The outstanding high-temperature oxidation resistance of SiC joint achieved via ultrafast high-temperature joining using FeCoCrNiCu high entropy alloy

In this paper, the SiC ceramic was successfully joined using FeCoCrNiCu high entropy alloy via the ultrafast high-temperature joining. UHJ is a novel joining approach using electrically heated carbon felts for ultra-fast sample heating via conduction and radiation. The sample could be rapidly heated to 1430 °C in 0.5 s. The joints are mainly composed of metal silicide, Cr(s,s), Cu₅Si and amorphous carbon. The effects of preparation current and holding time on microstructure evolution and high-temperature mechanical properties of joints are investigated. C particle content increases with current and time. The samples prepared at 40 A-45 s exhibit the best mechanical properties. The maximum shear strengths of the joints at room temperature and 1000 °C were 54 MPa and 33 MPa, respectively. The oxidation resistance of the joints is systematically studied at the high temperature of 1000 °C for 10 h. C particles are oxidized to CO₂ during oxidation, leaving holes in the reactive layer that provide channels for oxygen infiltration. The Cr and Si elements in the brazing seam center diffuse towards high oxygen partial pressure. After oxidation, the typical microstructure of the joint turns out to be CrO₂+(NiCoFe)Si/Si-O compound/(NiFeCoCu)₂Si/Si-O compound/CrO₂+(NiCoFe)Si. The oxidized joint features an excellent shear strength of 47 MPa. The increase in strength of the oxidized joint is related to the compressive stress generated by the oxidation.