The Effect of Heat Treatment on Microstructure and Mechanical Properties of FeCoNiAl<sub>0.25</sub>Mn<sub>0.75 </sub>High Entropy Alloy

The effect of heat treatment on the microstructure and mechanical properties of FeCoNiAl 0.25 Mn 0.75 high-entropy alloy was investigated. In the as-cast sample, the dendritic microstructure was observed with the FCC lattice, according to XRD analysis. After annealing at 700 °C within 24 hours, the needle-shaped precipitated phase (BCC phase) in the form of clusters along the grain boundaries and in the FCC matrix phase occurs, the fraction of this phase increases significantly and the distribution becomes more uniform when the temperature is increased to 800 °C, the average size of this phase is only about 1-2 µm. However, as the temperature reaches 1000 °C, the BCC phase disappeared and the grain boundary is remelted and looks like cracks. At an annealing temperature below 800 °C, the HV3 hardness of the alloy increases and reaches its highest value of approximately 194 HV3. The yield and tensile strength can reach 373 and 762 MPa, respectively. However, these values decrease significantly when the annealing temperature reaches 1000 °C because of the plastic flow at near-boundary zones. The best relative elongation is 51.2 % at the as-cast state.