부산대학교 도서관

The effect of post-bond heat treatment on precipitation of different strengthening phases in transient liquid phase (TLP) bonded IN718 joint is carried out in this work. TLP bonding of IN718 super-alloy was carried out using commercial BNi-2 amorphous interlayer. The bond microstructure of the IN718 joint was analyzed by field emission scanning electron microscope. The bond microstructure showed three distinct zones: viz., base material zone, where δ-phase was observed in the grain boundaries; diffusion-affected zone (DAZ) consisting of extensive diffusion-induced boride precipitates and isothermal solidification zone where a single-phase γ solid solution exists along with a small amount of silicides. The effect of post-bond heat treatment on the microstructure and precipitates formed at different zones was investigated in detail. The phase formed during post-bond heat treatment was analyzed by field emission transmission electron microscope and X-RD. The mechanical properties of as-bonded and post-bond heat treatment samples were also investigated. The results showed that a comparatively more homogeneous microstructure was achieved in the post-bond heat-treated samples. Post-bond heat treatment resulted in decrease in the volume fraction of borides at the DAZ, increase in volume fraction of hardening precipitates (γ’’ and γ’), and breaking up of grain boundary borides and increase in the DAZ size. An increased in γ’’ + γ’ precipitate volume was beneficial to the improvement of mechanical properties of the joint. Tensile strength of 1124 MPa with an elongation percentage of 10.5% was obtained after the post-bond heat treatment. [ABSTRACT FROM AUTHOR]