Two compositions of CuPd-V system filler alloy were designed for joining the Cf/SiBCN composite. Their dynamic wettability on the Cf/SiBCN composite was studied with the sessile drop method. The CuPd-8 V alloy exhibited a contact angle of 57° after holding at 1170℃ for 30 min, whereas for CuPd-13 V alloy,a lower contact angle of 28°can be achieved after heating at 1200 ℃ for 20 min. Sound Cf/SiBCN joints were successfully produced using the latter filler alloy under the brazing condition of（1170-1230）℃for 10 min. The results showed that the active element V strongly diffused to the surface of Cf/SiBCN composite, with the formation of V2 C/VN reaction layer. The microstructure in the central part of the joint brazed at 1200 ℃ was characterized by the V2 C/VN particles distributing scatteringly in CuPd matrix. The corresponding joints showed the maximum three-point bend strength of 82.4 MPa at room temperature.When the testing temperature was increased to 600 0 C, the joint strength was even elevated to 108.8 MPa.Furthermore, the joints exhibited the strength of 92.4 MPa and 39.8 MPa at 800 ℃ and 900 ℃, respectively.
With assistance of Mo interlayer, joining of Cf/SiC composite to GH783 superalloy was carried out using NiPdPtAu-Cr filler alloy. Under the brazing condition of 1200 C for 10 min, the maximum joint strength of 98.5 MPa at room temperature was achieved when the thickness of Mo interlayer was 0.5 mm. Furthermore, the corresponding joint strength tested at 800 ℃ and 900℃ was even elevated to 123.8 MPa and 133.0 MPa, respectively. On one hand, the good high-temperature joint strength was mainly attributed to the formation of the refractory Mo-Ni-Si ternary compound within the joint. On the other hand, the residual Mo interlayer as a hard buffer, can release the residual thermal stresses within the dissimilar joint. The Cf/SiC-Mo bonding interface was still the weak link over the whole joint, and the cracks propagated throughout the whole reaction zone between the Cf/SiC composite and the Mo interlayer.
The wettability and interfacial reactions of four kinds of PdNi-based brazing fillers on C-C composite were studied with the sessile drop method.The results showed that the wettability of these brazing fillers was improved with the increase of Cr content. Cr distributed at the interface of brazing filler/C-C composite and the formation of Cr23C6 phase was speculated.In the interface between Ni-33Cr-24Pd-4Si brazing filler and C-C composite,element Cr reacted with C-C to form Cr-C reaction layer.Pd together with Si participated in the interfacial reactions and formed Pd2Si and Pd3Si phases.Furthermore,in this reaction zone,the residual brazing alloy became Ni-rich and Pd-depleted.
G/SiBCN ceramic composite was joined using Ni-19Cr-10Si （BNi5） and Ni-33Cr-24Pd-3.5Si-0.5B filler alloys at 1170 ℃ for 10 min. Two kinds of Ni-based filler alloys exhibited good wettability on the CdSiBCN com- posite, with a contact angle of 13° and 4°, respectively, The microstructures of the brazed joints were investigated by electron-probe microanalysis （EPMA）, and three-point bend test was conducted for the joints at room temperature. When being brazed with BNi5 filler alloy, no evident reaction layer was ob- served at the surface of the joined composite, and the joint microstructure was characterized by Ni2Si matrix with scatteringly distributing mixture compounds of Cr23C6, Ni2Si and CrB. While Ni-Cr-Pd（Si,B） brazing alloy was used, a Cr23C6 reaction layer with a thickness of 11 μm was formed at the surface of the base composite. In the central part of the brazed joint, the phases were composed of Ni（Cr, Si） solid solution and complex compounds including Pd2Si, （Ni,Pd）2Si and Ni-B. The strength of Cf/SiBCN joint brazed with BNi5 filler alloy was 62.9 MPa at room temperature, whereas that with Ni-Cr-Pd（Si,B） filler alloy was at the same level.
Wenwen LiBo ChenYi XiongHuaping XiongYaoyong ChengWenjiang Zou
