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The effect of post-bond solution treatment and double aging on the microstructural evolution and mechanical properties of TLP-bonded IN718 joint

Tarai U. K., Pal Sukhomay, Robi P. S.

Archives of Civil and Mechanical Engineering

2023

Vol. 23, no. 2

art. no. e110, 2023

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.

Fabrication and effect of Mg–Zn solid solution via Zn foil interlayer alloying in FSW process of magnesium alloy

Sahu Prakash Kumar, Pal Sukhomay, Das Bipul, Shi Qingyu

Archives of Civil and Mechanical Engineering

2020

Vol. 20, no. 4

589--603

The present study demonstrates the friction stir welding (FSW) process can be used as a mechanical alloying tool to fabricate a solid solution. An attempt has been taken for alloying the AM20 Mg base matrix using Zn at the weld zone during friction stir welding. Successful joints with sound mechanical properties and enhanced quality attributes are observed in the welds. Use of Zn alloying element at the nugget zone, the joint efficiency reached 90% to that of the base material and also which is about 25% more than the strength obtained in the case of without alloying element set of experiments. The addition of Zn alloy to Mg substrate forms Mg–Zn binary solid solution reinforcing intermetallic compounds, namely MgZn and Mg7Zn3 resulting in improved joint properties. This research work also reports the investigative outcomes, namely flow in the joint area, metallurgical deviation, microstructural modification, and diffusion of the constituent alloying element during the welding process. The targeted objective was effectively accomplished and the Zn alloyed stir area can fulfil the required application. The findings from the selective alloying process may be relevant for the implementation of industrial users over Mg alloys using a FSW process with better weldability and improved strength.