固液界面与单晶连铸表面质量

本文研究固液界面对单晶连铸表面质量的影响,结果表明,形成中心向液体中凸出形状的固液界面,且保证铸锭表面在离开铸型之后自由凝固是获得高的表面质量的必要条件。     

钕对Ti—44Al合金组织和晶粒尺寸的影响

在真空电弧熔炼条件下研究稀土元素钕（Ｎｄ）（加入量范围为０．０５～０．３ａｔ％）对Ｔｉ－４４ａｔ％Ａｌ二元合金组织和晶粒尺寸的影响，实验结果表明，钕明显增加了铸锭柱状晶的长度和减小柱晶直径，同时细化了铸锭中心区的等轴晶粒，高温固溶处理后铸锭获全片层组织，不含钕的铸锭平均晶粒尺寸大于１４００μｍ含０．１ａｔ％Ｎｄ铸锭的平均晶粒尺寸的４５０μｍ拓该铸锭的顶部获得小晶粒尺寸（３４１μｍ）。     

籽晶法生长高温合金单晶凝固界面研究

研究了籽晶法生长单晶高温合金中固液界面的演变规律。实验结果表明：在籽晶法生长高温合金单晶的起始过程中,凝固系统经非稳态自组织过程达到稳态生长,凝固界面经历了由平界面—胞状界面—枝晶界面的转化过程,胞枝晶间距根据凝固参数及初始形态自行调整,其调整模式主要有竞争淘汰、尖端开裂和高次分枝三种。在生长起始端存在着籽晶与单晶的融合区,融合区的成分取决于籽晶成分和单晶成分。     

高温度梯度定向凝固高温合金单晶初始生长过程菲稳态自组织行为

用ＺＭＬＭＣ超高梯度定向凝固装置（固液界面前沿的温度梯度可达１３００Ｋ／ｃｍ）研究竟凝固速率范围内籽晶法制备含细亚结构的ＤＤ３单晶的起动生长段的组织演化与选择特征试验获得了直径为７ｍｍ的ＤＤ３单晶合金，起动生长段组织演化对界面前沿液相中的温度梯度ＧＬ，系统稳定抽拉速度Ｖ，系统起动时的升速模式及系统干扰等因素的基本依赖关系，并对该非稳态自组织过程的内在控制因素及其形成机制进行了初步的分析．     

多晶硅定向凝固过程中固-液界面特性研究

通过真空感应熔炼炉以不同拉锭速率制备了多晶硅铸锭,通过对铸锭的金相组织及少子寿命随凝固高度的变化及径向分布的分析,研究了多晶硅定向凝固过程中的固-液界面特性。结果表明:少子寿命随生长高度的增加先增加后减少,其径向分布与固-液界面相对应。由少子寿命分布图可以看出,固-液界面的曲率随拉锭速率的减小而减小,固-液界面形貌为胞状界面。计算分析表明,胞状的固-液界面造成Fe杂质的有效分凝系数增加了3个量级以上。     

抽拉速率对SRR99单晶高温合金组织和性能的影响

用螺旋选晶法制备镍基单晶高温合金SRR99,研究了抽拉速率对其组织和性能的影响．随着抽拉速率的增大,SRR99单晶合金的铸态组织由粗枝状晶向细枝状晶演变,枝晶干与枝晶间的γ’相尺寸减小,且枝晶间γ’相的形状逐渐趋向于规则立方体形状,而γ-γ’共晶的含量增加．热处理后,在高抽拉速度下生成的共晶组织更容易固溶,形成更加均匀的组织．随着抽拉速率的增大,SRR99单晶合金的持久寿命延长．     

抽拉速率对SRR99单晶高温合金组织和性能的影响

用螺旋选晶法制备镍基单晶高温合金 SRR99,研究了抽拉速率对其组织和性能的影响.随着抽拉速率的增大,SRR99单晶合金的铸态组织由粗枝状晶向细枝状晶演变,枝晶干与枝晶间的γ'相尺寸减小,且枝晶间γ'相的形状逐渐趋向于规则立方体形状,而γ-γ'共晶的含量增加.热处理后,在高抽拉速度下生成的共晶组织更容易固溶,形成更加均匀的组织.随着抽拉速率的增大,SRR99单晶合金的持久寿命延长.     

游离晶与凝固界面间的相互作用对晶区形成的影响

应用铸件在凝固时的倾出方法详细观察了工业纯铝试样中晶区的形成过程。研究结果表明,在低过热度浇注时,游离晶的运动速率和凝固界面生长速率之间的相互作用决定了晶区的形成以及晶粒的尺寸与形状。当游离晶的沉降堆积速率V大于底部凝固层增长速率R时,将形成尺寸、形状都较均匀的等轴晶。当界面生长方向与游离晶游离运动方向一致时,如果界面生长速率R与游离晶垂直于界面方向的运动速率V之差远远大于界面捕获游离晶的临界速率V临,即R—V》V临,被捕获的游离晶将形成尺寸、形状均匀的等轴晶;如果R—V仅稍大于V临,则形成拉长状等转晶;如果R—V小于V临,则形成柱状晶。对游冷等轴晶区的形成也以游离晶的捕获进行了解释。     

单晶高温合金晶体取向的研究进展

单晶高温合金晶体取向与轴向的偏离已成为单晶叶片的一个重要缺陷.简述了单晶生长过程中在不同界面形态下择优取向的转变规律,以及取向对枝晶形貌和尺度的作用;分析了不同取向晶粒的竞争机制,并展望了晶体取向今后研究发展方向;指出了温度梯度、界面形状、熔体等是影响单晶高温合金晶体择优取向的重要因素.     

电渣重熔工艺对GCr15轴承钢凝固组织的影响

基于CAFE法(元胞自动机-有限元模型),采用ProCAST对电渣重熔方法生产的GCr15轴承钢钢锭的微观组织进行数值模拟,得到了电渣钢锭的晶粒生长过程、熔池形状变化和晶区分布情况,并分析了不同的工艺参数对熔池形状以及凝固组织的影响.熔池深度随着钢锭固相区的扩展而变得越来越深,当钢锭长到一定高度,熔池深度和晶粒生长方向均不再变化.研究结果表明:结晶器冷却强度越大,熔池温度越低,熔池深度与钢锭半径之比h/R越小,而晶粒平均尺寸增大且柱状晶越多;渣池温度越高,h/R越大,晶粒平均尺寸增大;重熔速度是最显著的影响因素,熔速增大,h/R显著增大,柱状晶尺寸增大且数量增多.经过对电渣锭的凝固组织观察试验发现,模拟结果与试验结果有较好的一致性.     

数值模拟在单晶高温合金熔模铸造中的应用

由于单晶高温合金消除了晶界这一高温薄弱结构,已成为航空发动机首选的热端部件材料。为了满足航空发动机对推重比和涡轮燃气温度的更高需求,新型单晶高温合金中添加了越来越多的Re、Ru等难熔元素,致使单晶制备过程中缺陷形成倾向显著提高,研制周期和研制成本明显增加,严重限制了单晶高温合金的产业化应用。近年来,随着计算方法和熔模铸造技术的发展,数值模拟在单晶高温合金制备领域中得到了越来越广泛的应用,已成为减少单晶铸造缺陷,获得高质量单晶铸件的重要手段。以商用铸造模拟软件Procast为例,对单晶高温合金定向凝固过程的温度场分布和组织演化进行了分析,综述了数值模拟在单晶熔模铸造研究中的应用现状。首先,介绍了数值模拟中的前处理过程,即几何建模、网格划分等,强调了前处理过程的注意事项。随后,根据已有文献,分析了数值模拟技术在研究温度场和晶粒组织演化过程的作用。最后,指出数值模拟技术在单晶高温合金熔模铸造领域进一步发展需要解决的问题。     

Numerical Simulation of Morphology and Microsegregation Evolution during Solidification of Al-Si Alloy

A stochastic model coupled with transient calculations for the distributions of temperature, solute and velocity during the solidification of binary alloy is presented. The model can directly describe the evolution of both morphology and segregation during dendritic crystal growth. The model takes into account the curvature and growth anisotropy of dendritic crystals. Finite difference method is used to explicitly track the sharp solid liquid (S/L) interface on a fixed Cartesian grid. Two-dimensional mesoscopic calculations are performed to simulate the evolution of columnar and equiaxed dendritic morphologies of an AI-7 wt pct Si alloy. The effects of heat transfer coefficient on the evolution of both the dendrite morphology and segregation patterns during the solidification of binary alloys are analyzed. This model is applied to the solidification of small casting. Columnar-to-equiaxed transition is analyzed in detail. The effects of heat transfer coefficient on final casting structures are also studi     

Determination of Interfacial Heat Transfer Behavior at the Metal/Shot Sleeve of High Pressure Die Casting Process of AZ91D Alloy

The interfacial heat transfer behavior at the metal/shot sleeve interface in the high pressure die casting(HPDC) process of AZ91 D alloy is carefully investigated.Based on the temperature measurements along the shot sleeve,inverse method has been developed to determine the interfacial heat transfer coefficient in the shot sleeve.Under static condition,Interfacial heat transfer coefficient(IHTC) peak values are 11.9,7.3,8.33 k W m~(-2)K~(-1)at pouring zone(S2),middle zone(S5),and end zone(S10),respectively.During the casting process,the IHTC curve displays a second peak of 6.1 k W m~(-2)K~(-1)at middle zone during the casting process at a slow speed of 0.3 m s~(-1).Subsequently,when the high speed started,the IHTC curve reached a second peak of 12.9 k W m~(-2)K~(-1)at end zone.Furthermore,under different slow casting speeds,both the calculated initial temperature(TIDS) and the maximum temperature(Tsimax) of shot sleeve surface first decrease from 0.1 m s~(-1)to 0.3 m s~(-1),but increase again from 0.3 m s~(-1)to 0.6 m s~(-1).This result agrees with the experimental results obtained in a series of "plate-shape" casting experiments under different slow speeds,which reveals that the amount of ESCs decreases to the minimum values at 0.3 m s~(-1)and increase again with the increasing casting slow speed.     

AlCuFe准晶与纯Al的界面反应

分析了压铸的纯Al-AlCuFe准晶复合材料的界面反应行为，以及原始铸态的AlCuFe准晶组织，发现复合材料的界面反应行为与铸态AlCuFe准晶的原始组织有着密切的关系。要获得良好的界面，必须控制好铸态AlCuFe准晶及其类似相的相对含量和组织形态。     

钢-Al-20Sn复合板的非均匀扩散复合研究

提出了消除钢-Al-20Sn复合板复合界面脆化的非均匀扩散思想,并采用Al-20Sn半固态浆料与钢板进行铸轧复合,实现了非均匀扩散,改变了复合界面结构,消除了复合板复合界面的脆化。研究结果表明,在500℃钢板预热温度、10mm/s铸轧速度条件下,当半固态浆料固相率为34.3%时,复合界面由比例恰当的铁铝化合物和铁铝固溶体交替构成,脆化得以消除,相应的最大界面剪切强度为69.9MPa。     

In-situ observation of solid-liquid interface transition during directional solidification of Al-Zn alloy via X-ray imaging

The morphological instability of solid/liquid(S/L) interface during solidification will result in different patterns of microstructure. In this study, two dimension(2 D) and three dimension(3 D) in-situ observation of solid/liquid interfacial morphology transition in Al-Zn alloy during directional solidification were performed via X-ray imaging. Under a condition of increasing temperature gradient(G), the interface transition from dendritic pattern to cellular pattern, and then to planar growth with perturbation was captured. The effect of solidification parameter(the ratio of temperature gradient and growth velocity(v), G/v) on morphological instabilities was investigated and the experimental results were compared to classical "constitutional supercooling" theory. The results indicate that 2 D and 3 D evolution process of S/L interface morphology under the same thermal condition are different. It seems that the S/L interface in 2 D observation is easier to achieve planar growth than that in 3 D, implying higher S/L interface stability in 2 D thin plate samples. This can be explained as the restricted liquid flow under 2 D solidification which is beneficial to S/L interface stability. The in-situ observation in present study can provide coherent dataset for microstructural formation investigation and related model validation during solidification.     

A new method to evaluate the quality of single crystal Cu by an X-ray diffraction butterfly pattern method

A new method for the evaluation of the quality of an Ohno continuous cast (OCC) Cu single crystal by X-ray diffraction (XRD) butterfly pattern was brought forward. Experimental results show that the growth direction of single crystal Cu is inclined from both sides of the single crystal Cu rod to the axis and is axially symmetric. The degree of deviation from the [100] orientation from the crystal axis is less than 5° with a casting speed 10–40 mm/min. The orientation of single crystal Cu does not have a fixed direction but is in a regular range. Moreover, the orientation of stray grains in the single crystal Cu is random from continuous casting.     

The microstructure of silicate varying with crystal and melt properties under the same cooling condition

Diopside dendrites and plagioclase spherulites were formed from Ab–An–Di silicate melts under exactly the same cooling conditions. The effects of crystal and melt structure on the microstructure of silicate were studied by optical microscopy and Raman spectroscopy. The results show that the anisotropy is truly an important factor in the growth pattern evolution. The phenomena can be described by the morphology diagram. In spite of the dendritic shape, diopside dendrite behaves like a single crystal, while the plagioclase spherulite is polycrystalline. The silicates crystallized from a fast-cooling silicate melt can reflect the structural characteristics of the melts, as is apparent from the Raman spectra. The growth units for silicate crystals are mainly the segments of SiO polymers with different polymerization degree other than simple ions. The structural units in the silicate melt interact strongly with the crystal at the solid and melt interface; this acts as a buffer layer for structural transform from disordered or less ordered short-range structure to long-range ordered structure. The results imply that the phase-field approach to modelling the growth patterns has a realistic basis at the atomistic scale.     

铝单晶线材连续铸造工艺及其性能

单晶连铸技术是一项新型的ｎｅａｒ－ｎｅｔ－ｓｈａｐｅ生产技术，它将先进的定向凝固技术与高效的连续铸造技术相结合可连续制造无限长的，表面呈镜面状态，内部无缩孔，气孔等铸造缺陷的单晶金属型材。     

原位合成铁基复合材料中增强相VC的微结构特征

通过反应铸造法经普通的铸造工艺成功制备了原位VCp增强铁基复合材料.VC颗粒弥散分布在基体中,以近似等轴状为主.TEM及HRTEM表明,基体和增强颗粒结合良好,界面光滑干净,增强相晶体结构完整,组织细密.由于界面的捕获及推移效应,一部分VC被推移至奥氏体晶界,一部分充当异质形核核心.