Dynamic tensile behavior and spall fracture of GP1 stainless steel processed by selective laser melting
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摘要: 采用选择性激光熔化增材制造技术，制备了GP1不锈钢单轴拉伸板条试样和层裂圆片试样，并对材料微观结构进行了表征。借助Zwick-HTM5020 高速拉伸试验机，并结合数字图像相关性全场应变测量技术，开展了增材制造GP1不锈钢材料的轴向拉伸力学性能实验研究，得到了不同应变率下材料的拉伸应力-应变曲线，结果显示：(1) GP1不锈钢流动应力具有比较显著的应变强化效应；(2)通过回收试样的电子背散射衍射表征，发现GP1不锈钢在拉伸变形过程中会发生奥氏体与马氏体之间的相变；(3) GP1不锈钢的屈服应力随着应变率呈幂指数增大，断裂应变在中低应变率下保持不变，但在高应变率下则显著减小。采用一级轻气炮实验装置和激光干涉粒子速度测量技术，开展了增材制造GP1不锈钢的层裂实验，发现GP1不锈钢的层裂强度随着飞片撞击速度增大而减小。单轴拉伸试样断口和层裂试样断口的显微分析结果表明：随着应变率增大，单轴拉伸断裂模式和断裂机理都发生了转变；层裂损伤易成核于激光熔池边界线的交汇处，断口韧窝形貌明显区别于单向拉伸断口。
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关键词:
- 增材制造GP1不锈钢 /
- 单轴拉伸 /
- 应变率 /
- 层裂
Abstract: Samples for uniaxial tension and spallation experiments of GP1 stainless steel were produced by selective laser melting (SLM). The microstructure of SLM GP1 was characterized by using the optical metallography and electron-backscatter diffraction (EBSD). The tensile mechanical behavior of SLM GP1 as a function of strain rate was studied by using a Zwick-HTM5020 high-speed tensile testing machine and the digital image correlation (DIC) full-field strain measurement method. Significant austenite-to-martensite phase transformation was observed during tensile loading with accompanied plastic strain hardening. Yield stress increases exponentially with strain rate, but at high strain rates (40 and 600 s−1), the yield stress rapidly increases, while the fracture strain decreases significantly. The spallation response of SLM GP1 was investigated by using plate impact experiments. Based on the free-surface particle velocity profiles measured by a displacement interferometer system for any reflector (DISAR), the spall strength of SLM GP1 was found to decrease with increasing flyer impact velocity. Fractography revealed the variation of the fracture mode and fracture mechanism of SLM GP1 as a function of strain rate. Damage nucleates easily at the intersection of the laser melting pool boundary line and grows along the laser pool boundary line. Fracture dimple morphology of the spalled samples is obviously different from that of the samples under the uniaxial tensile loading.-
Key words:
- SLM GP1 stainless steel /
- uniaxial tension /
- strain rate /
- spallation
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图 1 GP1不锈钢粉末扫描电子显微镜形貌
Figure 1. Scanning electron microscope morphology of GP1 stainless steel powder
图 3 试样设计尺寸、成型后试样照片以及成型工艺过程示意图
Figure 3. Sample design dimension, sample photograph after moulding and schematic diagram of moulding process
图 4 激光选区熔化法制备的GP1不锈钢光学显微结构
Figure 4. Optical images of GP1 stainless steel processed by selective laser melting
图 5 激光选区熔化法制备的GP1不锈钢显微结构的电子背散射衍射表征
Figure 5. Electron backscattered diffraction images of GP1 stainless steel processed by selective laser melting
图 6 HTM-5020高速拉伸材料试验机、试样夹具及试样散斑图
Figure 6. HTM-5020 high-speed machine, sample fixture, and speckle image of specimen
图 7 应变片粘贴在GP1不锈钢试样的位置
Figure 7. Position of strain gauge pasted on GP1 stainless steel specimen
图 9 闭环控制时力与速度时程曲线
Figure 9. Force and velocity profiles under closed loading control mode
图 12 不同时刻的GP1不锈钢试样标距段应变分布云图(应变率为10−2 s−1)
Figure 12. Strain distributions of GP1 stainless sample at different times (strain rate is 10−2 s−1)
图 13 不同应变率下GP1不锈钢的真实应力-应变曲线
Figure 13. True stress-true strain curves of GP1 stainless steel at different strain rates
图 14 GP1不锈钢中奥氏体和马氏体体积分数电子背散射衍射表征(黄色代表奥氏体，红色代表马氏体)
Figure 14. Electron backscattered diffraction characterizations of volume fraction for austenite and martensite in GP1 stainless steel (yellow represents austenite, red represents martensite)
图 15 GP1不锈钢屈服应力随着应变率的变化曲线
Figure 15. Yield stress variation of GP1 stainless steel with strain rate
图 16 不同初始速度下GP1不锈钢的自由面速度剖面
Figure 16. Free-surface velocity profiles of GP1 stainless steel at different initial velocities
图 17 不同应变率下GP1不锈钢的宏观断口以及微观形貌
Figure 17. Macro-fracture and micro-morphology of GP1 stainless steel at different strain rates
图 20 GP1不锈钢层裂断口微观形貌
Figure 20. Micrographs of ductile fractures in GP1 stainless steel spallation
表 1 一维应变平板撞击实验结果
Table 1. Results of one-dimensional strain plane impact test
实验编号 初始速度/(m·s−1) Δu/(m·s−1) σHEL/GPa σy/GPa σs/GPa 1 250 176.23 1.78 1.01 3.91 2 270 174.97 1.79 1.02 3.88 3 350 169.99 1.85 1.05 3.76 
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