Investigation of Preparation and Mechanical Performance of (FeCoNi)₈₆Al₇Ti₇ High Entropy Alloy by Tailoring Three-dimensional Microstructures

FCC high-entropy alloys (HEAs) have great plasticity and high work hardening rate, but low yield strength limits their application. Heterogeneous materials such as harmonic structured alloys, are considered to be the key to solve the contradiction of strength and ductility. The harmonic structure successfully combines the high work hardening rate of coarse grain with the high strength of ultrafine grain, and thus improves the strength while maintaining tensile ductility. In this work, (FeCoNi)₈₆-Al₇Ti₇ alloy is selected to investigate the influence of the harmonic structure on the mechanical behavior of the material. A deformation layer is formed by grinding the alloy powders by ball milling. The processed powders are then consolidated by spark plasma sintering. The deformation layer recrystallizes in the sintering process to form the ultrafine grained network wrapping the undefor- med coarse crystal core. The phase composition and microstructure of alloy powders and sintered alloy blocks are studied by XRD, SEM, EDS, EBSD, TEM and other test methods. Tensile experiments are conducted to compare the mechanical properties of the alloys in different states and the effects of proclpitated phase and harmonic structure on the alloy strengthening are discussed. The yield strength of the alloy sintered from powders ball-milled for 70 hours is 1 087 MPa, which is 14.4% higher than that of the alloy sintered from powders unmilled, and the plasticity of the alloy sintered from powders milled for 70 hours is also improved compared with that of the alloy sintered from powders unmilled, showing good match of strength and ductility.