20120130406014

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME
127
POWDER METALLURGY AND ITS APPLICATION IN THE PRODUCTION
OF PERMANENT MAGNETS
Iessa Sabbe MOOSA
University of Buraimi, Buraimi, College of Engineering, Sultanate of Oman,
P. O. Box 890, P. C. 512, Al-Buraimi,
ABSTRACT
In this article, some aspects of powder metallurgy have been reported. Powder metallurgy
technique has been used in the production of permanent magnets since 1700s, and found to be the
best method of fabrication of this sort of magnets. Most of high performance permanent magnets
have been fabricated by employing powder metallurgy. Magnetic properties are so dependent on
starting materials, microstructures, magnetic alignment, and heat testament process, therefore powder
metallurgy represents an ideal route to control most of these factors.
Keywords: Powder Metallurgy, Permanent Magnets, Magnetic Alignment, Rear Earth Magnets.
HIGHLIGHTS
Powder metallurgy is a route of fabrication without full melting. Some aspects of this method
of production have been discussed. The application of powder metallurgy in the production of
permanent magnets has been reported. Magnetic properties are very sensitive to the chemical
composition and microstructure of the products.
1. INTRODUCTION: WHAT IS POWDER METALLURGY?
Powder metallurgy is a means of manufacturing, without full melting, objects having
properties which cannot be obtained by any other process. It is a technique that is applied for
consolidation and formation of materials into useful products with different shapes, starting with
powder mass. Powder metallurgy has played a vital role in solving many production problems,
especially with those materials having very high melting points. During the last period of time
powder technology has made remarkable progress for many fundamental reasons:
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(i) It can be used to manufacture articles which cannot be made by any other route, such as porous
bearing, filters, abrasive tools, electric lamp filaments, dynamo brushes, and a variety of soft and
hard magnets, etc.
(ii) High purity material can be produced through this technique by controlling the production
processes.
(iii) It may be used for products which may be made by other methods, but for which powder
metallurgy is more convenient and cheaper with better quality.
The development of powder metallurgy is due to its great advantages over other routes in
certain applications. It has now become the basis for the production of refractory metals, heat
resistances materials, cutting tools, especial alloys which cannot be produced by conventional
melting method, ceramic materials and most of magnets either in micro-scales or in nano-scales. The
aim of this article is to give a general idea about powder metallurgy and its employment in the
production of permanent magnets with especial specification according to their use.
2. SOME ASPECTS OF POWDER METALLURGY
a- Compaction
Compaction may be defined as the process for fabricating a desired shape by applying
pressure to a powder in a die. The pressures which are used for this purpose are either of a
mechanical or hydraulic type. The strength of the compacts made by pressing should be sufficient to
withstand transportation to the next metallurgical operation. More information about this subject has
been reported by Kuhn and Lawley 1978 [1]. There are many compacting techniques which have
been used for fabricating different shapes;
(i) Die compaction (ii) Isostatic compaction
(iii) Explosive compaction (iv) magnetic compaction
(v) Compaction by rolling (vi) Compaction by extrusion
(vii) Compressing shearing method which was successfully developed by Tetsuji et al. [2].
There are two kinds of isostatic pressing equipment, these are known as Cold Isostatic Pressing
(CIP) and Hot Isostatic Pressing (HIP) and both of them are either wet bag tooling or dry bag
tooling. Fig. 1 illustrates the principles of the both types of tooling [3]. The use of any compaction
technique depends on the shape of the magnet, and which one of these techniques is suitable for the
production process to reach the desirable magnet.
wet dry
Fig. 1. Wet and dry tooling isostatic pressing [3]

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b- Green density
Green density is an expression given to the density of the part after pressing by any powder
metallurgy route in which the starting material is a powder. One of the most useful properties to be
specified in the powder metallurgy process, generally the green density increases with;
(i) Increasing compaction pressure according to the type of the starting powder.
(ii) The use of a wide range of particle size.
(iii) Decreasing the hardness of the particles.
(iv) Addition of lubricants.
The green density distribution is much dependent on the length to the diameter (L/D) ratio of
the compact [4]. If this ratio decreases, the green density becomes more homogeneous. A schematic
illustration is given in Fig .2 for high and low (L/D) ratios.
Fig. 2. Schematic illustration of green density distribution for high and low L/D ratios
c- Solid state sintering
In most cases, a green density compact cannot be used as the finished article because of low
strength and brittleness. Sometimes a compact is required with a certain amount of porosity, but even
in this case mechanical properties need to be improved by means of a heat treatment, which increases
the cohesion between the particles of the green compact, or within a loose powder confined to a
required shape. This heat treatment is known as "sintering". Many authors have discussed the
phenomena occurring during sintering and it is agreed that sintering can occur in the solid state,
normally taking place at a temperature below the melting point of the main component [5-7]. The
Metals Handbook. Vol.7, American Society for metals, 1984, defines sintering as "the bonding of
adjacent particles in a powder mass or compact by heating below the melting point of the main
constituent". Six stages are considered during the sintering process; initial bonding, neck growth,
pore channel closure, pore rounding, pore shrinkage and pore coarsening [8].
d- Liquid phase sintering
Liquid phase sintering (LPS) can be defined as "sintering of a compact or loose powder to
produce consolidation under condition where a liquid is present during part of the sintering
cycle". This process is widely used for consolidating metallic powder, ceramic powder, or both of
them together, into final shapes. Liquid phase sintering is an important technological process for the
production of hard metals, ceramic materials, soft and hard magnets, which is very essential to
approach a value of about 99% of the theoretical density of the product. The advantages of
production by this sintering method are a very fast densification rate, and production of
microstructures which often provide mechanical and physical properties superior to those produced
by solid state sintering.
Single End Compaction
High L/D Low L/D
L
D

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Three stages in the liquid phase sintering process have been identified [9-11]; rearrangement,
solution-reprecipitation and solid-phase bonding. One case should be noted; that is the liquid phase
dose not wet the solid particles because there is no reaction between them. This condition is often
termed "sweating" and is shown by the presence of droplets on the compact surface. Fig. 3 shows
high magnification fracture surface of sintered magnet of Nd16 Fe76B8 which was fabricated by
hydrogen decrepitation (HD) process, and the sintering temperature was within the liquid phase
sintering of this magnet. It is very clear to recognise the Nd- rich phase at the grain boundaries,
surrounding almost all the particles of the hard phase Nd2Fe14B.
Fig. 3. SEM micrograph showing fracture surface of sintered specimen of Nd16Fe76B8 made from
powder of (HD) process [12, p. 171 ].
e- Sintering density
The density of the sintered mass is normally compared with the theoretical density of the
basic material. In general, the maximum value of this sintered density is usually considered as a
criterion of the quality of the sintering process, unless otherwise is specified.
3. THE ADVANTAGES OF POWDER METALLURGY IN THE PRODUCTION OF
PERMANENT MAGNETS
Powder metallurgy techniques have been found to offer advantages in the fabrication of
permanent magnets. It seems that the best magnetic properties probably often achieved by employing
Powder metallurgy routes rather than casting processes. Although in some cases a combination
between them is used in the manufacturing of permanent magnets. Careful control of particle size
and particle orientation, using a magnetic field to align the starting particles, are among two of the
greatest advantages of the powder metallurgy process.
Chemical composition, impurities, and metallic and non-metallic inclusions probably
controlled by using powder techniques. Additionally, extremely pure powders and freedom from
inclusions are easy to attain by powder metallurgy processing. Composition of the permanent
magnets may be limited in precision by the purity with which powder can be produced. In fact, all
these factors mentioned above play a vital role in controlling and enhancing the magnetic properties
of permanent magnets and soft magnets as well.

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The products of powder metallurgy almost semi-finished produced to specifications with
different shapes and sizes, so from this point of view the powder metallurgy technique is very
advantageous as the machining stage can be dispensed with, thus decreasing costs and saving
materials.
4. HARD MAGNETIC MATERIALS
Hard magnetic materials remain permanently magnetised after they are pulse magnetised in a
magnetic field. These materials are hard to magnetise and demagnetise. Magnetic hardness is
obviously related with the microstructure, heat treatment and chemical composition of the starting
material. Magnetically hard substances are made into permanent magnets which provide magnetic
field in working air, or vacuum gapes. The distinguishing characteristics of hard magnets are large
hysteresis loops, high remanence and corercivity with different Curie temperatures. Permanent
magnets are fundamentally energy storage systems when they are magnetised. Development of hard
magnetic materials is in the direction of obtaining improved magnetic properties, reducing the cost of
production and the volume of material required. Hard magnets are used to perform a wide variety of
magnetic functions, such as in electrical machines, motors, computers, direct drive motors, electro-
dynamic braking, clamping and holding devices for ferrous materials, loudspeakers, magnetic
sealing, head-phones, focusing and steering of charged particles, medical equipment, etc.
5. POWDER METALLURGY AND PERMANENT MAGNETS
In fact, powder magnets have been known for a long time, the first development was made
by Gowin Knight (1713-72), an English gentleman who stirred continuously a large amount of iron
in water until he got a suspension of divided of finely iron oxide. This was mixed with linseed oil,
the paste moulded into shape and baked hard. The resulting blocks were then magnetised and formed
strong magnets for that time, reputedly [13]. The beauty of this story shows that the beginning of the
development of the first permanent magnet by powder metallurgy primitive technique.
In the 1960's, the idea of this process of surrounding hard phase particles with non-magnetic
material has been strongly re-introduced for producing permanents magnets [14, 15]. Some ferrites
tend to be dissociated during heating at elevated temperature, so that the conventional route of
melting and casting is impractical for ferrites, and ferrites are normally fabricated by Powder
metallurgy [16].
6. MAGNETIC ALIGNMENT
(i) Magnetic field alignment
It is well known that magnetic alignment is one of the most important factors in the
manufacturing of magnetic materials and articles made from them. If a magnetic filed is applied
during the cooling or tempering while the temperature is just below the Curie point, a
crystallographic growth along the direction of the applied filed which is nearest to the easy axis is
encouraged. This process called magnetic annealing, the first attempt of this process was carried out
at Sheffield (UK), and in 1938 it was found that heat treatment in a suitable magnetic field could
enhance the magnetic properties of Alnicos permanent magnets [17]. This process was also used in
the production of Sm-Co permanent magnets to solidify the ingots from the liquid state in a magnetic
field produces oriented polycrystalline materials [18].
The production of magnets, by employing powder metallurgy technology probably give
improved products because of the simplicity of aligning most of the powder particles along the easy
direction at room temperature, and hence producing anisotropic compacts. These are manufactured

132
by pressing fine particles of the materials in a strongly aligning magnetic field and then sintering to
near theoretical density. The degree of alignment is influenced by particle shape, particle size
distribution, magnitude of aligning field, and pressing pressure. The remanennce and the energy
product are thereby sharply enhanced [19]. Magnetic alignment of Nd-Fe-B hydride powder using a
flexible bag is shown in Fig. 4.
In 2007, synthesis of magnetite particle-chain microwires by applying magnetic field during
the fabrication process has been firstly reported by Fashen et al. [20]. Their conclusions were that
Fe3O4 microwires are successfully produced under external magnetic field, and the connection of the
particles is very tight with each other. Fig. 5 shows the morphology of Fe3O4 magnetic powder, from
which we can see the chain agglomeration of the particles and the particle size is within the range of
mµ25.0 .
(a)
(b)
Fig. 4. Magnetic alignment using a flexible bag [12, p. 120]
(a) Schematic diagram
(b) Flexible bag filled with (HD) powder wetted with some cyclohexane
Magnetic Poles
Rubber Stoper
Flexible plastic Tube
HD powder of Nd-Fe-B
Flexible bag
Argon Atmosphere

133
Fig. 5. SEM micrograph showing the morphology of the Fe3O4 magnetic powder
(ii) Magnetic alignment by cold rolling
This method is limited to ductile ferromagnetic materials. Many of them exhibit a fairly
strong tendency to orientate their crystals when they are cold rolled or worked, depending upon the
fabricability of the materials. Plastic deformation can produce a grain orientation which gives
improved magnetic properties. An investigation of this phenomenon utilising a single crystal of
Ni3Fe was made by Chikazumi, et al. [21]. They found that the anisotropy is strongly dependent on
the crystallographic orientation during the rolling process. Textured anisotropic FePd /α -Fe
nanocomposite foils have been produced by combination between cold rolling process and magnetic
alignment under high magnetic field, after being annealed at Cο
600450 − for 2h [22]. Their
conclusions were that magnetic anisotropy could be induced in the magnetically annealed FePd /α -
Fe nano-composites due to their textured nanostructures.
(iii) Magnetic alignment by Thermo-mechanical route
Magnetic alignment may be achieved by Thermo-mechanical alignment means.
Crystallographically orientated or anisotropic magnets can be prepared by this route, which consists
of hot pressing followed by hot deformation. This was discovered in 1985 by R. W. Lee, Physics
Department, General Motors Research Laboratories (USA) and applied in the production of Nd-Fe-B
permanent magnets [23]. This method could be applied for many magnetic materials to see the
results of it to fabricate anisotropic magnets. Magnets prepared by this means have been further
improved by Croat [24, 25] who announced values of (BH)max up to 350 kJ/m3
and Hci of about 1080
kA/m. The relation between the % of height reduction and remanence of Nd-Fe-B permanent
magnets is shown in Fig. 6.
The great advantages of this technique include the fact that:
(i) Magnetic alignment may be induced with no magnetic field.
(ii) The product is almost in the final shape required.
(iii) The process is ideally suited to radial alignment, either for ring or arc shapes.

134
Fig. 6. Magnetic remanence versus % die upset for hot deformed Nd-Fe-B magnets [25]
7. POWDER METALLURGY OF CERAMIC PERMANENT MAGNETS
Powder metallurgy has been used in the production of ceramic permanent magnets since
1950s by Philips Company (USA) [26-28]. In general, these ferrites are based on Ba, Sr, Pb and have
a formula MFe12O19, where M is Ba, Sr, Pb. The representatives of this class of ferrites, which have
been given the name of Ferroxdure, have a hexagonal structure (the easy axis being along the c-axis).
Ferroxdure is manufactured either as a solid permanent magnet or in the form of ferrite particles
dispersed in plastic (bonded ferrites), which is the same idea of Gowin Knight. Production of
SrFe12O19 powders by direct use of celestite as a source of strontium has been reported by Mortaza
and Jamshid [29]. Their results were compared with those of powders fabricated by normal ceramic
route. They showed that their process is more covenant for production of SrFe12O19 powders than the
conventional one. Synthesis and orientation of barium hexaferrite ceramics by magnetic alignment
was studies by Denis AUTISSIER, who showed that the magnetic properties strongly depends upon
the structural quality of the produced ceramic, magnetic alignment, particle size and the density of
the sintered magnets [30]. Starting powder of BaFe12O19 and the production route of these hexaferrite
permanent magnets by powder injection molding have been reported by Zlatkov et al. [31].
Production and characterization of SrFe12O19 powder obtained by hydrothermal process at Cο
180
for 24h have been investigated by Malick Jean et al. [32]. Their results were shown that to produce a
quasi-pure SrFe12O19 phase, it is necessary to start with a solution that contains a ratio of Fe/Sr equal
to 8.
8. POWDER METALLURGY AND REAR EARTH MAGNETS
(i) The first generation
Over the last four decades, permanent magnets based upon Rear Earths have been
dramatically developed. The first generation of rear earth permanent magnets depends on SmCo5 and
% Height Reduction
4020 60 80
8.0
10.0
9.0
11.0
12.0

135
Sm (Co, Cu, Fe, Tm)7-8 alloys, where Tm ≡Zr, Ti, of Hf. Several intermetallic phases of the type
RCo5 where R ≡Y, Ce, Pr, Sm, or Y-rich, Ce-rich mischmetal were investigated by Srrnat et al. [15].
They concluded that these alloys promising candidates for fine particles permanent magnets with
high anisotropy. Magnets fabricated by compacting fine powders of SmCo5 in a magnetic field gave
different maximum energy products (BH)max according to the production factors [14, 33]. In 1969,
Das [34] reported a "Twenty Million Energy Product Samarium-Cobalt Magnet" with a value of
(BH)max of 158kJ/m3
(about 20MGOe). This result was achieved by improving the magnetic
alignment and reducing the particle size below mµ10 .
In the 1970s, the preparation and enhanced properties of SmCo5 magnets produced by liquid
phase sintering were reported by Benz et al. [35]. Their conclusions were that this route gives
improved magnetic properties and eliminates porosity. After the development of SmCo5 permanent
magnets in the early of 1970's, alloys with some quantity of copper as well as rare earth and cobalt
emerged. These alloys became known as the precipitation hardened family of R(Cu, Co) and
eventually led to the development of Sm (Co, Cu, Fe, Tm)7-8 [36].
(ii) The second generation
The Sm2Co17 compounds have emerged as second generation rare earth permanent magnets
and these were developed with some addition of Fe to became Sm2 (Co, Fe)17 [37]. The effects of
various additive elements on magnetic hardness of the Sm-Co-Fe-Cu system studied Ojimo et al.
[38]. The formula was Sm2 (Co, Cu, Fe, M)17, where M ≡ Nb, V, Ta, or Zr. It was found that Zr
addition to the Sm-Co-Fe-Cu system improves the hard magnetic properties whilst a post-sintering
annealing process enhances the coercivity. Production and development of these magnets have been
reviewed by Strant and Ormerod [39, 40].
(iii) Nd-Fe-B permanent magnets, the third generation
In the middle of 1983, new rare earth permanent magnets were discovered, and this led to
extensive research on these materials in many countries. These magnets based on Nd-Fe-B alloys
could be looked upon as the third generation of Rare-Earth permanent magnets. At the beginning,
and independently, two routes were developed for fabricating these new magnets, and these have
continued to be used.
The first is a conventional powder metallurgy route which was developed by Sagawa
et al. [41] in Sumitomo Special Metals Company Ltd (SSMC), Japan. This route is the well
established powder metallurgy technique traditionally employed for the production of ferrite
magnets. It is used by most magnets manufactures and was successfully employed by Sagawa and
his collogues to produce sintered Nd-Fe-B permanent magnets, starting from an as-cast ingot. After
preparing the ingots, the following steps were used for making magnets:
(i) The ingots were crushed to a particle size of about 1mm by using a jaw crusher under an inert gas
atmosphere.
(ii) Using a disc mill, a particle size of around mµ100 was achieved.
(iii) Pulverization by ball milling in a stainless steel container with an inert solution produced a
particle size of about mµ3 .
(iv) The powders thus obtained were aligned in a magnetic field at 200kA/m and pressed at a
pressure of 200MPa, giving a green compact.
(v) The green compacts were then sintered in argon gas at temperature of Cο
11251000 − for 1h and
then rapidly cooled. The sintered specimens were given a post-sintering to enhance the coercivity.
In the end of these steps, an energy product (BH)max of about 290kJ/m3
was obtained. Further
improvements which gave (BH)max values as high as 380kJ/m3
were later reported by Sagawa et al.

136
[42]. Liquid phase sintering is widely used in the fabrication of Sm-Co and Nd-Fe-B magnets. In the
case of Nd-Fe-B, a Nd content in excess of stoichiometric Nd2Fe14B is normally used for LPS of Nd-
Fe-B magnets [43]. Many fundamental investigations have been reported on this type of rear earth
permanent magnets [19, 44-47].
The second route for the production is rapid solidification to give an isotropic permanent
magnet, this method being announced by the General Motors Corp. (GM) USA. They announced in
1983 the fabrication of isotropic Nd-Fe-B hard magnets by employing the rapid solidification
technique [48, 49]. At the beginning the energy product of the magnets produced by this method was
about 114 kJ /m3
. Later, magnets prepared by employing thermomechanical deformation route have
been further improved by Croat, 1989 [24, 25], who announced a value of (BH)max of around
350kJ/m3
starting from stacks of ribbons, or fragments of ribbon material which were produced by
rapid solidification process.
9. HYDROGEN DECREPITATION (HD) PROCESS
In 1979, Harris et al. patented the hydrogen decrepitation (HD) process as a means of
producing powder of SmCo5 alloys (British patent 1554384, October 1979). Large lumps can be
crumbled up readily to obtain an extremely friable produced which is consequently very amenable to
further reduction in particle size. After the discovery of Nd-Fe-B permanent magnets, the (HD)
process was successfully re-applied to decrepitate as-cast ingots of the Nd15Fe77B8 alloy and related
compositions [50]. This subject has been fully reviewed by Harris, Harris and McGuiness, and Ragg
et al. [51-53]. The production of rare-earth-sintered magnets by a low-cost has been published by
Takiishi et a.l [54]. They showed that sintered Nd- based permanent magnets can be produced
without using glove box. In 2012, combination between the HD and HDDR has been used in the
recycling of Nd-Fe-B magnets [55]. The procedure for the use the (HD) method can be briefly
summarised as follows:
(i) The as-cast ingot is broken into pieces of about 20mm or less in diameter.
(ii) The broken lumps are exposed to hydrogen in a stainless steel vessel at room temperature, the
vessel being evacuated initially to avoid the oxidation problem. One bar of hydrogen pressure can be
used to decrepitate the Nd15Fe77B8 alloy.
(iii) The hydride is then removed from the vessel and milled by any milling technique available,
under protective atmosphere.
(iv) The particles obtained within a certain particle size are magnetically aligned and pressed. The
green compacts are heat treated in vacuum to remove the dissolved hydrogen and then sintered to
produce permanent magnets.
Very small particle size required probably achieved following decrepitation by different
technique of milling within a relatively short time, thus replacing the time consuming conventional
route. This reduction in processing time should decrease the oxygen content of the powder, which
leads to enhancement of the magnetic properties. Comparison between magnets produced by the
(HD) process and the conventional route has been made by Moosa et al. [56]. Fig. 7 shows the effect
of the hydrogen pressure on particle size at a certain milling time, whilst Fig .8 shows the
microstructures of Nd16Fe76B8 magnet produced by the two methods. The demagnetisation curve for
an example of a magnet produced from Nd16Fe76B8 alloy after a post-sintering anneal at Cο
640 for
1h, together with magnetic parameters are shown in Fig. 9. The curve shows very good squareness,
which indicates that, the hydride particles were well aligned by using powder metallurgy techniques.

137
Fig. 7. Micrographs showing the variation of particle size at the same milling time (30min.) for
different hydrogen pressure, (a) 2bar, (b) 10bar {12, P.154]
Fig. 8. SEM micrographs: (a) Magnet made by the (HD) process,
(b) Magnet produced by the conventional route [56]

138
Fig. 9. Demagnetisation curve of magnet of Nd16Fe76B8 produced by (HD) process after post-
sintering at for 1h [12, p. 169]
10. MECHANICAL ALLOYING ROUTE BY USING POWDER ELEMENTS
Mechanical alloying normally starts with mechanical milling of the elemental powders,
which are repeatedly welded together and sheared until mixing on a microscopic scale has occurred.
This is followed by pressing and sintering causes a solid state reaction within and between the
compacted particles, hence creating the required alloy and structure. In general the results obtained
depend on starting particle size, powder impurities, milling time, and heat treatment. Mechanical
alloying is one of the methods which has been employed in the production of Nd-Fe-B permanent
magnets [57-59]. This route has also been used in the production of Sm-Fe-N permanent magnet
[60]. The main drawback of this magnet is the sintering process at high temperature, because
Sm2Fe17N3 compound is not stable at high temperature and decomposes into α Fe and SmN phases
above 600 Cο
. Recently, Sm-Fe-N bulk magnets have been produced utilizing nonconventional
consolidation techniques of compaction such as deformation- shearing process and shock
compression route [2, 61, 62]. Mechanical alloying can be employed in the production of soft
magnets as well, so as the magnetic properties more easy to be controlled [63].
The vast of majority of the rare earth permanent magnets are fabricated by powder metallurgy
techniques. The general process steps are alloys preparation, milling, composition control, particles
alignment, pressing, sintering and post-sintering treatment, machining or grinding, and magnetizing
of the products as shown in the metallurgical process diagram, which represents the production steps
of sintered magnets with attainable magnetic properties.
Br=1.28 T, Hci=954 kA/m , (BH)max=313 kJ/m3

139
The magnetic p
11. CONCLUSION
At the end, we can see the significance of using powder metallurgy techniques in the
fabrication of permanent magnets. Important thing should be concluded here; that by employing
powder metallurgy techniques, superior magnetic properties can be achieved. The properties of
permanent magnets are critically dependent upon chemical composition, particle size of the hard
phase, magnetic alignment, pressing technique, type of materials, and heat treatment. Almost all
these parameters can be easily controlled by using powder metallurgical processing methods, and
hence enhancing the magnetic properties of the produced magnets. Most of the permanent magnets
are preferred to be fabricated by this route because the products are almost semi-finished to a certain
specifications, so as the machining can be avoided during the production process.
12. ACKNOWLEDGEMENTS
The author greatly appreciates Dr. Ismayadi Bin Ismail of the Institute of Advanced Material
Technology, Putra University Malaysia (U. P. M.), for providing a sample of Fe3O4 powder and
enabling to carry out the microstructure of the sample by using their SEM.
HD route
Alloy preparation according to
suggested processthe
Mechanical crushing near about
particle size of 0.5mm or less
Milling to a certain particle size
according to the plan of research
Magnetic alignment and pressing
Sintering and heat treatment
according to the research plan
Machining , or grinding
Magnetising
Mechanical
alloying
Metallurgical process steps for the production
of the most permanent magnets

140
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Francisco, London, (1978) p. 2.
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[5] W. D. Jones, "Fundamental Principles of Powder Metallurgy" London, Edward Arnold publishers
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[6] S. A. Tsukerman "Powder Metallurgy", Translated from the Russian, Pergamon Press, Oxford,
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[11] W. A. kaysser, G. Petzow, Powder Metall. 28 (1985) 145.
[12] I. S. MOOSA, Ph.D. thesis "The Production, Properties, and Microstructures of Nd-Fe-B
Magnets", The University of Leeds (UK), (1991).
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