镍基单晶合金枝晶型区域相成分最优化测算法

建立了用测算镍基单晶高温合金枝晶典型区域相成分的最优化数学模型，根据电子探针对枝晶典型区域成分的测定结果，运用BFGS拟Newton法及CONSTR约束优化算法，可以计算枝晶各典型区域中γ和γ′相成分，以镍基单晶合金CMSX－2和CMSX－4为对象，对优化测算结果进行了分析，证实了该方法的可行性。     

镍基单晶高温合金γ和γ′相合金元素分布特征

用测算的办法分析了镍基单晶高温合金中γ和γ′相元素的分布特征.枝晶干和枝晶间γ和γ′相的化学成分测算表明,Cr、Mo、Co主要分布在γ相中,Ta、Al主要分布在γ′相,Ta在γ和γ′相中的分配比最大,W的分配比最小,Cr、Mo、W元素的分布特征为01,为正分布.对枝晶干和枝晶间错配度的测算表明,枝晶干和枝晶间的错配度相差较大,枝晶间的γ-γ′错配度大于枝晶干的错配度,这与试样中这两个区域γ′的尺寸大小和形态特点相对应.     

Ni基单晶高温合金原树枝状晶结构典型区域γ和γ′相成分的测算

导出了高温合金γ和γ′相的元素分配比和分配系数,以CMSX-2合金为研究对象,用EDAX区域扫描测得热处理后未变形试样和经持久变形至断裂试样原树枝状晶三个典型区域（枝晶干、枝晶臂和枝晶间）的成分,使用分配系数法计算了各区域中γ和γ′相的成分,分析了各区成分分布的特点及其与合金持久寿命的对应关系。     

抽拉速率对含Ru镍基单晶高温合金凝固组织的影响

研究了不同抽拉速率对含Ru镍基单晶高温合金凝固组织的影响.结果表明,随着抽拉速率的加快,单晶合金的铸态组织由粗枝状晶向细枝状晶演变,枝晶干和枝晶间的γ′相尺寸减少,合金元素的偏析降低,γ-γ'共晶含量减少,NiAl基β相含量逐渐降低.同时,抽拉速率对合金的相变温度影响不大.     

抽拉速率对镍基单晶高温合金组织和偏析的影响（英文）

研究了抽拉速率对一种镍基单晶高温合金组织和成分偏析的影响。结果表明:随着抽拉速率的提高,一次枝晶间距与二次枝晶间距缩小,γ'相尺寸减小;γ/γ'共晶随着抽拉速率的提高,尺寸变小,但体积分数增加;同时,随着抽拉速率的提高,单晶成分偏析增加。     

Ta对镍基单晶合金铸态组织和偏析的影响

利用螺旋选晶法制备了不同Ta含量的镍基单晶合金,研究了Ta对镍基单晶合金铸态组织和偏析的影响.结果表明:镍基单晶铸态组织主要由枝晶组成,枝晶间的γ’较大,枝晶于的γ’较小;Ta对枝晶有较大影响,随着Ta含量的提高,枝晶间距减小,并且逐渐出现三次枝晶臂;Ta提高了Mo的偏析系数,促进了Mo在枝晶间的偏析;Ta改变了γ’的形貌,Ta含量较低时,γ’为圆形,Ta含量提高时,γ’向方形转变,同时合金的错配度增大.     

拉晶速率对Ni3Al基单晶合金IC6SX凝固组织和高温持久性能的影响

采用螺旋选晶法制备Ni3Al基单晶合金IC6SX试棒,研究了不同拉晶速率对凝固组织和高温持久性能的影响.结果表明,Ni3Al基单晶合金IC6SX凝固组织为树枝状,随着拉晶速率从1.5 mm/min增加到6 mm/min,一次枝晶间距逐渐减小.与普通镍基高温合金不同,位于枝晶干处的次生γ'相尺寸比枝晶间处的大.随着拉晶速率的增加,枝晶干和枝晶间处的γ'相尺寸都逐渐减小,由不规则形状逐渐立方化,枝晶间处的初生γ'相的数量逐渐增多.一次枝晶间距和γ'相尺寸对高温持久性能影响显著,随着拉晶速率的增加,组织细化,铸态IC6SX单晶合金的高温持久寿命增加.     

抽拉速率对一种镍基单晶高温合金组织和偏析的影响

研究了抽拉速率对一种镍基单晶高温合金组织和成分偏析的影响。结果表明：随着抽拉速率的提高,一次枝晶间距与二次枝晶间距缩小,γ''相尺寸减小;γ/γ''共晶随着抽拉速率的提高,尺寸变小,但体积分数增加;同时,随着抽拉速率的提高,单晶成分偏析增加。     

熔体超温处理对镍基单晶高温合金γ'相的细化作用

采用光学显微镜、扫描电镜等方法研究了熔体超温处理对镍基单晶高温合金γ'相的影响.结果表明,随熔体超温处理温度由1500℃升高至1640和1780℃时,一次枝晶间距由177 μm分别减小至150和125 μm:枝间Ti富集程度降低,W的偏析程度减小.枝晶干和枝晶间y'相尺寸均减小,枝间y'相由不规则转变成立方形,同时枝间与枝干区域γ-γ'错配度减小.     

Re、Ru对镍基单晶合金元素偏析行为的影响

通过设计并制备出四种Re、Ru含量不同的镍基单晶合金,通过组织形貌观察及浓度测量,研究了元素Re、Ru对铸态镍基单晶合金成分偏析行为的影响。结果表明,Ru主要富集于枝晶间区域,并提高Al、Ta等γ'相形成元素在枝晶干区域的偏析程度,使其他元素在枝晶间区域的偏析程度增加。Re强烈偏析于枝晶干区域,可促进枝晶形核并增加枝晶数量。凝固期间,高熔点的Re、W等元素与基体Ni优先凝固,发生液固转变,形成枝晶组织。由于Re阻碍Ni、Al、Ta等原子发生有序化排列,导致Al、Ta等γ'相构成元素在枝晶干区域的浓度降低,致使枝晶间区域Ni、Al、Ta等元素的浓度增加,最终形成大量共晶组织,是铸态含Re合金共晶组织数量较多、尺寸较大,及含Re合金中Al元素主要偏析于枝晶间区域的主要原因。     

An Optimization Method For Estimating Phase Compositions And Amounts In Two—Phase Nickel Base Superalloys

根据已知镍基合金成分和γ′相成分，运用分层宽容多目标优化法，分别计算了γ相成分及γ′相含量．优化测算过程的实现是通过建立使杠杆定律等式两端数值差最小和两相共格错配度最小的目标函数，并通过设置γ′相含量和基体相成分取值范围的约束条件而实现的．验证了该方法的可行性和准确性．     

热处理对定向凝固Ti-45Al-8Nb-（W,B,Y）合金组织的影响

研究两种热处理制度对Bridgeman法制备的典型定向凝固Ti-45Al-8Nb-（W,B,Y）（摩尔分数,%）合金组织的影响。两种典型的定向凝固显微组织分别为胞状生长形貌全片层组织和枝晶状生长形貌块状组织,对其热处理发现：热处理1250℃,24h＋900℃,30min＋AC能有效消除其定向凝固合金中的B2相,并将快速定向凝固时产生的块状组织转变为片层组织,在胞状间及枝晶臂上分别获得了宽度为150-200μm和50-100μm的柱状晶。热处理1400℃,2h＋900℃,30min＋AC能同时消除B2相、块状组织及凝固偏析,但造成了晶粒的严重长大。热处理能有效改进定向凝固合金的显微组织。     

MICRO-DESCRIPTION OF THE SOLUTE-FIELD AND THE PHASE-FIELD MODEL FOR ISOTHERMAL PHASETRANSITION IN BINARY ALLOYS

A new phase field method for two-dimensional simulations of binary alloy solidification was studied. A model basing on solute conservative in every unit was developed for solving the solute diffusion equation during solidification. Two-dimensional computations were performed for ideal solutions and Ni-Cu dendritic growth into an isothermal and highly supersaturated liquid phase.     

采用温度回升法对任意结晶区间的铸件凝固结晶潜热的数值计算

铸件凝固结晶潜热的释放行为与凝固传热、溶质传输及铸造合金种类与成分等诸多因素有关，合金凝固过程中其温度、固相体积分数与液相成分(T-fs—CL)三者之间一般存在着非线性强耦合关系．采用合金凝固传输统一模型及温度回升(补偿)法提出的处理任意结晶温度区间(包括零结晶区间)凝固潜热释放问题的数值迭代计算方法，对不同合金成分与不同固相反扩散效应的二维Al—Cu合金铸件定向凝固传输过程进行了数值计算，表明该方法对于从纯金属到共晶成分的不同成分合金及从Scheil模型到Lever-Rule模型之间的任意凝固模式均是有效的．将该方法推广应用于叶片铸件三维凝固传输过程的T-fs—CL耦合数值模拟仍显示出高的计算效率．通过对计算结果进行的三维图像数据处理，展示了铸件几何形状对凝固传输行为的重要影响．     

NUMERICAL SIMULATION OF SUCCINONITRITE DENDRITIC GROWTH IN A FORCED FLOW

Numerical simulation based on phase field method is performed to describe solidification process of pure material in a free or forced flow. The evolution of the interface is showed, and the effects of mesh grid and flow velocity on succinonitrite shape are studied. These results indicate that crystal grows into an equiaxial dendrite in a free flow and into an asymmetrical dendritic in a forced flow. With increasing flow velocity, the upstream dendritic arm tip grows faster and the downstream arm grows slower. However, the evolution of the perpendicular tip has no significant change. In addition, mesh grid has no influence on dendritic growth shape when mesh grid is above 300×300.     

Microstructure evolution in rapidly solidified Y added TiAl ribbons

In the present study, Ti–46Al–2Cr–2Nb (atomic ratio) based alloys with various yttrium additions (0, 0.5, 1.0, 1.5, 2.0 at.%) have been produced by melt spinning method and the microstructure evolution with Y additions was studied intensively. For comparison, cast alloys with the same compositions were also prepared by argon arc melting. Investigations revealed that Y additions have an evident influence on the microstructure of the both alloys. With the addition of up to 1.5 at.% Y, the microstructure of the as-cast alloys changed from lamellar, typical of the Y free alloy, to dendritic, while the addition of 2 at.% Y led to a finer dendritic structure than for the 1.5 at.% Y alloy. For the rapidly solidified TiAl based alloys, a considerably refined microstructure was produced. Increasing Y concentration progressively modified the phase constituents from γ-TiAl + α₂-Ti₃Al phase, to γ-TiAl + α₂-Ti₃Al + a small fraction of Al₂Y phase, and then to γ-TiAl + α₂-Ti₃Al + a small fraction of Al₂Y + B2 phase. Although the phase constitutions on the roll contact and free surfaces of the rapidly solidified ribbons were essentially the same, the microstructure of the former was finer than that of the latter.     

Quantitative analysis of phases formed in the aluminothermic reduction of Ta2O5 by plasma

A novel technique of aluminothermic reduction of tantalum oxide is developed to produce tantalum in form of powder. In this technique, hydrogen plasma is used to trigger the reaction in a plasma reactor. The reacted powders were analyzed by XRD and SEM. Rietveld method was used to quantify the phases present in the product of reaction. The results showed that a tantalum rich phase with a dendritic structure, typical of molten phases is formed. This phase occurred in significant amounts onto the surface and in bulk of the reacted grains.     

Phase-field simulation of dendritic growth for binary alloys with complicate solution models

1 INTRODUCTION The formation of complex microstructures during solidification of metals and alloys have fas- cinated researchers in materials science and related areas for so many years , especially the formation of dendritic structures . In many commercial al- loys , microstructural features that determine the mechanical integrity of a cast ingot ,such as solute segregation, grain size and porosity , all depend critically on the morphologies and velocities of in- dividual or arrays of gr…     

用相场方法模拟纯物质等轴枝晶生长

采用相场模型模拟了纯物质过程的等轴枝晶演化,并针对各向异性模数为４的金属镍进行了二维数值模拟,计算了正方形区域过冷熔液中的等轴枝昌基相场方程中采用３均匀网格的一般显示有限差分方法求解,通过数值计算显示了等轴枝晶的形态。     

CALCULATION OF PHASE BOUNDARIES IN BINARY PHASE DIAGRAMS

本文通过一些具体实例,说明下面两个问题: 1.用迭代法计算二元相图时,初值的允许变化范围; 2.用同素异构平衡点法选初值存在的问题。 在此基础上,提出用数值方向逼近法计算二元相图,并对真实相界提出了判断方法。