Berlin 2012 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 13: Magnetic Materials

MA 13.13: Vortrag

Montag, 26. März 2012, 18:15–18:30, H 0112

Study of the mechanisms of the Thermal Decomposition reaction in the magnetocaloric system La(Fe,Si,Co)₁₃ — •Konrad Löwe¹, Jian Liu¹, Hossein Sepehri-Amin², Kazuhiro Hono², Matthias Katter³, and Oliver Gutfleisch^4,1 — ¹IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany — ²NIMS, 1-2-1 Sengen, Tsukuba 305-0047 Japan — ³Vacuumschmelze GmbH u Co. KG, Grüner Weg 37, 63450 Hanau, Germany — ⁴TU Darmstadt, Institute for Materials Science, Petersenstr. 23 64287 Darmstadt, Germany

We report on the influence of the Co content in the magnetocaloric system La(Fe,Si,Co)₁₃ on the Thermal Decomposition (TD) reaction. In the course of the reaction, the magnetocaloric La(Fe,Si,Co)₁₃ phase reversibly decomposes into α-Fe(Co,Si) and the intermetallic LaFeSi phase, thus greatly enhancing the mechanical properties and therefore the machinability of the compound. The addition of Co significantly speeds up the reaction kinetics. The optimum temperature range for the TD was determined to be 973 - 1073 K, whereas the lower and upper limit lies at 873 K and 1173 K, respectively. With electron microscopy a pearlitic microstructure (lamellae) has been found in the decomposed state, indicating a eutectoid-type phase reaction. The thickness of the lamellae is about 20-30 nm in LaFe₁₂Si and decreases with increasing Co content. Also the pearlite seems to be more ordered with addition of Co. 3DAP measurements show the enrichment of Co in both the α-Fe(Co,Si) and the LaFeSi lamellae. We conclude that the addition of Co somehow changes the pearlitic growth mechanisms, which is the main reason for the greatly enhanced TD kinetics.