Phase formation and structure in rapidly quenched La(Fe0.88Co0.12)13−xSix alloys

La(Fe0.88Co0.12)13−xSixalloys were produced by arc-melting and melt spinning with various wheel speeds. The phase formation and microstructure were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The rapid quenching and the increase in Si content greatly facilitated the formation of the cubic NaZn13-type La(Fe, Co, Si)13 (1:13) in La(Fe0.88Co0.12)13−xSix alloys. Rietveld fitting results indicate that the amount of the 1:13 phase is 61, 82 and 100 wt.% in the rapidly quenched (RQ) alloys with x=1.5, 1.8 and 2.2, respectively. A single phase of 1:13 structure is formed in the rapidly quenched alloy with x=1.5 and 1.8 after a short annealing process (1273 K/20 min) compared to several weeks for attaining an almost single phase with the 1:13 structure for the arc-melted (AM) alloy. Microstructural analyses (TEM) indicate that the 1:13 phase with submicron grain size is the matrix phase while α-Fe is nano-size precipitate phase within the matrix in the rapidly quenched La(Fe0.88Co0.12)11.5Si1.5 alloy prepared with a wheel speed of 40 m/s. The fine microstructure of the rapidly quenched alloy is responsible for the rapid formation of the 1:13 phase during the annealing process.