Composition Design and Optimization of Microstructure and Properties for an AlCrFeCoNi Low-Expansion Alloy

doi:10.11900/0412.1961.2025.00348

Acta Metall Sin

2026, Vol. 62

Issue (6): 1021-1031 DOI: 10.11900/0412.1961.2025.00348

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Composition Design and Optimization of Microstructure and Properties for an AlCrFeCoNi Low-Expansion Alloy

XU Dingfeng¹^,², HAN Feiyang¹^,², JIANG Qicheng¹^,², WANG Huan¹^,², SHANG Liyuan¹^,², LU Yiping¹^,²(

)

1 Key Laboratory of Solidification Control and Digital Preparation Technology (Liaoning Province), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China
2 Engineering Research Center of High-Entropy Alloy Materials (Liaoning Province), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China

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XU Dingfeng, HAN Feiyang, JIANG Qicheng, WANG Huan, SHANG Liyuan, LU Yiping. Composition Design and Optimization of Microstructure and Properties for an AlCrFeCoNi Low-Expansion Alloy. Acta Metall Sin, 2026, 62(6): 1021-1031.

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Abstract

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 $×$ 10^-6-2.04 $×$ 10^-6^oC^-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.

Key words: Invar alloy low expansion thermomechanical processing martensite mechanical property

Received: 29 October 2025

ZTFLH:

TG132.1

Fund: National Natural Science Foundation of China(U2341261);Joint Program of the Liaoning Provincial Science and Technology Plan(2024JH2/102600019);Innovation Support Program for High-Level Talents of Dalian(2023RG006)

Corresponding Authors: LU Yiping, professor, Tel: (0411)84709400, E-mail: luyiping@dlut.edu.cn

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	XU Dingfeng
	HAN Feiyang
	JIANG Qicheng
	WANG Huan
	SHANG Liyuan
	LU Yiping

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https://www.ams.org.cn/EN/10.11900/0412.1961.2025.00348 OR https://www.ams.org.cn/EN/Y2026/V62/I6/1021

Table 1 Nominal compositions of the low-expansion alloys

Fig.1 Coefficients of thermal expansion (a) and tensile properties (b, c) of the low-expansion alloys after homogenization
(b) engineering stress-strain curves
(c) strain-hardening rate curves and true stress-strain curves

Table 2 Tensile strengths and ductilities of the low-expansion alloys after homogenization

Fig.2 Electron probe characterizations of the low-expansion alloys after homogenization (a, b) BSE images of Al0.5Cr0.5 (a) and Al1Cr1 (b) alloys (c) enlarged BSE image of the Al1Cr1 alloy and the corresponding elemental mappings (d, e) low (d) and high (e) magnified BSE images of Al1.5Cr1.5 alloy

Fig.3 Phase analyses of the Al1Cr1 alloy
(a) calculated phase diagram (b) synchrotron XRD pattern
(c) EBSD inverse pole figure (IPF) (d) EBSD phase distribution map

Table 3 Theoretical and measured intensities of diffraction peaks in Fig.3b

Fig.4 Coefficients of thermal expansion (a) and tensile properties (b) of the Al1Cr1 alloy after thermomechanical processing

Fig.5 Microstructure characteristics of the Al1Cr1 alloy after thermomechanical processing
(a) BSE image (b) synchrotron XRD pattern
(c) EBSD IPF (d) EBSD phase distribution map

Fig.6 In situ heating XRD patterns of the Al1Cr1 alloy after thermomechanical processing

Table 4 Lattice parameters and volume fractions of each phase at different temperatures for Al1Cr1 alloy after thermomechanical processing

Fig.7 Differential scanning calorimetry curve of the Al1Cr1 alloy

Fig.8 Ashby map of specific strength versus coefficient of thermal expansion^{[10,11,36-49]}

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