Invar Effect in the Wide and Higher Temperature Range by Coherent Coupling in Fe-Based Alloy

Invar alloys with zero thermal expansion (ZTE), isotropy, high operation temperature, and wide temperature range are of great significance in fields such as aerospace and modern industry. However, it is difficult to simultaneously meet the above characteristics in one material. The traditional methods like element or vacancies doping would increase the operation temperature but at the expense of ZTE behavior. Here, by the coherent coupling between two cubic phases, the isotropic ZTE metallic material with the higher cut-off temperature (560 K) and a wide operation temperature range (ΔT = 200 K) is obtained in Fe_2.75Co_0.25PtB_0.25. The operation temperature range is much higher than that of commercial Fe_0.65Ni_0.35 Invar alloy and meets the applications at elevated temperatures. High-angle annular dark field images and synchrotron X-ray diffraction prove that by the coherent interfacial coupling between the A1 and its coherent L1₂ nanodomains, the original negative thermal expansion or positive thermal expansion performances for them can be changed into the same ZTE performances. This thermal expansion regulation strategy realized by coherent coupling will lead to an innovative and significant revolution for ZTE design and promote its development and application.