镍基合金大应变量热塑成形过程的变形机制研究及模型建立

随着热变形应变量的增大，镍基合金在某些变形条件下表现出变形抗力和组织的波动，而非传统理论中的流变稳态。该现象会对一些涉及大应变量变形的镍基合金热加工过程产生较大影响。然而，现阶段针对镍基合金的大变形，普遍套用钢铁材料的相关理论，默认大应变量条件下稳态的存在，而并未对镍基合金的特殊性进行深入研究。针对此问题，本项目将围绕镍基合金的大应变量热变形行为进行研究。分析镍基合金热加工过程中硬化、动态回复和动态再结晶机制，以低回复加工硬化和多轮动态再结晶为突破口，建立综合微观参数（位错密度、孪晶比例），物理参数（表观激活能、层错能）和工艺参数（变形温度、应变速率）的物理模型。在机制研究的基础上，构建描述镍基合金多轮次动态再结晶比例、晶粒尺寸变化的组织演化模型和变形抗力的计算模型（工程性模型）。本项目可望对金属热变形理论的发展提供实验和理论基础，其工程化模型可以直接指导镍基合金的实际生产。

Nickel-base alloys exhibit both stress and microstructure oscillations in particular deformation conditions during hot working when true strain gets larger, instead of "steady state" in classical theory. This phenomenon may deeply affect the hot working process with large strain for nickel-base alloys. However, the hot deformation theories of steel were used indiscriminately, which predicts equilibrium for both flow stress and microstructure. Few investigations were carried out for the specialty of nickel-base alloys. To solve the above problem, this projects will studied the hot deformation behaviors for nickel-base alloys in large strain conditions. Work hardening, dynamic recovery and dynamic recrystallization in hot working will be analyzed for this type of alloys. Physical models are established with key points of low-recovery-hardening and cyclic dynamic recrystallization. The models may contain micro-parameters (dislocation density and twin ratio), physical-parameters (activation energy and stacking fault energy) and process-parameters (temperature and strain rate). On the base of mechanism research, engineering models of dynamic recrystallization fraction and grain size will be constructed for cyclic recrystallization. Furthermore, prediction of flow stress may also be involved for high strain stage. This project is expected to be the experimental and theoretical basis for the development of metal thermal deformation theory. Engineering models may provide direct guidance for the actual production of nickel-base alloy components.