脉冲电流对316L不锈钢拉伸性能和微观组织的影响

EFFECT OF ELECTROPULSING ON TENSILE PROPERTIES AND MICROSTRUCTURES OF 316L STAINLESS STEEL

曾志

11849227

硕士

机械工程

王帅

2020-06-04

2020-07-20

哈尔滨工业大学

深圳

脉冲电流能够改变金属材料的力学性能，通常表现为流变应力降低、延伸率增加。这种现象叫做电塑性效应。但目前对于电流影响材料性能的作用机理仍然充满了争论。材料的种类、电参数的改变都会使得材料的变形行为发生改变，这影响了电辅助加工技术的应用与推广。对内在作用机理的研究离不开材料的微观表征。由于316L不锈钢的应用广泛，关于它的研究成果丰富，且位错结构易于观察。因此本文选用316L不锈钢作为研究对象，采用电辅助拉伸装置进行了拉伸实验，探讨了脉冲电流的作用机理。在实验开始前，为了得到均匀而稀疏的位错组织，对材料进行了固溶处理。热处理结束后分别进行常温无电拉伸实验和通电拉伸试验。研究了不同的电流参数和应变速率对316L不锈钢力学性能的改变。实验发现，脉冲电流对于316L不锈钢的强度和延伸率有显著的影响，电压和频率越大，强度和延伸率下降得越明显，表现出与电塑性效应相异的实验结果。同时，随着电压和频率的增大，应变硬化指数呈现出下降的趋势，表明材料的均匀变形能力减弱。在无电流作用和有电流作用的两种情况下，应变速率对于316L不锈钢强度和延伸率的影响都非常小。同时，在有无通电的两种情况下，应变硬化指数随着应变速率的增加先增大后降低。应变速率为10-3 s-1时，应变硬化指数最大。拉伸实验结束后样品进行了断口观察、金相组织观察和位错表征。利用扫描电子显微镜，发现材料在脉冲电流的作用下，断口表面起伏变大，韧窝数量减小，出现了光滑的剪切面，断裂方式从韧性断裂转变为准解理断裂。通过金相组织观察发现，晶粒变形严重。当固定电压为30 V，频率在600 Hz以上时，发生了动态再结晶现象。当固定频率为200 Hz，升高电压没有发现动态再结晶。通过透射电子显微镜的观察，发现材料的位错密度和孪晶密度随着电压的增大而逐渐增大，从而呈现出与高温拉伸时不同的规律。脉冲电流的作用促进了位错的演化过程。

Pulsed current can change the mechanical properties of metallic materials, usually manifested as reduced flow stress and increased elongation. This phenomenon is called the electroplastic effect. However, at present, the mechanism of the effect of current on the materials’ performance is still full of controversy. Changes in the type of materials and electrical parameters will change the deformation behavior of the material, which affects the application and promotion of electrically-assisted processing technology. The study of the internal mechanism is inseparable from the microscopic characterization of materials. Due to the wide application of 316L stainless steel, the research results on it are rich, and the dislocation structure is easy to observe. Therefore, this article selects 316L stainless steel as the research object, and uses an electric auxiliary device to carry out the tensile tests, and discusses the mechanism of the pulse current.Before the experiments, the samples were solution treated in order to obtain a uniform and sparse dislocation structure. After the heat treatment, the tensile tests with and without application of electricity were carried out respectively. The changes of mechanical properties of 316L stainless steel with different current parameters and strain rates were studied. The results showed that the pulse current had a significant effect on the ultimate strength and the strain-to-failure of 316L stainless steel. The greater the voltage and frequency, the more obvious the decrease in ultimate strength and strain-to-failure. The results were different from the electroplastic effect. At the same time, as the voltage and frequency increase, the strain hardening exponent showed a downward trend, indicating that the uniform deformation ability of the material decreases. In both cases of without and with the application of current, the effect of strain rate on the ultimate strength and the strain-to-failure of 316L stainless steel was very small. At the same time, in both cases, the strain hardening exponent increased first and then decreased as the strain rate increased. When the strain rate was 10-3 s-1, the strain hardening exponent was the largest.After the tensile experiment, the fracture surface observation, metallographic observation and dislocation characterization of the samples were performed respectively. Using scanning electron microscopy, it was found that under the action of pulse current, the surface of the fracture became more undulating, the number of dimples decreased, and a smooth shear surface appeared. The fracture mode changed from ductile fracture to quasi-cleavage fracture. Through metallographic observation, it was found that the grain underwent severe deformation. When the fixed voltage is 30 V and the frequency is above 600 Hz, dynamic recrystallization occurs. When the fixed frequency is 200 Hz, no dynamic recrystallization is found at elevated voltage. Through the observation of transmission electron microscope, it was found that the dislocation density and twinning density of the material gradually increased with the increase of voltage, and thus showed a different rule from that at high temperature. The effect of pulse current promotes the evolution of dislocations.

AISI316L不锈钢 脉冲电流 拉伸性能 微观组织

AISI 316L stainless steel pulse current tensile properties microstructure

中文

联合培养

南方科技大学

曾志. 脉冲电流对316L不锈钢拉伸性能和微观组织的影响[D]. 深圳. 哈尔滨工业大学,2020.