Nucleation mechanism of nano-sized NaZn13-type and α-(Fe,Si) phases in La-Fe-Si alloys during rapid solidification

Abstract

The nucleation mechanism involving rapid solidification of undercooled La-Fe-Si melts has been studied experimentally and theoretically. The classical nucleation theory-based simulations show a competitive nucleation process between the α-(Fe,Si) phase (size approximately 10 to 30 nm) and the cubic NaZn13-type phase (hereinafter 1:13 phase, size approximately 200 to 400 nm) during rapid solidification, and that the undercooled temperature change ∆T plays an important factor in this process. The simulated results about the nucleation rates of the α-(Fe,Si) and 1:13 phases in La-Fe-Si ribbons fabricated by a melt-spinner using a copper wheel with a surface speed of 35 m/s agree well with the XRD, SEM, and TEM studies of the phase structure and microstructure of the ribbons. Our study paves the way for designing novel La-Fe-Si materials for a wide range of technological applications.

Microstructure and magnetocaloric properties in melt-spun and high-pressure hydrogenated La0.5Pr0.5Fe11.4Si1.6 ribbons*

“…When the undercooling degree is above 707 K for LaFe 11.6 Si 1.4 , the 1:13 phase is formed preferentially because of its higher nucleation rate than α-Fe's. [21] A larger undercooling is obtained by a faster wheel speed. Similarly, the content of 1:13 phase will increase with the wheel speed increasing.…”

Formation of tree-like and vortex magnetic domains of nanocrystalline α-(Fe,Si) in La–Fe–Si ribbons during rapid solidification and subsequent annealing

“…La-Fe-Si ribbons with a nominal composition of LaFe 11.5 Si 1.5 were fabricated by a melt-spinning technique. Details of the preparation have been reported elsewhere [20,21]. The resulting (as-spun) ribbons were sealed in evacuated quartz ampoules and subjected to isothermal heat treatment at 1273 K for 3 min or 2 h before rapid quenching to room temperature.…”

Microstructure and Magnetocaloric Effect by Doping C in La-Fe-Si Ribbons

“…Magnetic refrigeration, as a new pollution-free and efficient refrigeration technology, has attracted widespread attention and systematic research [ 1 ]. Among the magnetic refrigeration materials currently developed, the LaFe 13-x Si x (1.2 ≤ x ≤ 1.6) alloy is a promising candidate because of its large magnetocaloric effect, low cost, and environmentally friendly properties [ 1 , 2 , 3 , 4 , 5 , 6 ]. However, there are still some issues, such as the low Curie/working temperature and the long annealing time to generate the La (Fe, Si) 13 phase producing the large magnetocaloric effect, that hinder this kind of material from practical applications.…”