【作者】 禹宝军；

【导师】 关小军；

【作者基本信息】 山东大学 ， 材料加工工程， 2012， 博士

【摘要】 随着材料科学和计算机仿真技术的发展,材料制备科学正从传统的正向研究向逆向研究过渡：从材料的组分、微观组织结构出发,借助计算机模拟来设计工艺和预测材料性能,以便生产满足使用要求的材料。材料中存在的第二相粒子主要是加入合金元素以改善性能的产物。其中,随着合金化和控轧控冷技术的普遍应用,性能优越的合金钢和微合金钢不断得到开发和应用。这两类钢在热塑性变形过程中往往会形成一定数量和尺寸的第二相粒子,进而导致了它们的动态再结晶行为及其相应的微观组织变化,在很大程度上决定了最终钢材产品的组织结构和力学性能。元胞自动机(cellular automata,简称CA)模型是近年来发展起来的一种材料组织模拟模型,其算法结构简单、计算效率高,可直接考察体系局部交互作用及其产生的复杂行为对模拟系统的影响,在材料晶粒长大、静态再结晶和动态再结晶模拟中得到了成功应用。但是,在二相粒子材料动态再结晶行为模拟中的应用还未及时开展,特别是考虑位错密度非均匀分布的模拟模型也未见报道。构建含有第二相的材料动态再结晶CA模型不仅可以实现变形温度、应变速率、初始晶粒尺寸、非均匀变形、第二相粒子尺寸和体积分数等参数对流变应力、再结晶体积分数、稳态平均晶粒尺寸等动态再结晶表征参数影响的模拟研究,为更好地认识和控制热塑性变形组织以优化热塑性变形工艺提供指导,而且进一步挖掘了CA模型的潜力,拓展了其应用范围。因此,及时展开二相粒子材料动态再结晶CA建模、模拟技术开发及其模拟研究具有重要的理论和实际意义。本文依据CA法、金属材料热变形物理冶金相关理论和相关实验结果,建立了位错密度均匀分布及位错密度非均匀分布的单相材料动态再结晶CA模型,随后引入第二相粒子的影响,创建了位错密度非均匀分布的二相粒子材料动态再结晶CA模型；自主开发了相关动态再结晶模拟的关键技术；采用Visual Fortran语言编制上述模型的应用程序,并通过系统的模拟研究和相关的实验研究对所建模型及其模拟关键技术的合理性和应用效果进行了检验。首先,依据热变形物理冶金学原理,在变形均匀和位错密度均匀分布的假设前提下,建立了具有可靠物理机制的单相材料元胞自动机模型及其模拟算法,进行了相应的应用程序开发,并且以无氧高导电性铜(OFHC)为例,成功地模拟和解释了动态再结晶应力-应变曲线单峰／多峰现象。其次,考虑了材料热塑性变形时晶粒尺寸、晶界和局部缺陷等对位错运动及其分布的影响机制,提出了位错密度非均匀分布模型,并据其建立了新的单相材料动态再结晶CA模型。对相同变形条件下HPS485wf钢的动态再结晶仿真结果比较表明,新模型较原模型更有效地模拟了动态再结晶过程,位错密度非均匀模型更接近实际。应用新模型全面、合理地模拟和探讨了单一变形参数对HPS485wf钢动态再结晶行为的影响规律。然后,根据细小弥散的第二相粒子和大尺寸的第二相粒子对动态再结晶行为的影响机制,在新的单相材料动态再结晶CA模型的基础上,创建了位错密度非均匀分布的二相粒子材料动态再结晶CA模型。该模型综合考虑了第二相粒子对位错密度累积、动态再结晶形核及再结晶晶粒长大的影响,模拟结果较好地反映了第二相尺寸、体积分数及动态析出对动态再结晶组织演变、动力学的影响规律,且经受了相关实验和理论的有效检验。最后,为了验证本文创建的二相粒子材料动态再结晶CA模型的合理性及其应用效果,以典型二相粒子材料Q420qE钢为研究对象,进行了动态再结晶过程的热模拟实验研究；采用这一模型模拟了该钢的动态再结晶过程,并与热模拟实验相应结果进行了对比。结果表明：本文所建模型较准确地模拟了该钢动态再结晶形核位置、动态再结晶晶粒长大组织及动态再结晶完成时的微观组织；模拟的动态再结晶力学、动力学变化规律及变形参数对动态再结晶行为的影响规律与相关理论及热模拟实验结果相符合；同时,由于模型假设和实验精度等的影响,动态再结晶速度模拟值与实际值之间存在一定误差,进一步完善该模型有助于提高模拟精度从而提升其实际应用价值。更多还原

【Abstract】 Along with the development of materials science and computer simulation technology, materials fabrication science is changing from traditional design manner to its reverse one. By the aid of computer simulation, material properties can be predicted based on the components and microstructures, and the optimum manufacturing technology can be determined to produce materials which can satisfy the actual requirements.The second phase particles are the products to improve materials performance by adding alloy elements. With the application of alloying technology and controlled rolling and controlled cooling technology, alloyed and microalloyed steels with high performance are widely developed. The precipitation of second phase particles will occur during thermo-mechanical working of this kind of steels. The effects of these precipitated second phase particles on dynamic recrystallization behavior and corresponding microstructure evolution largely determine the microstructures and mechanical properties of the final product.Cellular automata (CA) model, which is of simplity, short run time and can directly investigate the local interaction and its influence, has been successfully used in the simulation of grain growth, static recrystallization and dynamic recrystallization in recent years. However, it is has not been applied in the simulation of dynamic recrystallization for hot deforming materials with second phase particles. Establishing dynamic recrystallization CA model for hot deformation materials with second phase particles can not only investigate the effects of deformation temperature, strain rate, initial grain size, heterogeneous deformation and the volume fraction and size of second phase particles on flow stress, recrystallization volume fraction and steady state mean grain size of dynamic recrstallization to understand and control the microstructure evolutions of hot deformation materials, in order to provide guidance for hot deformation technology optimization, but also extend the range of application for CA model. Therefore, it is of theoretical and practical significance to carry out the modeling and simulation research of dynamic recrystallization CA model for materials with second phase particles.In the present thesis, based on the CA model and metallurgical principles of hot deformation, dynamic recrystallization CA models with homogeneous distributed dislocation model and heterogeneous distributed dislocation model for single phase materials were established, respectively. On the basis of the two models, dynamic recrystallization CA model for materials with second phase particles was proposed. According to the CA models and the corresponding key technologies of dynamic recrystallization simulation, applications were written in the Visual Fortran6programming language. Related research on simulation and experiment of dynamic recrystallization were employed to verify the rationality of the CA models.Firstly, under the homogeneous deformation and homogeneous dislocation distribution hypothesis, based on the metallurgical principles of hot deformation, the dynamic recrystallization CA model with dependable physical mechanism for single phase materials was constructed and corresponding application was developed..Taking oxygen-free high-conductivity copper (OFHC) for example, the single peak/multiple peak phenomenon of stress-strain curves for dynamic recrystallization was successfully represented and explained.Secondly, taking consideration of the effects of grain size, grain boundary and local defect on dislocation movement and distribution, a new mesoscopic heterogeneous distributed dislocation model was established and dynamic recrystallization CA model with this heterogeneous distributed dislocation model for single phase materials was established. Compared with the homogeneous distributed dislocation model, the heterogeneous distributed dislocation model could simulate dynamic recrystallization more effectively. Then, the impact of deformation parameters on dynamic recrystallization of HPS485wf steel was simulated and discussed by using the heterogeneous distributed dislocation model.Then, according to the different acting mechanism of small and large second phase particles on dynamic recrystallization behavior, base on dynamic recrystallization CA model with heterogeneous distributed dislocation model for single phase materials, dynamic recrystallization CA model with heterogeneous distributed dislocation model for materials with second phase particles was constructed. In this model, the influence of second phase particles on dislocation accumulation, dynamic recrystallization nucleation and growth of recrystallized grain was considered. The simulated results are in good agreement with related theory and experiment results.To verify the rationality and application effect of dynamic recrystallization CA model for materials with second phase particles, experimental researches on hot compressive dynamic recrystallization behavior of Q420qE steel were carried out. Then, the CA model was applied to simulate the dynamic recrystallization of Q420qE steel. The comparison of simulated and experimental results indicates that the nucleation site, recrystallized microstructure and steady state microstructure can be accurately simulated by the CA model. Simulated dynamic recrystallization mechanics, kinetics rules and the effects of deformation parameters on dynamic recrystallization behavior are in agreement with related dynamic recrystallization theory and experimental results. Meanwhile, there is certain error between simulated and experimental dynamic recrystallization rate because of the hypothesis of CA model and the precision of experiment. To perfect the model further is helpful to improve its simulation accuracy and practical application.更多还原