*Article* **Microstructure and Mechanical Properties of Dissimilar Friction Welding Ti-6Al-4V Alloy to Nitinol**

**Ateekh Ur Rehman 1,\*, Nagumothu Kishore Babu 2, Mahesh Kumar Talari 2, Yusuf Siraj Usmani <sup>1</sup> and Hisham Al-Khalefah <sup>3</sup>**


**Abstract:** In the present study, a friction welding process was adopted to join dissimilar alloys of Ti-Al-4V to Nitinol. The effect of friction welding on the evolution of welded macro and microstructures and their hardnesses and tensile properties were studied and discussed in detail. The macrostructure of Ti-6Al-4V and Nitinol dissimilar joints revealed flash formation on the Ti-6Al-4V side due to a reduction in flow stress at high temperatures during friction welding. The optical microstructures revealed fine grains near the Ti-6Al-4V interface due to dynamic recrystallization and strain hardening effects. In contrast, the area nearer to the nitinol interface did not show any grain refinement. This study reveals that the formation of an intermetallic compound (Ti2Ni) at the weld interface resulted in poor ultimate tensile strength (UTS) and elongation values. All tensile specimens failed at the weld interface due to the formation of intermetallic compounds.

**Keywords:** friction welding; Ti-6Al-4V; nitinol; intermetallic compound; fractography; dissimilar metal joining
