Improving Mechanical and Tribological Characteristics of Cast Elektron 21 Alloy by Reinforcing its Surface with Al_0.3Cu_0.3Ni_0.1Si_0.1W_0.2 High Entropy Alloy via Friction Stir Processing Route

The primary objective of this investigation is to strengthen the mechanical and tribological properties of the cast Elektron 21 alloy (UNS M12310) by reinforcing its surface with a high entropy alloy (HEA) consisting of 0.3 wt% aluminum, 0.3 wt% copper, 0.1 wt% nickel, 0.1 wt% silicon, and 0.2 wt% tungsten fabricated by friction stir processing (FSP). The resulting Elektron 21/HEA surface composites (SCs) processed through casting followed by FSP were compared to the cast followed by FSPed Elektron 21 alloy, exhibiting significant enhancements in mechanical properties and wear resistance. The surface of the Elektron 21 matrix, which underwent casting followed by FSP, showed a homogeneous dispersion of HEA particles. These particles served as precipitates, creating geometrically necessary dislocations that hindered movement under applied force. The bonding between the HEA and the Elektron 21 alloy at the interface was excellent, and differential thermal contraction resulted in a strain misfit. Consequently, the microhardness, yield stress, and ultimate tensile stress of the FSPed Elektron 21/HEA SCs improved by 38%, 37%, and 32%, respectively, compared to the FSPed Elektron 21 alloy, although ductility decreased by 33%. Furthermore, the FSPed Elektron 21/HEA SCs showed a 33% enhancement in wear resistance and a 27% reduction in frictional force generation compared to the FSPed Elektron 21 alloy. The worn surfaces of the FSPed specimens showed that the FSPed Elektron 21 alloy revealed deep grooves, pits, micro-cutting, micro-grooving, and ploughing, while these features were absent in the FSPed Elektron 21/HEA SCs. These outcomes make it better suited for use in the aviation and automotive sectors.