Effect of friction stir processing on wire arc additively manufactured ER70S-6/SS308L bimetallic FGM
Manish Singh, Hemant Kaundal, Mandeep Kumar, Tarun Kumar Bera, Ratnesh Kumar Raj Singh
Abstract
In this research, wire arc additive manufacturing (WAAM) is employed to fabricate a bimetallic steels component using ER70S-6 and SS308L. However, this process involves high power densities and significant heat inputs, which elevate the risk of unfavorable grain structures and defects. To mitigate this issue, friction stir processing (FSP) is applied, utilizing a unique tool featuring a flat shoulder without a pin. The resulting samples undergo testing for mechanical and metallurgical properties. The microstructure of ER70S-6 reveals ferrite with small amounts of pearlite at the grain boundaries. The upper portion of the deposited sample exhibits more pronounced grain refinement compared to the lower section, largely due to the rapid cooling rate and thermal cycling effects during layer deposition. This grain refinement is attributed to dynamic recrystallization, which enhances the hardness of the FSP-treated sample relative to its initial as-deposited state. Tensile tests indicate a significant increase in tensile strength, accompanied by a reduction in percentage elongation after FSP. The fatigue crack growth rate is higher along the longitudinal direction of bi-metallic joint as compare to transverse to the joint.