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Phase and microstructure evolution during solidification of Nd-Fe-B melts processed by novel techniques

O. FILIP1,* , R. HERMANN2

Affiliation

  1. Department of Material Science 6, University of Erlangen-Nurnberg, Martensstr. 7, D-91058 Erlangen, Germany
  2. Leibniz Institute for Solid State and Materials Research (IFW) Dresden, P.O. Box 270016, D-01171 Dresden, Germany

Abstract

The influence of different techniques and process parameters like the cooling rate, undercooling level and melt convection on the phase and microstructure selection during the solidification process of stoichiometric Nd2Fe14B melts is discussed. Using an electromagnetic levitation technique, in-situ observation of the solidification kinetics was performed. Small additions of Ti and C were found to decrease significantly the growth rate of the Nd2Fe14B phase in the undercooled stages. Comparing with the stoichiometric Nd2Fe14B melt, here, only moderate quenching rates are necessary in order to suppress the formation of large unconsumed α-Fe dendrites. The microstructure formation appears to be strongly related with the precipitation mechanism of fine TiC particles during thermal processing of the melt prior to quenching on chil substrates. Additiona ly, an important change in the volume fraction and grain size of the residual α-Fe phase was observed to be produced by different melt motions at the crystallization front. A distinct reduction of the amount of α-Fe was measured in samples which were subjected to strong rotation in levitation, during the cooling process. A prove that the microstructure formation during the solidification process can be controlled by enhancement or suppression of the melt convection was given employing a specialy designed forced crucible rotation/vibration technique..

Keywords

Nd-Fe-B magnets, Undercooled melts, Growth kinetics, Melt convection.

Submitted at: Jan. 18, 2006
Accepted at: March 23, 2006

Citation

O. FILIP, R. HERMANN, Phase and microstructure evolution during solidification of Nd-Fe-B melts processed by novel techniques, Journal of Optoelectronics and Advanced Materials Vol. 8, Iss. 2, pp. 504-510 (2006)