Li Yongcun, Xu Feng, Hu Xiaofang, Dong Bo, Luan Yunbo, Xiao Yu
College of Mechanics, Taiyuan University of Technology, Taiyuan 030024, China.
CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei 230026, China.
Materials (Basel). 2016 Feb 26;9(3):132. doi: 10.3390/ma9030132.
In this paper, local spark sintering of a ceramic-metal system (SiO₂-Sn) during microwave processing was examinedby means of synchrotron-radiation-computed tomography technology. From the reconstructed 3-D and cross-section images of the specimen, adensification process was observed below the melting point of Sn, and then the specimen came into a rapid densification stage. These results may be due to the local spark sintering induced by the high-frequency alternating microwave electric fields. As the metallic particles Sn were introduced, the microstructure of "ceramic-metal" will lead to a non-uniform distribution and micro-focusing effect from electric fields in some regions (e.g., the neck). This will result in high-intensity electric fields and then induce rapid spark sintering within the micro-region. However, in the subsequent stage, the densification rate declined even when the specimen was not dense enough. The explanation for this is that as the liquid Sn permeated the gaps between SiO₂, the specimen became dense and the micro-focusing effect of electric fields decreased. This may result in the decrease or disappearance of spark sintering. These results will contribute to the understanding of microwave sintering mechanisms and the improvement of microwave processing methods.
本文利用同步辐射计算机断层扫描技术研究了微波处理过程中陶瓷-金属体系（SiO₂-Sn）的局部火花烧结。从重建的试样三维和横截面图像中，可以观察到在Sn熔点以下的致密化过程，然后试样进入快速致密化阶段。这些结果可能归因于高频交变微波电场引起的局部火花烧结。随着金属颗粒Sn的引入，“陶瓷-金属”的微观结构会导致电场在某些区域（如颈部）出现非均匀分布和微聚焦效应。这将导致高强度电场，进而在微区域内引发快速火花烧结。然而，在随后的阶段，即使试样还不够致密，致密化速率也会下降。对此的解释是，随着液态Sn渗透到SiO₂之间的间隙中，试样变得致密，电场的微聚焦效应减弱。这可能导致火花烧结的减少或消失。这些结果将有助于理解微波烧结机理并改进微波处理方法。
