Direct versus indirect particle strengthening in a strong, ductile FeNiMnAlTi high entropy alloy

Abstract In this paper, we show that the strengthening from (Ni, Al, Ti)-rich B2 particles in the recrystallized (Fe, Mn)-rich f.c.c. high entropy alloy (HEA) Fe 42 Ni 12 Mn 36 Al 8 Ti 2 arises indirectly by reducing the grain size thus providing increased Hall-Petch strengthening, rather than directly through dislocation pinning, a concept first introduced by P.M. Hazzledine (Scripta Metall. Mater. 26 (1992) 57–58). Thus, the yield strength increased from 200 MPa for the as-cast HEA to 509 MPa for the recrystallized HEA. The contributions to the increase of the yield strength were calculated to be 28 MPa from particle pinning and 281 MPa from Hall-Petch strengthening. We also show using high angle angular dark field imaging in a scanning transmission electron microscope that Fe 42 Ni 12 Mn 36 Al 8 Ti 2 exhibits no evidence of the severe lattice distortion that is a core tenet of HEAs. Both as-cast and recrystallized HEAs showed ductile fracture modes.