Mechanical behavior and microstructure evolution of deep gradient structural steel under dynamic impact
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摘要: 为探究梯度结构在动态条件下的力学行为,本文采用循环扭转方法在低碳钢中制备了深层梯度结构,并对其在宽应变率范围内(10−4~103 s−1)进行压缩实验与微结构演变分析。结果表明,梯度结构提升了低碳钢的屈服强度,并且表现出显著的应变率敏感性。此外,梯度程度会对变形机制产生影响:梯度程度较大的样品在变形过程中主要消耗中心软域的加工硬化能力,而边缘区域的硬化效果减弱,在动态条件下由于绝热温升效应,导致边缘硬域的位错密度反而降低。Abstract: The gradient structure (GS) has superior strength-ductility synergy due to its unique design strategy. This synergistic effect is mainly attributed to the heterogeneous deformation induced (HDI) strengthening caused by plastic strain gradient. The quasi-static mechanical behavior of gradient structures has been extensively revealed, but research on their mechanical property under dynamic conditions is almost blank, and the mechanical behavior of gradient structures under dynamic impact is not clear, which limits the application scope of gradient structures. Based on the above background, a series of experiments were conducted to reveal the mechanical response and deformation mechanism of gradient structures under dynamic conditions. Firstly, two gradient structures with different gradient layer thicknesses were prepared using the cyclic torsion method. The cyclic torsion process involved 150 cycles of 10° (GS1) and 50 cycles of 20° (GS2), respectively. Then, the compression tests were conducted under a wide strain rate range (10−4−103 /s). Finally, electron backscatter diffraction (EBSD) was used to characterize the microstructure in detail. The results indicate that the gradient structure significantly improves the yield strength of low carbon steel. At a strain rate of 0.001 /s, the yield strengths of GS1 and GS2 samples were 407.5 and 483.6 MPa, respectively. Compared to the initial state (203.2 MPa), the yield strengths increased by 100.5% and 137.9%, respectively. Moreover, as the strain rate increases, the yield strength also gradually increases, exhibiting significant sensitivity to positive strain rate. Under dynamic conditions, the strain rate sensitivity of GS1 and GS2 samples increases sharply, reaching 0.129 and
0.1097 , respectively, which is almost an order of magnitude higher than quasi-static conditions. In addition, the degree of gradient will have an impact on the deformation mechanism: samples with a higher degree of gradient mainly consume the work hardening ability of the central soft domain during the deformation process, while the hardening effect of the edge region is weakened. Under dynamic conditions, due to the adiabatic temperature rise effect, the dislocation density of the edge hard domain is actually reduced. This result deeply reveals the mechanical response and deformation mechanism related to strain rate in heterogeneous regions of gradient structures. On the one hand, it provides reference for the design of gradient structures, and on the other hand, it provides theoretical value for the future application of gradient structures in extreme service environments such as dynamic impact.-
Key words:
- gradient structure /
- dynamic compression /
- strain rate effect /
- deformation mechanism
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表 1 Z-A模型的拟合参数
Table 1. The fitted parameters of Z-A model
样品 $ \sigma _{0}^{*} $/MPa $ {\beta }_{0} $/K−1 $ {\beta }_{1} $/K−1 $ c $/s 初始态 610.1 0.0030 2.68×10−4 3.11×10−4 GS1 793.2 0.0021 1.22×10−4 3.15×10−4 GS2 841.6 0.0019 8.90×10−5 3.23×10−4 -
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