正常晶粒长大数值模拟

从统计角度建立了正常晶粒长大的三维模型,该模型假定在奥氏体晶粒长大过程中,每个粒子体积的变化不仅与最近邻的晶粒有关,而且与系统中所有晶粒均有关,界面能的降低是晶粒长大的驱动力。通过模型计算可获得任意时刻的晶粒尺寸分布以及平均晶粒大小。第二相粒子的阻碍作用被引入到模型。温度升高,第二相粒子溶解,对正常晶粒长大的阻碍作用减小。初始晶粒尺寸分布采用对数正态分布。     

基于VB的晶粒长大的蒙特卡罗模拟

介绍正常晶粒长大的一般规律及其常用方法——蒙特卡罗方法．并采用VB语言编写了模拟正常晶粒长大的仿真系统．最后通过一算例获取了晶粒长大演变及晶粒尺寸随时问变化的关系．该算例说明了蒙特卡罗方法在模拟晶粒长大方面的直观性和有效性。     

低碳钢轧后冷却过程中的晶粒长大模型

钢材轧后冷却过程中的晶粒长大很大程度上决定着室温组织的晶粒尺寸,定量研究这一晶粒长大规律不仅可建立描述冷却过程中晶粒尺寸变化的模型,以利于计算机对微观组织变化过程的模拟,而且还为进一步的性能预报奠定基础.     

低碳钢轧后冷却过程中的晶粒长大模型

钢材轧后冷却过程中的晶粒长大很大程度上决定着室温组织的晶粒尺寸,定量研究这一晶粒长大规律不仅可建立描述冷却过程中晶粒尺寸变化的模型,以利于计算机对微观组织变化过程的模拟,而且还为进一步的性能预报奠定基础。     

元胞自动机模拟晶粒长大的步长设定对模拟结果的影响

采用一种预先设定步长的元胞自动机模型模拟晶粒长大,研究了步长对模拟结果的影响.在等效时间相同的情况下,采用较大的步长导致模拟完成时晶粒尺寸较小,但其晶粒尺寸分布更符合Weibull函数,晶粒面积比(An/Aa)与晶粒边数之间也更符合线性关系.无论采用哪种步长,模拟过程中平均晶粒边数均接近6,模拟后的组织中晶粒边数分布符合正态分布,且随步长的减小符合程度提高.综合考虑,对于实际材料晶粒长大过程的模拟仿真,采用100s步长可以获得较好的结果.     

机车车轮用钢奥氏体晶粒的长大行为

采用金相显微镜和截距法,对不同加热温度和保温时间下机车车轮用钢的奥氏体晶粒长大行为进行研究,分析加热温度和保温时间对奥氏体晶粒尺寸的影响,应用简单动力学模型对奥氏体晶粒的长大过程进行分析,同时研究钢中第二相粒子变化对奥氏体晶粒长大的影响.随着加热温度的升高和保温时间的延长,奥氏体晶粒尺寸明显增加,加热温度对晶粒的长大影响更明显.奥氏体晶粒长大的动力学时间指数随着温度升高而增加且其值均接近理论值0.5;奥氏体晶粒长大和钢中第二相粒子AlN体积分数和尺寸的变化呈明显的相关性.      

热处理过程中FGH96合金的微观组织演变

通过热处理实验研究了热处理过程中FGH96合金的微观组织演化，量化了固溶温度和保温时间对晶粒尺寸、γ′相尺寸、面积分数及晶粒分布的影响，分析了γ′相和应变存储能对晶粒演变的影响。结果表明：在热处理过程中，含有大量应变存储能的变形晶粒发生静态再结晶，晶粒细化，而动态再结晶晶粒发生晶粒长大，当两者平衡时可获得均匀细小的晶粒组织。合金在1060℃保温120 min后，γ′相尺寸和晶粒尺寸分布较为均匀，平均晶粒尺寸为7.37μm。γ′相的面积分数随固溶温度和保温时间的增加而减小，一次γ′相在亚固溶保温过程中存在粗化和分裂现象，使得一次γ′相的面积分数和尺寸先增加后减小。γ′相的非均匀溶解会导致局部晶粒长大较快，形成混晶。     

界面追踪和拉格朗日粒子追踪耦合计算方法

对于气液两相流的计算,常用的有界面追踪法和拉格朗日粒子追踪法.界面追踪法用于计算两相界面的演化过程,拉格朗日粒子追踪法用于追踪雾化液滴.针对雾化过程中既有界面演化又有液雾分布的特点,将两种方法耦合在一起使用,对射流破碎和液滴雾化的完整过程进行了数值模拟.本方法对未完全破碎部分使用界面追踪法,破碎后使用拉格朗日粒子追踪法...     

温度和晶粒尺寸及分布影响下的氧化铝纤维烧结晶粒长大的相场模拟

采用相场法对溶胶凝胶法制备氧化铝纤维的高温烧结中α-Al_2O_3晶粒的生长进行仿真模拟,并结合实验,研究不同烧结温度和不同初始尺寸的α-Al_2O_3晶粒长大行为及动力学规律。相场模拟和实验结果均表明,在1 200～1 500℃烧结温度范围内,晶粒生长速率随烧结温度升高而明显增大,其中1 400～1 500℃温度区间内晶粒生长速率最快;初始晶粒尺寸越细小,晶粒生长速率越快。模拟结果显示,初始α-Al_2O_3晶粒尺寸不均匀性增加也会促进晶粒长大。     

新型镍基粉末高温合金晶粒长大行为研究

对第四代粉末高温合金FGH4108晶粒长大行为进行研究。结果表明，γ′相在完全溶解温度以下固溶处理时，晶粒长大幅度较小，与初始组织差别不大(锻态，3～4μm)；当达到γ′相完全溶解温度时，晶粒发生明显长大；超过γ′相完全溶解温度时，晶粒尺寸大幅增加(30～40μm)，过固溶的几个温度下晶粒尺寸差别不大；保温初期晶粒尺寸显著增加，一定保温时间后晶粒尺寸不再随时间明显变化。温度和时间对晶粒尺寸的影响都与γ′相对晶界迁移的阻碍作用有关，根据温度和时间的影响，对传统晶粒长大模型中界面迁移的表观激活能(Q)、时间指数(n)和广义迁移率常数(A₀)进行修正，构建了新的模型，模型预测值与实验值的决定系数(R²)为0.9997，均方误差为0.12μm，预测精度较高，晶粒长大曲线各项特征能被准确预测出来。     

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.     

Computer simulation of anisotropic grain growth in ceramics

Anisotropic grain growth in ceramics has been simulated by a Monte Carlo computer model. Microstructures, similar to experimental ones, were obtained and the influence of the energy anisotropy and the number of anisotropical grains on microstructure development were studied. It was shown that a single grain with higher energy in one direction, embedded in a matrix of grains with the isotropic boundary energy, grows anisotropically with a nearly constant rate. The growth rate is linearly proportional to the energy anisotropy of the grain. The aspect ratio increases with the cube root of time. Faceted grain boundaries were simulated. Microstructures with less than 50% of anisotropic grains develop, after a short time, a bimodal grain size distribution. At this point, the mean aspect ratio of anisotropic grains reaches a maximum. The heights of the maxima are proportional to the energy anisotropy and inversely proportional to the fraction of anisotropic grains. Weighted aspect ratio distributions and their mean values agree well with experimental data.     

CSP工艺轧制低碳锰钢组织演变模拟

为了选择合适的模型来模拟CSP工艺轧制低碳锰钢的组织变化,首先采用Jonas、Sellars、Saito、Yada等人开发的模型进行模拟,然后采用轧卡试验进行了工业试验验证.轧卡试验和计算结果表明:Jonas模型预测的晶粒尺寸在第一道次较实测值偏小,而在最后几道次较实测值偏大;Yada模型预测值较实测值偏小;Sella...     

Three-dimensional monte carlo simulation of grain growth in zone-refined iron

The evolution of the grain structure and topological-class distributions in zone-refined iron were modeled using a three-dimensional (3-D) Monte Carlo (MC) model. The effect of grain size on topological features was examined. The relationship between the topological features of grains and the geometry of their surrounding grains was studied. In particular, the average number of sides of the grains was related to the average number of sides of their neighbors. Both the computed grain-size distribution and the topological-class distribution were found to be invariant with time. A linear relationship existed between the average grain size and the average number of sides of grains. The number of sides of grains was inversely proportional to the average number of sides of the neighboring grains. The computed average grain size, grain-size distribution, and topological-class distribution agreed well with the corresponding independent experimental data. The results indicate significant promise for understanding grain growth and topological features using 3-D MC simulation.     

H型钢粗轧微观组织演化的数值分析

在ABAQUS软件的基础上,利用基于稳态判断的数值分析流程,构建了对H型材任意轧制道次进行微观组织演化模拟的分析平台。以某中型H型钢11道次热轧过程为研究对象,详细分析了粗轧过程轧件内奥氏体晶粒直径、温度、动态再结晶区域、动态再结晶奥氏体体积分数,以及道次间隙期间晶粒的长大和温度分布情况。     

Microstructural evolution in two-dimensional two-phase polycrystals

In two-dimensional polycrystals composed of α-phase and β-phase grains the stability of ααα, βββ, ααβ and αββ three-grain junctions and αβαβ four-grain junctions depends on the α−α, β−β and α−β interfacial energies. A computer simulation which generates thermodynamically consistent microstructures for arbitrary interfacial energies has been utilized to investigate microstructural evolution in such polycrystals when phase volume is not conserved. Since grain shapes, phase volume, and phase arrangements are dictated by interfacial energies, clustered-, alternating-, isolated-, and single-phase microstructures occur in different interfacial energy regimes. Despite great differences in microstructure, polycrystals which contain only three-grain junctions evolve with normal grain growth kinetics. In contrast, structures containing flexible four-grain junctions eventually stop evolving. We conclude that two-dimensional polycrystals continually evolve when grain junction angles are thermodynamically fixed, while grain growth ultimately ceases when grain junction angles may vary. Predictions concerning three-dimensional and phase-volume conserved systems are made.     

Tube Reversing and Extrusion (TRE) as a Novel Method for Producing UFG Thin Tubes

In the present research, a new severe plastic deformation method has been introduced for producing thin walled tubes with ultrafine grained substructure. The tube reversing and extrusion (TRE) technique was applied to a CP-aluminum and thin walled tubes with ultra-fine grained microstructure were successfully processed. The obtained results from tensile tests at room temperature showed the significant increase in mechanical properties of TRE processed thin walled tubes including yield and ultimate strengths and micro-hardness due to grain refinement. The microstructure evolution and deformation behaviour of commercially pure aluminium under TRE processing was simulated by the constitutive model as a micromechanical approach implemented in the finite element framework. The continuous dynamic recrystallization (the evolution of dislocation density and grain size) of aluminum tubes during TRE was considered as the main grain refinement mechanism in micromechanical constitutive model. Also, the flow stress of material in macroscopic scale was related to microstructure quantities. This was in contrast to the previous approaches in FEM simulations of SPD methods where the microstructure parameters such as grain size were not considered at all. The FEM simulated grain refinement behavior was consistent with the experimentally obtained results.     

Dynamic Recrystallization of Hot Deformed 3Cr2NiMnMo Steel: Modeling and Numerical Simulation

Hot compression tests of 3Cr2NiMnMo steel were performed at temperatures in the range of 850 to 1100 °C and with strain rates of 10^?2s^?1 to 1s^?1. Both the constitutive equations and the hot deformation activation energy were derived from the correlativity of flow stress, strain rate and temperature. The mathematical models of the dynamic recrystallization of 3Cr2NiMnMo steel, which include the dynamic recrystallization kinetics model and the crystallization grain size model, are based on Avrami's law and the results of thermosimulation experiments. By integrating derived dynamic recrystallization models with the thermal-mechanical coupled finite element method, the microstructure evolution in hot compressive deformation was simulated. The distribution of dynamic recrystallization grains and grain sizes were determined through a comparison of the simulation results with the experimental results. The distribution of strain and dynamic recrystallization grain is also discussed. The similarity between the experimental results and the simulated results indicates that the derived dynamic recrystallization models can be applied effectively to predict and analyze the microstructure evolution in hot deformed 3Cr2NiMnMo steel.     

高速线材生产过程组织性能预测模型仿真

 采用计算机对高速线材生产过程进行模拟,开发出具有较高准确度同时具有对不同轧制工艺有较好通用性的高线生产仿真系统。利用有限元方法计算了线材在待轧、轧制、水冷及风冷过程的温度场;通过对再结晶动力学模型的解析,得到了静态再结晶、动态再结晶的分数以及奥氏体晶粒在轧制过程中的变化情况;通过组织演变模型和温度模型的耦合计算,模拟出斯太尔摩风冷线上线材的组织变化过程;建立了利用初始化学成分和组织组成预测高线产品力学性能的BP神经网络模型,通过生产过程数据的训练,实现了对线材力学性能的预测。仿真计算的结果对线材控轧、控冷工艺的改进有一定的指导意义。     

Coupling Thermomechanical and Microstructural FE Analysis in Plate Rolling Process

Using three-dimensional rigid-viscoplastic finite element method （FEM）, a coupling multivariable numerical simulation model for steel plate rolling has been established based on the physical metallurgy microstructural evolution rule and experiential equations. The effects of reduction, deformation temperature, and rolling speed on the deformation parameters and microstructure in plate rolling were investigated using the model. After a typical rolling process of steel plate 16Mn is simulated, the strain, temperature, and microstructure distributions are presented, as well as the ferrite grain transformation during the period of cooling. By comparing the calculated ferrite grain sizes with measured ones, the model is validated.