SiC-Al_(2)O_(3)-Y_(2)O_(3)中间层放电等离子扩散连接SiC陶瓷的接头组织与强度

Microstructure and Strength of SiC Ceramic Joints Diffusion Bonded by Spark Plasma Sintering with the SiC-Al_(2)O_(3)-Y_(2)O_(3) Interlayer

采用无压烧结SiC作为母材,SiC基SiC-Al_(2)O_(3)-Y_(2)O_(3)粉末作为中间层,使用放电等离子扩散连接SiC陶瓷。通过金相显微镜、扫描电子显微镜、能谱仪、电子背散射衍射分析、剪切试验等手段对SiC接头的微观组织和力学性能进行了表征评价。微观组织表征结果表明,SiC接头界面结合质量较高,各个位置中间层厚度均匀。接头的主要相组成为β-SiC和Y-Al-Si-O-C,中间层SiC为细小的β-SiC晶粒,母材与中间层处晶粒没有表现出明显的择优取向。由于放电等离子扩散连接的快速连接过程,接头处未发生明显的β→α相变。同时,由于接头为近同质SiC接头,界面处未出现明显应力集中。通过剪切试验,对比不同温度热处理前后的接头剪切强度。SiC接头的初始室温剪切强度为219.9 MPa,在经过800ºC/2 h的空气中热处理后接头强度升至320.8 MPa,进一步提高热处理温度至1300ºC,接头强度升至389.1 MPa,接头断裂主要发生在母材,断口呈现河流状花样,为脆性断裂。接头强度的上升归因于热处理过程中产生的SiO2与Y-Al-Si-O-C的交互作用愈合了中间层两侧母材中存在的微裂纹等缺陷。

In this study,the pressureless-sintered SiC and SiC-based powder(SiC-Al_(2)O_(3)-Y_(2)O_(3))were used as the substrate and interlayer,respectively,for joining of SiC ceramics by spark plasmas sintering.The microstructure and strength of SiC joints were investigated by means of metalloscope,scanning electron microscopy,energy spectroscopy,electron backscatter diffraction and shear test.The microstructural characterization indicated that the SiC joint exhibited a high-quality interface bonding with uniform thickness in the interlayer.The main phase compositions of the joint wereβ-SiC and Y-Al-Si-O-C.The fineβ-SiC grains in the interlayer exhibited a random orientation.No significantβ→αphase transition occurred at the joint due to the fast process of diffusion bonding by spark plasma sintering.Meanwhile,no significant stress concentration was observed at the interface because of the near-homogeneous SiC joint formed.The initial room temperature shear strength of the SiC joint was 219.9 MPa,which increased to 320.8 MPa after heat treatment in air at 800ºC for 2 h.Further increasing the heat treatment temperature to 1300ºC,the joint strength increased to 389.1 MPa.The joint fracture occurred mainly at the substrate with a river-like pattern,as a representative of brittle fracture.The increase of joint strength may be attributed to the interaction of Y-Al-Si-O-C and SiO2 produced during the heat treatment process,healing the defects presented in the SiC substrate such as microcracks.