# Dissimilar Rotary Friction Welding of Inconel 718 to F22 Using Inconel 625 Interlayer
## 3 Results and Discussion
### Microstructure: Welds  
The macrograph of the weld cross-sections with and without Inconel 625 interlayer are shown in Figure 5a,b, respectively. Weld cross-section showed good metallurgical bonding at both F22-625 and 625-718 interfaces. Sound weld joint was obtained without any delamination areas and other weld defects. The presence of excellent flash at 625-718 interface indicated sufficient plasticisation of the interface materials during the welding. The Inconel718/F22 joins prepared without interlayer in Figure 5b show a bigger flash on the F22 side than the Inconel 718. Inconel 718 retains strength at higher temperatures compared to the F22, resulting in higher plasticised material on the F22. Optical micrographs  
Figure 4: Scanning electron micrograph and EDS analysis of the precipitates present in (**a**) Inconel 718 and (**b**) 625 base metals.  
of the 718-625 and 625-F22 interfaces showed deformed grain structure and intermixing zones, as shown in Figure 5c,d, respectively. The heat generated during the welding caused the plasticisation of the interface metals and resulted in the mechanical intermixing due to the rotational motion of the sample rods under the influence of the frictional and upsetting forces.  
Line scan data were obtained to investigate the mechanical intermixing and compositional variation across the weld interfaces. The EDS line scan data analysis of the Inconel 718/Inconel 625 and Inconel 625/F22 interfaces are shown in Figure 6a,b, respectively. It can be seen that the intermixing zone width was of the order of 30 \(\upmu\)m for the Inconel 625/F22 interface, while the intermixing zone was relatively smaller at the Inconel 718/Inconel 625 interface. The Inconel 718 yielded at relatively higher stress values compared to the Inconel 625 and F22. Thus, Inconel 625 and F22 base metals experienced relatively higher deformation during friction welding. Under the influence of the rotational motion, the softened metal at higher temperatures underwent intermixing at the weld interface. SEM micrographs clearly showed the intermixed lamellae of the Inconel 625 and F22 (Figure 6b). As a result of the softening and squeezing of the material at higher rotational speed during the friction welding, parallel banded layers (viz., intermixing zone) of Inconel 625 and F22 formed at the weld interface. During the etching process, which revealed the microstructure, the F22 in the intermixing zone reacted aggressively with the etchant, relative to the 625. Hence, the regions of F22 in the intermixing zone were observed as dark lines parallel to the weld interface. Higher burn-off lengths were observed at the Inconel 625/F22 interface (7 mm) compared to the Inconel 718/Inconel 625 interface (5 mm) during  
Figure 5: The macrograph of the F22-718 friction weld joint (**a**) with 625 interlayer, (**b**) without 625 interlayer, optical micro graph of (**c**) 718/625 weld interface, and (**d**) 625/F22 weld interface.  
the friction welding. Similar formation of the intermixing layers was reported during the dissimilar joining of the SAE1045 to 316L using the friction welding technique [24].