Balancing negative and positive thermal expansion effect in dual-phase La(Fe,Si)13/α-Fe in-situ composite with improved compressive strength

Abstract

Materials with near-zero thermal expansion are helpful in improving the reliability of devices. One way to synthesize such materials is mixing material showing positive thermal expansion with that displaying negative thermal expansion. Large negative thermal expansion has been widely observed in NaZn13-type La(Fe,Si)13-based alloys during the magnetic transition. It suggests that these materials have potential applications as thermal-expansion compensators. However, how to compensate the negative thermal expansion and simultaneously improve its strength are two considerable questions. Here, we introduce in-situ precipitated α-Fe phase to compensate the negative thermal expansion of 1:13 phase, and thus achieve a near-zero thermal expansion in La(Fe,Si)13/α-Fe in-situ composite. On the other hand, the distributed ductile α-Fe phase greatly enhances the compressive strength, solving the brittleness problem of 1:13 phase. The yield compressive stress of the in-situ composite with near-zero thermal expansion reaches 970 MPa. This work opens up an effective way to the design of materials with both near-zero thermal expansion and improved strength.