High-speed temperature measurements during rapid solidification of iron-silicon ribbons,produced by planar flow casting

In order to investigate the melt undercooling and the non-equilibrium solidification of crystalline Fe 5 wt.% Si melt spun ribbons, produced by planar flow casting (PFC), high speed temperature measurements and appropriate process simulations have been performed. Using a rotating fibre optical system with a fast response double pyrometer, the temperature radiation of the solidifying ribbon during the casting process has been recorded with a measuring frequency of 50 kHz. The obtained cooling curves have been interpreted by computer simulations. It is shown that with increasing wheel temperature the overall cooling becomes more efficient. This is caused by an improved wetting behaviour of the melt-wheel system and an increase in the heat transfer coefficient at the interface of the solidifying ribbon and the wheel from 6 · 10⁴ to about 2 · 10⁵ W/(m²K). The solidification of 100 to 200 μm thick ribbons takes place in a time interval of 2 to 5 ms. The average growth rate varies between 10 and 60 mm/s. The high cooling rate results in a fine dendritic solidification morphology with diminishing microsegregations.     

真空单棍非晶态快速凝固装置的研制

本文报道了自行设计,制造真空单辊快速凝固装置研制过程,该装置真空度高达4×10~(-3)Pa,加热温度1300℃～1600℃,冷却速度10~6℃/s,喷射压力0～0.4MPa,并可以无级调整,配置电磁阀以达到喷射快速稳定。基本上达到形成非晶合金的技术要求,具有价廉,简单可靠的特点。     

Effects of scandium on rapid solidified hypo-eutectic aluminium copper

ABSTRACT

This paper reports on the characterisation of rapidly solidified Al-4.5?wt% Cu-xSc (x?=?0.1, 0.2 or 0.4?wt %). The effect of micro-additions of Sc (up to 0.4?wt %) was examined through microstructural analysis of rapidly solidified, as well as aged samples, by means of electron microscopy, x-ray and neutron diffraction and microhardness measurements. The effect of micro-additions of Sc on the scale of the rapid solidified microstructure was negligible. The Sc additions were supersaturated mainly in the interdendritic regions. However, upon aging of the samples, directly after rapid solidification, nano-precipitates rich in Sc were observed in the matrix and some Sc was also associated with the θ phase. No W-phase was observed in either as atomised or aged samples. Furthermore, dramatic improvements in mechanical properties (specifically hardness) were achieved. This work highlights the use of various and complementary tools to characterise the effect of micro-additions of Sc to hypoeutectic Al-Cu alloys over a wide range of solidification thermal histories. It also demonstrates the capability of designing alloys and process strategies with unique microstructures and mechanical properties superior to age hardened Al-4.5?wt% Cu alloys.     

氩气雾化高温合金粉末的凝固组织特征

为深入了解高温合金粉末粒度细化对粉末涡轮盘性能的影响,对不同尺寸氩气雾化高温合金粉末的凝固组织特点进行了分析和研究.结果表明:AA粉表面和内部凝固组织主要为树枝晶和胞状晶组织,晶界和枝晶间分布少量富Ti、Nb的MC型碳化物.随着粉末尺寸的减小,冷却速率增大,组织从树枝晶向胞状晶转变,基体γ相晶面间距和点阵常数增加.小尺...     

冷却速率对奥氏体不锈钢凝固过程影响的原位观察

通过采用激光共聚焦扫描显微镜对AISI304奥氏体不锈钢的凝固过程进行了原位动态观察研究.发现当冷却速率为0.05℃·s^-1时,奥氏体不锈钢以胞状晶方式凝固,其凝固模式为FA模式,即δ铁素体相先从液相中形核并长大,γ相在1 448.9℃时通过与液相发生包晶反应(L+δ→γ)在δ铁素体相界形成,当温度降到1 431.3℃时液相消失,δ铁素体相通过固态相变转变为γ相,富Cr贫Ni的残留铁素体位于胞状晶之间.当冷却速率为3.0℃·s^-1时,奥氏体不锈钢以枝晶方式生长,冷却到1346.4℃时包晶反应在液相与δ铁素体相界之间进行,其残留铁素体位于枝晶干,与冷却速率为0.05℃·s^-1时相比,其残留铁素体的数量增多,残留铁素体富Cr贫Ni的程度减轻.     

连铸初始凝固区域传热研究进展

连铸初始凝固阶段的传热决定了初始凝固坯壳的形成,讨论了初始凝固坯壳的两大形成机理,探讨了初始凝固阶段的传热行为,分析了连铸中各种因素对初始凝固阶段传热的影响,进一步解释了电磁连铸技术对初始凝固传热的改善.     

不同拉速对薄板坯凝固过程及组织的影响

针对薄板坯在凝固过程中容易出现铸坯裂纹、疏松、缩孔等质量问题,以某厂生产的高拉速薄板坯为研究对象,通过建立传热凝固有限元和元胞自动机相结合的CAFE模型,基于ProCAST平台开展凝固传热全过程数值计算,探究不同拉速下的结晶器末端坯壳生长情况、不同拉速对凝固传热过程的温度场和三维凝固组织的影响.结果表明,在不同的拉速下...     

单辊快速凝固法制备Co-Cu-Pb合金颗粒的结构与形成机制

分别以Co_(47.5)Cu_(47.5)Pb_5和Co_(42.5)Cu_(42.5)Pb_(15)三元偏晶合金作为母合金,采用单辊法急冷快速凝固制备Co-Cu-Pb三元难混溶合金颗粒,对颗粒的微观组织结构与尺寸进行观察与分析,并对不同结构颗粒的形成机制进行研究。结果表明:Co-Cu-Pb合金颗粒的直径为70~600μm,得到实心颗粒、空心颗粒及多层壳核结构3种不同结构的颗粒。Co-Cu-Pb合金颗粒发生包晶反应形成富Co(Cu)相的初生枝晶,富Pb相主要富集于枝晶间隙处。随辊面线速度从15 m/s增大到30 m/s,初生Co(Cu)相枝晶发生粗大枝晶→细小等轴晶的转变,合金颗粒的凝固组织显著细化,并且由于液态难混溶合金发生Marangoni运动,形成快速凝固多层壳核结构,最终获得均质化的Co-Cu-Pb合金凝固组织。     

电渣重熔过程中金属凝固的控制方法

分析了表征凝固质量的各种参数及凝固过程参数对凝固质量的影响.讨论了电极熔化速度与凝固质量之间的关系,及如何计算合理的熔化速度.通过数学模拟计算凝固过程的温度场,进而计算二次枝晶间距是获得合理凝固组织的有效手段.     

Investigation on dendritic solidification and microsegregation in presence of melt convection using phase field simulation

Abstract

A phase field model has been used to simulate dendritic solidification of a binary alloy in the presence of forced melt convection. The influence of melt flow on morphology and solute distribution was investigated for various conditions. The results showed that incorporation of fluid flow causes asymmetric dendritic growth which is amplified by increasing fluid velocity. Moreover, it has been found that the effects of melt flow on the growth of different arms depend on the preferred growth orientation of the dendrite with respect to flow direction. Solid microsegregation study of the growing dendrite arm perpendicular to the flow direction indicated that the position of the arm axis varied almost linearly with flow velocity. Introducing an adjusting term called an antitrapping current in the concentration equation prevents solute from being highly trapped in the solid phase and causes the phase field simulations to be more realistic, especially for high undercoolings.

On a utilisé un modèle de champ de phase pour simuler la solidification dendritique d’un alliage binaire en présence de convection forcée du bain. On a examiné l’influence de l’écoulement du bain sur la morphologie et la distribution de soluté sous des conditions variées. Les résultats ont montré que l’incorporation de l’écoulement du fluide produisait une croissance dendritique asymétrique qui est amplifiée par l’augmentation de la vitesse du fluide. De plus, on a trouvé que l’effet de l’écoulement du bain sur la croissance de différentes branches dépendait de l’orientation préférée de la croissance de la dendrite par rapport à la direction de l’écoulement. L’étude de la microségrégation solide de la branche de dendrite en croissance perpendiculaire à la direction de l’écoulement indiquait que la position de l’axe de la branche variait presque linéairement avec la vitesse de l’écoulement. L’introduction d’un terme d’ajustement, appelé courant de contre-piégeage, dans l’équation de concentration empêche le soluté d’être trop piégé dans la phase solide et rend les simulations de champ de phase plus réalistes, particulièrement dans les cas de surfusions élevées.     

水平连铸圆坯凝固及铸坯质量的研究

以水平连铸圆坯连铸生产工艺为研究对象,通过射钉实验并采用Fluent数值模拟软件建立凝固传热模型,研究了在不同工艺条件下圆坯结晶器内的温度场分布与凝固传热过程,并对铸坯质量进行了相关的检测分析.通过本研究进一步明确了结晶器内钢液的温度场分布,及不同拉坯工艺对结晶器内钢液温度场变化的影响.结果表明:通过射钉实验并采用Fluent数值模拟软件建立凝固传热模型,可以有效分析水平连铸钢液的凝固传热过程,对改善钢水质量有积极作用.     

Columnar to equiaxed transition of metals during solidification by using electric current pulse

 A new approach of applying the Electric Current Pulse (ECP) with parallel electrodes to promotion of the transition from columnar to equiaxed crystals and improvement of macrosegregation was introduced. And the experiments of application of ECP in the different stage of solidification have been carried out. The results show that applying ECP in both the initial and the late stage of solidification can promote the columnar to equiaxed transition (CET). Analysis shows that during solidification application of ECP induce a large number of nuclei around the upper surface, which subsequently showers down into the melt and impinges growth front of the columnar crystal. Therefore the CET occurs. In addition, this method is also employed to influence the solidification processing of bearing steel, the results show that the structrue is changed from columnar to equaixed, indicating that ECP can enhance the homogeneity of structure and composition of bearing steel.     

Effect of rapid solidification treatment on structure and electrochemical performance of low-Co AB5-type hydrogen storage alloy

The effect of rapid solidification on structure and electrochemical performance of the LaNi4.5Co0.25Al0.25 hydrogen storage alloy was investigated by X-ray powder diffraction and a simulated battery test, including maximum capacity, cycling stability, self-discharge, and high-rate discharge ability （HRD）. All the melt-spun alloys were single-phase with the CaCu5-type structure （space groupP6/mmm）. In comparison to the as-cast alloy, the rapidly quenched alloys manifested an improved homogeneity of com-position and expanded lattice parameters. The electrochemical measurements showed that the activation property, cycling stability and self-discharge of the alloy electrodes were also improved for the rapid solidified alloys. The HRDof the as-cast alloy was better than those of all the rapidly solidified alloys. As the quenching rate increased, the HRD and exchange current density first decreased and then increased.     

旋转电极电渣重熔过程熔滴滴落及熔池形状的模拟

建立了瞬态三维耦合数学模型以探索旋转电极对电渣重熔过程中电磁场、流场、温度场和熔池形状的影响.通过求解麦克斯韦方程组得到电磁场的相关信息,利用VOF方法描述金属熔滴的运动,采用焓-多孔介质模型计算凝固过程.当电极旋转,金属熔滴在离心力作用下,从电极边缘抛出,增加了金属熔滴在渣池中停留的时间与沿途路径,有利于提高电渣重熔...     

镍钛形状记忆合金线坯连续定向凝固温度场的数值模拟

连续定向凝固过程中结晶器的温度分布对固-液界面位置和形状具有重要影响.在建立三维物理模型以及确定材料热物性参数、边界条件与冷却水对流换热系数计算方法的基础上,采用ANSYS有限元软件对不同参数组合条件下镍钛形状记忆合金线坯连续定向凝固的稳态温度场进行了数值模拟.研究结果表明,在所给定的模型及各种参数条件下,镍钛形状记忆合金在结晶器内可以完成凝固过程,且固-液界面呈平直状,具备了进行连续定向凝固制备的基本条件.

     

连铸凝固传热时液相有效导热系数的定量化

在已验证的电磁-热-溶质传输耦合模型的基础上,以某钢厂同时装配有M-EMS和F-EMS的方、圆坯先进铸机为研究对象,对二维切片凝固传热模型中液相有效导热系数的放大倍数m值进行了定量化研究。结果表明,溶质再分配作用下,方、圆坯凝固终点处的钢液液相线温度较浸入式水口入口处的分别约下降了23.27和5.54℃;与二维切片模型相比,采用耦合模型计算时,铸坯凝固终点位置分别后移了1.8和0.9m;为保证同时准确获取铸坯表面温度分布状态及其内部凝固终点位置,在本方、圆坯工况下,二维切片模型中纯液相和糊状区内液相有效导热系数放大倍数的推荐值范围分别为2.2~2.4和1.1~1.2。     

快速凝固耐热铝合金FVS0812真空脱气工艺的研究

采用氮气雾化制粉及冷等静压制取实验样品,通过对快速凝固粉末及冷等静压坯的脱气实验,成功地使粉末表面呈非晶态含水的Al_2O_3·3H_2O氧化膜转变为晶态的脆性的γ-Al_2O_3。研究发现:该粉末的最佳脱气温度为400℃左右,冷等静压坯的最佳脱气温度为450℃;通过干收集的粉末中结晶水多于吸附水,且其结晶水和吸附水均远远少于水收集粉末中的结晶水和吸附水。     

Numerical simulation of fluid flow and solidification in continuous slab casting mould based on inverse heat transfer calculation

Abstract

A mathematical model based on an inverse heat transfer calculation was built to determine the heat flux between the mould and slab based on the measured mould temperatures. With K–? turbulence model, a mathematical model of three-dimensional heat transfer and solidification of molten steel in continuous slab casting mould is developed. Solidification has been taken into consideration, and flow in the mushy zone is modelled according to Darcy’s law as is the case of flow in the porous media. The heat flux prescribed on the boundaries is obtained in the inverse heat conduction calculation; thus, the effect of heat transfer in the mould has been taken into consideration. Results show that the calculated values of mould temperature coincide with the measured ones. Results also reveal that the temperature distribution and shell thickness are affected by the fluid flow and heat transfer of slab which is governed by the heat flux on the mould/slab interface.     

基于反算热流的结晶器内流动-传热-凝固耦合模拟

基于Navier-Stokes动量方程和湍流低雷诺数k-ε方程,综合考虑能量守恒和钢液凝固与糊状区对流动过程的影响,建立了描述结晶器内钢液流动、传热及凝固过程的三维耦合数学模型.以实测温度和结晶器反问题模型计算出的热流为边界条件,模拟计算了结晶器内钢水的流动、传热和凝固行为.钢液流动决定结晶器内的温度和热流分布,铸坯凝固受钢液流动和结晶器热流双重因素的影响.建立的模型以及由此得到的铸坯凝固非均匀特征可为进一步考察浇铸过程中纵裂和其他表面缺陷提供借鉴和参考.