Twin Nucleation by Slip Transfer across Grain Boundaries in Commercial Purity Titanium

The role of strain transfer in the activation of deformation twinning at grain boundaries has been characterized in commercially pure titanium deformed in bending. Two different orientations of a textured polycrystal were deformed in bending and were analyzed using electron backscattered diffraction (EBSD) to determine the active slip and twinning systems in the surface tensile region. Prismatic slip and { 10[`1]2 } á [`1]011 ñ \left\{ {10\bar{1}2} \right\}\left\langle {\bar{1}011} \right\rangle twinning were the most widely observed deformation modes in both orientations. Nonprismatic slip systems were also activated, most likely to accommodate local strain heterogeneities. A slip-stimulated twin nucleation mechanism was identified for soft/hard grain pairs: dislocation slip in a soft-oriented grain can stimulate twin nucleation in the neighboring hard grain when the slip system is well aligned with the twinning system. This alignment was described by a slip-transfer parameter m′.[24] Twins activated by this mechanism always had the highest m′ value among the six available { 10[`1]2 } á [`1]011 ñ \left\{ {10\bar{1}2} \right\}\left\langle {\bar{1}011} \right\rangle twinning systems, while the Schmid factor, based on the global (uniaxial tensile) stress state, was a less significant indicator of twin activity. Through slip transfer, deformation twins sometimes formed despite having a very low global Schmid factor. The frequency of slip-stimulated twin nucleation depends strongly on the texture and loading direction in the material. For grain pairs having one grain with a large Schmid factor for twinning, nonparametric statistical analysis confirms that those with a larger m′ are more likely to display slip-stimulated twinning.     

Normal Transmission of S-Wave Across Parallel Fractures with Coulomb Slip Behavior

When an elastic wave propagates through a rock mass, its amplitude is attenuated and velocity is slowed due to the presence of fractures. During wave propagation, if the shear stress at a fracture interface reaches the fracture shear strength, the fracture will experience a large shear displacement. This paper presents a study of the normal transmission of S-waves across parallel fractures with Coulomb slip behavior. In our theoretical formulation, the method of characteristics combined with the Coulomb slip model is used to develop a set of recurrence equations with respect to particle velocities and shear stress. These equations are then solved numerically. In a comparison with the theoretical study, numerical modeling using the universal distinct element code (UDEC) has been conducted. A general agreement between UDEC modeling and theoretical analysis is achieved. The magnitude of the transmission coefficient is calculated as a function of shear stress ratio, nondimensional fracture spacing, normalized shear stiffness, and number of fractures. The study shows that the shear stress ratio is the most important factor influencing wave transmission, and the influence of other factors becomes more apparent when the shear stress ratio is small.     

Interdiffusion in Intermetallics

Recently, Tiwari and Mehrotra asserted that the vacancy flux in interdiffusion is driven by a vacancy concentration gradient and also that interdiffusion in intermetallics cannot proceed by the six-jump cycle, triple defect, and antistructural bridge mechanisms. It is shown that those authors’ arguments are incorrect according to classical diffusion theory, by the numerous simulations that have been performed, and by analysis of these mechanisms.     

钛,铝的连续络合滴定

用苦杏仁酸作掩蔽剂，在ｐＨ＝５５时，同时测定钛铁、不含锡的钛合金、粘土等材料中钛、铝。     

无熔剂型铝合金钛添加剂的研究

研究了钛粉粒度和含氧量及铝粉含氧量对无熔剂铝合金钛添加剂吸收率的影响,研制出高吸收率的无熔剂型钛添加剂。     

在纯铝熔铸中加入钛剂的试验

文中分析了纯铝半连续铸锭裂纹产生的原因,并在熔铸过程中,试验一种新型的钛剂——含40％Ti,4％B和熔剂块。确定了合理的添加量和工艺规程,铝液温度710±10℃,对铸锭的晶粒细化效果显著,可防止铸锭裂纹。     

钛与碳在金属铝液中反应动力学模型

利用反应动力学和扩散理论,建立钛与碳在金属铝液中反应动力学模型.提出了Ti与C在铝液中的反应机理,即:Ti原子以铝液为传质媒介,向碳颗粒表面扩散,与C逐层反应并生成TiC,TiC颗粒在铝液的对流作用下,不断地向铝液中分散.讨论了铝液的温度、各元素的浓度以及生成TiC的体积分数对其反应速度的影响规律.     

Chemical Vapor Synthesis of Titanium Aluminides by Reaction of Aluminum Subchloride and Titanium Tetrachloride

A new process for developing titanium aluminides (TiAls) using chemical vapor synthesis was investigated in a laboratory experiment. Aluminum subchloride (AlCl) was used as the reducing agent in the reaction with TiCl₄ and the source of aluminum for Ti-Al alloy. Two types of products, with large crystals and fine particles, were fabricated. The large crystals were determined to be TiAl, with small amounts of Ti and Ti₃Al phases. The composition of fine particles, on the other hand, varied in wide range.     

钛白粉直接合金化制备钛铝合金理论及工艺研究

对铝热还原工艺制备钛铝合金的热力学进行计算与分析,探索了配石灰系数(即理论用量的倍数)及单位热效应对钛收率的影响,并分析了配铝系数对合金中钛和铝的影响以及影响钛铝合金中氧含量的因素。结果表明,最佳工艺参数为:配石灰系数0.9,单位热效应2 850kJ/kg。     

Crystallographic fatigue crack growth in incompatible Aluminum Bicrystals: Its Dependence on Secondary Slip

The secondary slip behavior ahead of crystallographic fatigue cracks and its effect on the crack growth near the grain boundaries (GBs) in\([12\bar 1]\) tilt nonsymmetrical aluminum bicrystals under constant cyclic stress amplitude have been systematically examined. The displacement field ahead of short crack tips near the interfaces in two specimens has been measured by using a microfiducial grid technique. It has been observed that the critical persistent slip band (PSB) ahead of a short crack tip near the GB in a middle misoriented bicrystal was able to develop as long as the primary one and resulted in a temporary stage II growth. As a longer crystal- lographic crack grew into the grain boundary affected zone (GBAZ), activation of the critical slip ahead of the crack front and crack branching along the critical PSB occurred in all groups of the aluminum bicrystals, which reveals a crucial role of the critical slip in increasing the crack opening and triggering the slip in the adjacent grain. On the other hand, cross slip became the dominant slip mode ahead of the crystallographic crack front near the GB in a bicrystal of larger misfit angles and drove the crack along the cross PSB, a steep path with a remarkably high growth rate, until it propagated into the GBAZ. The resultant stress on the secondary slip system ahead of a crack front near the interface contributed by the internal stress due to both intergranular and intragranular incompatible strain, as well as the enhanced crack tip stress, has been evaluated and rationalizes the activation of the secondary slip systems.     

镁还原四氯化钛生产海绵钛过程传热分析

对镁还原四氯化钛生产海绵钛还原过程中的传热进行了数值模拟分析,提出了强化传热的方案,并对强化传热的效果进行了模拟分析.对比两者分析结果表明,通过降低反应器壁及大盖底板温度来强化传热效果明显,强化后的传热作用可以达到强化前的2倍.通过强化传热可以大幅提高还原加料速度,缩短还原生产周期,提高生产效率.     

铝、镁、钛合金材料在汽车工业中的应用和发展

介绍了铝、镁、钛合金材料的性质及特点，指出铝、镁、钛材料在汽车工业中的应用和发展前景。     

The Effect of Solute Content on the Slip Behavior in 7XXX Series Aluminum Alloys

The microstructures of three high strength, high purity Al-Zn-Mg-Cu alloys, in the T6 temper, were characterized extensively using quantitative optical metallography and quantitative transmission electron microscopy. Only the solute content (Mg + Zn) of these alloys was varied for this study. These alloys were shown to be identical in grain size and shape, dispersoid (E-phase) and grain boundary precipitate (ν) populations, and precipitate free zone widths. The matrix microstructures consisted of ordered GP zones and ν′ and differed only in the volume fraction of these strengthening precipitates. The higher solute alloys had the higher yield strengths and volume fractions of matrix precipitates. Subsequent slip behavior analysis of prestrained tensile specimens demonstrated that slip band spacings and slip step heights increased with increasing solute content for the same macroscopic strain (ε_p = 0.02). A work softening model by Hornbogen and Gahr was shown to predict this tendency toward increased strain localization with higher solute levels. Formerly a Research Assistant at Carnegie-Mellon University     

Rate of Transfer of Manganese Across Metal-Slag Interface and Interfacial Phenomena

Abstract

The rate of oxidation of manganese in liquid iron by oxidizing slag and rate of reduction of manganese oxide in liquid slag by liquid iron were measured at 1873 K. At the same time the liquid iron-slag interface was observed by an X-ray TV and the shape of iron drops was photographed on a film to determine the interfacial tension. From the results of the rate measurements it was found that the reaction proceeded rapidly over the initial period in the case of oxidation, but not in the case of reduction. The rate of reaction was analysed on the assumption that the reaction was controlled by simultaneous transport of manganese and oxygen. The change of interfacial tension during a run was small in spite of the transfer of surface active oxygen.

Résumé

Les vitesses d'oxydation et de réduction du manganèse ont été mesurées à l'interface métal-scorie d'un bain de fonte liquide à 1873 K. Simultanément, l'interface fonte-scorie a été observée à l'aide d'une caméra de télévision R-X et les goutelettes de fonte photographiées afin de déterminer la tension interfaciale. A partir des résultats des vitesse de réaction, il s'est avéré que la réaction s'effectue rapidement lors de la période initiale d'oxydation, mais non lors de la réduction. La vitesse de la réaction a été analysée en supposant qu'elle était contrôlée par le transport simultané du manganèse et de l'oxygène. Le changement de tension interfaciale lors d'un essai étai faible malgré le transfert d'oxygène actif en surface.     

Measurement and Modeling of Heat Transfer Across Interfacial Mold Flux Layers

Abstract

Surface quality problems in continuous cast steel are greatly affected by heat transfer across the interfacial layers in the gap between the solidifying steel shell and the mold. An experimental apparatus has been constructed to measure temperatures in the steel, mold flux layers, and copper under conditions approximating those in continuous casting. The flux solidified in multiple layers similar to those observed from continuous casting molds and contained many gas bubbles. Flux conductivities average about 1.0 Wm K and appear to evolve with time. Contact resistances at both interfaces are significant and average about 0.0015 m². KW. Flux crystallization appears to be the only significant effect of flux composition. The one glassy flux tested had much greater thermal conductivities, presumably due to radiation transport. Temperature and gap thickness had a negligible effect on the properties. These properties depend on the model used to extract them. They are being implemented into a mathematical model to simulate heat transfer in the mold, interface, and solidifying shell of a continuous slab-casting machine. © 2000 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.

Résumé

Les problèmes de qualité de surface de l'acier de coulée continue sont grandement affectés parle transfert de chaleur à travers les couches interfaciales dans l'intervalle entre la gaine d'acier en train de se solidifier et le moule. On a construit un appareil expérimental afin de mesurer la température de l'acier, des couches d'écoulement du moule et du cuivre sous des conditions appro chant celles de la coulée continue. L'écoulement s'est solidifié en couches multiples similaires à celles observees dans les moules de coulée continue et celles-ci contenaient plusieurs bulles de gaz. La moyenne de conductivité de l'écoulement est d'environ 1.0 Wm K et semble évoluer avec le temps. La résistance de contact aux deux interfaces est importante et atteint en moyenne environ 0.0015 m².kw. La cristallisation de l'écoulement parait etre le seul effet important de la composition du flux. Le seul écoulement vitreux évalué avait une conductivité thermique beaucoup plus élevée, vraisemblablement dil au transport parradiation. La température et la largeur de l'intervalle avaient un effet négligeable sur les propriétés. Ces propriétés dépendent du modèle utilisé pour les extraire. On est en train de les développer en un modéle mathématique afin de simuler le transfert de chaleur dans le moule, à l'interface et dans la gaine de solidification d'un appareil de coulée continue de brame. © 2000 Canadian Institute of Mining and Metallurgy.Published by Elsevier Science Ltd. All rights reserved.     

铬天青-S分光光度法测定钛合金中铝的分析

以甘露醇作为钛掩蔽剂,用铬天青-S作为显色剂测定钛合金中铝的方法,成功解决了传统分析中须沉淀分离来消除干扰的问题,简化分析手续,缩短分析时间,测定结果准确。     

Literature Survey on Diffusivities of Oxygen,Aluminum, and Vanadium in Alpha Titanium,Beta Titanium,and in Rutile

A survey of diffusion data of interstitial oxygen and of the substitutional elements aluminum and vanadium is presented for alpha and beta titanium. It is based on a survey of literature. Oxygen is an important interstitial element in titanium alloys. Oxygen’s large chemical affinity to titanium is indicated by Ti—O bond energy of 2.12 eV,¹ comparable to the Ti—Ti bond energy of 2.56 eV.² Oxygen is difficult to eliminate completely from titanium, and commercial titanium alloys usually contain from 0.10 to 0.20 wt pct oxygen. Oxygen significantly affects the mechanical properties of titanium alloys^1,3 and is sometimes used as an alloying element. The effects of oxygen on phase transformation ,^4,5,6 Youngs modulus,^7,8 hardness,^9,10 fracture toughness,¹¹ and other mechanical properties¹² have been amply documented. Aluminum and vanadium are the most frequently used substitutional alloying elements. Aluminum is an alpha stabilizer and vanadium is a beta stabilizer. An erratum to this article is available at .