Reactive diboride redirects phase evolution towards hierarchical ordering in a multicomponent alloy

Trace ceramic additions can redirect phase selection in multicomponent alloys. We introduce a nominal 0.05 wt% TiB₂ addition via an Al–TiB₂ master alloy into Fe₃₅Co₃₀Ni₂₅Al₇Nb₃ (at.%) and compare it with a base-composition-matched control under identical heat treatment. The cast processed state contains AlB₂-type (Nb,Ti)B₂ and substantially coarser FCC grains. After solution treatment and ageing, the processed alloy retains a continuous FCC matrix with L1₂ precipitates, interfacial B2 and B2 laths, whereas the control remains FCC-dominant. It reaches 1,209.5 ± 48.3 MPa tensile strength and 37.64 ± 1.61% total elongation (mean ± s.d., n = 3), with renewed work hardening. The measured L1₂ geometry yields an Orowan-form scale of approximately 356 MPa, far above the adopted-coefficient Hall–Petch estimate of 46.4 MPa. These findings associate a reaction-modified cast precursor with hierarchical ordering and a high strength–ductility response.