Microstructures and Mechanical Properties of High-entropy Carbide Ceramics and Its Brazed Joints
To realize large-sized and complex-shaped forming of high-entropy carbide ceramics(HECs),seven HECs with different compositions are successfully prepared by hot-pressing sintering,and the sintered HECs are all solid-solution phases with single rock salt structures.Among which,(TiZrHfNbTa)C and(VNbTaMoW)C possesses the higher bending strengths of 494 MPa and 476 MPa,respectively,and the hardness of(TiZrHfNbTa)C is higher than that of(VNbTaMoW)C.On this basis,by selecting(TiZrHfNbTa)C as the substrate,HEC joints with good metallurgical bonding are prepared employing TiNi-20at.％Nb alloy and FeCoCrNiTi0.2 high-entropy alloy(HEA)fillers.Active Ti atoms in the two liquid fillers are enriched on the HEC surface and induced interfacial reaction,which led to the formation of interfacial(Ti,Nb)C phase and high-entropy carbide phase(HEC').The resulting interfacial structures of the HEC/TiNiNb/HEC joint and the HEC/HEA/HEC joint are HEC/(Ti,Nb)C/(Ti,Nb)2Ni/TiNi/(Ti,Nb)2Ni/(Ti,Nb)C/HEC and HEC/HEC'/HEA'/HEC'/HEC,respectively.The HEC/TiNiNb/HEC joint obtaind at the brazing process of 1 180 ℃-10 min had the shear strength of 201 MPa.The weak zone of the joint is the(Ti,Nb)2Ni phase and its interface with the(Ti,Nb)C layer.In comparison,the HEC/HEA/HEC joint showes a higher shear strength(>245 MPa),while its brazing process required the higher temperatures(1 400-1 490 ℃)and longer time(30 min).
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