A comprehensive review on fusion welding of high entropy alloys – Processing, microstructural evolution and mechanical properties of joints

The high entropy alloys (HEAs) are relatively a new class of materials that have attracted significant attention of engineering sector in recent years due to their extensive mechanical properties, high strength to weight ratio, thermal stability and resistance to corrosion and oxidation. HEAs are characterized by their unique composition that is typically composed of five or more elements in equal or somewhat substantial proportions. This leads to the evolution of highly complex microstructure that makes it challenging to weld. To fulfil the key requirements of the design and manufacturing, these HEAs must be capable of being welded in a satisfactory manner. The joining of similar and dissimilar combinations of HEAs and other engineering materials system have been proved to be feasible which further expands their structural applications in aerospace, nuclear and defence sector. Additionally, the fillers of HEAs disclosed greater potential in suppressing the evolution of detrimental intermetallics and enhancing the mechanical properties of joints. So, in this study, a comprehensive review on the current state of research in fusion welding of HEAs particularly Al_xCoCrFeNi and CoCrFeMnNi is provided to address the weldability of HEAs under the diversity of composition, initial working condition, welding processes, operating parameters, configuration of joint and operating conditions. The latest challenges, progress and future perspectives in fusion welding of HEAs are reviewed critically with a particular focus on microstructure and mechanical properties of joints. The effect of fusion welding processes such as gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), electron beam welding (EBW) and laser beam welding (LBW) on microstructural characteristics, mechanical properties and corrosion behaviour of HEAs joints is reviewed and discussed. The effect of post weld heat treatment and HEAs fillers on the mechanical properties and microstructural evolution of welded joints is also discussed. Further, an insight into the potential application of HEAs in advanced engineering applications is provided. The current review article aims to provide an overview of challenges, opportunities, current state of research and main directions in fusion welding of Al_xCoCrFeNi and CoCrFeMnNi HEAs and to highlight their potential as high-performance material in a range of applications.