二元合金非等温凝固相场法模拟

利用耦合温度场与溶质场的相场模型对Al-Cu二元合金非等温凝固时枝晶生长过程进行了模拟。研究了人为变化的不同热扩散系数对枝晶生长行为的影响。计算结果表明：随着热扩散系数的减小，潜热释放对熔体内原有温度场的影响也减小，熔体内过冷度能够更好地保持；而枝晶尖端生长速度将增大．枝晶呈现出更发达的侧向分支；同时，溶质偏析程度也越小。将计算模拟结果和实验结果进行了比较，两者吻合良好。     

C-103铌合金的热扩散率、比热和热导率

本文用激光脉冲法测量了室温至1800℃间C-103铌合金的热扩散率和室温至300℃的比热。从所测得的热扩散率和比热,以及由卡计法测定的平均比热经换算求得的瞬时比热数据,计算了C-103铌合金室温到1800℃的热导率。C-103铌合金的热扩散率和热导率比充分退火纯铌约低20-30%。C-103铌合金的热扩散率随温度变化的曲线可分为斜率不同的两段。在室温到800℃范围内,热扩散率随温度升高而增大。800℃以上,热扩散率基本上不随温度变化,约为0.21厘米~2/秒。室温到300℃间,C-103铌合金的比热接近纯金属铌的比热。     

DFP优化算法在热传导反问题中的应用及其改进

通过运用反算法求解液态铝合金的有效热扩散率,介绍了DFP优化算法在热传导反问题中的应用。并且针对热传导反问题的非线性特点,在常规的DFP算法中引入改进的牛顿迭代下山法,还采用了数值精度高的理查得外推法求解梯度。计算结果表明:改进的DFP算法具有更好的数值稳定性、更快的收敛速度及更高的优化结果可靠度。     

液态锂锡合金中氚解吸行为的模拟

液态锂锡合金是很有前途的聚变-裂变混合堆(FFHR)包层产氚材料。为完成FFHR包层氘-氚燃料循环系统的概念设计,以金属与氢的作用理论为基础,建立了液态Li25Sn75中氚解吸行为的动力学模型,模拟和分析了合金温度、氚分压、氦流量对解吸气中氚分压的影响以及氚在液态Li25Sn75中的传质系数、解吸率和吸附率。计算结果表明：在673~873 K的温度范围内,氚从液态Li25Sn75到气相的整个解吸过程,虽然包含了氚在熔融合金气泡中的扩散与对流、氚通过与气-液界面相连合金层的扩散、在界面发生的氚原子重组多相反应、氚通过气相边界层的扩散和气相中氚的扩散与对流5个子过程,但起决定作用的是氚在合金内的扩散和气-液界面的多相反应重组     

铝锂合金流动性及其数值模拟的研究

采用石墨型真空浇注，对铝锂合金的流动进行正交试验，找出了影响铝锂合金流动性的主要因素。基于伯努利方程和能量方程，模拟了铝锂合金液在条形试样中流动的速度，温度场分布及动长度；采用体积函数法（ＶＯＦ法），将流场和温度场耦合计算，不仅模拟了二维速度场和温度场，而且模拟了流动停止过程，为预测和防止冷隔，浇不足等缺陷提供了理论依据。     

铸件充型过程流场和温度场数值模拟

本文采用ＳＩＭＰＬＥ算法，研究开发了铸件充型过程三维流动和传热数值模拟软件，计算结果表明，在该软件能准确地模拟浇注充型过程中液态金属的流动状态。自由液面的波动，以及温度场分布。     

ZA22合金急冷凝固组织的研究

采用极小试样快速液淬方法研究了ZA22合金从不同温度快速冷却所获得的凝固组织的差异。在研究的温度范围内，液淬前液态合金温度越高获得的凝固组织越细密，且ZA22合金凝固组织中富铝相的晶内成分偏民随着液态合金温度的升高而减轻。结合液态合金的微观结构，对造成凝固组织差异的原因进行了初步分析。     

金属熔体中的液-液结构转变现象及其对凝固的影响（英文）

液态合金结构和性质的研究一直是凝聚态物理和金属材料科学领域的重要研究方向之一。液态合金并非理想的均质液体,在温度和压力等作用下会发生不连续转变。液-液结构转变广泛存在于金属和合金中,并且对最终凝固组织和性能有着很大的影响。系统阐释金属熔体中液-液结构转变现象,总结液-液结构转变对最终凝固组织和宏观性能的影响等方面的主要研究进展。结果表明,利用熔体液-液结构转变可以有效调控金属及合金的组织,改善其宏观性能。     

钛合金筒形件真空热胀形过程数值模拟及模型优化

利用MSC-Marc有限元分析软件，建立了BT20合金筒形件真空热胀形的热力耦合有限元模型。在优化模型中引用了步长自适应控制技术和两步法模拟。计算了BT20合金筒形件真空热胀形过程的温度场和变形场。结果表明：采用步长自适应控制技术和两步法模拟，有效的缩短了模拟时间，在精度变化不大的情况下，显著提高运算效率。计算结果与实验结果吻合较好。     

相场法模拟Ni-Cu合金枝晶生长中过冷度的影响

用相场法模拟了Ni30Cu70合金非等温凝固中的枝晶生长过程。研究了过冷度对过冷合金熔体中的枝晶生长以及溶质场和温度场的分布的影响。模拟结果表明：随着过冷度的增大，二次枝晶臂发达，溶质扩散层厚度减小、溶质浓度梯度增大，热扩散层厚度减小。     

Al-Si合金枝晶形貌的三维相场模拟

基于包含固相扩散系数的Karma薄界面相场模型,采用三维自适应网格划分法,研究了界面宽度、热噪声幅值对Al-Si合金过冷熔体中枝晶生长行为的影响。模拟结果表明：随着界面宽度的增加,枝晶形貌的复杂度下降,枝晶尖端速度下降,尖端液相处溶质的富集程度下降;随着热噪声幅值的增加,枝晶尖端变化较小,位于枝晶主干两侧的二次枝晶的数量和不对称度增加。     

铝合金压铸件凝固过程中的瞬态温度场分析

建立了铝合金压铸件的有限元模型,确定了温度场模拟的初始条件和边界条件;结合材料的热物性,利用AN-SYS软件对A380.0铝合金压铸件凝固过程中的温度场进行了模拟,得到了铸件各点温度随时间变化的规律,模拟结果反映了铸造系统温度的变化过程。结果表明：利用ANSYS模拟温度场运算速度快、结果比较准确,为热应力分析提供了温度场条件,并给压铸优化设计提供了依据。     

A Physically Consistent Path-Weighted Diffusivity Function for Modeling of Drop-by-Drop Liquid Metal Deposition

A physically consistent path-weighted diffusivity function is derived for parametric representation of heat diffusion patterns occurring within a volume of material where in there exists inhomogeneous or anisotropic thermal diffusivity. A physically consistent parametric representation of energy deposition processes, where there exists spatially dependent thermal diffusivity, provides for more optimal inverse analysis of such processes. The path-weighted diffusivity function presented here further extends an inverse analysis approach presented previously. The general functional characteristics of the path-weighted diffusivity function derived are examined via a prototype simulation of drop-by-drop liquid metal deposition upon a material characterized by anisotropic thermal diffusivity. The results of this simulation are compared with previous simulations concerning path-weighted thermal diffusivity. The parametric representations presented, which are constructed using path-weighted sums of analytic basis functions, are examined from the perspective of discrete numerical methods. This perspective provides a foundation for the development of control algorithms for process optimization with respect to achieving specific microstructures within a fabricated structure.     

Diffusivities of an Al–Fe–Ni melt and their effects on the microstructure during solidification

A systematical investigation of the diffusivities in an Al–Fe–Ni melt was presented. Based on the experimental and theoretical data about diffusivities, the temperature- and composition-dependent atomic mobilities were evaluated for the elements in Al–Ni, Al–Fe, Fe–Ni and Al–Fe–Ni melts via an effective approach. Most of the reported diffusivities can be reproduced well by the obtained atomic mobilities. In particular, for the first time the ternary diffusivity of the liquid in a ternary system is described in conjunction with the established atomic mobilities. The effect of the atomic mobilities in a liquid on microstructure and microsegregation during solidification was demonstrated with one Al–Ni binary alloy. The simulation results indicate that accurate databases of mobilities in the liquid phase are much needed for the quantitative simulation of microstructural evolution during solidification by using various approaches, including DICTRA and the phase-field method.     

Thermophysical properties of Ti-5Al-5V-5Mo-3Cr-1Zr titanium alloy

The thermophysical properties of the Ti-5Al-5V-5Mo-3Cr-1Zr titanium alloy in a wide range of temperatures from room temperature to 1000°C have been studied by the methods of differential scanning calorimetry, the laser flash method, and dilatometry. The obtained data on heat capacity, thermal diffusivity, and thermal expansion have been used for calculating coefficient of thermal conductivity. The sequence and temperatures of structural transformations during heating of the alloy have been established. It has been shown that the studied alloy possesses a coefficient of thermal conductivity that is 3.5–4 times smaller than that of pure titanium.     

焊接热力耦合仿真热边界条件研究

热边界条件定义是焊接热力耦合仿真前处理设置的重要环节,直接影响到仿真结果的准确性,尤其是对于铝合金类高导热材料焊接仿真而言。本文研究了焊接热力耦合仿真热边界条件的定义方法,通过实验与仿真,对温度场和残余应力分布模拟结果的影响因素进行了探讨。     

Effect of Alloying Elements on Thermal Diffusivity of Gray Cast Iron Used in Automotive Brake Disks

The purpose of this work was to experimentally investigate the thermal diffusivity of four different gray cast iron alloys, regularly used to produce brake disks for automotive vehicles. Thermal diffusivity measurements were performed at temperatures ranging from room temperature to 600 °C. The influence of the thermal conductivity on the thermomechanical fatigue life is also briefly presented. The measurements were sensitive to the influence of the carbon equivalent and alloying elements, such as molybdenum, copper and chromium. Molybdenum, unlike copper, lowered the thermal diffusivity of the gray cast iron, and alloy E (without molybdenum), besides presenting a relatively low carbon equivalent content and an increase in the values of the thermal diffusivity, presented the best performance during the thermomechanical fatigue. The molybdenum present in alloys B and C did not fulfill the expectations of providing the best thermomechanical fatigue behavior. Consequently, its elimination in the gray cast iron alloy for this application will result in a significant economy.     

Simulation of thermal behavior of a CNC machine tool spindle

The thermal deformations of a CNC machine tool spindle are the major contributor of thermal error. It is very significant both theoretically and practically to study how to accurately simulate the thermal error of the spindle. Firstly, this paper proposes a method for computing the coefficient of convection heat transfer of the spindle surface by referencing the theory on computing the coefficient of convection heat transfer of a flat plate when air flows along it. Secondly, the temperature field and thermal errors of the spindle are dynamically simulated under the actions of thermal loads using the finite element method. Thirdly, the characteristics of heat flow and thermal deformation within the spindle are analyzed according to the simulation results. Fourthly, the selection principle of thermal key points, which are indispensable for building a robust thermal error model, is provided based on the thermal error sensitivity technology. At last, a verification experiment is implemented on a CNC turning center, and the results show the simulation results are satisfying to replace the experiment results for further studies.