A method of hot hydrostatic pressing of ceramics is described. A detailed description of the invention is given. The invention is explained through an example, and a figure illustrates the temperature and pressure during the hot hydrostatic pressing treatment

Fujikawa, T.

Miyanaga, J.

Moritoki, M.

English

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https://ntrs.nasa.gov/search.jsp?R=19850001881 2020-03-20T21:42:25+00:00Z
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON D.C. 20546	 AUGUST 1984
NASA TECHNICAL MEMORANDUM
	
NASA TM-77603
11
(NASA-TM-77603) PROCESSING CFBAHICS
	 H85-10188
(National Aeroadutics and Space
Adainistr.tion)	 13 p HC A02/1IF A01 CSCL 11B
33	 Onclas
X0/27 24176
PROCESSING CERAMICS
t
M. Moritoki, T. Fujikawa, j. Miyanaga
Translation of Japanese patent no. 58-88179,
May 26, 1;33, pp. 411-414.
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Translation of Japanese patent no.
	 53-88179, May 26,
	 1983,
pp.	 411-414.
la. Abe~ '
A method of hot hydrostatic pressing of
ceramics is described. 	 A detailed
description of the invention is given.
The invention is explained through an
actual example, and a figure illustrates
the temperature and pressure during
HIP treatment.
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19 THE PATENT OFFICE OF JAPAN (JP)	 /411*
12 OFFICIAL GAZETTE FOR UNEXAMINED PATENTS (A)
11 Disclosure Number
	 58-88179
51 Int. C1. 2	Identification	 Intra-agency File Nos.
Symbols
C 08 B 35/64	 7158-4G
B 22 F 3/14	 6641-4K
43 Date of Provisional Publication	 May 26, 1983
Number of Inventions 	 one
Request for Examination 	 Not requested
(total 4 pages)
f!
56-396566
November 19, 1981
Masahito Moritoki
Miki-shi, Midorigaoka-
ch- Higashi 3 chome 11-6
Takao Fujikawa
Kobe-shi, Suma-ku,
Kaminc.tani 7 chome 7-
100-301
Junic'ii Miyanaga
Kobe-shi, Nada-ku,
Uenodori 2 chome 1-18
Kobe Steel, Ltd.
Kobe-shi, Chuo-ku,
Wakihama-cho 1 chome 3-
18
Attorney, Yasukazu Miyamoto
54 Hot hydrostatic pressing of ceramics
21 Application Number
22 Filing Date
72 Inventors
71 Applicant
74 Agent
1_
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* Numbers in margin indicate pagination of foreign text.
-1-
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Specifications
1. Title of Invention
Hot hydrostatic pressing of ceramics.
2. Scope of Patent Claim
(1) A method of hot hydrostatic pressing of ceramic powder
mold immersed in a glass bath through compression sintering using
pressure-transmitting gas at a high temperature in which the
entire surface of the aforementioned mold is covered with powder
consisting of material which does not melt during hot hydrostatic
pressing and which is sintered at a temperature lower than the
sintering temperature of the aforementioned mold ma}erial with BN
as the inner layer, this method characterized by sintering the
aforementioned coating powder material in the course of the
aforementioned hot hydrostatic pressing treatment to form an air-
tight layer followed by heating to the sintering temperature of
the aforementioned mold.
(2) The method of hot hydrostatic pressing of ceramics of
Claim 1 in which the ceramic powder mold is a mold consisting
primariy of silicon nitride, silicon carbide or boron carbide.
(3) The method of hot hydrostatic pressing of ceramics of
Claims 1 and 2 in which the coating material is Al 20 31 Zr0 2 or
BN.
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(4) The method of hot hydrostatic pressing of ceramics of
Claims 1, 2 and 3 in which the glasE is pyrex glass.
3. Detailed Description of the Invertion
This invention concerns hot hydrostatic pressing treatment
using pressure-transmitting gas, especially a method of improving
the sealing properties of the aforementioned hot hydrostatic
pressing treatment through the using of glass with a low
softening point in which pressure-transmitting gas is dissolved
as sealant.
The method of hot hydrostatic pressing (below abbreviated
HIP) using glass as the sealant has the advantages of forming
different shaped molds and usinq copper or [illegible], which are
ordinarily used as capsule material, even at high temperatures at
which they could nGt be used. The glass capsule method (consult
Patent Publication No. 46-2731) and the method of embedding mold
in glass powder (consult Patent Disclosure No. 55-89405) are well
known. At present, these are used extensively as high
temperature structural material in molding processing of ceramic
powder whose development has been progressing.
However, heat -esistant ceramic powder has a high sintering
temperature. Since the HIP temperature is higher than the
previous temperature during metal powder molding, the same state
develops whether using the aforementioned glass sealing method or
the glass bath method since the HIP temperature reaches 1700°C in
treating ceramics such as silicon nitride (Si 3 N6 ) or silicon
/412
i
7
-3-
carbide (SiC) using glass with a low softening point. In fact,
the ceramic mold to be treated is immersed in a glass bath and it
is covered with molten glass. Thus, in this case, part of the
mold floats out of the glass bath since the specific gravity of
the ceramic mold is 1.8 to 2.1 g/cm2 until high density is
reached, which is lower than the specific gravity of 2.2 to 2.3
of glass, and sealing is incomplete. This is due to the reaction
between slight amounts of oxygen contained in the gas and the
ceramic which is induced through the direct contact made between
the pressure-transmitting gas and the mold when Al or N 2 gas is
used as the pressure medium during HIP treatment.
In addition, when using pyrex glass, for example, as glass
with a low softening point, the pressure-transmitting gas
dissolves at specific temperatures and pressures, thereby
resulting in the collection of this gas in the pores of the mold
which results in internal pressure and the inability to achieve
high density due to HIP treatment.
However, in spite of these defects, glass with a low
softening point has the advantages of being easy to handle and
being inexpensive. Thus, improvemLnt of the aforementioned
defects is desired because these advantages are extremely
beneficial in industry.
The objective of this invention is to provide a method of
improved sealing which can effectively utilize glass sealant,
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which is an extremely useful sealant, by overcoming the
aforementioned defects of glass.
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Specifically, the features of this invention which achieve
the aforementioned objectives are realized through a method of
HIP of ceramic powder mold immersed in a glass bath by 	 R
compression sintering at a high temperature using air as the
pressure medium in which the entire surface of the aforementioned
mold is covered wick powder consisting of material which is
sintered at a temperature lower than the sintering temperature of
the mo^.d material with BN powder as the inner layer. This method
is cha-:acterized by sintering the aforementioned coating material
in the course of HIP treatment to form an air-tight layer
fol]c;wed by heating to the sintering temperature of the
aforementioned mold.
The concrete modes of implementation of the aforementioned
are explained below.	
i
First, the HIP treatment mei:hod which is the basic method of
treatment in this inventi3n is a method of compression sintering
in which ceramic powder mold is sealed in a glass capsule or is
embedded in glass powder followed by compression sintering at a
high temperature using an inert gas such as Ar or N 2
 ,as as the
pressure medium while the ceramic is immersed in the glass bath.
The ceramic powder used here would be composed primarily of
silicon nitride, silicon carbide or boron carbide (B 4C). It
would be formed as a preliminary mold or as a preliminary
sintered substance followed by sealing in a glass capsule or
i
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embedding in glass powder and HIP treatment.
1
-5-
The mold to be treated which has been subjected to
preliminary molding or preliminary sintering may also contain
sintering promotors such as Y 2O 3 powder, Al 2O 3 powder or MgO
powder in addition to the --eramic powder itself.
Conversely, means of coating the aforementioned mold to be
treated include sealing in glass capsules or embedding in glass
powder, and the same state is exhibited upon heating in either
case to a temperature above the softening point of glass.
However, degasification is simple in the former case since only
the degasified section is enclosed in the capsule in
degasification sealing in order to avoid the effects of residual
_,r upon sealing, while degasification of the entire heating
furnace is necessary in the latter case, which constitutes some
difference.
Possible examples of the glass used in this invention
include silica g?ass, Vycor glass or pyrex glass, but pyrex glass
is the most desirable since silica glass forms a reactive lave:
with the mold while Vycor glass is difficult to remove following
treatment. HIP treatment is usually carried out by temperature-
and pressure elevation in an atmosphere of Ar or N 2 etc. in the
HIP furnace, but the temperature should first be elevated above
the softening point of glass to form fluid glass whi p the
atmospheric pressure is under 100 atmospheres in order to prevent
the development of local strain by the glass capsule or the
trapping of high pressure gas within the material to be treated
through the formation of a dense glass layer on the outer surface
it
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of the material through fusion of the glass powder, thereby
making HIP * reatment impossible. When glass powder is used, a
dense glass layer forms on the o , .ter surface of the treated
materal followed by temperature- and pressure elevation to the
treatment and pressure levels set for HIP treatment. However,
the aforementioned HIP process is not always appropriate since
the coating material between the glass coating and the mold to be
treated forms a sintered .layer in this invention, as stated
below.
Specifically, this invention forms a specific coating layer
over the entire surface of the material to be treated which
ensures complete sealing in the HIP treatment, as stated above.
Accordingly, the entire outer surface of the mold to be
treated would be sintered at a temperature below the mold
sintering temperature before sealing the aforementioned glass
capsule or before embedding in glass powder, thereby completing a
layer of powder material which is not melted even at the HIP
treatment temperature.
Al 20 3 , Zr0 2 or BN may be us--d as the coating material, and
BN powder would be the most desirable among these, but the
material is not restricted to BN powder because of the relation
to the ceramic mold to be subjected to HIP treatment. However,
BN powder has good mold releasing properties and a BN powder
layer must be formed directly on the outer surface covering the
mold to be treated. Accordingly, a BN powder layer is formed on
the inside to facilitate mold release while coating material
-7-
which is characteristic of this invention is affixed to the outer
surface.
While metal powder is not excluded from the coating
material, the metals are restricted to Mo, Pt or Cr, but Cr
presents difficulty in mold release fol,.)wing treatment.
Thus, these coating materials should be in a form such as a
al rubber flexible sealant as required in order to maintain the
shape. The interior of the mold would be packed with coating
material powder, and the required mold to be treated would be
therein. A layer would be formed by hydrostatic treatment at
normal temperature.
The thickness of one layer of the coating material should
exceed 0.3 mm, preferably 0.5 mm- In any case, the coating
material must form an air-tight sintered layer on the surface of
the mold to be treated at a temperature of 1200°C preferably
during HIP treatment, and the material must be suited for
densification through HI P treatment.
The types of coating material, the temperature and pres:ire
conditions in sintering until an air-tight layer is formed, the
types of ceramic molds subjected to HIP treatment and the HIP
temperature and pressure are given in the following table.
Coating material
Al	 12000C° 	 1000 kgf/cm2
ZrO2	 1350°C	 1000
BN	 1650°C	 1800
.1
1 0	 -8-
22 Ceramic mold
SiCN4	
1750°C	 2000 kgf/cm2
1850°C
B4C	 1850°C
The coating material would first be sintered at position A
on the curve of pressure and temperature illustrated in the
appended figure when selecting the aforementioned coating
material for the material to be treated which has been selected
from the aforementioned ceramic molds and conducting treatment
thereof. This would be followed by sintering at position B of
the mold to be treated which is covered with said coating
material.
Accordingly, in treatment using pressure-transmitting gas in
a glass bath based on the method of this invention, there are
differences in the specific gravity, but the seal is complete
even if some of the material were to float up from the glass bath
during treatment. Th l, ^., high densification can be expected due
to suitable uniform compression in HIP treat.me nt.
As indicated above, the method of this invention utilizes
the advantage of utilization of glass with a low softening point
as the sealant, thereby overcoming the defect of sealing
properties. Thus, this invention has great industrial utility.
When using glass in which pressure-transmitting gas is
dissolved, for example pyrex glass, as the sealant, compression
sintering would be followed by revaporization of the pressure-
transmitting gas in which glass is melted, thereby converting '.ile
glass into bubbling form. By cooling this, the appended glass
-9-
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can be removed with slight mechanical external force, thereby
getting two birds with one stone.	 /414
Below, this invention is explained through an actual
example.
(Actual Example)
Si 3 N 4
 powder containing 2.58 Y 2O3 with 708 a phase and mean
particle diameter of approximately 1= was -ubjected to uniform
compression under pressure of 5,000 kgf/cm 2 , thereby producing
mold to be treated with relative density of 628.
Bn was coated on the surface of this mold to a thickness of
0.3 mm followed by embedding in pyrex glass in a graphite
crucible and insertion in an HIP device. A sintered state was
achieved at a specific position (position A in appended figure)
during HIP treatment since Al 2O 3 is s:ntered at 1200°C, 1,000
kgf/cm 2 as stated above. BN also was sintered at the
afoi.ementioned specifie9 temperature and pressure through
temperature elevation and pressure elevation. Finally, the
temperature and p, essure were elevated to 1750°C, 2000 kgf/cm2
(position B in figure) which is the temperature and pressure for
HIP treatment of Si 3N d
 mold.
fhe temperature was reduced to 500°C while the pressure was
maintained at 2000 kgf/cm 2 followng HIP treatment, and the
pressure was then gradually released. A mold covered with glass
was removed from the crucible, ane this was then held for 30
minutes under heating to 1100°C in an electric furnace, followed
by cooling.
-10-
pressur
HH	 (kgf/an )
KN
1.
1~
temperature (°C)
NN
The glass which covered the mold became bubbling glass due
to vaporization of the pressure—transmitting gas which eras
dissolved in the glass, and the t ,slant could be removed very
easily. The resulting mold was a high density sintered material
with relative density of 98.5%, and the compression over the
entire surface was uniform, resulting in a quality product.
4. Brief Description of Drawing
The figure illustrates the temperature and pressure during
HIP treatment.
OF i
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time (hr)
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