金属铝微波烧结微结构演化的在线观测与相场模拟

On-line observation and phase field simulation of microstructure evolution of aluminum during microwave sintering

材料内部微结构及其演化与材料宏观力学性能密切相关,而孔隙是微结构的一种重要形态。在金属粉末微波烧结过程中,由于烧结机理复杂,且受限于传统实验观测手段,目前对金属微波烧结孔隙演化机理的认识尚不清晰。本文采用SR-CT(Synchrotron Radiation Computed Tomography),同步辐射计算机断层扫描技术,对金属铝粉末微波烧结过程中的孔隙演化进行了在线观测,观测到呈条状的孔隙沿短轴闭合这一独特现象,与常规烧结中孔隙圆滑化和球化过程截然不同。基于这一现象,针对金属颗粒在微波电磁场作用下进行了受力分析,认为在微波电磁场中金属颗粒表面产生电子涡流,颗粒受到沿表面法线方向并指向孔隙内部的安培驱动力作用,促进了孔隙沿短轴方向的闭合,据此提出了条状孔隙演化的安培力驱动模型。将这一模型引入相场模拟,基于实验图像模拟孔隙的演化过程,得到了与实验一致的模拟结果,从而验证了安培力驱动模型的正确性。

The internal microstructure and its evolution are closely related to macroscopic mechanical properties of material,and the pore is an important form of microstructure.In the process of metal powder microwave sintering,due to the complexity of sintering mechanism and limited by the traditional experimental observation means,the understanding of pore evolution mechanism of metal microwave sintering is not clear at present.In this paper,synchrotron radiation-computed tomography(SR-CT)technique is used to observe the pore evolution during microwave sintering of aluminum powder.The unique phenomenon of stripe pore closure along the short axis is observed,which is entirely different from pore sleekness and spheroidization process in conventional sintering.Based on this phenomenon,the stress analysis of metal particles under the action of microwave electromagnetic field was carried out.The authors believe that in the microwave electromagnetic field,the surface of metal particles produces an electron eddy current,and the particles are subjected to Ampere driving force along the normal direction of the surface and pointing to the interior of the pore,which promotes the closure of the pore along the short axis.Based on this,an Ampere force drive model for stripe pore evolution is proposed.Introducing this model into the phase field simulation,based on the experimental images,pore evolution process is simulated.Simulation results are consistent with the experimental results,which verifies the correctness of the Ampere driving model.