SiC陶瓷在钎焊过程中的6H到3C多型相变

6H to 3C Polytypic Transformation in SiC CeramicsDuring Brazing Process

为探究钎焊过程对SiC陶瓷晶体结构的影响,为钎焊工艺设计提供理论及试验数据支撑,本研究采用纯Ni箔作为中间层在1100~1245℃下实现了6H-SiC的钎焊连接,并研究了焊缝以及6H-SiC基体与焊缝界面处的微观形貌。研究结果表明,少量Ni原子在钎焊过程中会扩散进入6H-SiC陶瓷,并以固溶形式存在,降低了6H-SiC层错能。随着钎焊温度升高,6H-SiC/焊缝界面处的焊后残余应力增大,当钎焊温度达到1245℃时,界面处的6H-SiC的(0001)面沿1/3<1100>方向产生滑移,6H-SiC切变形成3C-SiC。因此,SiC陶瓷在钎焊过程中受应力和钎料组成元素的作用发生相变,针对特殊环境使用的SiC陶瓷需要斟酌钎焊工艺对其晶体结构及性能的影响。

In this paper,pure Ni foil was used as an intermediate layer to achieve brazing connection of 6H-SiC at 1100~1245℃.The microstructure of the brazed joint and the interface between the brazed joint and the 6H-SiC substrate were studied to investigate the effect of brazing process on the crystal structure of SiC ceramics and provide theoretical and experimental data supports for brazing process design.The results show that a small amount of Ni atoms diffuse into the 6H-SiC ceramics during the brazing process and exist in solid solution form,which reduces the dislocation energy of 6H-SiC.The residual stress at the 6H-SiC/brazed joint interface increases with the increase of brazing temperature,and when the brazing temperature reaches 1245℃,the(0001)plane of 6H-SiC at the interface slips along the 1/3<1100>direction,and the 6H-SiC is sheared to form 3C-SiC.Therefore,SiC ceramics can undergo phase transformation under the influence of stress and brazing material composition during the brazing process,and the effect of brazing process on their crystal structure and properties should be considered for SiC ceramics used in special environments.