Solid state joining of nickel based alloy, Haynes 230

Haynes 230 is a nickel based, solid-solution strengthened alloy that is used for high-temperature applications in the aero-engine and power generation industries. Addition of carbon promotes the formation of carbides to enhance creep resistance and control grain size. Although the alloy has been formulated for high temperature stability, cracking issues are still observed in fusion welding applications. To avoid formation of common fusion weld defects, this study considers the use of a solid state technique variation of friction stir welding (FSW) called thermal stir welding (TSW). An 85% reduction in grain size was observed in the TSW region along with a 30-60% reduction in the size of the W6C carbide phase. Negligible change in the area fraction of the tungsten rich carbides indicated the W6C carbides fragmented rather than dissolved. A slight decrease of 12% from the parent material properties was observed in the tensile strength and elongation to failure of the TSW specimens. No cracks were observed in the TSW region during bend testing. Based on the TSW region morphology and lack of cracking, use of solid state joining provides an alternative to fusion welding and its associated defects.