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Improved and novel materials for pernament magnets based on rare Earth alloys

Objective

The aim of the project is to improve ND-FE-B magnets or to find novel materials with improved properties. They may replace ferrites with the advantage of a smaller and less heavy device with better performance in starter motors, high quality motors for consumer electronics (CD, VCR, laser vision) and professional stepping motors. They can also replace SM-CO because of their lower price and better performance due to their higher flux density and lower specific weight.

AT THE MOMENT THERE ARE SIGNIFICANT LIMITATIONS, HOWEVER, IN THE APPLICATION OF ND-BE-B MAGNETS, DUE TO THE TEMPERATURE INSTABILITY OF THEIR MAGNETIC PROPERTIES AND THEIR INSUFFICIENT OXIDATION AND CORROSION RESISTANCE.
The application of neodymium iron boron magnets is significantly hampered by the temperature dependence of the magnetic properties and by an insufficient resistance against oxidation and corrosion. This project aims at an improvement of these limitations following 2 basic routes. First, novel compounds and phases will be studied and secondly investigations will be performed to improve the existing neoymium iron boron materials. Investigations will include meltspun metastable compounds and novel ternary alloys as well as phase relations with oxygen and corrosion protection of the existing materials. Such improved materials could considerably extend applications in areas such as automotive, consumer electronics and industrial automation.
The coercivity and corrosion resistance of sintered neodymium iron boron magnets have been improved by introducing the concept of 2 phase magnets in which the eutectic neodymium containing intergranular region is replaced by a ternary intermetallic compound. A new magnetic material based on iron boron has been developed which has a 50%higher remanence than magnequench but only a modest coercivity. The applicability of this material is limited to rod or ring shaped magnets. Several new classes of intermetallic compounds have been discovered that may lend themselves for future permanent magnet applications. The peculiar phase relationships in the neodymium iron carbon have been utilised to prepare a novel type of rare earth base magnet in which large coercivities (800 kAm{-1}) are obtained already in the ingot after annealing.

The effect of several additives (aluminium, aluminium oxide gallium) on the quality of sintered magnets based on neodymium (2) iron (14) boron was investigated. These additives were found to have a strong influence on the wettability of the liquid phase during sintering, which in turn affects the ultimate grain size and the shape and nature of the intergranular phase. In particular the addition of aluminium was found to lead to an enhancement of the coercivity which is explained in terms of a more uniform separation of the neodymium (2) iron (14) boron grains by a nonmagnetic neodymium rich intergranular phase.
The magnetic properties of several classes of novel strongly ferromagnetic intermetallic rare earth compounds were investigated including the metastable compound iron (3) boron doped with a few per cent of neodymium. Alloys consisting primarily of the compound neodymium (2) iron (14) carbon offer the opportunity to manufacture ingot magnets falling in the range of medium performance and medium price. Also bonded magnets prepared from melt spin iron (3) boron type alloys fall into the same category although these magnets are restricted to special applications owing to their comparatively low coercivities.
The application of the present generation of ND-FE-B magnets is significantly hampered by the temperature dependence of the magnetic properties and by an insufficient resistance against oxidation and corrosion. Accordingly, this project will follow two main routes. Philips will study novel compounds and phases in the RE-FE-X system, whereas BOSCH, together with MPI, will perform investigations to improve the existing materials of ND-FE-B.

Investigations will include studies on metastable coumpounds fabricated by melt-spinning; completely new and novel ternary alloys of the form RE-FE-X where x is v, cr, w, mo, nb, hf. In addition, the phase relations with oxygen, absorption characteristics of oxygen during magnet fabrication and corrosion protection will be fully studied with the aim to reduce the sensitivity of the magnets and powders to the effects of oxidation and corrosion.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Philips Gloeilampen Fabrieken NV
Address

5600 JM Eindhoven
Netherlands

Participants (1)

ROBERT BOSCH GMBH.
Germany
Address
Robert-bosch Platz 1
70049 Stuttgart