Influence of aging temperature on physical properties of a 40NiCrTiAl Elinvar alloy

Abstract

This study investigates the effect of aging temperature on the physical properties of Fe–40.32Ni–5.51Cr–2.63Ti–0.47Al–0.55Mn–0.40Si–0.016C (wt.%) alloy using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, a physical-property measurement system, and a dilatometer, among others. After a solution treatment, the microstructure of the experimental alloy was composed of the γ phase. The aging process involved the precipitation of the γ’ and η phases to regulate the Elinvar effect. No martensite or ferrite phases were observed in either the solid-solution or aged samples using X-ray diffraction and transmission electron microscopy. The Elinvar effect for traditional Fe–Ni–Cr ferromagnetic Elinvar alloys is related to spontaneous magnetisation, resulting in spontaneous volume magnetostriction. The inflection temperature of the elastic modulus exceeded the Curie temperature. The larger the precipitation amount, the weaker the ΔE effect, and the larger the Young’s modulus value. For a holding time of 2 h, the amount of precipitation was maximised at an aging temperature of 650 °C, while Young’s modulus and its temperature coefficient achieved maxima of 190 GPa and 9.0 × 10⁻⁵ °C⁻¹, respectively. In addition, the lattice constant at room temperature indirectly reflects the amount of precipitation. Young’s modulus, the temperature coefficient of Young’s modulus, the Curie temperature, and the linear-expansion coefficient obeyed an approximately parabolic law as functions of the lattice constant or its reciprocal. Moreover, Young’s modulus and its temperature coefficient can be estimated using the Curie temperature and linear-expansion coefficient, respectively.