知,沿晶断裂为其主要的断裂方式。     

电石渣代替氧化钙对镍渣深度还原提铁的影响

采用深度还原法处理镍渣,以电石渣或氧化钙作单一添加剂,通过X射线衍射(XRD)、扫描电子显微镜(SEM)和能谱(EDS)等方法,对比分析了两种添加剂分别作用时所得还原产物中的物相和微观结构特征。结果表明,以电石渣代替氧化钙作单一添加剂进行镍渣深度还原提铁是可行的;两者所得金属精选粉的铁指标变化趋势基本一致,所得还原产物的物相组成基本相同,但微观结构存在差异;电石渣作添加剂时,还原产物内部的金属相成片连接,内部气孔形态不规则,气孔表面形成更密集的金属相层,生成的金属相向气孔表面迁移富集趋势较使用氧化钙时更显著;电石渣作添加剂在二元碱度1.0时,所得金属精选粉的铁品位、铁回收率和铁金属化率分别为91.07%、91.20%和92.35%。     

40%Ni—Ti（C,N）金属陶瓷热冲击疲劳的研究

对４０％Ｎｉ－Ｔｉ（Ｃ,Ｎ）金属陶瓷在热冲击条件下缺口试样裂纹的形成及扩展进行了研究。结果表明,裂纹的形成存在孕育期,且随循环温度的升高,孕育期缩短,扩展速率增加;裂纹的形成与组织中陶瓷相／金属相界面微孔洞的形成有关。扫描电镜观察发现,断口形貌中存在着疲劳条纹,断裂沿陶瓷相／金属相界面及金属相中进行     

Yb2O3或Y2O3掺杂Cu-(NiFe2O4-10NiO)惰性阳极的导电性和耐蚀性

在氧分压约为100 Pa的氮气氛下烧结制备了掺杂Y2O3、Yb2O3的10Cu-(NiFe2O4-10NiO)金属陶瓷,并对其进行导电性能测试和10h(Na3A1F6-Al2O3体系中)铝电解实验.采用XRD、SEM和EDS分析稀土氧化物以及其与陶瓷基体反应产物的分布,考查电解实验后材料表层显微结构变化尤其是金属相的流失情况,评价稀土氧化物的添加对金属陶瓷电解初期腐蚀行为的影响.结果表明:掺杂稀土氧化物均使NiO相呈连通迹象,掺杂Yb2O3金属陶瓷晶粒较未掺杂的粗大,其与陶瓷相反应生成物成点线状分布于NiFe2O4相晶界,Y2O3与陶瓷相反应生成物则分布于NiO与NiFe2O4相间;所制备材料具有半导体特征,随着稀土氧化物的掺杂,材料导电性呈下降趋势;掺杂稀土氧化物尤其是Yb2O3有利于提高材料的耐蚀性能.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.