PUBLICATION: MATERIALS CHARACTERIZATION

AUTHORS: He, YM; Xiao, F; Sun, Y; Lu, CY; Chen, SJ; Chen, WJ; Li, HX; Zheng, WJ; Ma, YH; Ding, ZY; Yang, JG; Gao, ZL

In this work, the Hastelloy N superalloy was joined using a newly-designed BNiCrWBSi brazing filler alloy. Effects of brazing processing parameters and post thermal exposure on microstructure and mechanical performance of the joints were evaluated. The microstructure in the joints was revealed with the aid of scanning electron microscope, electron back-scattered diffraction and transmission electron microscope analyses. The nano indentation technique and shear test were employed to appraise the mechanical properties (such as nano scale elastic modulus/hardness of specific phases and joint bond strength) of the joints. The results showed that the typical joint constitution could be depicted as Hastelloy N alloy/diffusion-affected zone (DAZ) or finegrained zone (FGZ)/isothermal solidification zone (ISZ)/diffusion-affected zone (DAZ) or fine-grained zone (FGZ)/Hastelloy N alloy. The appearance of the FGZ was dependent on the brazing temperature, irrespective of the soaking time. The optimum joint bond strength of 588.9 MPa was produced at 1240 degrees C for 10 min. The typical fracture procedure and mechanism were discussed based on the detailed microstructural examinations and theoretical calculations. Apart from the brazing processing parameters, the post thermal exposure could also modify the microstructure through importing tiny boride phases into the ISZ, posing a reduction in shear strength. The microstructural evolution of Hastelloy N alloy joints unveiled and relationship built between the microstructure and mechanical properties will give a significant guidance for the design and application of the superalloy brazed joint.