Synergistic control of thermal expansion and oxidation resistance in novel invar-type alloys

Abstract

Low thermal expansion alloys are critical for applications requiring high dimensional and thermal stability, particularly in industrial equipment and precision instruments. To broaden their usability in high-temperature environments, such alloys must also exhibit a high Curie temperature and strong oxidation resistance. In this study, the Invar effect was utilized for alloy design, supported by thermodynamic predictions performed with Thermo-Calc software. Seven novel alloys were developed, incorporating intermetallic compounds with intrinsically low coefficients of thermal expansion (CTE). The effects of Al and Mn content on the thermal and oxidation behavior of alloys P1 to P6 were systematically investigated. A seventh alloy, P7, was designed to outperform commercial counterparts by incorporating Ti to promote TiB₂ precipitation and Si to enhance Al activity. Among all tested compositions, alloy P7 exhibited the lowest CTE and the best oxidation resistance, outperforming the commercial alloy HRA929. These findings demonstrate that P7 is a promising candidate for high-temperature structural applications requiring both low thermal expansion and excellent oxidation resistance.