Interface geometry modification to trap plasticized flash for improved joint strength of dissimilar rotary friction welds

Abstract

Rotary friction welding is a highly effective solid-state technique for joining dissimilar materials, which offers the potential for significant weight reduction without compromising strength. Traditionally, during rotary friction welding, the severely deformed material, or flash, is expelled from the interface and machined away to achieve the desired joint geometry. However, this work introduces a novel approach: trapping the flash within the joint to improve joint properties. The study investigates two different interface geometry combinations—flat-flat and flat-taper interfaces. Previous research shows that Ni interlayer between steel and titanium can enhance the joint strength. This study builds on the existing knowledge (effect of Ni interlayer) by examining the influence of interface geometry to further improve the dissimilar joint performance. The experimental results, including tensile testing and microstructural characterization, highlight the superior performance of the flat-taper interface. The modified geometry minimizes flash loss, providing a cavity that retains both the flash and the Ni interlayer within the joint. This retention promotes dynamic recrystallization, resulting in refined grain structures near the interface. Moreover, the trapped Ni interlayer effectively prevents the formation of brittle Fe-Ti intermetallic compounds at the dissimilar material interface. The findings reveal that the flat-taper interface improved joint strength by an impressive 105% compared to the flat-flat interface. This innovative geometry modification demonstrates the potential to enhance mechanical properties of dissimilar joints through better flash and interlayer management.