Unlocking the potential of non-ferromagnetic Invar-type alloys in space exploration

The effects of Fe and Mn on the thermal expansion characteristics of non-ferromagnetic Cr-Fe-Mn alloys, which exhibit the Invar effect, were investigated. It was found that the temperature range in which the alloy exhibits low thermal expansion characteristics is below 273 K when the Mn content is less than 0.3%. Conversely, this range shifts to between 273 and 350 K when the Mn content increases to 0.9% or higher. By incorporating small amounts of rare earth elements, the Cr_94.6Fe_4.7Mn_0.7 alloy achieved an average coefficient of thermal expansion of 0.94 × 10⁻⁶/K between 273 and 350 K, which is lower than the 1.2 × 10⁻⁶/K observed in conventional Invar alloys. Additionally, measurements of magnetic hysteresis loops were conducted to assess the residual magnetization, which is critical for structural components near magnetic measurement equipment. The results indicated that the residual magnetization of the Cr-based Invar-type alloy is approximately 0.0033 mT, significantly lower than the 35 mT typically found in conventional Invar. These substantial differences underscore the potential of Cr-based Invar-type alloys as a superior alternative for applications requiring low thermal expansion and low residual magnetization.