高速冲击表面处理对金属材料力学性能和组织结构的影响

高速冲击表面处理过程中的应变率对金属材料的宏观力学性能和微观组织结构都具有重要影响。根据当前应变率效应的研究成果，从宏观与微观相结合的角度出发，综述了高速冲击表面处理过程中应变率对金属材料强度和塑性的影响规律，并重点阐述了不同应变率下金属材料内部微观组织结构的演变规律，主要包括晶粒结构、绝热剪切带、相变、位错组态和析出相以及变形孪晶等。此外，还分析了组织结构随应变率的演化和微观变形机制的转变对材料力学性能的强化和弱化机理。最后，对高速冲击表面处理梯度组织的变形特点进行了总结。提出了不同组织结构对材料性能影响的综合效应模型，以期为应变率效应的深入研究奠定基础。

A review on the influences of high speed impact surface treatments on mechanical properties and microstructures of metallic materials

The strain rate during the process of high speed impact surface treatments has a significant effect on the mechanical properties as well as the microstructures of metallic materials. In this paper, the effects of strain rate during the process of high speed impact surface treatments on the variation of both strength and ductility of metallic materials are reviewed from macroscopic and microscopic prospective based on the current research achievements. The emphases are concentrated on the microstructural evolution under various strain rates, including grain structures, adiabatic shear bands, phases, dislocation structures, precipitates and deformation twins. At relatively low strain rates, grains tend to be elongated with respect to the loading direction, and they may be refined when the strain increases to a certain extent. In comparison, with the increment of strain rates, the free path of dislocation motion is remarkably reduced so that grains can be further refined to consume the impact energy and dislocations are multiplied significantly. However, the relatively high strain rates may also bring about adiabatic temperature rise and frictional heat, which may give rise to dynamic recovery and recrystallization in some materials so that the dislocation density would in turn be reduced. Moreover, precipitates can be formed and they may interact with dislocations owing to the combined effects of high strain rates and temperature rise. When the strain rates increase to the extremely high level, the movement of dislocations may be inhibited and deformation twins can be triggered to coordinate the deformation. As a result, the strain rate effects are complicated phenomena which comprehensively affect the microstructural strengthening and softening effects. Based on these, the influences of both microstructural evolution and the transition of microscopic deformation mechanisms with strain rates on the enhancement and deterioration of mechanical properties are analyzed. Finally, the characteristics of deformation mechanisms of the gradient microstructures derived from high velocity impact surface treatments are concluded. Furthermore, a comprehensive model embodying the influences of different microstructures is proposed, which can provide a foundation for the further researches of strain rate effects.