电渣重熔GH984G定向凝固组织CAFE法模拟

 电渣重熔凝固组织的控制直接关系到高温合金的品质与实际生产应用。针对电渣重熔GH984G的定向凝固过程,同时考虑传热和溶质扩散,基于CAFE法与C语言结合,建立了三维电渣重熔凝固过程组织演变的CAFE模型,并对凝固过程温度场和凝固组织演变进行模拟预测。结果表明,铸锭温度场和熔池深度都是首先为较浅平状态,然后不断加深至最后稳定;在电极熔化初始,金属熔池浅平,枝晶生长方向是竖直向上,之后金属熔池不断加深,底部竖直向上的柱状晶方向变为斜向上约26°。同时在铸锭的中心线上出现了等轴晶,等轴晶形核长大后与柱状晶镶嵌生长。此外,随着电极熔速变大,渣金界面上涨速度也随之变大,且熔池深度相应变宽变深。模拟结果与试验结果基本吻合,从而验证了模型与形核参数的适用性。     

真空自耗电弧熔炼TC4铸锭的凝固组织和缩松缩孔的模拟

建立三维轴对称有限元模型,采用移动边界法模拟了真空自耗电弧熔炼( VAR)TC4合金铸锭凝固过程的温度场分布,并基于元胞自动机和有限元耦合法(CAFE法)计算了VAR过程中TC4铸锭的凝固组织、缩松和缩孔的形成.结果表明,模拟结果与试验观察在晶粒结构、柱状晶生长方向,柱状晶-等轴晶转变及缩松和缩孔等方面相符合.     

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...     

超声对7050铝合金凝固组织影响的数值模拟

采用Procast-CAFE模块,建立了7050铝合金形核和晶粒生长的数学模型,模拟了7050铝合金在不同功率超声作用下组织的演化过程。结果表明,随着超声功率增大,熔体形核率增大,晶粒细化效果更好,组织分布更均匀,平均晶粒尺寸更小。模拟结果与试验结果符合。     

CAFE compliance by light trucks: economic impacts of clean diesel engine

With the popularity of light trucks increasing in the United States, their share of the US light vehicle market had doubled between 1980 and 1996, climbing from 20 to 40%. By 1996, annual energy consumption for light trucks had risen to 5.97×10¹⁵ Btu [5.97 quadrillion Btu, or “quad,” or 6.30×10¹⁸ joule (J)], compared to 7.94 quad (8.38×10¹⁸ J) for cars. In recent years (since 1995), the fuel economy of US - manufactured light trucks (almost 99% of which use gasoline engines) has been below the Corporate Average Fuel Economy (CAFE) standards. This paper analyzes a strategy to reduce the CAFE shortfalls by adopting the new, highly energy-efficient clean diesel engine. Research on such engines has been funded by the US Department of Energy, Office of Heavy Vehicle Technologies, under its Light Truck Clean Diesel Engine Program. A clean diesel engine market penetration trajectory is developed, representing an industry response to meet the CAFE standards. Whether the engine will be produced inside the country or imported remains uncertain, so two cases are defined. Values of exports/imports of clean diesel engines/trucks under these cases are estimated. The macroeconomic benefits are estimated by using a model of the US economy developed by Standard & Poor's Data Resources, Inc. On the basis of gains in the gross domestic product projected under the alternative cases, domestic production of the clean diesel engine is favored over importing it.     

Numerical simulation of solidification structure during electroslag remelting casting of ZG06Cr13Ni4Mo ingot based on CAFE and moving boundary method

A comprehensive mathematical model of the solidification structure during the process of electroslag remelting casting (ESRC) of low carbon martensite stainless steel ZG06Cr13Ni4Mo has been established. The change of metal pool profile and grain growth and the microstructure evolution process from the beginning to the steady stage of the ESRC process were investigated by using the moving boundary method and the coupled technology CAFE method (cellular automaton – finite element method). The transition from equiaxed grains at the lateral wall of the mould to columnar grains has been revealed. In addition, casting of this steel has been carried out and the microstructure of the ingot obtained after grinding and acid leaching. According to the comparison of the metal pool profile, morphology and growth direction of the dendrite and the secondary dendrite arm spacing (SDAS) between the experimental results and the simulation results, the validity of the model has been demonstrated, which can provide a favourable theoretical foundation to optimise the process parameters for the control of solidification structure of ESRC of low carbon martensite stainless steel ZG06Cr13Ni4Mo.     

Validation of Multi‐scale Model Describing Microstructure Evolution in Steels

Properties of deformed steels depend on various microstructure parameters such as distribution of grain size and precipitates. Strain, strain rate and temperature inhomogeneities make quantitative prediction of microstructure difficult but the Finite Element method is able to model these inhomogeneities. Different scales of phenomena occurring in deformed materials are another difficulty in modelling. Microstructure evolution can be described by more realistic methods (e.g. Cellular Automata CA, Monte Carlo), which, on the other hand, are unable to simulate larger samples. Therefore, development of the methods capable of spanning multiple scales became a current challenge. CAFE modelling, which couples FE and CA methods, is the objective of the paper. The model consists of two layers. The micro‐scale layer, simulated by CA, represents microstructure evolution including nucleation and growth of the grains. Evolution of a dislocation density is described for every grain separately by solving differential equation. The FE thermal‐mechanical model is used as a macro‐scale part. Multistage plane strain compression tests for niobium steel are considered. Distributions of initial and final grain size are measured during the tests. The results from the CAFE model are compared to the measurements and to the predictions by a conventional model. The comparisons confirm the capability of the CAFE method to predict flow stress, recrystallized fraction and grain size distribution. Conventional approach gives a good agreement with experiments for an average grain size only.     

超声场作用下7050铝合金的溶质再分配与组织形成的建模仿真与分析

对不施加超声、施加300 W、1 000 W功率超声处理的半连铸成形7050铝合金大扁锭进行晶粒细化的实验研究,并基于元胞自动机-有限元(CAFE)法,建立7050铝合金形核和晶粒生长的数学模型,得到形核参数对仿真结果的作用规律。依靠成分过冷发展的初始阶段建立生长限制因数Q的物理模型,对超声细化晶粒的机制进行说明。模拟和实验结果表明:1 000 W功率超声的晶粒细化效果最佳,此时晶粒的平均尺寸为204μm;模具表面形核的高斯分布平均过冷度、模具表面以及熔体内部形核的高斯分布标准方差对预测晶粒结构影响不大,模具表面及熔体内部形核的高斯分布最大形核密度、熔体内部形核的高斯分布平均过冷度对仿真结果影响显著;晶粒尺寸随Q值增大呈大致单调递减趋势,晶粒大小与Q具有良好的关联性。