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Phase Transformations in Metals Stimulated by a Pulsed High-Energy Electromagnetic Field

机译：脉冲高能电磁场刺激的金属相变

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Processes occurring in metals with microdefects when metallic specimens are treated by short high-density electric current pulses are considered. The variations in the electric and temperature fields in the material and their influence on the phase transformations and the stress-strain state in the vicinity of microdefects in the form of plane cracks with linear sizes of the order of 10 μm are studied. A mathematical model of the effect of an electromagnetic field on a predamaged thermoelastoplastic material with an ordered system of defects is proposed. The model takes into account melting and evaporation of the material and the dependence of all of its physical and mechanical properties on temperature. The solution of the resulting system of equations is sought by the finite element method on moving grids with the use of the combined Euler-Lagrange method. The dependence of the processes on the boundary conditions of the model is considered. We estimate the error that occurs when solving the problem for one representative cell rather than for the whole sample with an ordered system of defects. The influence of the distance between the cracks on the deformation and healing of microdefects is investigated. Numerical modeling has shown that a high-density current with large field gradients arises in the vicinity of microdefects, which leads to intensive local heating accompanied by thermal expansion and melting of the metal on the tips of the microcracks. This results in high compressive stresses near microcracks, intensive plastic flow of the material and, as a consequence, clamping of microcrack sides, decrease in microcrack length, and ejection of the molten material into the crack. As a result, the microcrack is completely healed. The numerical results obtained by the proposed model agree with experiments. Computations showed that if the distance between microcracks is equal to or greater than ten of their lengths, then the time for complete defect healing weakly depends on the distance between defects and the micro-defect interaction can be neglected. The interaction between microcracks in the metal significantly affects their healing process if the distance between them is reduced to about 5÷6 of microcracks lengths. With further decrease in the distance between the defects up to one microcrack length, the healing process does not change qualitatively, but slows down significantly: the ejection of molten material into the crack still happens, but the crack size reduction, especially in the transverse direction, is substantially smaller.
机译：考虑使用短高密度电流脉冲处理金属样品时，在具有微碎片的金属中发生的过程。研究了材料中的电气和温度场的变化及其对相变的相变和应力 - 应变状态的平面裂缝形式的微碎片附近，具有10μm的线性尺寸的线性尺寸。提出了一种具有有序缺陷的偏转热弹性材料上电磁场对具有有序系统的效果的数学模型。该模型考虑了材料的熔化和蒸发和所有物理和机械性能的温度。通过使用组合的欧拉拉格兰测图方法，通过有限元方法寻求所得到的方程式的方程式的解决方案。考虑了过程对模型的边界条件的依赖性。我们估计在解决一个代表小区的问题时出现的错误，而不是用有序的缺陷系统对整个样本进行解决。研究了裂缝之间的距离对微碎片变形和愈合的影响。数值建模表明，具有大场梯度的高密度电流在微碎片附近产生，这导致密集的局部加热伴随着微裂纹的尖端上的金属的热膨胀和熔化。这导致微裂纹的高压缩应力，材料的密集塑料流动，因此，夹紧微裂纹侧，微裂纹长度降低，并将熔融材料喷射到裂缝中。结果，微裂纹完全愈合。所提出的模型获得的数值结果与实验一致。计算显示，如果微裂纹之间的距离等于或大于其长度的十个，则完全缺陷愈合的时间弱取决于缺陷之间的距离，并且可以忽略微缺陷相互作用。如果它们之间的距离降至约5°6的微裂纹长度，则金属中微裂纹之间的相互作用显着影响其愈合过程。随着缺陷之间的距离进一步减小到一个微裂纹长度，愈合过程不会定性变化，但显着减慢：将熔融材料喷射到裂缝中仍然发生，但裂缝尺寸减小，特别是在横向上，基本上更小。

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