Realization of zero thermal expansion in La(Fe,Si)13-based system with high mechanical stability

Abstract

A stable, zero thermal expansion material with enhanced mechanical properties was achieved by introducing in-situ secondary phases into a La(Fe,Si)13 matrix. In the Cu-doped LaFe10.6-xCuxSi2.4 system, a large amount of 1:1:1 and α-Fe phases are also clearly found, except for cubic 1:13 phase. With the increase of Cu-content, the number of precipitated phases increased gradually. Due to the positive thermal expansion of the secondary phases, the effect of the negative thermal expansion was compensated for in the composites. For the LaFe10.1Cu0.5Si2.4 sample, a low thermal expansion coefficient, about 2.8×10−7K−1, was achieved between 185 and 250K. This near-zero thermal expansion effect also showed high reversibility with the temperature variation because of the characteristics of second-order transitions. Moreover, the compressive yield strengths of the composites were improved, owing to the strengthening mechanism of the secondary phases. The enhancement of the mechanical properties impeded the degradation of geometric integrity and promoted the mechanical stability during cyclic thermal measurements. This work supports the design of Invar-type materials with low structural fatigue for technological application.