Recent Advances in High Entropy Alloy Fillers for Brazing Similar and Dissimilar Materials: A Review

Continuous development of novel materials for various engineering and industrial applications including automotive, aerospace, electrical and petrochemical industries demands the continuous advancement of novel brazing filler metals to join similar and dissimilar materials. Furthermore, developing complex materials, for which traditional fillers cannot adequately form joints, necessitates the evolution of novel fillers. High entropy alloys (HEAs) fillers are one of the most exciting developments in the field of materials science in recent years. The aim of this review is to provide the current status and progress on HEAs brazing filler metals to join similar and dissimilar materials including metal-to-ceramics joining. HEAs constitute a new class of materials, containing five or more than five elements in equimolar or near equimolar compositions with the possible alloying concentration of each principal element varying from 5 to 35 at%. HEAs as a brazing filler metal exhibits an excellent set of desirable properties including mechanical and functional properties, good corrosion and oxidation resistance, exceptional wear resistance, and high-temperature stability. In brazing applications, the use of traditional filler metals leads to the formation of brittle intermetallic compounds (IMCs), segregation of elements, and residual stresses at the joint interface that eventually affect the joint performance. These microstructural changes become more serious during dissimilar joining especially metal-to-ceramic brazing. Owing to the high entropy effect, HEAs filler results in better mixing of filler elements, forming random solid solution structure, thus hindering the formation of brittle IMCs. Graphical Abstract