Sheng-Jin He,Ling-Feng Su,Chuang-Tian Zhan,Xiu-Bin Chen,Wei-Ming Guo,Shi-Kuan Sun,Li-Xiang Wu,Jia-Xiang Xue,Hua-Tay Lin
Low-temperature joining of SiC ceramics using raw CaO-Al 2 O 3 -MgO-SiO 2 mixed powders (CAMS-P) and CaO-Al 2 O 3 -MgO-SiO 2 glass (CAMS-G) as additives for the liquid-phase sintering of SiC nanopowders (NITE phase) in combination with surface oxidation was studied. Using CAMS-P as an additive for SiC joining required 1650 °C and produced a lower shear strength of 77.2 ± 3.5 MPa, compared to untreated SiC (108.2 ± 15.8 MPa). Using CAMS-G as an additive, the compactness of SiC joints obtained at 1550 °C was higher than that of NITE joints obtained at 1650 °C with CAMS-P as an additive. Nonetheless, the low joining temperature resulted in gaps and delaminations at the interface, and the joints strength was only 48.3 ± 5.6 MPa. Incorporating CAMS-G as an additive and surface oxidation achieved reliable NITE phase joining at 1550 °C, with no observed gaps or delaminations at the interface. The resulting joints strength was as high as 100.0 ± 0.8 MPa. The joining mechanism was discussed and compared, involving microstructural analysis .
In this study, CaO–Al 2 O 3 –MgO–SiO 2 glass was utilized to join SiC after surface polishing and etching, without the application of pressure. To join polished SiC at 1250 °C using CaO–Al 2 O 3 –MgO–SiO 2 glass proved unsuccessful. However, when polished SiC was joined at 1350 °C, the joint shear strength was 108.0 ± 15.5 MPa. Etching polished SiC with a NaOH–K 3 [Fe(CN) 6 ] solution effectively removed surface carbon, resulting in numerous micro-pits, that increased the joining area and improved the wettability of CaO–Al 2 O 3 –MgO–SiO 2 glass. The joint strengths of etched SiC joined at 1250 °C and 1350 °C were 29.0 ± 11.6 MPa and 125.1 ± 19.6 MPa, respectively. After ablation at 1200 °C for 10 min, the retained strength of the etched joints (joined at 1350 °C) was 61.9 ± 4.0 MPa, whereas the strength of the polished joints decreased to only 36.6 ± 10.7 MPa. Surface etching demonstrates the potential to significantly enhance the strength and high-temperature resistance of SiC joints.
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