Effect of Ti content on the microstructure and mechanical behavior of (Fe36Ni18Mn33Al13)100−xTix high entropy alloys

Abstract The microstructure and mechanical properties studies of a series of two-phase f.c.c./B2 (ordered b.c.c.) lamellar-structured, high entropy alloys (HEA) Fe 36 Ni 18 Mn 33 Al 13 Ti x with x up to 6 at. % Ti have been investigated. X-ray microanalysis in a TEM showed that the Ti resided mostly in the B2 phase. The lamellar spacing decreased significantly with increasing Ti content from 1.56 μm for the undoped alloy to 155 nm with an addition of 4 at. % Ti, leading to a sharp increase in room-temperature yield strength, σ y , from 270 MPa to 953 MPa, but with a concomitant decrease in ductility from 22% elongation to 2.3%. Annealing at 1173 K for 20 h greatly increased the lamellar spacing of Fe 36 Ni 18 Mn 33 Al 13 Ti 4 to 577 nm, producing a corresponding decrease in σ y to 511 MPa. The yield strengths of all the doped alloys decreased significantly when tensile tested at 973 K with a concomitant increase in ductility due to softening of the B2 phase. The fracture mode changed from cleavage at room temperature to a ductile dimple-type rupture at 973 K. The results are discussed in terms of the Hall-Petch-type relationship.