Dynamic Plastic Flow Behavior Of High-Entropy Alloys

In recent years,researchers have pioneered a new method of designing alloys with nearly equal atomic ratios of multiple components.And they have prepared a variety of chemically disordered and topologically ordered high-entropy alloys.Due to their excellent physical and mechanical properties,high-entropy alloys have shown great potential in national defense engineering,energy,aerospace,and other fields.High-entropy alloys inevitably face the challenge of shock loads in the service environment of practical applications.However,the mechanical behavior and micromesoscopic deformation mechanism of high-entropy alloys under high strain rate and cryogenic temperature are still unclear.To make up for the lack of relevant research,this paper studied the dynamic plastic flow behavior of high-entropy alloys by various improved Hopkinson tensile bar dynamic test techniques.The dynamic tensile testing of CrMnFeCoNi high-entropy alloys is performed using a split Hopkinson tensile bar(SHTB)setup equipped with high-speed photography.The deformation process of the sample surface is captured in real-time,and its strain field distribution is analyzed.The multi-scale microstructure and morphology characterization of the material was carried out,and the electron backscatter diffraction(EBSD)experiments were performed on samples with.different strains.We quantified the dislocation density and twinning integral of the material.We revealed the evolution law of the alloy microstructure and establish a hot-viscoplastic constitutive model based on it.The constituti ve model described the hardening mechanism related to the strain rate of the CrMnFeCoNi high-entropy alloy.The split Hopkinson tensile bar is improved to expand the single-pulse loading method.The CrMnFeCoNi high-entropy alloy samples were subjected to singlepulse low-temperature dynamic tensile loading with different pulse widths and the same amplitude.The quasi-static low-temperature tensile deformation interruption experiment was carried out.The EBSD experiments were performed on all collected samples to characterize and analyze the microstructural evolution of the materials quantitatively.Based on the previous constitutive model,the temperature-dependent hardening mechanism of CrMnFeCoNi high-entropy alloys and the effects of temperature and strain rate on the microstructure evolution are analyzed and discussed.Based on the above results,we established finite element models of CrMnFeCoNi high-entropy alloys quasi-static and dynamic tensile samples.A series of quasi-static and dynamic tensile finite element simulation experiments were planned using the Box-Behnken design method.We established a prediction model of damage parameters,and obtained the damage parameters of the alloy under different tensile conditions at different temperatures and strain rates.The temperature dependent and strain rate dependent behaviors of the damage parameters of highentropy alloys are revealed.The wire is one possible application for high-entropy alloys.In order to explore the dynamic mechanical behavior of high-entropy alloy wires,this paper have independently designed three types of fixtures for Hopkinson tensile bar,which are suitable for 1 mm high-strength low-plastic alloy wire,0.5mm and below thin alloy wire,and 1mm high-plastic alloy wire,respectively.We introduced data correction methods of dynamic tensile test and low-temperature dynamic test of alloy wire.This paper focuses on the dynamic tensile mechanical behavior of CoCrNi mediumentropy alloy wire at room temperature and 77K.We characterized the microstructure of the deformed wires,and discuss the effect of the microscopic deformation mechanism of the alloy wires on the properties.