U.S. patent application number 11/886629 was filed with the patent office on 2008-10-23 for coating method and apparatus, a permanent magnet, and manufacturing method thereof.
Invention is credited to Hiroshi Nagata, Yoshinori Shingaki.
Application Number | 20080257716 11/886629 |
Document ID | / |
Family ID | 37023634 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080257716 |
Kind Code |
A1 |
Nagata; Hiroshi ; et
al. |
October 23, 2008 |
Coating Method and Apparatus, a Permanent Magnet, and Manufacturing
Method Thereof
Abstract
A film is formed at a high rate on the surface of an
iron-boron-rare-earth-metal magnet having a given shape, while
effectively using dysprosium or terbium as a film-forming material.
Thus, productivity is improved and a permanent magnet can be
produced at low cost. A permanent magnet is produced through a film
formation step in which a film of dysprosium is formed on the
surface of an iron-boron-rare-earth-metal magnet of a given shape
and a diffusion step in which the magnet coated is subjected to a
heat treatment at a given temperature to cause the dysprosium
deposited on the surface to diffuse into the grain boundary phase
of the magnet. The film formation step comprises: a first step in
which a treating chamber where this film formation is performed is
heated to vaporize dysprosium which has been disposed in this
treating chamber and thereby form a dysprosium vapor atmosphere
having a given vapor pressure in the treating chamber; and a second
step in which a magnet kept at a temperature lower than the
internal temperature of the treating chamber is introduced into
this treating chamber and the dysprosium is selectively deposited
on the magnet surface based on a temperature difference between the
treating chamber and the magnet until the magnet temperature
reaches a given value.
Inventors: |
Nagata; Hiroshi; (Kanagawa,
JP) ; Shingaki; Yoshinori; (Kanagawa, JP) |
Correspondence
Address: |
RADER FISHMAN & GRAUER PLLC
LION BUILDING, 1233 20TH STREET N.W., SUITE 501
WASHINGTON
DC
20036
US
|
Family ID: |
37023634 |
Appl. No.: |
11/886629 |
Filed: |
March 14, 2006 |
PCT Filed: |
March 14, 2006 |
PCT NO: |
PCT/JP2006/305034 |
371 Date: |
September 18, 2007 |
Current U.S.
Class: |
204/192.12 ;
148/105; 204/298.02 |
Current CPC
Class: |
C23C 14/243 20130101;
C23C 14/541 20130101; H01F 1/0571 20130101; H01F 41/20 20130101;
H01F 10/126 20130101; H01F 41/0293 20130101; C23C 14/16
20130101 |
Class at
Publication: |
204/192.12 ;
204/298.02; 148/105 |
International
Class: |
C23C 14/54 20060101
C23C014/54; C23C 14/22 20060101 C23C014/22; H01F 1/053 20060101
H01F001/053; H01F 10/12 20060101 H01F010/12; H01F 41/20 20060101
H01F041/20 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2005 |
JP |
2005-080021 |
Claims
1. A coating method comprising a first step for heating a process
chamber and generating metallic vapor atmosphere within the process
chamber by vaporizing vaporizable metallic material previously
arranged within the process chamber, and a second step for
introducing into the process chamber articles to be coated held at
a temperature lower than that within the process chamber and then
selectively depositing the vaporizable metallic material on a
surface of article to be coated by an effect of temperature
difference between the temperature within the process chamber and
that of the articles to be coated.
2. A coating method of claim 1 wherein the metallic vapor
atmosphere is in a saturated condition within the process
chamber.
3. A coating apparatus comprising a process chamber which can heat
substantially uniformly an inside of the process chamber to a high
temperature by a heating means, a preparatory chamber communicating
to the process chamber, an evacuating means for holding both the
process and preparatory chambers at a predetermined degree of
vacuum, an open/close means moveable between an opened position in
which the process and preparatory chambers are communicated each
other and a closed position in which the process chamber is tightly
closed, and a conveying means which can move the articles to be
coated between the process chamber and the preparatory chamber and
can tightly close the process chamber when the articles to be
coated are moved into the process chamber at the opened position of
the open/close means, wherein the process chamber is heated at the
closed position of the open/close means, metallic vapor atmosphere
is generated by vaporizing vaporizable metal material previously
arranged within the process chamber, the articles to be coated
within the preparatory chamber are moved into the process chamber
by the conveying means with the open/close means being moved to the
opened position so as to selectively deposit the vaporizable
metallic material on a surface of article to be coated by an effect
of temperature difference between the temperature within the
process chamber and that of the articles to be coated.
4. A coating apparatus of claim 3 wherein the process chamber is
arranged within a vacuum chamber equipped with another evacuating
means and defined by a uniformly heating plate formed with an
opening at one side thereof, a heat insulating member is arranged
so that it encloses the uniformly heating plate except for said
side of the uniformly heating plate in which said opening is
formed, and a heating means for heating the uniformly heating plate
is arranged between the uniformly heating plate and the heat
insulating member.
5. A coating apparatus of claim 3 further comprising a gas
introducing means for introducing inert gas into the preparatory
chamber, and the inert gas is introduced into the preparatory
chamber via the gas introducing means so as to hold the pressure
within the process chamber at a negative pressure relative to that
of the preparatory chamber.
6. A coating apparatus of claim 3 wherein the preparatory chamber
is equipped with a gas introducing means for introducing He gas
into the preparatory chamber, and the He gas is introduced into the
preparatory chamber via the gas introducing means so as to hold the
pressure within the process chamber at substantially same as that
within the preparatory chamber.
7. A coating apparatus of claim 6 wherein the process chamber is
arranged below the preparatory chamber.
8. A coating apparatus of claim 3 further comprising a placement
means on which the vaporizable metallic material can be placed
within the process chamber, and the placement means is formed as an
annulus so that the vaporizable metallic material can be arranged
around the articles to be coated when the articles to be coated are
moved into the process chamber by the conveying means.
9. A coating apparatus of claim 3 wherein the preparatory chamber
is equipped with a plasma generating means for cleaning the surface
of article to be coated by using plasma.
10. A coating apparatus of claim 3 wherein the preparatory chamber
is equipped with another heating means for cleaning the surface of
article to be coated by heat treatment with introducing the inert
gas into the vacuum atmosphere or the preparatory chamber via the
gas introducing means connected thereto.
11. A coating apparatus of claim 3 wherein the vaporizable metallic
material is alloy including either one of Dy or Tb or including at
least one of Dy and Tb, and the article to be coated is a sintered
magnet of Fe--B-rare earth elements having a predetermined
configuration.
12. A method for manufacturing a permanent magnet comprising steps
for coating vaporizable metallic material including at least one of
Dy and Tb on a surface of a magnet of Fe--B-rare earth elements
having a predetermined configuration, and diffusing the vaporizable
metallic material coated on the surface of the magnet into crystal
grain boundary phases of a sintered magnet by heat treating the
vaporizable metallic material at a predetermined temperature
characterized in that the coating step comprises a first step for
heating a process chamber used for carrying out the coating step
and generating metallic vapor atmosphere within the process chamber
by vaporizing vaporizable metallic material previously arranged
within the process chamber, and a second step for introducing into
the process chamber the magnet held at a temperature lower than
that within the process chamber and then selectively depositing the
vaporizable metallic material on a surface of the magnet by an
effect of temperature difference between the temperature within the
process chamber and that of the magnet by the magnet reaches a
predetermined temperature.
13. A method for manufacturing a permanent magnet of claim 12
wherein the metallic vapor atmosphere is in a saturated condition
within the process chamber.
14. A method for manufacturing a permanent magnet of claim 12
wherein the vaporizable metallic material further includes at least
one of Nd, Pr, Al, Cu, Ga and Ta.
15. A method for manufacturing a permanent magnet claim 12 wherein
the predetermined temperature in the second step is lower than
250.degree. C. or higher than 450.degree. C.
16. A method for manufacturing a permanent magnet claim 12 further
comprising a step for cleaning the surface of the magnet within the
vacuum atmosphere prior to introduction into the process chamber of
the magnet held at a temperature lower than that within the process
chamber.
17. A method for manufacturing a permanent magnet claim 12 wherein
the temperature within the process chamber in the first step is set
at a range of 1,000.about.1,700.degree. C.
18. A method for manufacturing a permanent magnet claim 12 wherein
the grain diameter of the vaporizable metallic material arranged
within the process chamber in the coating step is in a range of
10.about.1,000 .mu.m.
19. A permanent magnet comprising a magnet of Fe--B-rare earth
elements having a predetermined configuration, and a surface of the
magnet being selectively deposited by the vaporizable metallic
material by an effect of temperature difference between the
temperature within the process chamber and that of the magnet by
the magnet reaches a predetermined temperature with generating
metallic vapor atmosphere within the process chamber by vaporizing
vaporizable metallic material including at least one of Dy and Tb
and with introducing into the processing chamber the magnet held at
a temperature lower than that within the process chamber, then the
magnet being heat treated so as to diffusing at least one of Dy and
Tb on the surface of the magnet into crystal grain boundary phases
of the magnet.
20. A permanent magnet of claim 19 wherein the surface and crystal
grain boundary of the magnet have a rich phase including at least
one of Dy and Tb.
21. A permanent magnet of claim 19 wherein the surface of the
magnet is covered by the rich phase, and the crystal grain boundary
includes 1.about.50% rich phase.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to coating method and
apparatus, a permanent magnet, and a manufacturing method thereof,
and more particularly to a permanent magnet and a manufacturing
method thereof in which the permanent magnet is manufactured by
coating vaporizable metallic material including at least one of Dy
and Tb on a surface of a magnet of Fe--B-rare earth elements, and
then diffusing at least one of Dy and Tb into crystal grain
boundary phases of a sintered magnet by heat treating the
vaporizable metallic material at a predetermined temperature, as
well as to coating method and apparatus suitable for coating
vaporizable metallic material including at least one of Dy and Tb
on the surface of the magnet.
[0003] 2. Description of Background Art
[0004] A sintered magnet of Nd--Fe--B (a so-called "neodymium
magnet") has been used in various products e.g. motors for a hybrid
vehicle and generators etc. recently since the neodymium magnet can
be made of combination of elements Fe, Nd and B which are cheap and
sufficiently and stably obtainable resources and also has high
magnetic properties (its maximum energy product is 10 times that of
ferritic magnet). On the other hand the sintered magnet of
Nd--Fe--B has a problem that it is demagnetized by heat when it is
heated beyond its predetermined temperature since its Curie
temperature is low such as 300.degree. C.
[0005] Accordingly when manufacturing the sintered magnet of
Nd--Fe--B, since Dy and Tb have the magnetic anisotropy of 4
f-electron larger than that of Nd and have the negative Stevens
factor similarly to that of Nd, it can be appreciated to add Dy or
Tb to remarkably improve the magnetocrystalline anisotropy of the
principal phase. However, since Dy and Tb take the ferrimagnetism
structure in which Dy and Tb take a spin orientation opposite to
that of Nd in the principal phase crystal lattice, it is caused a
problem that the magnetic field strength, therefore the maximum
energy product exhibiting the magnetic properties is greatly
reduced.
[0006] For solving such a problem, it is proposed to firstly coat
Dy or Tb on a whole surface of a sintered magnet of Nd--Fe--B
having a predetermined configuration such as a rectangular
parallelopiped at a predetermined coating thickness (thickness more
than 3 .mu.m determined based on a volume of the magnet) and then
to uniformly diffusing Dy and Tb coated on the surface of the
magnet into the crystal grain boundary phases of the magnet with
carrying out heat treatment at a predetermined temperature (see
non-patent document 1 mentioned below).
[0007] The permanent magnet manufactured according to this method
has merits in that the coercive force generating mechanism of
nucleation-type is reinforced by an effect that Dy and Tb diffused
in the crystal grain boundary phases increase the
magnetocrystalline anisotropy in each crystal grain surface and by
the result of which the coercive force is remarkably improved
almost without causing loss of the maximum energy product (for
example, the non-patent document 1 discloses that it is possible to
have a magnet having the coercive force of 23 K0 e (3 MA/m) at the
remanent magnetic flux density of 14.5 kG (1.45 T) and the maximum
energy product of 50 MG0 e (400 Kj/m.sup.3). When coating Dy or Tb
on the surface of the sintered magnet of Nd--Fe--B, it can be
appreciated to use the sputtering method that exhibits an excellent
adhesion of Dy or Tb coating to a surface of sintered magnet.
[0008] Note: non-latent document 1; "Improvement of coercive on
thin Nd2Fe14B sintered permanent magnets" (Park Ki Te, A doctor's
thesis of Touhoku University, Mar. 23, 2000).
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0009] However since the sputtering method is bad in usage
efficiency of its target and in yield of vaporizable metallic
material for coating, it is not suit for coating of Dy or Tb which
is scarce material and thus cannot be expected to sufficiently and
stably supply. In addition in order to coat a whole surface of a
magnet having a predetermined configuration such as a rectangular
parallelopiped by using the sputtering method, it is necessary to
rotate the magnet itself and thus it is required to provide a
mechanism for rotating the magnet. This further increases
manufacturing cost of the magnet in addition to a cost for making a
sputtering target of Dy or Tb which is rare resources and
expensive.
SUMMARY OF THE INVENTION
[0010] It is, therefore, a first object of the present invention to
provide a permanent magnet and a manufacturing method thereof which
can manufacture the magnet at a low cost with effectively using Dy
and Tb as coating material and coating them on a surface of the
magnet of Fe--B-rare earth elements having a predetermined
configuration.
[0011] It is also a second object of the present invention to
provide a coating method and a coating apparatus which can exhibit
high yield of vaporizable metallic material to be coated and
achieve a substantially uniform coating at a high speed over a
whole surface of an article to be coated (i.e. a sintered magnet)
having a predetermined configuration and which is suit in
particularly to coating of Dy and Tb on a surface of a magnet of
Fe--B-rare earth elements having a predetermined configuration.
Means for Achieving the Objects
[0012] For achieving the object of the present invention, there is
provided, according to the present invention, a coating method
comprising a first step for heating a process chamber and
generating metallic vapor atmosphere within the process chamber by
vaporizing vaporizable metallic material previously arranged within
the process chamber, and a second step for introducing into the
process chamber articles to be coated held at a temperature lower
than that within the process chamber and then selectively
depositing the vaporizable metallic material on a surface of
article to be coated by an effect of temperature difference between
the temperature within the process chamber and that of the articles
to be coated.
[0013] According to this coating method of the present invention,
since the metallic coating is formed by selectively depositing the
vaporizable metallic material on a surface of article to be coated
by an effect of temperature difference between the temperature
within the process chamber and that of the articles to be coated,
it is possible to achieve high yield of the vaporizable metallic
material to be coated and to coat a whole surface of article to be
coated having a predetermined configuration at a high speed.
[0014] In such a case, it is preferable that the metallic vapor
atmosphere is in a saturated condition within the process chamber
so as to have the coating at a higher speed.
[0015] Also according to the present invention, there is provided a
coating apparatus comprising a process chamber which can heat
substantially uniformly an inside of the process chamber to a high
temperature by a heating means, a preparatory chamber communicating
to the process chamber, an evacuating means for holding both the
process and preparatory chambers at a predetermined degree of
vacuum, an open/close means moveable between an opened position in
which the process and preparatory chambers are communicated each
other and a closed position in which the process chamber is tightly
closed, and a conveying means which can move the articles to be
coated between the process chamber and the preparatory chamber and
can tightly close the process chamber when the article to be coated
are moved into the process chamber at the opened position of the
open/close means, wherein the process chamber is heated at the
closed position of the open/close means, metallic vapor atmosphere
is generated by vaporizing vaporizable metal material previously
arranged within the process chamber, the articles to be coated
within the preparatory chamber are moved into the process chamber
by the conveying means with the open/close means being moved to the
opened position so as to selectively deposit the vaporizable
metallic material on a surface of article to be coated by an effect
of temperature difference between the temperature within the
process chamber and that of the articles to be coated.
[0016] In this coating apparatus, both the process chamber and the
preparatory chamber are evacuated to a predetermined degree of
vacuum via the evacuating means after the articles to be coated
have been arranged within the preparatory chamber. Then when the
process chamber is heated after the open/close means has been moved
to the closed position to tightly close the process chamber, the
metallic vapor atmosphere is generated within the process chamber
with the vaporizable metallic material previously arranged within
the process chamber being vaporized. Then the open/close means is
moved to the opened position and the articles to be coated are
moved from the preparatory chamber to the process chamber by the
conveying means. When articles to be coated held at a temperature
lower than that within the process chamber (e.g. articles of
ordinary temperature) are introduced into the process chamber,
metallic atoms in the metallic vapor atmosphere are selectively
deposited only on the surface of article to be coated at a high
speed. Thus, it is possible to achieve high yield of the
vaporizable metallic material to be coated and to coat a whole
surface of article to be coated having a predetermined
configuration at a high speed.
[0017] In such a case, it is preferable that the process chamber is
arranged within a vacuum chamber equipped with another evacuating
means and defined by a uniformly heating plate formed with an
opening at one side thereof, a heat insulating member is arranged
so that it encloses the uniformly heating plate except for said
side of the uniformly heating plate in which said opening is
formed, and a heating means for heating the uniformly heating plate
is arranged between the uniformly heating plate and the heat
insulating member. Such a structure makes it possible to
substantially uniformly heat the process chamber by heating the
uniformly heating plate with the use of the heating means and by
indirectly heating the process chamber via the uniformly heating
plate.
[0018] Also it is preferable that the coating apparatus further
comprises a gas introducing means for introducing inert gas into
the preparatory chamber, and the inert gas is introduced into the
preparatory chamber via the gas introducing means so as to hold the
pressure within the process chamber at a negative pressure relative
to that of the preparatory chamber. Such a structure makes it
possible to prevent the vaporizable metallic material from flowing
into the preparatory chamber by a pressure difference between the
process chamber and the preparatory chamber when the open/close
means is moved to the opened position in order to introduce the
articles to be coated into the process chamber after the metallic
vapor atmosphere has been generated within the process chamber.
[0019] On the other hand, it is preferable that the preparatory
chamber is equipped with a gas introducing means for introducing He
gas into the preparatory chamber, and the He gas is introduced into
the preparatory chamber via the gas introducing means so as to hold
the pressure within the process chamber at substantially same as
that within the preparatory chamber. Such a structure makes it
possible to prevent the vaporizable metallic material from flowing
into the preparatory chamber by a difference in specific gravity
between the process chamber and the preparatory chamber when the
open/close means is moved to the opened position in order to
introduce the articles to be coated into the process chamber after
the metallic vapor atmosphere has been generated within the process
chamber.
[0020] In such a case, it is preferable that the process chamber is
arranged below the preparatory chamber.
[0021] It is also preferable that the coating apparatus further
comprises a placement means on which the vaporizable metallic
material can be placed within the process chamber, and the
placement means is formed as an annulus so that the vaporizable
metallic material can be arranged around the articles to be coated
when the articles to be coated are moved into the process chamber
by the conveying means. This makes it possible to uniformly heat
the vaporizable metallic material at any portion of the placement
means and thus to obtain a further uniform coating.
[0022] In addition, it is preferable that the preparatory chamber
is equipped with a plasma generating means for cleaning the surface
of article to be coated by using plasma.
[0023] On the other hand, it is also preferable that the
preparatory chamber is equipped with another heating means for
cleaning the surface of article to be coated by heat treatment with
introducing the inert gas into the vacuum atmosphere or the
preparatory chamber via the gas introducing means connected
thereto.
[0024] It is preferable that the vaporizable metallic material is
alloy including either one of Dy or Tb or including at least one of
Dy and Tb, and the article to be coated is a sintered magnet of
Fe--B-rare earth elements having a predetermined configuration.
[0025] Further according to the present invention there is provided
a method for manufacturing a permanent magnet comprising steps for
coating vaporizable metallic material including at least one of Dy
and Tb on a surface of a magnet of Fe--B-rare earth elements having
a predetermined configuration, and diffusing the vaporizable
metallic material coated on the surface of the magnet into crystal
grain boundary phases of a sintered magnet by heat treating the
vaporizable metallic material at a predetermined temperature
characterized in that the coating step comprises a first step for
heating a process chamber used for carrying out the coating step
and generating metallic vapor atmosphere within the process chamber
by vaporizing vaporizable metallic material previously arranged
within the process chamber, and a second step for introducing into
the process chamber the magnet held at a temperature lower than
that within the process chamber and then selectively depositing the
vaporizable metallic material on a surface of the magnet by an
effect of temperature difference between the temperature within the
process chamber and that of the magnet by the magnet reaches a
predetermined temperature.
[0026] According this manufacturing method, the metallic vapor
atmosphere is generated by heating the process chamber after the
vaporizable metallic material including at least one of Dy and Tb
of the coating material has been arranged within the process
chamber. Then, when articles to be coated held at a temperature
lower than that within the process chamber (e.g. articles of
ordinary temperature) are introduced into the process chamber
heated to a high temperature, metallic atoms including Dy and Tb in
the metallic vapor atmosphere are selectively deposited only on the
surface of article to be coated at a high speed. Then the
vaporization is stopped after having held the magnet in this
condition for a predetermined time duration until the magnet
reaches a predetermined temperature. Accordingly vaporizable
metallic material including at least one of Dy and Tb can be coated
at a high speed on the surface of the magnet at a predetermined
coating thickness and thus the productivity of the magnet can be
improved. In addition since the vaporizable metallic material
including at least one of Dy and Tb is selectively deposited only
on the surface of article to be coated, it is possible to
effectively use Dy and Tb which are rare resources and expensive
and thus to reduce the manufacturing cost of magnet.
[0027] It is preferable the metallic vapor atmosphere is in a
saturated condition within the process chamber in order to coat at
a higher speed the vaporizable metallic material including at least
one of Dy and Tb on the surface of magnet. Although it is possible
to contain within the process chamber inert gases in addition to
vapors of the vaporizable metallic materials including at least one
of Dy and Tb, coating at a maximum speed can be attained when the
total pressure within the process chamber is filled with saturated
vapors of vaporizable metallic materials including at least one of
Dy and Tb.
[0028] The melting point of Dy and Tb is high and thus it is
preferable that the vaporizable metallic material further includes
at least one of Nd, Pr, Al, Cu, Ga and Ta in order to generating
the metallic vapor atmosphere within the process chamber in a short
time. This enables to further increase the coercive force as
compared with a permanent magnet made by heat treatment for example
after coating of Dy only.
[0029] By the way, when the magnet of ordinary temperature is
introduced into the process chamber heated to a high temperature,
the magnet itself is also heated by the radiant heat. Then when
this magnet is heated and thermally expanded, peeling of the
coating deposited on the surface of magnet is liable to be caused
by a fact that the thermal expansion exhibits abnormality like as
inver alloy at a temperature below the Curie point. Thus
Accordingly, it is preferable that the predetermined temperature in
the second step is lower than 250.degree. C. or higher than
450.degree. C. This is because that the peeling of the coating
deposited on the surface of magnet is hard to be caused since
strain due to thermal expanding abnormality is reduced at a
temperature lower than 250.degree. C. and on the other hand,
adhesion between the magnet and at least one of Dy and Tb deposited
on the surface of magnet is improved due to melting of part of the
magnet and thus the peeling of the coating deposited on the surface
of magnet is hard to be caused at a temperature higher than
450.degree. C.
[0030] In this case, it is preferable that the method for
manufacturing a permanent magnet further comprises a step for
cleaning the surface of the magnet within the vacuum atmosphere
prior to introduction into the process chamber of the magnet held
at a temperature lower than that within the process chamber. This
makes it possible to remove for example oxide film on the surface
of magnet and thus to increase the adhesive strength of the
vaporizable metallic material including one of Dy and Tb to the
surface of magnet as well as to uniformly diffuse Dy and Tb coated
on the surface of magnet into crystal grain boundary phase of the
magnet during diffusing step.
[0031] It is also preferable that the temperature within the
process chamber in the first step is set at a range of
1,000.about.1,700.degree. C. This is because that a vapor pressure
which can coat the vaporizable metallic material including at least
one of Dy and Tb at a high speed on the surface of magnet cannot be
obtained at a temperature lower than 1,000.degree. C. and on the
other hand the coating time duration of the magnet becomes too
short to obtain a uniform coating at a temperature higher than
1,700.degree. C.
[0032] It is also preferable that the grain diameter of the
vaporizable metallic material arranged within the process chamber
in the coating step is in a range of 10.about.1,000 .mu.m. This is
because that handling of grains of Dy and Tb having inflammability
is difficult at a grain diameter smaller than 10 .mu.m and on the
other hand the surface area of the grains is reduced and thus a
longer time duration for vaporization is required at a grain
diameter larger than 1,000 .mu.m.
[0033] Further according to the present invention, there is
provided a permanent magnet comprising a magnet of Fe--B-rare earth
elements having a predetermined configuration, and a surface of the
magnet being selectively deposited by the vaporizable metallic
material by an effect of temperature difference between the
temperature within the process chamber and that of the magnet by
the magnet reaches a predetermined temperature with generating
metallic vapor atmosphere within the process chamber by vaporizing
vaporizable metallic material including at least one of Dy and Tb
and with introducing into the processing chamber the magnet held at
a temperature lower than that within the process chamber, then the
magnet being heat treated so as to diffusing at least one of Dy and
Tb on the surface of the magnet into crystal grain boundary phases
of the magnet.
[0034] The neodymium magnet of the prior art has nature of being
easily corroded and thus its surface is covered by a protecting
film such as resin coating or nickel plating. On the contrary, the
surface of the magnet of the present invention is covered by a
coating including at least one of Dy and Tb having extremely high
corrosion and weather resistance. Thus at least one of Dy and Tb
plays a role of the protecting film of the magnet and thus it is
possible to obtain a permanent magnet having excellent corrosion
and weather resistance without requiring any additional protecting
film. Accordingly it is possible to further improve the
productivity and to reduce the manufacturing cost.
[0035] In this case, it is preferable that the surface and crystal
grain boundary of the magnet have a rich phase including at least
one of Dy and Tb. According to this structure, it is possible to
have a permanent magnet having extremely excellent corrosion and
weather resistance due to the presence of the rich phase including
at least one of Dy and Tb in addition to the presence of the rich
phase on the surface of magnet.
[0036] It is further preferable that the surface of the magnet is
covered by the rich phase, and the crystal grain boundary includes
1.about.50% rich phase. If the crystal grain boundary includes the
rich phase exceeding 50%, the maximum energy product, the remanent
magnetic flux density and the coercive force exhibiting the
magnetic properties are extremely reduced.
EFFECTS OF THE INVENTION
[0037] The permanent magnet and its manufacturing method of the
present invention have effects that the magnet can be manufactured
at a high productivity and a low cost with effectively using Dy and
Tb of coating materials and coating them at a high speed on the
surface of magnet of Fe--B-rare earth elements having a
predetermined configuration and that the magnet has excellent
corrosion resistance and weather resistance without any additional
protective film.
[0038] In addition, the coating method and apparatus of the present
invention have effects that they can carry out coating of
vaporizable metallic material at high yield and speed and
substantially uniformly on a whole surface of the magnet having a
predetermined configuration and are especially suitable for coating
of vaporizable metallic material including Dy and Tb on a surface
of magnet of Fe--B-rare earth elements having a predetermined
configuration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] Additional advantages and features of the present invention
will become apparent from the subsequent description and the
appended claims, taken in conjunction with the accompanying
drawings, wherein:
[0040] FIG. 1 is an explanatory schematic view showing a structure
of the coating apparatus of the present invention;
[0041] FIG. 2 is an explanatory view showing a support means for
supporting sintered magnets i.e. articles to be coated within a
process chamber;
[0042] FIG. 3 is an explanatory view showing steps of manufacture
of a permanent magnet of the present invention;
[0043] FIG. 4 is a graph showing a relation between the temperature
and the density of Ar, He and Dy;
[0044] FIG. 5 is a table showing average values of magnetic
properties of permanent magnets manufactured in an embodiment
1;
[0045] FIG. 6 is a table showing average values of coating
thickness coated in an embodiment 2 and magnetic properties of
permanent magnets manufactured in the embodiment 2;
[0046] FIG. 7 is a table showing average values of coating
thickness and maximum temperature of Dy coated in an embodiment 3
and magnetic properties of permanent magnets manufactured in an
embodiment 3;
[0047] FIG. 8 is a table showing average values of magnetic
properties of a permanent magnet manufactured in an embodiment
4;
[0048] FIG. 9 is a table showing average values of coating
thickness on the surface of a magnet coated in an embodiment 5;
[0049] FIG. 10 is a table showing magnetic properties and the
percent defective of adhesion of coating of a permanent magnet
obtained in an embodiment 6;
[0050] FIG. 11 is a table showing the magnetic property, the
corrosion resistance and the weather resistance respectively of an
embodiment 7 and comparative examples 1.about.4; and
[0051] FIG. 12 is a table showing magnetic properties of a
permanent magnet manufactured in an embodiment 8.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Best Mode for Carrying out the Invention
[0052] With reference to FIGS. 1 and 2, a numeral 1 denotes a
coating apparatus suitable for selectively coating vaporizable
metallic materials such as Dy and Tb at a high speed on the surface
of article S, e.g. sintered magnet of Fe--B-rare earth elements.
The coating apparatus 1 has a process chamber 2 and a preparatory
chamber 3 connected vertically each other. The process chamber 2
positioned above the preparatory chamber 3 is arranged within a
cylindrical vacuum chamber 11 which can be held in a predetermined
degree of vacuum through an evacuating means 11a such as a
turbo-molecular pump, a cryopump, a diffusion pump etc.
[0053] The process chamber 2 is defined by a uniformly heating
plate 21 having a cylindrical configuration opened at its bottom
end communicating with the preparatory chamber 3. The uniformly
heating plate 21 is surrounded except for its opened bottom by a
heat insulating member 22 of carbon arranged within the vacuum
chamber 11. For example, a plurality of electric heaters 23
consisting of W forming a heating means are arranged between the
uniformly heating plate 21 and the heat insulating member 22. Thus
a space within the process chamber 2 can be heated substantially
uniformly by heating the uniformly heating plate 21 surrounded by
the heat insulating member 22 with use of the heating means 23
within vacuum and thus by indirectly heating the space within the
process chamber 2 via the uniformly heating plate 21.
[0054] As most clearly shown in FIG. 2, an acceptor 24 having a "U"
shaped cross-section is arranged within the process chamber 2. The
acceptor 24 is used for placing the vaporizable metallic material
thereon and thus forms a placement means. The acceptor 24 is
mounted on the inner surface of the uniformly heating plate 21 and
has an annular configuration so that the vaporizable metallic
material conveyed into the process chamber 2 by a conveyor
mentioned below can be arranged around the articles to be coated S.
The vaporizable metallic material is selected according to the
coating to be coated on the surface of article to be coated and the
vaporizable metallic material of pellet configuration is uniformly
arranged on the acceptor 24 therealong. The acceptor 24 is not
necessary to be formed as a continuous annulus and may be
separately formed at equidistant in a circumferential
direction.
[0055] A first space 4 is formed under the process chamber 2 and an
open/close means 5 is arranged within the first space 4. The
open/close means 5 comprises a valve body 51 and a driving means 52
such as a pneumatic cylinder and can be displaced by the driving
means 52 between an opened position (FIG. 1) in which the process
chamber 2 and the preparatory chamber 3 are communicated with each
other via the valve body 51 and a closed position in which the
process chamber 2 is tightly closed with the valve body 51 being
contacted with a top plate 41 forming the first space 4 and sealing
an opening formed in the top plate 41. The valve body 51 is
provided with a second heating means (not shown).
[0056] A second space 3a is arranged under the first space 4. A
side wall 30 defining the second space 3a is provided with a gate
valve (not shown) through which articles S to be coated are
introduced into the preparatory chamber 3 and taken out therefrom.
The articles S to be coated are supported on a supporting means 6.
The supporting means 6 comprises three posts 61 and two supporting
members 62 arranged respectively spaced from the bottom of the
posts 61 at a predetermined distance and supported by the posts 61.
Each post 61 has a small diameter so as to minimize heat
transmission therethrough. This is because to minimize heat
transmission from a pusher member 74 mentioned below to articles S
i.e. sintered magnets via the posts 61.
[0057] Each supporting member 62 is formed as a net of wires of
0.1.about.10 mm .phi. so that a bottom surface of the articles S
placed on the supporting member 62 can be coated. The distance
between the supporting members 62 is set in view of the height of
the articles S placed thereon. The supporting means 6 is arranged
within the second space 3a and mounted on a disc 63 formed with a
central opening 63a through which a supporting table mentioned
below can pass. The disc 63 is adapted to be placed on a supporting
ring 64 arranged within the process chamber 2.
[0058] A third space 3b is formed under the second space 3a and
these second and third spaces 3a and 3b define the preparatory
chamber 3. A evacuating means 31 such as a turbo-molecular pump, a
cryopump and a diffusion pump etc. is connected to the preparatory
chamber 3. Thus the preparatory chamber 3 and process chamber 2
communicated with the preparatory chamber 3 via the first space 4
are held at a predetermined degree of vacuum by the evacuating
means 31. A driving means 71 such as a pneumatic cylinder is
arranged at the bottom of the preparatory chamber 3 and a
supporting disc 73 is mounted on the tip end of a shaft 72 of the
driving means 71 projected into the preparatory chamber 3. The
driving means 71 and the supporting disc 73 form a conveying means
7 and the supporting disc 73 can be moved upward and downward
between a predetermined position (elevated position) within the
process chamber 2 and a predetermined position (lowered position)
within the preparatory chamber 3.
[0059] A pusher member 74 having an inverted "T" shaped
cross-section is mounted on the shaft 72 below the supporting disc
73. When the conveying means 7 is moved to the elevated position,
the pusher member 74 pushes the disc 63 upward and thus forces a
sealing member (not shown) such as a metal seal arranged at outer
periphery of the disc 63 against the periphery of the opening
formed in top plate 41 to tightly close the process chamber 2. The
pusher member 74 is provided with a third heating means (not
shown).
[0060] The second space 3a forming the preparatory chamber 3 is
provided with a plasma generating means comprising a coil (not
shown) connected to a high frequency power source and a gas
introducing means 32 for introducing inert gas into the preparatory
chamber 3. The inert gas includes e.g. rare gas such as He and Ar
etc. A pretreatment of cleaning the surface of article S using
plasma is carried out within the preparatory chamber 3 prior to the
coating carried out within the process chamber 2 with generating
plasma within the preparatory chamber 3. In this case, it is
possible to carry out a pretreatment of cleaning the surface of
article S using heat treatment for example by providing an electric
heater (not shown) of W within the preparatory chamber 3 and
further carry out heat treatment of the article S completed the
coating within a vacuum atmosphere.
[0061] Then manufacture of the permanent magnet of the present
invention with carrying out the present method using the present
apparatus 1 will be described with reference to FIGS. 1.about.3.
First of all, a sintered magnet of Fe--B-rare earth elements being
an article to be coated is manufactured using any known method. For
example, the sintered magnet can be manufactured by high frequency
melting blend of Fe, B and Nd of a predetermined composition ratio
and casting it to have an ingot, then by grinding the ingot to
powder and molding the magnetically oriented powder to a
predetermined configuration, and finally by sintering the molded
article to obtain a sintered magnet S (FIG. 3(a)). Then the
sintered magnets S of a predetermined configuration are placed on
the supporting members 62 of the supporting means 6. In this case,
it is preferable to arrange the sintered magnets S on the
supporting members 62 so that the direction of easy magnetization
of the sintered magnets S corresponds to a direction parallel to
the supporting members 62.
[0062] Then the vaporizable metallic material Dy is arranged on the
acceptor 24 within the process chamber 2. The grain diameter of Dy
is preferably in a range of 10.about.1,000 .mu.m. This is because
that handling of grains of Dy and Tb having inflammability is
difficult at a grain diameter smaller than 10 .mu.m and on the
other hand a longer time duration for vaporization is required at a
grain diameter larger than 1,000 .mu.m. For increasing the yield of
Dy, gross of Dy placed on the acceptor 24 is determined as an
amount required to hold the Dy vapor atmosphere within the process
chamber 2 until the magnet reaches a predetermined temperature
(temperature at which the vaporizable metallic material diffuses
not only into the crystal grain but into the crystal grain
boundary).
[0063] Then the gate valve arranged on the side wall 30 is opened
to introduce the supporting means 6 supporting the sintered magnets
S into the second space 3a and the supporting means 6 is laid on
the disc 63. Then the gate valve is closed and evacuating means 11a
and 31 are actuated to evacuate the vacuum chamber 11 as well as
the preparatory chamber 3 and the process chamber 2 via the first
space 4 until they reach a predetermined pressure (e.g.
10.times.10.sup.-6 Pa). In this case, the open/close means 5 is in
the opened position.
[0064] Then, when the pressure in the process chamber 2 and the
preparatory chamber 3 reach a predetermined value, the open/close
means 5 is moved to the closed position by the driving means 52 so
that the valve body 51 closes the process chamber 2. Then the
heating means 23 and the second heating means of the valve body 51
of the open/close means 5 are actuated to heat the process chamber
2 until the temperature within the process chamber 2 reaches a
predetermined temperature. The temperature within the process
chamber is preferably set in a range of 1,000.about.1,700.degree.
C. This is because that a vapor pressure which can coat Dy at a
high speed on the surface of magnet S cannot be obtained at a
temperature lower than 1,000.degree. C. and on the other hand the
coating time duration of the sintered magnet S becomes too short to
obtain a uniform coating at a temperature higher than 1,700.degree.
C. The temperature within the process chamber 2 is preferably in a
range 1,200.about.1,500.degree. C., and more preferably in a range
1,200.about.1,400.degree. C. A desirable coating thickness can be
obtained at a high speed in these temperature ranges.
[0065] Then generating Dy vapor atmosphere having a vapor pressure
e.g. of 10 Pa at 1,300.degree. C. in the process chamber 2. Since
convection is caused within the process chamber 2 under a vapor
pressure of 10 Pa, coating is formed on a whole surface of the
sintered magnet S of ordinary temperature when it is introduced
into the process chamber.
[0066] When the uniformly heating plate 21 defining the process
chamber 2 is formed of Al.sub.2O.sub.3 widely used in a general
vacuum apparatus, it is afraid that Dy in vapor atmosphere reacts
with Al.sub.2O.sub.3 and forms reaction products on its surface and
Al atoms would enter into the Dy vapor atmosphere. For such a
reason, the uniformly heating plate 21 defining the process chamber
2, the supporting means 6 for supporting the sintered magnets S and
the supporting disc 73 of the conveying means 7 is formed of
materials which do not react with vaporizable metallic materials
used for coating, for example, Mo, W, V, Ta, alloys of these
elements, CaO, Y.sub.2O.sub.3, or oxides of rare earth elements. In
addition, coating formed of these materials may be applied to a
surface of heat insulating member as a lining film.
[0067] While Dy vapor atmosphere is formed within the process
chamber 2, a pretreatment of surface cleaning is carried out within
the preparatory chamber 3, for example, for removing an oxide film
on the sintered magnet S therefrom. In this case, it may be
possible carry out the cleaning of surface of the sintered magnet
by plasma generated within the preparatory chamber 3 by introducing
inert gas e.g. Ar into the preparatory chamber 3 via the gas
introducing means 32 and then by actuating the high frequency power
source until the pressure within the preparatory chamber 3 reaches
a predetermined value (e.g. 10.times.10.sup.-1 Pa). When the
pretreatment is completed, the temperature of the sintered material
will be from the room temperature to 200.degree. C.
[0068] When the formation of Dy vapor atmosphere within the process
chamber 2 and the cleaning of the surface of sintered magnet S are
completed, inert gas e.g. Ar is introduced into the preparatory
chamber 3 via the gas introducing means 32 until the pressure
within the preparatory chamber 3 reaches a predetermined value
(e.g. 1,000 Pa) so as to once generate a pressure difference more
than two digits relative to the process chamber 2. When the
pressure within the preparatory chamber 3 has reached a
predetermined value, the process chamber 2 and the preparatory
chamber 3 are communicated with each other by displacing the
open/close means 5 to its opened position. In this case, since the
pressure within the process chamber 2 is differentiated from that
in the preparatory chamber 3, Ar is flowed into the process chamber
2 from the preparatory chamber 3 and as the pressure within the
process chamber 2 is increased. Thus, although the vaporization is
once stopped (however operation of the heating means 23 is not
stopped), entering of Dy vaporized within the process chamber 2
into the preparatory chamber 3 is prevented.
[0069] Then, when the pressure within the process chamber 2 and the
preparatory chamber 3 is evacuated again via the evacuating means
31 until it reaches a predetermined value (e.g. 10.times.10.sup.-2
Pa), Dy is vaporized again. Then the supporting means 6 supporting
sintered magnets S is conveyed into the process chamber 2 with
actuation of driving means 71 of the conveying means 7. In this
case the process chamber 2 is tightly closed with a sealing member
such as a metal seal provided on the periphery of the disc 63 being
closely contacted against a surface around the opening formed in
the top plate 41.
[0070] Then, when the process chamber 2 being heated is tightly
closed again, e.g. Dy saturated vapor atmosphere of 10 Pa at
1,300.degree. C. is generated within the process chamber 2 and this
condition is held for a predetermined time duration. In this case,
since sintered magnets S having a temperature lower than that
within the process chamber 2 have been introduced into the process
chamber 2, Dy in the vapor is selectively deposited on the surface
of the sintered magnets S due to the temperature difference between
the temperature within the process chamber 2 and that of the
magnets S (coating step). Thus Dy can be coated at a high speed
only on the surface of the sintered magnets S (FIG. 3(b)). During
which, no Dy is deposited on the pusher member 74 of the supporting
table 73 since the pusher member 74 is heated to a temperature
substantially same as that of the uniformly heating plate 21 by a
third heating means (not shown).
[0071] Since not only Dy but the sintered magnets S themselves are
heated by radiant heat when sintered magnets S having the ordinary
temperature are introduced into the process chamber 2 heated to a
high temperature, the holding time duration within the process
chamber 2 in which saturated vapor atmosphere is generated is a
term by the sintered magnets S reach 900.degree. C. and also a term
by a necessary amount of Dy is deposited on the surface of the
sintered magnets S (in which "necessary amount of Dy" means an
amount that Dy is diffused only into the crystal grain boundary to
improve the magnetic properties of the sintered magnets S). If the
sintered magnets S are heated to a temperature exceeding
900.degree. C., Dy would be diffused into grains (crystal grains of
the principal phase) of the magnets S. Eventually such a situation
would be same as that of admixture of Dy during manufacturing of
the permanent magnet and thus it is afraid that the magnetic field
strength therefore the maximum energy product exhibiting the
magnetic properties would be greatly reduced.
[0072] By the way, when the sintered magnet S is thermally expanded
due to heating, the thermal expansion of the sintered magnet S
exhibits abnormality like an invar alloy at a temperature lower
than the Curie temperature (about 300.degree. C.) and thus peeling
of the coating deposited on the surface of magnet S is liable to be
caused. Accordingly the holding time duration is preferably so that
the maximum temperature of the sintered magnet S is lower than
250.degree. C. or higher than 450.degree. C. This is because that
the peeling of the coating deposited on the surface of magnet is
hard to be caused since strain due to thermal expanding abnormality
is reduced at a temperature lower than 250.degree. C. and on the
other hand, adhesion between the magnet and Dy deposited on the
surface of magnet is improved due to melting of part of the magnet
and thus the peeling of the coating deposited on the surface of
magnet is hard to be caused at a temperature higher than
450.degree. C.
[0073] On the other hand, an inert gas such as Ar is introduced
into the preparatory chamber 3 via the gas introducing means 32
until the pressure within the preparatory chamber 3 reaches a
predetermined value (e.g. 1,000 Pa). After a lapse of predetermined
time duration after conveyance of the sintered magnets S into the
process chamber 2, the supporting disc 73 is moved from the
elevated position within the process chamber 2 to the lowered
position within the preparatory chamber 3 and the open/close means
5 is moved from the opened position to the closed position. During
which, no Dy in the vapor is deposited on the valve body 51 of the
open/close means 5 since the valve body 51 is heated by the second
heating means (not shown) to a temperature substantially same as
that of the uniformly heating plate 21. The vaporization is stopped
due to a fact that Ar enters from the preparatory chamber 3 to the
process chamber 2 and the sintered magnets S on which Dy is coated
are cooled in the Ar atmosphere.
[0074] Then the preparatory chamber 3 isolated from the process
chamber 2 is evacuated by the evacuating means 31 until the
pressure within the preparatory chamber 3 reaches a predetermined
value (10.times.10.sup.-3 Pa), and heat treatment is carried out on
the sintered magnets S on which Dy having been coated for a
predetermined time duration under a predetermined temperature (e.g.
700.about.950.degree. C.) with actuation of the heating means
arranged in the preparatory chamber 3 (diffusing step). In this
case, it is preferable, continuously with the heat treatment within
the preparatory chamber 3, to carry out heat treatment for removing
strain of permanent magnets for a predetermined time duration (e.g.
30 minutes) under a predetermined temperature (e.g.
500.about.600.degree. C.) lower than that in said heat treatment
(annealing step). Finally the supporting means 6 is taken out from
the preparatory chamber 3 by opening the gate valve on the side
wall 30 after having cooled for a predetermined time duration.
[0075] Thus it is possible to obtain permanent magnets on which Dy
is coated over a whole surface of the sintered magnets S and heat
treatment is carried out to uniformly diffuse Dy coated on the
surface of the magnets S into crystal grain boundary phases of the
magnets (FIG. 3(c)). The neodymium magnet of the prior art has
nature of being easily corroded and thus its surface is covered by
a protecting coating of resin such as epoxy or PPS or surface
treatment such as nickel plating. On the contrary, the surface of
the magnet of the present invention is covered by a coating of Dy
having extremely higher corrosion and weather resistance than those
of Nd and thus it is possible to obtain a permanent magnet having
excellent corrosion and weather resistance without requiring any
additional protecting film. Accordingly owing to omission of the
additional surface treating steps, it is possible to coat Dy on
surfaces of magnets at a high speed and at a predetermined coating
thickness as well as to further improve the productivity and to
reduce the manufacturing cost.
[0076] It is preferable that the surface and crystal grain boundary
of the magnet have a Dy rich phase (phase including 5.about.80%
Dy). The neodymium magnet of the prior art has three phases
comprising the principal phase, Nd rich phase and B rich phase.
According to the present invention since Dy rich phase is present
in the Nd rich phase in the crystal grain boundary which is weak in
the corrosion resistance and weather resistance, it is possible to
manufacture permanent magnets having extremely strong corrosion
resistance and weather corrosion conjointly the fact that Dy rich
phase is present on the surface of the sintered magnets S.
[0077] It is more preferable that the surface of sintered magnets S
is covered by the Dy rich phase and the crystal grain boundary
includes the Dy rich phase of 1.about.50%. On the other hand, when
the crystal grain boundary includes the Dy rich phase more than
50%, the maximum energy product, remanent magnetic flux density and
coercive force exhibiting the magnetic properties are extremely
reduced.
[0078] Although the present invention has been described as to
carrying out coating of Dy on a surface of sintered magnets S of
Fe--B-rare earth elements, the coating method and apparatus 1 of
the present invention is not limited to such an embodiment and can
be applied to coating of other vaporizable metallic materials. In
this case, conditions such as the heating temperature within the
process chamber 2 and holding time duration etc. are suitably set
in accordance with articles to be coated and properties of the
vaporizable metallic materials. In addition, it is possible to use
Tb in place of Dy and to coat Tb at a high speed and selectively on
the surface of sintered magnets of Fe--B-rare metal elements using
the coating method and apparatus of the present invention.
Furthermore, it is possible to carry out the diffusion step within
the process chamber 2 after the coating has been completed.
[0079] In addition, it is possible to use as vaporizable metallic
material to be coated an alloy including at least one of Dy and Tb
and at least one of Nd, Pr, Al, Cu, Ga and Ta for increasing the
coercive force. Such an alloy can further increase especially the
coercive force as compared with permanent magnets obtained with
being carried out the heat treatment. In this case, since Dy and Tb
have a high melting point, it is preferable to use materials having
a lower melting point than them to generate vaporizable metallic
material at a shorter time duration.
[0080] Although the preparatory chamber 3 is arranged under the
process chamber 2 in the illustrated embodiment, it is possible to
arrange the process chamber 2 under the preparatory chamber 3. As
shown in FIG. 4, when measuring the density of Ar, He and Dy
relative to a constant pressure and temperature, the density of Dy
and Ar under a constant pressure is analogous for example in cases
of Ar density under a pressure of 10 Pa and a room temperature
(about 27.degree. C.) and Dy density under a pressure of 10 Pa and
a high temperature (about 1,300.degree. C.). From this fact, it is
possible to securely prevent a leakage of Dy vapor from the process
chamber 2 to the preparatory chamber 3 due to a difference in
specific gravity while the sintered magnets S are taken out from
the process chamber 2, by introducing He gas having a large
difference in density relative to a constant pressure into the
preparatory 3 so that the pressure in the process chamber 2 and
that in the preparatory chamber 3 are substantially same when the
process chamber 2 is arranged under the preparatory chamber 3.
[0081] Although it is structured in the illustrated embodiment that
heat is hard to be transmitted to the sintered magnets S through
the posts 61, the present invention is not limited to such a
structure and it may be possible to provide any cooling means to
forcedly suppress temperature rise of the sintered magnets S. In
this case, it is possible to provide a cooling means to suppress
temperature rise of the sintered magnets S heated by radiant heat
when the magnets S of ordinary temperature are introduced into the
process chamber 3 heated to a high temperature by circulating a
coolant (cooling water) through the posts 61 with enlarging a
diameter of each post 61.
Embodiment 1
[0082] Each sintered magnet of Fe--B-rare earth elements was made
as a rectangular parallelopiped of 50.times.50.times.8 mm using a
raw material having a composition of 31Nd-1Co-1B-0.1Cu-bal.Fe
("NEOMAX-50 manufactured by NEOMAX Co.). The surface of sintered
magnet S was cleaned using acetone after having finished it as
having a surface roughness of less than 20 .mu.m.
[0083] Dy was coated on the surface of sintered magnet S using the
coating apparatus 1 and method of the present invention. Dy of
99.9% degree of purity was used as the coating material and Dy of
gross 500 g was laid on the receptor 24. A wire forming the mesh
type supporting member 62 of the supporting means 6 is made of Mo
and has a diameter of 1 mm. Then four (4) cleaned sintered magnets
S were laid on each supporting members 62 on a circle of a diameter
(80 mm) oppositely in a diametrical direction each other (totally
eight (8) sintered magnets S were placed on two supporting members
62 of upper and lower stages. A space between the supporting
members 62 of the upper and lower stages is 60 mm.
[0084] Prior to coating of Dy, Ar was introduced into the
preparatory chamber 3 and cleaning by plasma treatment of the
surface of sintered magnet S was carried out for 60 seconds under
conditions of a pressure of 10.times.10.sup.-1 Pa and of a high
frequency voltage of 800 V. The temperature of the sintered magnet
S after this cleaning was 60.degree. C.
[0085] On the other hand, the process chamber 2 was closed by the
open/close means 5 at its closed position and heated to
1,350.degree. C. to vaporize Dy and to fill the process chamber 2
with Dy vapor. The pressure within the process chamber 2 and the
preparatory chamber 3 when introducing the sintered magnets S into
the Dy vapor atmosphere was set at 10.times.10.sup.-2 Pa and the
holding time duration after the sintered magnets S having been
introduced into the process chamber 2 was set at 40 seconds.
Furthermore, as conditions of heat treatment within the preparatory
chamber 3, the pressure within the preparatory chamber 3 was set at
10.times.10.sup.-3 Pa and the holding time duration was set at 5
minutes at 800.degree. C. and 30 minutes at 600.degree. C.
[0086] FIG. 5 is a table showing average values of magnetic
properties of eight (8) permanent magnets manufactured under
conditions described above. Magnetic properties of magnets on which
Dy is not coated are also shown in the table of FIG. 5 as
comparative examples. From these results, it is found that
permanent magnets were obtained having a high magnetic properties
such as the maximum energy product of 50.3 MG0 e, the remanent
magnetic flux density of 14.4 kG and the coercive force of 23.5 K0
e. The temperature of the sintered magnet S after being held for 40
seconds was about 600.degree. C. and the coating thickness was
about 100 .mu.m and the coating was formed substantially uniformly
on the surface of sintered magnet S.
Embodiment 2
[0087] In this embodiment 2, permanent magnets were manufactured at
same conditions as those in the embodiment 1 except for that heat
treatment was not carried out. However, the holding time duration
of the permanent magnets within the Dy vapor atmosphere was set at
one (1) minute and the temperature within the process chamber was
varied. FIG. 6 is a table showing average values of a coating
thickness of Dy when the coating was carried out under these
conditions, and the magnetic properties of permanent magnets
manufactured in this embodiment. According to this embodiment 2, it
can be found that little coating is formed at a temperature lower
than 1,000.degree. C., but coating can be formed at a high speed
more than 20 .mu.m/sec at a temperature higher than 1,200.degree.
C. In this case, it is found that it is possible to obtain a
permanent magnet having a maximum energy product of about 50 MG0 e
of little loss and a high coercive force of 17 K0 e or more in a
range of 1,100.about.1,700.degree. C.
Embodiment 3
[0088] In this embodiment 3, permanent magnets were manufactured at
same conditions as those in the embodiment 1 except for that
pretreatment (cleaning treatment) was not carried out. However, the
holding time duration of the permanent magnets within the Dy vapor
atmosphere was varied. FIG. 7 is a table showing average values of
the coating thickness of Dy coated with the holding time duration
being varied, the maximum and the magnetic properties of permanent
magnets manufactured in this embodiment. According to this
embodiment 3, it can be found that a vapor depositing velocity
exceeding 17 .mu.m can be obtained and the temperature rise of
sintered magnet itself is at most 743.degree. C. although it is
held for 60 seconds. In this case, it is found that it is possible
to obtain a permanent magnet of high coercive force having a
maximum energy product of about 50 MG0 e, a remanent magnetic flux
density of 14.5 kG and a coercive force of 15.4.about.21.3 K0
e.
Embodiment 4
[0089] In this embodiment 4, permanent magnets were manufactured at
same conditions as those in the embodiment 1 except for that
pretreatment (cleaning treatment) was not carried out. However, the
wire for forming the mesh type supporting member 62 of the
supporting means 6 is made of Mo and has a diameter of 3 mm. FIG. 8
is a table showing the magnetic properties when such a wire of Mo
and having a diameter of 3 mm is used for making the supporting
member 62. According to this embodiment 4, it can be found that
although there are remained mesh shaped non-coated portions on the
surface of the sintered magnet S facing to the supporting member 62
with using a thick wire, there is scarcely influenced on the
coating of the magnet S by carrying out the coating operation on
the mesh type supporting member 62 with laying the magnet S on the
supporting member 62 in view of the direction of easy magnetization
and thus it is possible to obtain a permanent magnet of high
coercive force having a maximum energy product of 50.0 MG0 e, the
remanent magnetic flux density of 14.4 kG and the coercive force of
21.3 K0 e.
Embodiment 5
[0090] In this embodiment 5, permanent magnets were manufactured at
same conditions as those in the embodiment 1 however the holding
time duration of the sintered magnet within the Dy vapor atmosphere
was varied. FIG. 9(a) is a table showing average values of
variation of the coating thickness of Dy at measuring points shown
in FIG. 9(b) (measuring points (1).about.(15)). According to this
table of FIG. 9(a), it is found that substantially uniform coating
can be obtained.
Embodiment 6
[0091] In this embodiment 6, each sintered magnet of Fe--B-rare
earth elements was made as a rectangular parallelopiped of
3.times.50.times.40 mm using a raw material having a composition of
22Nd-5Dy-0.9B-4Co-bal.Fe. In this case, a surface of the sintered
magnet S was finished as having the surface roughness less than 50
.mu.m.
[0092] Then a metallic coating was formed on a surface of the
sintered magnet S by using the coating apparatus 1 and method of
the present invention. Raw material having a composition of
10Dy-5Tb-50Nd-35Pr was used as coating material and laid on the
receptor 24. A wire forming the mesh type supporting member 62 of
the supporting means 6 is made of Mo and has a diameter of 1 mm.
One hundred (100) sintered magnets S cleaned as mentioned above
were arranged so that they were diametrically opposed on the
supporting member 62.
[0093] On the other hand, the process chamber 2 was tightly closed
at the closed position of the open/close means 5 and heated to
1,250.degree. C. to vaporize the vaporizable coating material
having a composition mentioned above to generate metallic vapor
atmosphere within the process chamber 2. The pressure within the
process chamber 2 and the preparatory chamber 3 when the sintered
magnets S are introduced into the metallic vapor atmosphere was set
at 10.times.10.sup.-2 Pa and the pressure within the preparatory
chamber 3 was set at substantially same as that within the process
chamber 2 by introducing He gas into the preparatory chamber 3.
[0094] The holding time duration after the sintered magnets S
having been conveyed into the process chamber 2 was set at
10.about.300 seconds so that the maximum temperature of each
sintered magnet became 100.about.1,000.degree. C. In this case,
each post 61 was water cooled. In addition, as conditions of the
heat treatment within the preparatory chamber 3, the pressure
within the preparatory chamber 3 was set at 10.times.10.sup.-3 Pa
and the holding time duration was one (1) hour at 800.degree. C.
(diffusing step) and 30 minutes at 600.degree. C. (annealing step).
Then the pressure within the preparatory chamber 3 was returned to
the atmosphere pressure and the magnets were taken out
therefrom.
[0095] FIG. 10 is a table showing the magnetic properties as to one
hundred (100) permanent magnets manufactured under conditions
mentioned above and the fraction deflection of adhesion after
having carried out the tape peeling method (tape test). According
to these results, it is found that when the maximum temperature of
the sintered magnets S does not reach 100.degree. C., the coating
material does not deposit on the surface of the sintered magnets S
and thus a high coercive force cannot be obtained. On the other
hand, it is found that when the maximum temperature is in a range
of 100-1,050.degree. C., the coating material of a thickness of 10
.mu.m or more is deposited on the surface of the sintered magnet S
and a permanent magnet of high coercive force having the maximum
energy product of 44 MG0 e or more, the remanent magnetic flux
density of 13.8 kG or more and the coercive force of 28 K0 e or
more is obtainable. However it is also found that when the
temperature of the sintered magnet S is in a range of
250-450.degree. C., the percent defective of adhesion of less than
10% was caused. In the embodiment 6, since cleaning of a surface of
the sintered magnets is not carried out prior to Dy coating,
ingress of Dy into grains of the sintered magnet during coating
operation is suppressed and thus it is found that the maximum
energy product exhibiting the magnetic properties is not reduced
although the maximum temperature of the sintered magnets exceed
900.degree. C.
Embodiment 7
[0096] In this embodiment 7, each sintered magnet of Fe--B-rare
earth elements was made as a rectangular parallelopiped of
5.times.50.times.40 mm using a raw material having a composition of
28Nd-1B-0.05Cu-0.17Zr-bal.Fe. In this case, a surface of the
sintered magnet S was finished as having the surface roughness less
than 5 .mu.m and then cleaned by using acetone.
[0097] Then Dy was coated on a surface of the sintered magnet S by
using the coating apparatus 1 and method of the present invention.
In this case Dy of 99.9% degree of purity was used as coating
material and laid on the receptor 24. One hundred (100) sintered
magnets S cleaned as mentioned above were arranged so that they
were diametrically opposed on the supporting member 62.
[0098] Prior to coating operation, Ar was introduced into the
preparatory chamber 3 and cleaning by plasma treatment of the
surface of sintered magnet S was carried out for 60 seconds under
conditions of a pressure of 10.times.10.sup.-1 Pa and of a high
frequency voltage of 800 V. The temperature of the sintered magnet
S after this cleaning was 60.degree. C.
[0099] On the other hand, the process chamber 2 was closed by the
open/close means 5 at its closed position and heated to
1,200.degree. C. to vaporize Dy and to generate metallic vapor
atmosphere within the process chamber 2. The pressure within the
process chamber 2 and the preparatory chamber 3 when introducing
the sintered magnets S into the Dy vapor atmosphere was set at
10.times.10.sup.-2 Pa and the holding time duration was set so that
Dy coating of 20 .mu.m in average can be formed after the sintered
magnets S having been introduced into the process chamber 2.
Furthermore, as conditions of heat treatment within the preparatory
chamber 3, the pressure within the preparatory chamber 3 was set at
10.times.10.sup.-3 Pa and the holding time duration was set at one
(1) hour at 950.degree. C. (diffusion step) and 30 minutes at
500.degree. C., (annealing step). Then the pressure within the
preparatory chamber 3 was returned to the atmosphere pressure and
the magnets were taken out therefrom.
Comparative Examples
[0100] Sintered magnets S were manufactured under same conditions
as those in the embodiment 7 as comparative examples 1.about.3. In
the comparative example 1, permanent magnets were obtained by
applying resin coating of epoxy of 20 .mu.m in average on the
surface of one hundred (100) sintered magnets S using a known
method in place of forming Dy coating and heat treatment on the
surface of magnets S. In the comparative example 2, Ni plating of
20 .mu.m in average was applied on the surface of one hundred (100)
sintered magnets S using a known plating method. In the comparative
example 3, Al of 20 .mu.m coating thickness in average was vapor
deposited on the surface of one hundred (100) sintered magnets S
using a known vapor depositing method.
[0101] FIG. 11 is a table showing results of comparison between
permanent magnets of the embodiment 7 and comparative examples
1.about.3, and the sintered magnets S (comparative example 4)
respectively as to the magnetic properties, corrosion resistance
and weather resistance. Following corrosion resistance test and the
weather resistance test were carried out: a visual inspection test
confirming if or not generation of corrosion after a lapse of 100
hours from spraying of saline water on the surfaces of permanent
magnets and sintered magnets; a saturated steam pressure test (PCT:
pressure cooker test) for 100 hour; and a visual inspection test
confirming if or not generation of corrosion after a lapse of 1,000
hour under a condition of temperature of 80.degree. C. and humidity
of 90%.
[0102] According to this comparison, it is found that the permanent
magnet of the embodiment 7 of the present invention has high
magnetic properties of the maximum energy product of 56 MG0 e, the
remanent magnetic flux density of 15.0 kG or more, and the coercive
force of 28 K0 e relative to the coercive force of 10 K0 e in the
comparative examples 1.about.4. In addition, it is also found that
although generation of corrosion was confirmed in the corrosion
resistance test or weather resistance test as to the comparative
examples 1.about.4, no generation of corrosion is confirmed in
these test as to the embodiment 7 of the present invention and thus
the permanent magnets manufactured in accordance with the present
invention have strong corrosion resistance and weather
resistance.
Embodiment 8
[0103] In this embodiment 8, each sintered magnet of Fe--B-rare
earth elements was made as a rectangular parallelopiped of
50.times.50.times.8 mm using a raw material having a composition of
31Nd-1Co-1B-0.1Cu-bal.Fe ("NEOMAX-50 manufactured by NEOMAX Co.).
The surface of sintered magnet S was cleaned using acetone after
having finished it as having a surface roughness of less than 20
.mu.m.
[0104] Vaporizable metallic material was coated on the surface of
sintered magnet S using the coating apparatus 1 and method of the
present invention. Alloy comprising Dy and Nd, Pr, Al, Cu, Ga, Ta
mingled with Dy respectively at stoichiometric ratio 1:1 was used
as the vaporizable metallic material and laid on the receptor 24.
Prior to coating of the vaporizable metallic material, Ar was
introduced into the preparatory chamber 3 and cleaning by plasma
treatment of the surface of sintered magnet S was carried out for
60 seconds under conditions of a pressure of 10.times.10.sup.-1 Pa
and of high frequency voltage of 800 V. The temperature of the
sintered magnet S after this cleaning was 60.degree. C.
[0105] On the other hand, the process chamber 2 was closed by the
open/close means 5 at its closed position and heated to
1,350.degree. C. to vaporize the vaporizable metallic material and
to fill the process chamber 2 with metallic vapor. The pressure
within the process chamber 2 and the preparatory chamber 3 when
introducing the sintered magnets S into the metallic vapor
atmosphere was set at 10.times.10.sup.-2 Pa and the holding time
duration was set so that a coating having a coating thickness of
about 30 .mu.m was formed after the sintered magnets S having been
introduced into the process chamber 2. Furthermore as conditions of
heat treatment within the preparatory chamber 3, the pressure
within the preparatory chamber 3 was set at 10.times.10.sup.-3 Pa
and the holding time duration was set at 5 minutes at 800.degree.
C. (diffusing step) and 30 minutes at 600.degree. C. (annealing
step).
[0106] FIG. 12 is a table showing the magnetic properties of
permanent magnets manufactured under conditions described above.
Magnetic properties as to magnets in which only Dy was used as
vaporizable metallic material and as to magnets in which alloy
comprising Dy and Ni, Co, Fe, Au, Pt, Ag mingled with Dy
respectively at stoichiometric ratio 1:1 was used as the
vaporizable metallic material are also shown in the table. From
these results, it is found that permanent magnets of comparative
examples are substantially reduced especially in the coercive force
and the maximum energy product as compared with the permanent
magnets comprising coating of only Dy. On the other hand, it is
found that the permanent magnets of the embodiment 8 of the present
invention is superior especially in the coercive force as compared
with the magnets comprising coating of only Dy and that it is
possible to obtain permanent magnets having high magnetic
properties of the maximum energy product ((BH)max) of 50.6 MG0e or
more, the remanent magnetic flux density (Br) of 14.0 kG or more,
and the coercive force (Hcj) of 24.1 K0 e or more.
[0107] The present invention has been described with reference to
the preferred embodiment. Obviously, modifications and alternations
will occur to those of ordinary skill in the art upon reading and
understanding the preceding detailed description. It is intended
that the present invention be construed as including all such
alternations and modifications insofar as they come within the
scope of the appended claims or the equivalents thereof.
* * * * *