Effect of Process Parameters on Thermal Expansion Coefficient of Invar 36 Alloy Formed by Selective Laser Melting Additive Manufacturing

WANG Chaochao; LIU Fencheng; LIU Fenggang; YOU Qifan; HE Wenbin; WANG Jun

doi:10.16490/j.cnki.issn.1001-3660.2026.20.009

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Surface Technology ›› 2026, Vol. 55 ›› Issue (20) : 102-114. DOI: 10.16490/j.cnki.issn.1001-3660.2026.20.009

Effect of Process Parameters on Thermal Expansion Coefficient of Invar 36 Alloy Formed by Selective Laser Melting Additive Manufacturing

WANG Chaochao, LIU Fencheng^*, LIU Fenggang, YOU Qifan, HE Wenbin, WANG Jun

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Abstract

Invar 36 alloy is a typical low thermal expansion alloy, which exhibits an ultra-low thermal expansion coefficient (<2×10^-6 ℃^-1) at room temperature. The ultra-low thermal expansion behavior of Invar 36 alloy at room temperature is generally attributed to the "magnetostrictive" effect locking inherent to the alloy itself. With the limitations of traditional processing technologies in meeting the emerging application requirements for Invar 36 alloy structures, selective laser melting (SLM) technology has been adopted as an alternative approach. However, the inherent thermal cycling mode of SLM technology can alter the microstructure and properties of Invar 36 alloy. Therefore, it is essential to investigate the effects of SLM on the microstructure and properties of Invar 36 alloy, particularly its thermal expansion properties. Meanwhile, to achieve more straightforward control over the thermal expansion performance of Invar 36 alloy, an approach for artificially regulating the alloy's expansion behavior by controlling its porosity is proposed. It is necessary to first explore the correlation mechanism between the microstructure, pore defects, and thermal expansion coefficient of Invar 36 alloy. Ultimately, the goal is to artificially control the porosity of Invar 36 alloy by adjusting laser process parameters, thereby regulating its thermal expansion coefficient. In this study, Invar 36 alloy samples were fabricated via SLM under different process parameters, and their density and porosity were calculated. The microstructure was characterized using techniques such as EBSD and SEM. Finally, the thermal expansion coefficients of the Invar 36 alloy samples prepared under different laser process parameters were measured. The results indicated that the density of SLM-fabricated Invar 36 alloy first increased and then decreased with the increase of energy density. The maximum density of Invar 36 alloy was achieved when the energy density was 108.33 J/mm³. Microstructural observations revealed that the molten pool morphology of SLM-fabricated Invar 36 alloy was significantly influenced by heat input, with an overall "fish scale" or "cup-like" appearance. The solidification structure inside the molten pool was dominated by coarse columnar grains grown epitaxially. Within these columnar grains, a fine cellular substructure with an average size of approximately 0.7 μm was observed, and high-density dislocations were entangled at the boundaries of the cellular substructure. A significant correlation existed between the thermal expansion coefficient and porosity of Invar 36 alloy: the average thermal expansion coefficient increased with the decrease of porosity. High porosity could offset the thermal expansion of the structure, and the low expansion performance was affected by high stress, porosity, and the "Invar effect". Additionally, it was found that as the temperature increased, the difference in thermal expansion coefficients among Invar 36 alloy samples prepared at different energy densities decreased. This indicated that with increasing temperature, the ability of Invar 36 alloy to offset thermal expansion through hysteretic shrinkage was weakened, and the expansion space of internal pores was gradually reduced. It can be predicted that the growth trend of the thermal expansion coefficient of Invar 36 alloy will tend to be uniform above the Curie temperature. In conclusion, Invar 36 alloys with different thermal expansion coefficients can be fabricated by adjusting the porosity of the alloy through the optimization of SLM process parameters.

Key words

selective laser melting / Invar 36 alloy / coefficient of thermal expansion / metallurgical defects / microstructure

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WANG Chaochao, LIU Fencheng, LIU Fenggang, YOU Qifan, HE Wenbin, WANG Jun. Effect of Process Parameters on Thermal Expansion Coefficient of Invar 36 Alloy Formed by Selective Laser Melting Additive Manufacturing[J]. Surface Technology. 2026, 55(20): 102-114

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