陶瓷和金属微波烧结在线实验及微观机理分析

为研究陶瓷和金属微波烧结时的微观演化机理,从而为优化不同材料的烧结过程提供依据,本文采用同步辐射技术对陶瓷(SiC)和金属(Al)的微波烧结微结构演化过程进行实时、无损的观测,并结合有限元模拟分析两者的微结构演化特征及微观机理。通过滤波反投影等数字图像处理技术得到烧结过程中样品内部的二维、三维重建图像,清晰地观察到SiC和Al在颗粒表面和界面演化上存在差异。定量地统计了陶瓷和金属烧结颈相对尺寸与时间的双对数关系,并与陶瓷和金属双球模型的微波烧结模拟结果进行了对比。运用模拟分别对实验中的烧结颈和微观形貌演化进行分析,得出结论:陶瓷和金属微波烧结时的加热机制不同,分别为整体介质损耗加热和表面涡流损耗加热。陶瓷的整体加热将会在材料内部特别是界面产生较高的温度,而金属的表面加热使颗粒表面温度高于界面。由相应的加热机制产生的温度分布差异,将会对材料的物质扩散过程产生不同程度的影响,进而产生不同的微结构。

Online Experiment and Microscopic Mechanism Analysis of Ceramic and Metal Microwave Sintering

In order to study ceramic and metal microstructure evolution mechanism during microwave sintering process, so as to provide the basis for optimizing different materials' sintering process, real-time and non-destructive observation of ceramic (SiC) and metal (aluminum) microstructure evolution during microwave sintering process was realized by synchrotron radiation X-ray computerized tomography technique. Finite element method was combined to analyze the microstructure evolution and microscopic mechanism simultaneously. 2-D and 3-D reconstructed images of samples during the whole sintering process were obtained based on filtered back projection algorithm and digital image processing technology. The difference of surface and interface evolution in particles of silicon carbide and aluminum was clearly observed. The double logarithmic relationship between sintering neck relative size and time of ceramic and metal were obtained and compared with two-sphere model simulation results. The sintering neck and morphology evolution during sintering process were analyzed based on simulation. Results show that the heating mechanism of ceramic and metal during microwave sintering is different, namely the whole dielectric loss and surface eddy current loss, respectively. The overall heating mode of ceramic generates high temperature inside the material particularly at the interface, while the surface heating mode of metal causes the temperature of metal particle higher than interface. Different temperature distribution inside materials caused by corresponding heating mechanism will produce different effect on material diffusion process, thereby will generate different microstructures.