高合金钢热成形中微观组织演变的位错与缺陷相互作用机制及计算建模

This project chooses nuclear-power large-forgings material X12CrNiMoWVNbN.10.1.1 and high-temperature alloy IN718 as subjects investigated, which play a significant role in national economy development. First, interaction mechanisms between dislocation and microstructures are studied by discrete dislocation dynamics (DDD) and mesoscopic dislocation patterns are simulated by continuum dislocation dynamics (CDD). By converting the interaction rules obtained by DDD into the control parameters used in CDD, an approach of combination of DDD with CDD is put forward. By this proposed method, dislocation motion laws are revealed and dislocation wall splitting mechanism and dislocation cell hierarchical forming mechanism are simulated in the development of dynamic recrystallization during hot deformation. Moreover, the interaction mechanisms between dislocations and grain boundaries, voids, micro-cracks and precipitation phases are uncovered and the effects of grain boundaries, voids, micro-cracks and precipitation phases on hot formability,microstructual evolution and mechanical properties are obtained. The new approach breaks through the dislocation dynamic restriction of only applying in the small scale and small strains, and can be taken on as a through polycrystalline mesoscale dislocation pattern evolution modelling method considering interaction between dislocations and defects. The research results provide a necessary mean for multiscale and whole-process modeling of material forming and optimization of process parameters, which makes process establishment and control of microstructure and property more scientific in practical production.

该项目以在国民经济发展中具有重要地位的核电大锻件材料X12CrNiMoWVNbN.10.1.1和高温合金IN718为研究对象，采用离散位错动力学研究位错与微结构的交互机制，采用连续位错动力学进行位错组态的演化计算，将离散位错动力学得到的规律转化为连续位错动力学所需的控制参数，建立新的离散位错动力学和连续位错动力学相结合的计算方法。通过此方法揭示动态再结晶中的位错墙劈开形成机制和位错胞分级形成机制，阐述位错与晶界、空洞、微裂纹和沉淀强化相的相互作用机制及对材料变形、微观组织演化和性能的影响规律，进行材料热变形过程位错组态演化的模拟和性能预报。新方法突破目前位错动力学局限于小尺度和小应变的限制，可被看作是一套比较完备的考虑位错与缺陷交互作用的多晶工程材料位错组态演变建模方法，为材料成形的多尺度、全流程建模和工艺参数优化提供必要的手段，为生产中的工艺制定和组织性能控制提供依据。

该项目以在国民经济发展中具有重要地位的镍基高温合金为研究对象，采用离散位错动力学研究位错与微结构的交互机制。一方面，针对镍基单晶合金，考虑了位错的受力、位错的运动、模拟区的周期性边界条件、位错与沉淀相的交互作用等，重点讨论了位错穿过沉淀相的行为分析为及双位错在沉淀相中的运动。通过研究沉淀相形状，沉淀相所占体积百分比，沉淀相大小及反向畴界能等因素对性能的影响，定量地揭示了镍基单晶合金的力学性能的变化与微观组织之间的关系。另一方面，临界分切应力是滑移系开动所需的最小切应力，其数值在一定程度上反应了材料抵抗塑性变形的能力，也是多尺度计算的关键。由于材料制备的难度和测量方法的局限，位错动力学是预测临界分切应力较好的方法。基于位错与颗粒的切过机制，采用位错动力学方法建立颗粒强化模型，研究有序强化机制下不同γ’沉淀相体积分数和平均半径、反向畴介能以及位错类型对临界分切应力大小的影响。本项目揭示位错与晶界、和沉淀强化相的相互作用机制及对材料变形、微观组织演化和性能的影响规律，进行材料的性能预报。新方法为材料成形的多尺度、全流程建模和工艺参数优化提供必要的手段，为生产中的工艺制定和组织性能控制提供依据。