Improvement of the shear strength of SiC joint with CaO–Al2O3–MgO–SiO2 glass filler by surface etching

In this study, CaO–Al2O3–MgO–SiO2 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–Al2O3–MgO–SiO2 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–K3[Fe(CN)6] solution effectively removed surface carbon, resulting in numerous micro-pits, that increased the joining area and improved the wettability of CaO–Al2O3–MgO–SiO2 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.