Effect of aluminum alloying on microstructure and mechanical behaviors of Fe35Ni35Cr20Mn10 high-entropy alloy

The microstructure and mechanical properties of the (Fe35Ni35Cr20Mn10)100-xAlx (X = 0, 2.91, 4.76, 6.54, 8.26, 9.91, at%) high-entropy alloys (HEAs) with varying Al content were investigated through microstructure observation and tensile testing. The phase structure of the prepared HEAs changes gradually from a single facecentered cubic phase structure to a combination of face-centered cubic and body-centered cubic phase structures with an increase in aluminum content. The volume fraction of the body-centered cubic phase increases gradually as well, being rich in Ni and Al elements and having a coherent relationship with the face-centered cubic phase of the matrix. With increasing Al content, both the microhardness and tensile strength of the (Fe35Ni35Cr20Mn10)100-xAlx HEAs also increase gradually. At an aluminum content of 8.26 %, specifically for (Fe35Ni35Cr20Mn10)91.74Al8.26 HEA has higher tensile strength and yield strength at approximately 926 MPa and 867 MPa respectively; while maintaining an elongation after fracture at about 11 %. The main reason for its strength improvement is attributed to dislocation proliferation along with hindrance from second-phase bodycentered cubic structure relative to dislocations during tension process; whereas maintaining higher elongation is mainly due to congruent relationship between second-phase and matrix phases allowing some dislocations slip through congruent interface.