双相高强钢FeNiAlC的动态剪切行为及微结构机理

绝热剪切带是金属材料在高应变率载荷下常见的一种失效模式。利用霍普金森压杆装置，对双相钢Fe-24.86Ni-5.8Al-0.38C不同微结构的帽形样品施加冲击载荷，研究它的动态剪切变形行为及微结构机理。先通过对固熔处理得到的粗晶态样品进行大应变冷轧获得冷轧态样品，再使用透射电子显微镜和扫描电子显微镜表征两种样品冲击前后微结构的变化差异。结果表明，双相钢FeNiAlC拥有较优异的动态剪切性能，剪切强度达1.3 GPa，均匀剪切应变达1.5。变形前，材料由奥氏体相和马氏体相构成，马氏体体积分数约为20%。变形过程由位错滑移和孪生变形主导，但因应变速率较高致使马氏体相变被抑制。不同微结构样品内均形成绝热剪切带，带内发生动态再结晶，形成超细晶粒，平均晶粒尺寸约300 nm，且剪切带内不发生相变；冷轧态剪切带宽度的实验值（14.6 μm）与理论计算值(12.3 μm)较好吻合，而粗晶态剪切带宽度的实验值（14.6 μm）与理论计算值（30 μm）相差甚远，初步分析可能是因为粗晶态样品应变较大基本不满足完全绝热的理论条件。在变形过程中，粗晶态因塑性变形做功产生的绝热温升高达720 K，而冷轧态的只有190 K。通过实验结果与热塑模型分析，得出绝热温升不是形成绝热剪切带的唯一因素，而应考虑材料的微观结构和局部化变形等的共同影响。

Dynamic shear behaviors and microstructural deformation mechanisms in FeNiAlC dual-phase high strength alloy

Adiabatic shear band (ASB) is a common failure mechanism of metals and alloys under high strain rate dynamic loading. The hat-shaped samples of Fe-24.86Ni-5.8Al-0.38C dual-phase steel with different microstructures were impacted by the Hopkinson pressure bar device to investigate their dynamic shear behaviors and microstructural deformation mechanisms. The coarse grained (CG) structure after solution treatment was subjected to cold rolling (CR) in order to obtain various microstructures. The evolution of microstructure during dynamic shear deformation was extensively studied using transmission electron microscopy (TEM) and scanning electron microscope (SEM). The results revealed that the FeNiAlC dual-phase steel has excellent dynamic shear properties with dynamic shear strength of 1.3 GPa and uniform dynamic shear strain of 1.5. The dual-phase steel was found to be composed of austenite phase (γ) and around 20% martensite phase (α) before deformation. The deformation process was found to be dominated by dislocations slip and twinning. Moreover, martensite transformation was found to be suppressed due to the high strain rates. ASBs were observed to be formed in all samples with various microstructures after impact, and dynamic recrystallization was found to occur with formed ultra-fined grains of about 300 nm and without transformation in ASBs. For the width of ASBs, the theoretical result (about 12.3 μm) was found to be in good agreement with the experimental value (about 14.6 μm) in CR samples. However, the measured width of ASBs was found to be about 15.8 μm, which is far smaller to the calculated value (about 30 μm) in CG samples. This may be attributed to the incompletely adiabatic conditions in CG samples. The adiabatic temperature rise due to the plastic work was found to be about 720 K (for CG sample) and 190 K (for CR sample). Through the analysis of the experimental results and the theory of the thermoplastic model, it can be concluded that the adiabatic temperature rise is not the only factor for ASB formation in the course of impact loading, and the localized deformation induced microstructure evolution in materials should also be considered.