针对传统因瓦(Invar)合金因室温屈服强度不足而难以应用于承重件的问题，本工作通过在FeCoNi合金体系中引入Al、Cr元素并结合热机械处理，旨在开发兼具低膨胀与高强度的新型Al₁Cr₁(Fe₆₅Co₄Ni₃₁)₉₈合金。结果表明，该合金经热机械处理后晶粒显著细化，马氏体体积分数升高至8.91%，并伴随孪晶和高密度缺陷的生成。在-60~100 ℃范围内，合金热膨胀系数降低至1.10 × 10^-6~2.04 × 10^-6 ℃^-1。除了Invar效应外，这种低膨胀行为还源于升温过程中马氏体相减少引起的体积收缩部分抵消了晶格热振动，以及界面和缺陷抑制了非谐性晶格振动，同时该微观组织特征使合金的屈服强度和抗拉强度分别达到324和452 MPa，断后伸长率保持在20%以上。与典型的Fe-Ni系Invar合金相比，本工作设计的合金在具有高比强度的同时保持了较低的热膨胀系数，表明合金成分设计与热机械处理的协同优化能够在低膨胀与力学性能之间实现优异平衡，为形变敏感构件的材料设计提供了新思路。

Low-expansion alloys are essential structural-functional materials for advanced technologies requiring stringent dimensional stability. They are key components in precision metrology, electronic and microwave devices, cryogenic systems, and ultraprecision manufacturing equipments, where thermal deformation must be strictly controlled. However, conventional Fe-Ni Invar alloys possess insufficient mechanical strength despite their exceptionally low coefficient of thermal expansion, which limits their applicability in load-bearing environments. Design concept of high-entropy alloys offer a promising pathway to overcome this limitation through multiprinciple element alloy design and the associated synergistic effects. In this work, a novel low-expansion alloy, Al₁Cr₁(Fe₆₅Co₄Ni₃₁)₉₈, was developed by introducing Al and Cr into the multicomponent system and applying thermomechanical processing to tailor and refine its microstructure. This design strategy aims to achieve the synergistic optimization of thermal expansion behavior and mechanical performance. Additionally, in situ XRD during heating was employed to elucidate the underlying mechanism and monitor phase evolution. After thermomechanical processing, the alloy exhibited pronounced grain refinement and an increased martensite volume fraction of 8.91%. The microstructure further contained abundant deformation twins and a high density of lattice defects, which collectively enhanced the mechanical strength and thermal stability. Within the temperature range of -60 ^oC to 100 ^oC, the coefficient of thermal expansion decreased to 1.10\times10^-6-2.04\times10^-6oC^-1. In addition to the Invar effect, this ultralow expansion behavior is attributed to the partial compensation of lattice thermal vibrations by the volume contraction associated with martensite reduction during heating, together with the suppression of anharmonic lattice vibrations induced by interfaces and defects. Meanwhile, the refined microstructure delivered an excellent combination of strength and ductility, achieving a yield strength of 324 MPa, an ultimate tensile strength of 452 MPa, and a fracture elongation greater than 20%. Compared with conventional Invar alloys, the designed alloy exhibited a higher specific strength while maintaining a low coefficient of thermal expansion. These results demonstrate that the synergistic optimization of compositional design and thermomechanical processing enables the exceptional integration of low thermal expansion with robust mechanical properties, offering valuable guidance for developing dimensionally stable structural alloys.