Isothermal precipitation and growth process of perovskite phase in oxidized titanium bearing slag

The isothermal precipitating behavior of perovskite phase in oxidized titanium bearing slag was studied by quenching method. The kinetics of precipitating process and crystal growth of perovskite phase was analyzed. The results show that the precipitating and growth of perovskite are non-equilibrium process at the beginning of isothermal treatment. There are two factors influencing the growth rate of perovskite phase on non-equilibrium condition, one is the supersaturation concentration of perovskite and the other is the coarsening arising from the growth of larger perovskite at the expense of smaller ones. The precipitation kinetics of perovskite phase can be nearly described by the JMAK equation.     

IMI834钛合金等温和非等温热处理过程中片层α相析出行为的定量表征

为了揭示冷却速度对片层α相析出的影响机制,采用试验分析方法对IMI834钛合金在等温和非等温热处理过程中片层α相的析出行为进行定量表征.通过热膨胀试验获得不同冷却速度下片层α相的临界析出温度.基于金相显微镜和电子探针分析以及数据拟合方法,建立片层α相的平均宽度、体积分数以及α和β相内的溶质浓度随温度和冷却速度的定量演化...     

PRECIPITATION SELECTIVITY AND GROWTH OF PEROVSKITE PHASE FROM TITANIUM BEARING BLAST FURNACE SLAG

The effects of transformation of slag composition and additive agents on the morphology, the precipitation behavior, the crystal growth, and the volume fraction (VF) of perovskite (CaO·¤TiO_2) crystal in the Ti-bearing blast furnace slags were investigated. As the morphology of perovskite is dispersed in molten slags, the crystal growth mechanism of the melting of fine dendrites and the coarsening of large grains exist throughout the solidification of molten slags. With the increase of CaO and Fe_2O_3 content, VF of perovskite obviously increases. However, high basicity leads to the viscosity of slag, which results in the reduction of the average equivalent diameter (AED). The experimental results showed that the presence of the additives CaF_2 and MnO efficiently decreased the viscosity of the slags, and obviously improved the morphology of perovskite and promoted its growth.     

Q345B钢保护渣显微结构及矿相组成研究

保护渣科学应用是高效化连铸的关键技术,连铸保护渣的重要功能是液渣的润滑和结晶层的传热作用,这些关键作用主要取决于显微结构和矿相组成。然而,Q345B钢连铸保护渣的显微结构及矿相组成国内外相关报道较少,本次研究以实际生产过程中连铸结晶器内坯壳上残留的保护渣渣膜为研究对象,通过岩石学和分析软件相结合的方法开展了研究,取得以下认识：（1） 渣膜结构从铸坯表面至结晶器内壁包括结晶层、玻璃层、结晶层和玻璃层4层结构,渣膜厚度分布在0.15～5.00 mm之间,结晶层厚度分布在0.1～1.5 mm之间。（2） 渣膜结晶矿相由黄长石、枪晶石和硅灰石组成,同时具有分带性和流动构造,靠近结晶器内壁析出的枪晶石和硅灰石具有晶体成核速率高和成长慢的特点,而分离析晶形成的黄长石晶体发育较粗,黄长石晶体体积的变大可能导致晶内裂缝增多,是导热率下降的主要原因。本次研究有助于改善保护渣成分,提高保护渣的润滑和传热性能,控制铸坯质量,具有一定的理论意义和实际运用价值。     

Selective enrichment of TiO2 and precipitation behavior of perovskite phase in titania bearing slag

1 Introduction China is rich in mineral resources of titanium, 92.4% of which is vanadium-titanium bearing magnetite, deposited mostly around the southwestern part. About 53% titanium is in the iron concentrate after mineral processing, after smelting pro…     

等温过程含Ti炉渣中钙钛矿相弥散颗粒长大研究

影响非平衡态含Ｔｉ炉渣中钙钛矿相长大因素有两个，一个是析出过程中自身长大，另一个是由大颗粒吞并小颗粒而产生的粗化。通过对非平衡态含Ｔｉ炉渣中钙钛矿相的析出长大研究，给出了描述非平衡态下由扩散控制弥散钙钛矿晶粒长大的动力学模型。     

A theoretical method for determining the crystallized fraction and kinetic parameters by DSC, using non-isothermal techniques

A procedure has been developed for determining expressions for the volume fraction crystallized and for the kinetic parameters in non-isothermal reactions in solid systems involving the formation and growth of nuclei. This method makes use of an equation for the evolution with time of the volume fraction crystallized. This equation has been integrated under non-isothermal conditions and assuming an Arrhenian temperature dependence of the nucleation frequency and of the crystal growth rate, thus obtaining a general expression for the volume fraction crystallized for each value of the related parameter with the dimensionality of the crystal. The kinetic parameters have been deduced, obtaining the maximum crystallization rate, bearing in mind the fact that, in the non-isothermal processes, the reaction rate constant is a time function through its Arrhenian temperature dependence. Finally, the theoretical expressions of the kinetic parameters have been applied to the experimental data corresponding to a set of glassy alloys, quoted in the literature, thus obtaining mean values that agree very satisfactorily with the published data. This fact shows the reliability of the theoretical method developed.     

Effect of Continuous Cooling on Secondary Phase Precipitation in the Super Duplex Stainless Steel ZERON-100

The precipitation of secondary phases in super duplex stainless steels (SDSS) is a subject of great relevance owing to their dangerous effects on both mechanical and corrosion-resistance properties. This paper examines the effect of continuous cooling after solution annealing treatment on secondary phase precipitation in the ZERON-100 SDSS. It considers the influence of cooling rate on volume fraction, morphology and chemical composition. It has been found that the formation of sigma and chi phases can be avoided only at cooling rates higher than 0.7 °C/s. In addition, at the lowest cooling rate the sigma phase amount approaches the equilibrium value, but the chi phase amount remains significantly low.     

Effect of rutile crystal shapes on its settlement

The effect of rutile crystal shapes on its settlement in a modified slag was studied by theoretical analysis, FactSage simulation, X-ray diffraction and scanning electron microscopy. The results show that the settling velocities of spherical rutile crystals are faster than those of other shapes of rutile crystals under the same volume conditions, and the shape transformation of rutile crystals from rod to sphere can be achieved by adding titanium slag to Ti-bearing blast furnace slag. The volume fractions of the rutile crystals in the upper and lower parts of the modified slag are 30% and 71% when the added titanium slag increases to 278 g, indicating that rutile settling is obvious. Due to the rutile settling, half shaker sorting task is saved, and the recovery rate of TiO₂ is significantly increased. The TiO₂ content of rutile is greater than 93%, and the total content of CaO and MgO is less than 0.4%, meeting the requirements for the raw materials of titanium white in the chloride process.     

非等温时效对一种铝锂合金力学性能与微观组织的影响

比较研究了一种Mg、Ag、Zn多元复合微合金化铝锂合金等温T8时效及非等温(降温)T8时效时的微观组织与力学性能。结果表明,该铝锂合金主要时效强化相为T1相(Al_2Cu Li),同时还存在θ相(Al_2Cu)及δ相(Al_3Li)的补充强化作用。相比于等温T8时效而言,降温T8时效可在不降低延伸率的同时,提高铝锂合金的强度。另外,降温T8时效时T1相析出及生长速度较慢,而且峰时效时θ相及δ相含量较高,补充强化作用更大。     

控制冷却工艺对Ti微合金化中碳钢板组织和性能的影响

采用控制轧制-控制冷却-淬火-回火工艺制备20 mm 厚的Ti微合金化中碳钢板,研究了控制冷却工艺(冷却速度)对该钢有效晶粒尺寸和析出相的影响,并探讨了其强韧化机理。结果表明:冷却速度越快,有效晶粒尺寸越小,马氏体板条宽度越窄,含Ti析出相越细小,使其兼具高强度和良好的塑性韧性。主要是由于快速冷却保留了轧制时获得的晶体缺陷和形变能,使再加热奥氏体细化,而且快速冷却抑制了Ti在冷却过程中析出,使Ti处于过饱和状态,再加热过程中逐渐析出细小的含Ti析出相,能更有效地阻止奥氏体晶粒长大。有效晶粒细化以及纳米级含Ti析出相使该钢板具有良好的力学性能。     

Effect of oxidization on enrichment behavior of TiO2 in titanium-bearing slag

1. Introduction There are around 50 million tons of titanium slag piled up in China. Such slag usually contains about 20%-22% TiO2 and cannot be discarded, so this quantity is still increasing at a rate of 3 million tons per year. However, owing to the dispersed distribu-tion of titanium component in various mineral phases, and very fine grains (<10 μm) and complex interfacial combination, it is very difficult to recover titanium component from the slag by conventional separating technique. …     

熔盐电解制备低成本Ti12LC钛合金的研究

利用覆盖渣技术在非真空条件下成功制备出了直径为3 mm的Zr55Ni5Al10Cu30块体非晶合金.采用差示扫描量热法(DSC),将Johnson-Mehl-Avrami理论拓展应用于非晶合金的非等温晶化过程研究.结果表明,Zr55Ni5Al10Cu30块体非晶合金的连续升温晶化过程Avrami指数及形核率随升温速率的升高而呈下降趋势,同时随晶化过程进行呈先增加后减小的规律.Avrami指数最大值出现在晶化体积分数0.3～0.4之间,在低升温速率下Zr55Ni5Al10Cu30块体非晶合金部分晶化过程出现三维形核界面控制长大的形式.     

控轧控冷对Ti-Mo-Nb复合微合金化低碳钢组织和力学性能的影响

研究了控轧控冷的冷却速度对Ti-Mo-Nb微合金高强钢组织与性能的影响。结果表明,随着冷却速度的降低,试验钢中铁素体逐渐等轴化,铁素体的体积分数、晶粒尺寸逐渐增加。冷却速度的降低可显著细化析出相尺寸并增加其体积分数,析出方式由弥散析出向相间析出转变。铁素体通过析出强化实现提升材料强度的同时,成形性能得到改善。当冷却速度为28℃/s时,试验钢获得了优异的综合力学性能,抗拉强度为853 MPa,屈服强度为750 MPa,伸长率为18.6%,扩孔率为68.5%。组织细化与析出强化是试验钢的主要强化机制,当冷却速度为28℃/s时,细晶强化和析出强化强度增量分别为206 MPa和328 MPa。     

定向凝固NiAl-9Mo共晶合金的凝固组织特性

采用液态金属冷却法在恒定温度梯度GL=334 K/cm,大生长速率范围内（2~300μm/s）对Ni-45.5Al-9Mo （摩尔分数,%）共晶合金进行定向凝固制备。研究生长速率（v）对纤维间距（λ）、纤维直径（d）和纤维体积分数的影响。在实验中发现平界面和胞界面两类共晶生长界面。在平界面和胞界面组织中,生长速率（v）与纤维间距（λ）和纤维直径（d）的关系经回归分析分别为：λv1/2=5.90μm·μm1/2·s1/2和 dv1/2=2.18μm·μm1/2·s1/2。Mo纤维的体积分数可在一定的范围内随生长速率进行调整,这是由生长过程中界面前沿过冷度的增加及共晶组织中各组成相的生长特性引起的。     

A theoretical method for analyzing the glass-crystal transformation observed by DSC in the continuous heating regime. Application to the Sb0.16As0.36Se0.48 semiconducting alloy

A theoretical procedure has been developed for deriving the evolution equation with time of the actual volume fraction transformed, for integrating the above mentioned equation under non-isothermal regime, for deducing the kinetic parameters and for analyzing the glass-crystal transformation mechanisms in solid systems involving formation and growth of nuclei. By defining an extended volume of transformed material and assuming spatially random transformed regions, a general expression of the extended volume fraction has been obtained as a function of the temperature. Considering the mutual interference of regions growing from separate nuclei (impingement effect) and from the above mentioned expression the actual volume fraction transformed has been deduced. The kinetic parameters have been obtained, assuming that the reaction rate constant is a time function through its Arrhenian temperature dependence. Besides, it has been shown that the different models, used in the literature for analyzing the glass-crystal transformation, are particular cases of the general expression deduced for the actual volume fraction transformed. The theoretical method described has been applied to the crystallization kinetics of the Sb_0.16As_0.36Se_0.48 glassy alloy, thus obtaining values for the kinetic parameters that agree satisfactorily with the calculated results by the Austin–Rickett kinetic equation, under non-isothermal regime. This fact shows the reliability of the theoretical method developed.     

保存环境对不同结构水淬渣活性的影响

采用将矿渣在不同温度重新熔融并水淬的方法制备了不同水淬渣样品，应用XRD、DTA等分析手段对不同样品的结构特征进行了分析，同时结合胶凝材料抗压强度实验，研究了不同水淬样品在潮湿环境保存7d后的胶凝活性变化特点及原因。研究表明，形成过程对水淬渣在不同保存环境下胶凝活性的影响不同，较低水淬温度下形成水淬渣的胶凝活性在潮湿环境中下降最大，样品玻璃相中存在不同程度的分相结构是产生这一影响的主要原因。     

Phase formation and mechanical properties of Cu-Zr-Ti bulk metallic glass composites

The effect of the type of the crystalline phase and its volume fraction on the mechanical property of Cu₅₀Zr_50-xTi_x alloys (x = 0-10) bulk metallic glass composites has been investigated in this study. Up to 6 at% of Ti, B19’ phase particles distributed in the glassy matrix, while at 8 and 10% of Ti, B2 phase particles are retained in the glass matrix due to suppression of the eutectoid transformation of B2 phase and by avoidance of martensitic transformation of B2 into B19’. The volume fraction of crystalline phase is strongly dependent on the cooling rate. The larger volume fraction of the crystalline phases results in the lower yield stress, the higher plastic strain, and the more pronounced work hardening behavior. At the crystalline volume fraction below ~30%, the variation of the yield strength can be described by the rule of mixture model (ROM), while at the crystalline volume fraction higher than ~50% by the load-bearing model (LBM). At the crystal fractions between 30 and 50%, there is a yield strength drop and a transition from the ROM to the LBM. This transition is due to the formation of the crystalline structural framework at higher crystal fraction.     

Evolution mechanism of recrystallization in a nickel-based single crystal superalloy under various cooling rates during heat treatment

The recrystallization behaviors of a nickel-based single crystal superalloy during heat treatment at 1,200℃ for 4 h with various cooling rates were studied.Results show that the thickness of recrystallization layer decreases with the increase of cooling rate.In addition,the microstructures ofγ′phase in the recrystallization region are different in various cooling rates.In the high cooling rates(70,100℃·min^-1),small size and high volume fraction ofγ′phases are formed in the recrystallization region.It is also found that irregular fine secondaryγ′phases are precipitated between matrix channels with an average size of 150 nm in the original matric(100℃·min^-1).The sizes of the secondaryγ′phase decrease with the increase of cooling rate.In contrast,large size and small volume fraction ofγ′phases are formed in the recrystallization region,and a grain boundary layer is formed under a low cooling rate(10℃·min^-1).The evolution mechanism of recrystallization at various cooling rates during heat treatment is analyzed.     

Particle Size of Gamma Prime as a Result of Vacuum Heat Treatment of INCONEL 738 Super Alloy

In this paper, the influence of the cooling rate and cooling media after a standard solution heat treatment on the size and distribution of the gamma prime phase (γ′) in the nickel-based super alloy INCONEL 738 in over-aged conditions is described. The volume fraction of the gamma prime depends on the chemical composition of the alloy, the solution treatment temperature and the cooling rate; in over-aged alloys (i.e., with more than 25,000 h of service) the volume fraction of γ′ is about 78.8%. However, it has been demonstrated that in order to maintain excellent creep strength a volume fraction of at least 60% or lower is required. In this work the volume fraction was optimized between 40 and 55% by means of a standard solution heat treatment at 1120 °C using different cooling gases. A γ′ volume fraction of 54.8% was obtained by using argon as the cooling medium at a cooling rate of 87 °C/min, producing a precipitate of partial distribution of primary and secondary γ′. Better results were obtained in a nitrogen atmosphere at a cooling rate of 287 °C/min, leading to a volume fraction of 40% and obtaining a total re-precipitation of primary and secondary γ′.