Effects of Shock Peak Stress and Pulse Duration on Spall Damage of NbTiZr Medium-Entropy Alloy
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摘要: 中、高熵合金因很好地兼顾了强度和韧性而备受关注,在多种极端工况下具有重要的应用前景。然而,在强冲击载荷等极端条件下,其动态力学行为和损伤失效机制仍不清楚。为此,研究了NbTiZr中熵合金在平板冲击载荷下的层裂损伤,探讨了冲击应力和加载脉宽的影响。通过波剖面分析,获得了冲击应力、加载脉宽和层裂强度信息。研究表明,NbTiZr中熵合金的层裂强度随冲击应力的增大而线性增大,随加载脉冲宽度的增大呈指数减小,介于3.77~4.80 GPa之间。利用光学显微镜、扫描电子显微镜和电子背散射衍射,分析了冲击加载后回收样品的微观组织结构,发现冲击应力和加载脉冲宽度对NbTiZr的层裂损伤形貌有显著影响,层裂损伤形式为准解理断裂,未观察到固-固相变或变形孪晶。Abstract: Dynamic mechanical behaviors of high entropy alloys (HEAs) or medium-entropy alloys (MEAs) have attracted significant attention due to their exceptional strength-toughness balance and promising potential applications in extreme conditions. This work investigates the effects of peak shock stress and pulse duration on the spall damage of the NbTiZr MEA under dynamic shock loading. Peak shock stresses, pulse durations and spall strengths are determined by analyzing free surface velocity profiles, with postmortem microstructural analysis to reveal the underlying deformation and failure mechanisms. The measured spall strength of NbTiZr MEA ranges from 3.77 GPa to 4.80 GPa, showing minimal dependence on the peak shock stress but high sensitivity to the pulse duration. Furthermore, the damage morphologies are significantly influenced by pulse durations. The damage is recognized as a quasi-cleavage fracture mode. No phase transition or deformation twins are observed within the recovered NbTiZr alloy.
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Key words:
- NbTiZr /
- spall damage /
- shock loading history /
- microstructure
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图 4 平板冲击实验得到的回收样品的OM图像:(a)~(d) 不同冲击应力下的层裂损伤形貌,(e)~(f) 不同加载脉冲宽度下的层裂损伤形貌,(g) 沿冲击方向的损伤度分布统计(Shot A4除外),(h) 不同加载脉冲宽度下层裂损伤的伸长率指数与孔洞及裂纹等效尺寸的关系
Figure 4. Optical graphs of the recovered samples and damage degree analysis: (a)−(d) damage of samples for different peak stresses, and (e)−(f) damage of samples for different pulse durations; (g) damage degree distributions along the impact direction for all shots except Shot A4; (h) elongation index as a function of equivalent diameter of voids and cracks with different pulse durations
图 5 回收样品层裂损伤的SEM图像:(a)~(c) Shot A1的回收样品,(d) Shot B1的回收样品,(e) Shot A4的回收样品层裂面断口形貌,(f) 图5(e)红框区域的局部放大图像(冲击方向为y轴)
Figure 5. SEM images of damage in the spallation region: (a)−(c) recovered sample in Shot A1, (d) recovered sample in Shot B1, (e) fracture morphology of the spall plane of the recovered sample in Shot A4, (f) magnified view of the region indicated by the red rectangle in Fig.5(e) (The impact direction is the y-axis.)
表 1 不同冲击应力和脉宽加载条件下的层裂实验参数和实验结果
Table 1. Experimental parameters and results for different impact stresses and pulse durations
Shot No. uimp/(m·s−1) σH/GPa Lf/mm Ls/mm τ/μs Δu/(m·s−1) σsp/GPa ${ \dot{\varepsilon }} $/(105 s−1) ar/(107 m·s−2) A1 325 4.64 0.92 1.79 0.19 257.5 3.77 3.11 5.08 A2 400 5.68 0.90 1.82 0.17 262.1 3.84 3.10 11.17 A3 493 7.00 0.91 1.81 0.17 281.0 4.13 3.08 29.92 A4 680 9.34 0.91 1.78 0.20 273.9 4.01 3.32 33.55 B1 487 6.86 0.56 1.80 0.07 328.0 4.80 4.61 59.77 B2 480 6.89 1.15 1.83 0.28 258.5 3.78 2.86 24.02 -
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