Interaction of MWCNTs and GNPs with the elements on the development of equiatomic Fe25Co25Cr25Cu25 High Entropy Alloys (HEAs)

This work is focused on developing equiatomic Fe25Co25Cr25Cu25-based HEAs, adding 2 wt% of Multi-Walled Carbon Nanotubes (MWCNTs) and Graphene Nanoplates (GNPs) as a reinforcement. Particularly, the addition of copper (Cu) to the other alloy systems is the best way to enhance thermal and phase stability. Still, elemental segregation is an important limitation while adding Cu to other elements, which reduces the strength-ductility balance. MWCNTs and GNPs are added to control the Cu segregation level by acting as structural reinforcement and altering the microstructure. The alloy fabrication is done through Mechanical Alloying (MA) followed by the Vacuum Arc Melting (VAM) process. The fabricated samples are annealed at a temperature of 1100 °C for 24 h to improve the elemental homogenization and reduce the internal stress of the alloys. The Fe25Co25Cr25Cu25 alloys with FCC phases are confirmed from the X-ray diffraction (XRD) analysis. Thermal stability and thermal transition of MA powders are confirmed with the help of Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The Electron Backscatter Diffraction (EBSD) analysis reveals the grain and grain boundary interaction behaviour resulted due to the addition of reinforcement. Fe25Co25Cr25Cu25 alloy exhibited a microhardness value of 91.50 HV, which reached 382.30 HV and 448.15 HV due to the addition of MWCNTs and GNPs, respectively. Based on the results, adding 2 wt% of GNPs has better interfacial bonding and mechanical properties than Fe25Co25Cr25Cu25 and Fe25Co25Cr25Cu25 + MWCNTs HEAs.