Achievement of zero thermal expansion covering room temperature in the La(Fe,Al)13-based bulks with reduced annealing time

Abstract

In this paper, we adopt copper-mould casting to prepare the compound with nominal composition of LaFe10·3Al2.7, which has been reported to exhibit isotropic zero thermal expansion (ZTE). The rapid cooling rate provided by copper-mould makes the α-Fe phases in both as-cast and annealed sheets have similar size and homogeneously distributed. This improvement is helpful to prepare bulks with uniform and stable thermal expansion. On the other hand, the rapid cooling rate reduces the size of the α-Fe phases in the as-cast sheet. It facilitates the formation of NaZn13 phase during annealing. For the sheet with thickness = 2 mm, annealing time can be shorten to be 2 days. Moreover, we add Co in the composition to enhance the magnetic ordering-disordering temperature of the NaZn13 phase. The ZTE temperature region is successfully enlarged to room temperature. Our results provide a strategy to design LaFe13-xAlx bulks with ZTE reaching room temperature.