Physical Properties of Ternary Re-Fe Base Alloys and their Relationship to Permanent Magnet Applications
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PHYSICAL PROPERTIES OF TERNARY RE-Fe BASE ALLOYS AND THEIR RELATIONSHIP TO PERMANENT MAGNET APPLICATIONS.
K.H.J. BUSCHOW Philips Research Laboratories P.O.Box 80000, 5600 JA Eindhoven, The Netherlands
ABSTRACT Several ternary compounds of tetragonal structure and with the composition R2FeI 4B have found an application as starting materials for permanent magnets. Several physical properties of R2Fel 4B compounds will be discussed in relation to the modification in properties that can be obtained by substituting other elements for R, Fe or B. Also investigated is the extent to which it will be possible to find alternative materials differing in structure and composition from R2Fel 4B. For this purpose the results obtained on 3d-rich ternaries based on well-known structure types will be reviewed. Included in this survey will be novel ternary intermetallics made by crystallization from the amorphous state. These compounds, though stable enough for applications, are actually metastable. They are not found in the corresponding equilibrium diagrams.
INTRODUCTION Permanent magnets based on Nd-Fe-B can be manufactured in two different ways. One of the methods consists of powder metallurgy of cast Nd-Fe-B alloys and includes liquid phase sintering [1[. In the other method the starting material consist of melt-spun Nd-Fe-B which is then hot pressed in one or two different stages [2]. Both manufacturing processes lead to magnet bodies with favourable values of the energy product (BH)max. The intrinsic coercive force jHc and Br would hardly justify the enormous scientific activity which has taken place during the last few years [3], since it is not to be expected that there will be any major improvements in these magnetic properties. However, these magnetic materials also have some less favourable properties, such as a relatively low corrosion resistance and a relatively high temperature coefficients of the magnetization and coercive force. This poor thermal stability of the magnets comes into play when these magnets are applied in electrical machines requiring a recoil line coincident with their demagnetization characteristic over a fairly large temperature range. In the new Nd-Fe-B magnets this temperature range is rather limited, so that an increase in temperature leads to irreversible demagnetization by armature reaction fields. The research efforts devoted to 3d-rich ternary rare earth intermetallics comprise three distinct directions. One of these directions encompasses experimental and theoretical studies of the exchange interaction and crystal field effects in the ternary compounds in relation to similar types of interactions found in the large class of binary rare earth 3d intermetallics. The two other directions aim at finding materials in which the deficiencies mentioned above are less serious or are absent altogether. One way of looking for such materials is to investigate the modifications in properties that can be Mat. Res. Soc. Symp. Proc. Vol. 96- 1987 Materials Research Society
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obtained by substituting
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