Interlayer-Assisted Friction Welding: A Solution for Joining Incompatible Materials
Authors: Cheepu Murali Mohan , Shanmugam Ragavanantham , Kantumuchu Venkata Charan 
Published: January 2025

Abstract
Diverse industrial applications often necessitate the combination of dissimilar materials due to their unique physical properties. While some materials exhibit favorable weldability, others present challenges due to their incompatibility for welding. Traditional welding methods frequently struggle to join such dissimilar materials owing to differences in melting points and elemental reactions at elevated temperatures. Despite applying various precautions to obtain suitable joints, these methods often fall short. Moreover, conventional fusion welding techniques face limitations regarding the thickness of materials and design complexities. To address the welding of complex designs or incompatible materials, alternative welding methods are needed alongside traditional approaches.
This study focuses on the intricate joining of dissimilar materials, specifically titanium and stainless steel, which are often used in high-temperature applications. Titanium, known for its reactivity and tendency to oxidize at high temperatures, poses distinct challenges during welding due to its significantly different melting point compared to stainless steel. Conventional welding techniques like arc and laser welding are inadequate for joining these materials because they lead to the formation of brittle FeTi and CrTi-based intermetallic compounds. Consequently, friction welding emerges as a promising alternative. Friction welding produces joints that meet required performance standards while minimizing the formation of deleterious intermetallic compounds. Unlike fusion welding methods, friction welding keeps the maximum temperature during the process below the melting points of the substrates, reducing the likelihood of intermetallic compound formation or secondary precipitates along the interface.
However, achieving joints with enhanced strength and reliability presents significant hurdles due to the formation of FeTi and CrTi-based intermetallic compounds at the weld interface, especially when joints are formed without the protection of inert gas, as seen in fusion welding methods. To overcome these challenges and prevent intermetallic compound formation, an interlayer technique compatible with both substrates is introduced. Results demonstrate the successful prevention of FeTi-based intermetallic compound formation, leading to improved joint strength and ductility, thereby meeting the demands for reliable welded joints in high-temperature applications. The friction-welded joints with an interlayer between stainless steel and titanium exhibit more reliable joints with more ductile and less harmful NiTi-based intermetallic compounds. The presence of these intermetallic compounds along the interface was characterized and confirmed through microstructural and X-ray diffraction analysis. The mechanical properties of the joints were also evaluated, revealing that the peak hardness was recorded at the interface where the NiTi intermetallic compounds formed. The joint properties showed significant improvement compared to the welds formed without an interlayer. This innovative approach provides a viable solution for industries requiring the reliable joining of dissimilar materials with complex designs and stringent performance standards.