Microstructure evolution and its influence on the thermal expansion of La(Fe0.79Al0.21)13 alloy prepared by arc-melting

Abstract NaZn13-type La(Fe1-xAlx)13 alloys show tunable thermal expansion. However, whether the arc-melted alloys contain secondary phase, which can obviously influence the thermal expansion, is still unclear. Facing to this question, we take arc-melted La(Fe0.79Al0.21)13 as an example and investigate its microstructure evolution. The as-cast ingot consists of NaZn13, α-Fe and amorphous La-rich phases. Their size and distribution are different at different positions, indicating the existence of microstructure segregation. During annealing,NaZn13 phase grows up through a reaction between α-Fe and amorphous La-rich phases, but a single-phase sample still can’t be obtained even after 15-days-annealing. Nonuniformly distributed α-Fe phase, which is a result of microstructure segregation, exists in the NaZn13 main phase. Our measurements on different parts of the annealed sample indicate that the thermal expansion is highly related with the local concentration of α-Fe phase.