Abstract: Unlike conventional Elinvar alloys that rely on magnetoelastic effects or phase transitions, NiTi-type multi-principal element B2 intermetallics, such as CoNiTiZr, exhibit the Elinvar effect through intrinsic modulus hardening due to the thermal alleviation of lattice distortion. While both the atomic size mismatch and sublattice frustration contribute to lattice strain, the specific role of sublattice frustration in lattice distortion and elastic behavior across temperatures remained unclear. We show that atomic size mismatch introduces localized strain fields, while electronic structure randomness frustrates symmetry-breaking transformations and delocalizes lattice strain, thus mitigating overall distortion. Further, we proposed a sublattice engineering model that quantitatively predicted the temperature-dependent elastic modulus of both multiple-element B2 intermetallics and body-centered cubic alloys. The model revealed a strong distortion-modulus coupling in the B2 structure due to covalent bonding contributions and accurately illustrated the Elinvar mechanism. This framework offers a physically grounded approach for designing lattice-distortion-induced Elinvar alloys with improved thermoelastic stability.

Key words: Multi-principal element intermetallics, B2 intermetallics, Elinvar effect, Lattice distortion