CA1079935A - Method of making a duo-density silicon nitride article - Google Patents
Method of making a duo-density silicon nitride articleInfo
- Publication number
- CA1079935A CA1079935A CA244,845A CA244845A CA1079935A CA 1079935 A CA1079935 A CA 1079935A CA 244845 A CA244845 A CA 244845A CA 1079935 A CA1079935 A CA 1079935A
- Authority
- CA
- Canada
- Prior art keywords
- silicon nitride
- die
- silicon
- article
- density
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
- F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
- F01D5/34—Rotor-blade aggregates of unitary construction, e.g. formed of sheet laminae
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
- C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
- C04B35/591—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride obtained by reaction sintering
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
- C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
- C04B35/593—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride obtained by pressure sintering
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Turbine Rotor Nozzle Sealing (AREA)
- Ceramic Products (AREA)
- Laminated Bodies (AREA)
Abstract
METHOD OF MAKING A DUO-DENSITY SILICON NITRIDE ARTICLE
Abstract of the Disclosure A method of making a duo-density article of silicon nitride is disclosed. A first element is made of silicon metal particles. The first element is nitrided so that the silicon particles are transformed into sub-stantially pure silicon nitride. All but a bonding surface of the first element is encapsulated to form a die member. The die member is placed in a pressing die structure so that its bonding surface forms a portion of the internal surface of the die volume. The die volume of the die structure is filled with a mixture consisting of silicon nitride particles and a densification aid.
The mixture is compacted in the die volume to at least 98% of theoretical density thereby forming a second element of the duo-density article while simultaneously bonding the second element to the first element along the first element's bonding surface. The encapsulant is removed from the first element to produce the final article of silicon nitride having two zones of different density.
Abstract of the Disclosure A method of making a duo-density article of silicon nitride is disclosed. A first element is made of silicon metal particles. The first element is nitrided so that the silicon particles are transformed into sub-stantially pure silicon nitride. All but a bonding surface of the first element is encapsulated to form a die member. The die member is placed in a pressing die structure so that its bonding surface forms a portion of the internal surface of the die volume. The die volume of the die structure is filled with a mixture consisting of silicon nitride particles and a densification aid.
The mixture is compacted in the die volume to at least 98% of theoretical density thereby forming a second element of the duo-density article while simultaneously bonding the second element to the first element along the first element's bonding surface. The encapsulant is removed from the first element to produce the final article of silicon nitride having two zones of different density.
Description
~ . ~
` 1079935 ..
;` ~
, The present invention is directed to the pro-duction of silicon nitride articles.
:
~ Silicon nitride has a wide variety of uses based - on its physical and chemical properties. These uses, to name a few, include thermocouple protection tubes, crucibles for foundry use, substrates for electron~c applications and structural components for gas turbine engines.
~ Silicon nitride can be produced by a number of ;~ different processing techniques with each technique yielding !~, ii 10 a different final density. Each technique also has a ,.... .
r~ definite restriction on the final shape which can be pro-duced. Simple shapes ~f better thanl98% of theoretical density can be made by hot pressing silicon nitride powder .i to form the final article. Complex shapes, however, generally cannot be manufactured by this processing technique.
,.~.
As an alternate to the hot pressing technique, silcion nitride articles of complex shape having densities of 70 to 75 percent of theoretical density are produced by ; ~ an injection molding technique. In this technique, silicon . . .
~ 20 metal particles and a thermoplastic are formed into a ~.
~-` mixture. This mixture is injection molded to form the ~ shape of the article. Subsequent operations include the i~ heating of the article to burn out the thermoplastic and the nitriding operation to produce the final silicon nitride article.
Another processing technique for manufacturing fairly intricate shapes of silicon nitride is slip casting.
A slip casting technique generally produces a final article having a density in the range from 80-85% of theoretical density. In the slip casting technique, silicon metal particles are cast into the desired shape. The silicon
` 1079935 ..
;` ~
, The present invention is directed to the pro-duction of silicon nitride articles.
:
~ Silicon nitride has a wide variety of uses based - on its physical and chemical properties. These uses, to name a few, include thermocouple protection tubes, crucibles for foundry use, substrates for electron~c applications and structural components for gas turbine engines.
~ Silicon nitride can be produced by a number of ;~ different processing techniques with each technique yielding !~, ii 10 a different final density. Each technique also has a ,.... .
r~ definite restriction on the final shape which can be pro-duced. Simple shapes ~f better thanl98% of theoretical density can be made by hot pressing silicon nitride powder .i to form the final article. Complex shapes, however, generally cannot be manufactured by this processing technique.
,.~.
As an alternate to the hot pressing technique, silcion nitride articles of complex shape having densities of 70 to 75 percent of theoretical density are produced by ; ~ an injection molding technique. In this technique, silicon . . .
~ 20 metal particles and a thermoplastic are formed into a ~.
~-` mixture. This mixture is injection molded to form the ~ shape of the article. Subsequent operations include the i~ heating of the article to burn out the thermoplastic and the nitriding operation to produce the final silicon nitride article.
Another processing technique for manufacturing fairly intricate shapes of silicon nitride is slip casting.
A slip casting technique generally produces a final article having a density in the range from 80-85% of theoretical density. In the slip casting technique, silicon metal particles are cast into the desired shape. The silicon
2 ~
, .
-"
:
` 107993S
metal is then converted in a nitriding operation, into silicon nitride.
It is generally impossible to fabricate a complete rotor for a gas turbine engine of hot pressed silicon nitride material. The impossibility of manufacturing such a com-plete rotor by a hot pressing technique comes about because of the complex shape of the rotor blades. The complex ,1 shape of such blades can be formed easily by either an injection molding technique or a slip casting technique.
It is generally impossible, however, to form a complete rotor by an injection molding technique or slip casting technique as the hub portion of the rotor formed by such a technique cannot withstand the mechanical and thermal stresses imposed upon that portion of the rotor during its use in an engine.
This invention teaches a method wherein the best ~- characteristics of a hot pressed silicon nitride material are used in conjunction with either an injection molded or a slip cast silicon nitride material to form a complex article of manufacture such as a rotor for a gas turbine engine.
- The method of this invention has the following ` general steps. A first element is formed of silicon metal particles in a silicon metal forming operation. The first element is nitrided so that the silicon metal particles forming the first element are converted to substantially pure silicon nitride. An encapsulant release agent is applied to the first element. All but a bonding surface of -- the first element is encapsulated with silicon nitride thereby to form a die member. The die member is placed in a pressing die structure so that the bonding surface of the ''" ' ;1.".
., .
~0799~5 die member forms a portion of the total die surface defining the interior surface of a die volume formed within the pressing die structure. The die volume is filled with a mixture consisting of from about 94 to 99.5 by weight silicon nitride particles and from about 6.0 to 0.5% by weight of a densification aid. The mixture is hot pressed under the simultaneous application of heat and pressure in the die volume to at least 95% of theoretical :
density thereby forming a second element of the duo-density , 10 article while simultaneously bonding a surface area of the second element to the first element along the first element's -~ bonding surface. The encapsulant formed about the first ~ element is removed to produce the final article of silicon - nitride having two zones with different densities.
The first element of silicon metal particles may be formed by either a slip casting operation of an injection molding operation. The encapsulation of the first element with silicon nitride may be accomplished by coating the first element with a material which forms a thin protective barrier and then by injection molding or slip casting silicon particles therearound, the silicon particles subsequently - being nitrided to form an encapsulating material. The encapsulant may be applied in one or more steps so as to ease the removal of the encapsulant material.
The invention is described further, by way of illustration, with reference to the accompanying drawings, in which:
Figure 1 is a schematic drawing, in cross-section showing apparatus capable of performing the method of this invention; and Figure 2, 3 and 4 illustrate graphically the manner ~ - 4 -.
., 1079935 ~: ~
in which a first element of silicon nitride can be encap-sulated.
A process for making a duo-density article of silicon nitride will now be described with reference to the drawings, as required. This article to be described will be a rotor for a gas turbine engine. The first element , ~-.
~ of the rotor is its outer blade ring of complex shape over , . . .
` which the hot gases of the engine flow to turn the rotor.
~ .
,,, 10 ., , 1.'', .;, . .
~, ,.....
.:,.
,.,, ,.,; .
~,,~' , i ,:. I
., .... .
~ .
.
. .
..' .'','' .' . .
.:
, -.;
, ............................................... .
,. .
, ,,.:'' ." ' ,~ .
., ' . ~
,. . .
. ., -'. ' - 4a -., .
. J. ' , , 1 .
. .
~, ~ .
~o~799;~5 1 ll The method of making a duo-densit:~ article of silicon ; 2 ¦ nitride in accordance with the teachings o~ this invention
, .
-"
:
` 107993S
metal is then converted in a nitriding operation, into silicon nitride.
It is generally impossible to fabricate a complete rotor for a gas turbine engine of hot pressed silicon nitride material. The impossibility of manufacturing such a com-plete rotor by a hot pressing technique comes about because of the complex shape of the rotor blades. The complex ,1 shape of such blades can be formed easily by either an injection molding technique or a slip casting technique.
It is generally impossible, however, to form a complete rotor by an injection molding technique or slip casting technique as the hub portion of the rotor formed by such a technique cannot withstand the mechanical and thermal stresses imposed upon that portion of the rotor during its use in an engine.
This invention teaches a method wherein the best ~- characteristics of a hot pressed silicon nitride material are used in conjunction with either an injection molded or a slip cast silicon nitride material to form a complex article of manufacture such as a rotor for a gas turbine engine.
- The method of this invention has the following ` general steps. A first element is formed of silicon metal particles in a silicon metal forming operation. The first element is nitrided so that the silicon metal particles forming the first element are converted to substantially pure silicon nitride. An encapsulant release agent is applied to the first element. All but a bonding surface of -- the first element is encapsulated with silicon nitride thereby to form a die member. The die member is placed in a pressing die structure so that the bonding surface of the ''" ' ;1.".
., .
~0799~5 die member forms a portion of the total die surface defining the interior surface of a die volume formed within the pressing die structure. The die volume is filled with a mixture consisting of from about 94 to 99.5 by weight silicon nitride particles and from about 6.0 to 0.5% by weight of a densification aid. The mixture is hot pressed under the simultaneous application of heat and pressure in the die volume to at least 95% of theoretical :
density thereby forming a second element of the duo-density , 10 article while simultaneously bonding a surface area of the second element to the first element along the first element's -~ bonding surface. The encapsulant formed about the first ~ element is removed to produce the final article of silicon - nitride having two zones with different densities.
The first element of silicon metal particles may be formed by either a slip casting operation of an injection molding operation. The encapsulation of the first element with silicon nitride may be accomplished by coating the first element with a material which forms a thin protective barrier and then by injection molding or slip casting silicon particles therearound, the silicon particles subsequently - being nitrided to form an encapsulating material. The encapsulant may be applied in one or more steps so as to ease the removal of the encapsulant material.
The invention is described further, by way of illustration, with reference to the accompanying drawings, in which:
Figure 1 is a schematic drawing, in cross-section showing apparatus capable of performing the method of this invention; and Figure 2, 3 and 4 illustrate graphically the manner ~ - 4 -.
., 1079935 ~: ~
in which a first element of silicon nitride can be encap-sulated.
A process for making a duo-density article of silicon nitride will now be described with reference to the drawings, as required. This article to be described will be a rotor for a gas turbine engine. The first element , ~-.
~ of the rotor is its outer blade ring of complex shape over , . . .
` which the hot gases of the engine flow to turn the rotor.
~ .
,,, 10 ., , 1.'', .;, . .
~, ,.....
.:,.
,.,, ,.,; .
~,,~' , i ,:. I
., .... .
~ .
.
. .
..' .'','' .' . .
.:
, -.;
, ............................................... .
,. .
, ,,.:'' ." ' ,~ .
., ' . ~
,. . .
. ., -'. ' - 4a -., .
. J. ' , , 1 .
. .
~, ~ .
~o~799;~5 1 ll The method of making a duo-densit:~ article of silicon ; 2 ¦ nitride in accordance with the teachings o~ this invention
3 lis initiated by forming the first element, which in this case, ¦ is the blade ring of the rotor. The first element may be ¦formed by any generally known forming tech]lique. Illustrative 1 6 ¦ types of forming techniques are slip castillg and injection 7 molding.
8 In the case of forming the first element by a slip 9 casting technique, silicon metal particles, suspended in a - 10 vehicle, are cast into a mold having the shape desired for 11 the blade ring. The mold is positioned against a porous 12 material capable of drawing the vehicle of the slip out of the ;
13 casting volume thereby leaving behind a consolidated mass of ~; 14 silicon metal particles. In such a manner the first element is formed of silicon metal particles by a slip casting 16 ' technique.
17 As an alternative approach, the general shape of the . 18 first element may be formed by an injection molding technique. ;19 a typical injection molding compound for forming the first element is one which would have about 60 to 66 percent by 21 volume of silicon metal particles with the remainder being 22 a thermoplastic binder. In general, the particle size of the 23 metal will be such that the material will have a maximum 24 particle size in the range of 40 to 60 microns and a mean particle size in a range of from 10 to 13 rnicrons. Once a 26 molding composition is formed, the composition is fed into 27 a cylinder of an injection molding machine. The machine heats 28 the thermoplastic above its melting point. Pressure is applied 29 to the cylinder and th~ molding composition is shot into a ~ cold moldiDg having the configuration of the blede ring _ 5 _ : 11 .' ' 1~
107993~
. .
~ to be produced. The thermoplastic solidifies into the desired '~ shape thereby locking the silicon metal particles carried along with it into the desired shape.
The so fo~medblade ring of silicon metal particles and thermoplastic is gradually heated in a furnace to a temperature of about 350C. The heating program may take as long as three days so that no stresses are created in the article during heating. During this heating, the thermoplastic binder is burned out.- This action leaves behind silicon metal particles in the desired shape of the blade ring.
No matter how the silicon metal particles are formed into the blade ring shape desired, the so formed first element is thereafter nitrided in order to produce a finished body of silicon nitride. Since the first element is formed of silicon metal particles, the nitriding operation is effective to change the first element into a silicon nitride.
, In the nitriding operation the element is heated while exposed to nitrogen gas at a temperature and for a sufficient period of time that all of the silicon is transformed into silicon nitride. A full procedure for nitriding silicon to form silicon nitride is disclosed in U.K. Paten~ No. 1,448,915. If the article nitrided had been originally formed by an injection molding process, the final article will have a density of 70 to 75 percent of theoretical density. If the original article has been formed by a slip casting technique, the finished article ''' , "' ,~ .
-" ,' ' ' ' :
10~9935 will have a density in the range of 80 to 85 percent of theoretical density. Upon completion of the nitriding step, the finished first element is a blade ring 10 (Figure 2) having a plurality of blades 12 thereon attached to a support portion 14. The support portion 14 also defines an -inwardly facing bonding surface 16, best seen in Figure 1.
The method of this invention teaches the formation and simultaneous bonding of a second element, in this case a hub, to the bonding surface 16 of the first element.
The hub serves as a support for the blade ring 10. In order to carry out the bonding operation it is necessary to `- encapsulate the blade ring so that it is capable of -i withstanding the pressures encountered in a hot press :-forming and bonding operation. In order to carry out theencapsulation, the steps shown generally in Figures 2, 3 and 4 are followed.
One procedure for encapsulating the blade ring 10 is to coat the blade ring in its entirety with a thin coat of boron nitride powder to serve as a release material for subsequent ease in removing the encapsulant. The blade ring is then placed in a mold which closes off the volume between each of the blades thereby defining a plurality of individual cavities. A casting slip of silicon metal particles is supplied to each of the cavities to build up slip cast silicon material. After the slip casting operation, the material now in place between the blades is nitrided to produce individual silicon nitride support portions 18, see Figure 3, between each of the blades 12.
After placing the support portions 18 between each of the blades 12, the article is once again coated with boron nitride powder. The article is placed in a second '' , ~079935 !
forming mold and a silicon metal slip is cast around the entire volume of the blade ring 10 with the exception of - the bonding surface 16. After the slip casting operation, the slip cast silicon particles are nitrided to produce a silicon nitride body 20 as an encapsulant. Thus, after this operation the silicon nitride body 20 contains there-within the blades 12 and leaves exposed only the bonding surface 16 thereof. The body 20 is sized so as to be receivable in a pressing die structure shown in Figure 1.
The pressing die structure includes a contoured bottom graphite piston 24, tapered graphite inside wedges ~:' 26, tapered graphite outside wedges 28, a graphite restrain-- ing sleeve 3Q, a contoured top graphite piston 32, an ... .
outside graphite piston 34 for applying pressure to the wedges 28, an outside graphite sleeve 36, an inside cooling ; ram 38 and an outside cooling ram 40.
~ After the body 20 is formed with only the bonding '!' ' surface 16 of the blade ring 10 being exposed, the body is placed on the contoured bottom graphite piston 24 as shown in Figure 1. At that time, the various graphite wedges ,"~
;~ and restraining sleeves are positioned about the body 20.
,........ .
, A measured volume of a silicon nitride powder suitable for a hot pressing operation is poured into a volume defined between surfaces of the contoured bottom graphite piston ; 24, the bonding surface 16 and the graphite restraining sleeve 30. The contoured top graphite piston 32 is then ~; placed between the graphite restraining sleeve and pressure is applied to the material in the defined volume.
The powder used in the pressing operation is a mixture consisting of from about 94 to 99.5% by weight of ; silicon nitride particles and from about 6.0 to 0.5 percent ., ~ ~ 8 --, , ~ , .
, j.,. ~
1079~35 by weight of a densification aid. In general, the silicon nitride used in the compacting operation is alpha silicon nitride powder. The powder is generally a ceramic grade and is preferably all minus 325 mesh. The silicon nitride powder is wet ball milled in a rubber lined mill with alumina ~ or tungsten carbide balls and alcohoI for a time ranging -~ from one day to two weeks. A densification aid, such as magnesium oxide or any other suitable material, is mixed ` thoroughly with the silicon nitride powder during the milling operation. Concentrations of densification aid are generally in the range of from 0.5 to 6.0 weight percent.
The aid helps in the powder compaction process. After milling, the silicon nitride powder slurry is dried and screened through a 100 mesh screen in preparation for a hot pressing operation.
As stated above, the silicon nitride powder 42 is ;
^- placed in the volume defined between the various die members in order to initiate a pressing operation. A measured amount of the material is placed therein so as to produce - 20 a final article of a particular size. The material will be ~- hot pressed to form a second element which in this case is a hub 44 for the blade ring 10. The hub will be formed and simultaneously bonded to the blade ring during this processing and the hub will exhibit its final dimensions and contours. A barrier material can be coated on the graphite die system to minimize any reaction between the silicon nitride powder and the die system. Barrier materials commonly used are graphite foil and boron nitride. The materials would be placed on all of the surface of the interior volume of the pressing die structure except the bonding surface 16 of the blade ring 10. r : 107g935 The silicon nitride material 42 is hot pressed at a temperature în a range from about 1650C to about 1800C
:--and a pressure from about 2,000 psi to about 4,000 psi.
The heating of the material is accomplished by an induction heating unit, not shown. The pressure, of course, lS
applied by applying a compressive force on the contoured bottom piston 24 and the inside cooling ram 38 thereby compacting the silicon nitride material. The final hot pressed hub 44 will have a density of about 98 percent . .
~ 10 theoretical or greater. The silicon nitride hub 44 will .
readily withstand both the temperatures and the stress conditions imposed upon it when used as the hub portion of a rotor in a gas turbine engine.
After the pressing operation the pressing apparatus is turned off and allowed to cool slowly back to room '"~' ?.~ temperature. The press bonded rotor assembly is allowed to , cool simply by leaving it in ambient conditions. When the 'i; - assembly is cooled, the removable graphite die elements are removed to take the now almost finished turbine rotor therefrom. The one thing left to finish on the article is :: ;
.,~
~ to remove the encapsulant from the blade ring 10. As ,i~
preveiously mentioned, the blade ring had been treated with a release agent such as boron nitride to help in its ,~., releasing the encapsulant from its surfaces. It has been - found that if the finished article is immersed in a bath to .- which ultrasonic energy is applied, the barrier material along the planes of association will loosen and open up i~ which allows easy removal of the individual support portions between the blades.
.;, . .
~ 30 The so finished article is thus one which has a ~ . ~
~` silicon nitride hub of near theoretical density and a complex .
,:
.
~.
blade ring of a different density. The finished article can be used as a rotor for a gas turbine engine.
; There has been disclosed herein a method of making a duo-density article of silicon nitride. In view of the teachings of this specification, those skilled in the art -` will be led to make modification of the invention. It is intended that all modifications which fall within the spirit and scope of this invention be included within the appended ` claims.
. ~ .
,...
. .
. . .
' :
'.". ' :;
. .
.. : .
'; ' :
~. :
~ .
:' ' :
8 In the case of forming the first element by a slip 9 casting technique, silicon metal particles, suspended in a - 10 vehicle, are cast into a mold having the shape desired for 11 the blade ring. The mold is positioned against a porous 12 material capable of drawing the vehicle of the slip out of the ;
13 casting volume thereby leaving behind a consolidated mass of ~; 14 silicon metal particles. In such a manner the first element is formed of silicon metal particles by a slip casting 16 ' technique.
17 As an alternative approach, the general shape of the . 18 first element may be formed by an injection molding technique. ;19 a typical injection molding compound for forming the first element is one which would have about 60 to 66 percent by 21 volume of silicon metal particles with the remainder being 22 a thermoplastic binder. In general, the particle size of the 23 metal will be such that the material will have a maximum 24 particle size in the range of 40 to 60 microns and a mean particle size in a range of from 10 to 13 rnicrons. Once a 26 molding composition is formed, the composition is fed into 27 a cylinder of an injection molding machine. The machine heats 28 the thermoplastic above its melting point. Pressure is applied 29 to the cylinder and th~ molding composition is shot into a ~ cold moldiDg having the configuration of the blede ring _ 5 _ : 11 .' ' 1~
107993~
. .
~ to be produced. The thermoplastic solidifies into the desired '~ shape thereby locking the silicon metal particles carried along with it into the desired shape.
The so fo~medblade ring of silicon metal particles and thermoplastic is gradually heated in a furnace to a temperature of about 350C. The heating program may take as long as three days so that no stresses are created in the article during heating. During this heating, the thermoplastic binder is burned out.- This action leaves behind silicon metal particles in the desired shape of the blade ring.
No matter how the silicon metal particles are formed into the blade ring shape desired, the so formed first element is thereafter nitrided in order to produce a finished body of silicon nitride. Since the first element is formed of silicon metal particles, the nitriding operation is effective to change the first element into a silicon nitride.
, In the nitriding operation the element is heated while exposed to nitrogen gas at a temperature and for a sufficient period of time that all of the silicon is transformed into silicon nitride. A full procedure for nitriding silicon to form silicon nitride is disclosed in U.K. Paten~ No. 1,448,915. If the article nitrided had been originally formed by an injection molding process, the final article will have a density of 70 to 75 percent of theoretical density. If the original article has been formed by a slip casting technique, the finished article ''' , "' ,~ .
-" ,' ' ' ' :
10~9935 will have a density in the range of 80 to 85 percent of theoretical density. Upon completion of the nitriding step, the finished first element is a blade ring 10 (Figure 2) having a plurality of blades 12 thereon attached to a support portion 14. The support portion 14 also defines an -inwardly facing bonding surface 16, best seen in Figure 1.
The method of this invention teaches the formation and simultaneous bonding of a second element, in this case a hub, to the bonding surface 16 of the first element.
The hub serves as a support for the blade ring 10. In order to carry out the bonding operation it is necessary to `- encapsulate the blade ring so that it is capable of -i withstanding the pressures encountered in a hot press :-forming and bonding operation. In order to carry out theencapsulation, the steps shown generally in Figures 2, 3 and 4 are followed.
One procedure for encapsulating the blade ring 10 is to coat the blade ring in its entirety with a thin coat of boron nitride powder to serve as a release material for subsequent ease in removing the encapsulant. The blade ring is then placed in a mold which closes off the volume between each of the blades thereby defining a plurality of individual cavities. A casting slip of silicon metal particles is supplied to each of the cavities to build up slip cast silicon material. After the slip casting operation, the material now in place between the blades is nitrided to produce individual silicon nitride support portions 18, see Figure 3, between each of the blades 12.
After placing the support portions 18 between each of the blades 12, the article is once again coated with boron nitride powder. The article is placed in a second '' , ~079935 !
forming mold and a silicon metal slip is cast around the entire volume of the blade ring 10 with the exception of - the bonding surface 16. After the slip casting operation, the slip cast silicon particles are nitrided to produce a silicon nitride body 20 as an encapsulant. Thus, after this operation the silicon nitride body 20 contains there-within the blades 12 and leaves exposed only the bonding surface 16 thereof. The body 20 is sized so as to be receivable in a pressing die structure shown in Figure 1.
The pressing die structure includes a contoured bottom graphite piston 24, tapered graphite inside wedges ~:' 26, tapered graphite outside wedges 28, a graphite restrain-- ing sleeve 3Q, a contoured top graphite piston 32, an ... .
outside graphite piston 34 for applying pressure to the wedges 28, an outside graphite sleeve 36, an inside cooling ; ram 38 and an outside cooling ram 40.
~ After the body 20 is formed with only the bonding '!' ' surface 16 of the blade ring 10 being exposed, the body is placed on the contoured bottom graphite piston 24 as shown in Figure 1. At that time, the various graphite wedges ,"~
;~ and restraining sleeves are positioned about the body 20.
,........ .
, A measured volume of a silicon nitride powder suitable for a hot pressing operation is poured into a volume defined between surfaces of the contoured bottom graphite piston ; 24, the bonding surface 16 and the graphite restraining sleeve 30. The contoured top graphite piston 32 is then ~; placed between the graphite restraining sleeve and pressure is applied to the material in the defined volume.
The powder used in the pressing operation is a mixture consisting of from about 94 to 99.5% by weight of ; silicon nitride particles and from about 6.0 to 0.5 percent ., ~ ~ 8 --, , ~ , .
, j.,. ~
1079~35 by weight of a densification aid. In general, the silicon nitride used in the compacting operation is alpha silicon nitride powder. The powder is generally a ceramic grade and is preferably all minus 325 mesh. The silicon nitride powder is wet ball milled in a rubber lined mill with alumina ~ or tungsten carbide balls and alcohoI for a time ranging -~ from one day to two weeks. A densification aid, such as magnesium oxide or any other suitable material, is mixed ` thoroughly with the silicon nitride powder during the milling operation. Concentrations of densification aid are generally in the range of from 0.5 to 6.0 weight percent.
The aid helps in the powder compaction process. After milling, the silicon nitride powder slurry is dried and screened through a 100 mesh screen in preparation for a hot pressing operation.
As stated above, the silicon nitride powder 42 is ;
^- placed in the volume defined between the various die members in order to initiate a pressing operation. A measured amount of the material is placed therein so as to produce - 20 a final article of a particular size. The material will be ~- hot pressed to form a second element which in this case is a hub 44 for the blade ring 10. The hub will be formed and simultaneously bonded to the blade ring during this processing and the hub will exhibit its final dimensions and contours. A barrier material can be coated on the graphite die system to minimize any reaction between the silicon nitride powder and the die system. Barrier materials commonly used are graphite foil and boron nitride. The materials would be placed on all of the surface of the interior volume of the pressing die structure except the bonding surface 16 of the blade ring 10. r : 107g935 The silicon nitride material 42 is hot pressed at a temperature în a range from about 1650C to about 1800C
:--and a pressure from about 2,000 psi to about 4,000 psi.
The heating of the material is accomplished by an induction heating unit, not shown. The pressure, of course, lS
applied by applying a compressive force on the contoured bottom piston 24 and the inside cooling ram 38 thereby compacting the silicon nitride material. The final hot pressed hub 44 will have a density of about 98 percent . .
~ 10 theoretical or greater. The silicon nitride hub 44 will .
readily withstand both the temperatures and the stress conditions imposed upon it when used as the hub portion of a rotor in a gas turbine engine.
After the pressing operation the pressing apparatus is turned off and allowed to cool slowly back to room '"~' ?.~ temperature. The press bonded rotor assembly is allowed to , cool simply by leaving it in ambient conditions. When the 'i; - assembly is cooled, the removable graphite die elements are removed to take the now almost finished turbine rotor therefrom. The one thing left to finish on the article is :: ;
.,~
~ to remove the encapsulant from the blade ring 10. As ,i~
preveiously mentioned, the blade ring had been treated with a release agent such as boron nitride to help in its ,~., releasing the encapsulant from its surfaces. It has been - found that if the finished article is immersed in a bath to .- which ultrasonic energy is applied, the barrier material along the planes of association will loosen and open up i~ which allows easy removal of the individual support portions between the blades.
.;, . .
~ 30 The so finished article is thus one which has a ~ . ~
~` silicon nitride hub of near theoretical density and a complex .
,:
.
~.
blade ring of a different density. The finished article can be used as a rotor for a gas turbine engine.
; There has been disclosed herein a method of making a duo-density article of silicon nitride. In view of the teachings of this specification, those skilled in the art -` will be led to make modification of the invention. It is intended that all modifications which fall within the spirit and scope of this invention be included within the appended ` claims.
. ~ .
,...
. .
. . .
' :
'.". ' :;
. .
.. : .
'; ' :
~. :
~ .
:' ' :
Claims (5)
1. A method of making a duo-density article of silicon nitride which comprises the steps of:
making a first element of silicon metal particles by forming silicon metal particles in a forming operation;
nitriding said first element so that said silicon metal particles forming said first element are converted to substantially pure silicon nitride;
applying an encapsulant release agent to the first element;
encapsulating all but a bonding surface of said first element with silicon nitride to form a die member;
placing said die member in a pressing die structure so that said bonding surface of said die member forms a portion of the total die surface defining the interior surface of a die volume formed by said pressing die structure;
filling said die volume o said pressing die structure with a mixture consisting of from about 94 to 99.5% by weight silicon nitride particles and from about 6.0 to 0.5% by weight of a densification aid;
compacting said mixture in said die volume to at least 98% of theoretical density thereby forming a second element of the duo-density article while simultaneously bonding said second element to said first element along said first element's bonding surface; and removing said encapsulant about said first element to produce the final article of silicon nitride having two zones of different density.
making a first element of silicon metal particles by forming silicon metal particles in a forming operation;
nitriding said first element so that said silicon metal particles forming said first element are converted to substantially pure silicon nitride;
applying an encapsulant release agent to the first element;
encapsulating all but a bonding surface of said first element with silicon nitride to form a die member;
placing said die member in a pressing die structure so that said bonding surface of said die member forms a portion of the total die surface defining the interior surface of a die volume formed by said pressing die structure;
filling said die volume o said pressing die structure with a mixture consisting of from about 94 to 99.5% by weight silicon nitride particles and from about 6.0 to 0.5% by weight of a densification aid;
compacting said mixture in said die volume to at least 98% of theoretical density thereby forming a second element of the duo-density article while simultaneously bonding said second element to said first element along said first element's bonding surface; and removing said encapsulant about said first element to produce the final article of silicon nitride having two zones of different density.
2. The method of Claim 1 wherein: said first element of silicon metal particles is made by slip casting operation.
3. The method of Claim 1 wherein: said first element of silicon metal particles is made by an injection molding process.
4. The method of Claim 1 wherein: said encapsulating of all but said bonding surface of said first element is carried out by one or more repetitions of a process wherein silicon particles are slip cast on said element and subsequently nitrided, the release agent being applied to the surfaces to be encapsulated prior to each repetition of the encapsulating process.
5. The method of Claim 1 or 4 wherein: said release agent is boron nitride.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US57189775A | 1975-04-25 | 1975-04-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1079935A true CA1079935A (en) | 1980-06-24 |
Family
ID=24285500
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA244,845A Expired CA1079935A (en) | 1975-04-25 | 1976-01-30 | Method of making a duo-density silicon nitride article |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS51129899A (en) |
| CA (1) | CA1079935A (en) |
| DE (1) | DE2617336C2 (en) |
| GB (1) | GB1470949A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4127684A (en) * | 1977-12-23 | 1978-11-28 | Ford Motor Company | Crack protection method |
| DE3337025A1 (en) * | 1983-10-12 | 1985-05-02 | Feldmühle AG, 4000 Düsseldorf | METHOD FOR PRODUCING A SILICON NITRIDE COMPONENT |
| SE456322B (en) * | 1986-03-04 | 1988-09-26 | Asea Stal Ab | SET FOR MANUFACTURE OF METAL PRODUCTS THROUGH HEATISOSTAT COMPRESSION OF POWDER USING CORE |
| DE10331397A1 (en) | 2003-07-11 | 2005-01-27 | Mtu Aero Engines Gmbh | Production of blade segments for gas turbines comprises using a powder metallurgical injection molding |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB779474A (en) * | 1954-07-29 | 1957-07-24 | Union Carbide Ltd | Method of preparing silicon nitride articles by slip casting |
| DE2135648A1 (en) * | 1971-07-16 | 1973-01-25 | Lucas Industries Ltd | Silicon nitride - assembly of two blocks |
-
1976
- 1976-01-30 CA CA244,845A patent/CA1079935A/en not_active Expired
- 1976-03-08 GB GB912176A patent/GB1470949A/en not_active Expired
- 1976-04-16 JP JP51042617A patent/JPS51129899A/en active Pending
- 1976-04-21 DE DE19762617336 patent/DE2617336C2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS51129899A (en) | 1976-11-11 |
| DE2617336A1 (en) | 1976-11-04 |
| GB1470949A (en) | 1977-04-21 |
| DE2617336C2 (en) | 1983-04-14 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US3887411A (en) | Making a triple density article of silicon nitride | |
| US3887412A (en) | Method of making a triple density silicon nitride article | |
| US3854189A (en) | Method of making a bonded silicon nitride article having portions of different density | |
| EP0399727A1 (en) | Ceramic mould material | |
| US3885294A (en) | Method of making a bonded silicon nitride article having portions of different density | |
| US5297609A (en) | Investment casting of metal matrix composites | |
| US3441078A (en) | Method and apparatus for improving grain structures and soundness of castings | |
| US5956561A (en) | Net shaped dies and molds and method for producing the same | |
| EP3391982B1 (en) | Systems, devices and methods for spark plasma sintering | |
| JP2004507367A (en) | Superplastic forming dies and mold inserts | |
| CA1079935A (en) | Method of making a duo-density silicon nitride article | |
| US2942970A (en) | Production of hollow thermal elements | |
| US4087500A (en) | Method of making a duo density silicon nitride article | |
| US4127684A (en) | Crack protection method | |
| US3717694A (en) | Hot pressing a refractory article of complex shape in a mold of simple shape | |
| JP2004025308A (en) | Investment casting process by filling molten material | |
| US4153666A (en) | Hot-pressing of shapes of non-uniform cross-sectional thickness | |
| JPH1034280A (en) | Mold for precision molding of single crystal | |
| EP0240190A2 (en) | Process for manufacturing ceramic sintered bodies and mold to be used therefor | |
| JPH0436117B2 (en) | ||
| CA1221529A (en) | Method of forming dense ceramic bodies | |
| US5623727A (en) | Method for manufacturing powder metallurgical tooling | |
| US5989483A (en) | Method for manufacturing powder metallurgical tooling | |
| US2754570A (en) | Method of producing a cast alloy coated oxidizable metal article | |
| JPS609570A (en) | Production of piston consisting of reinforcing material |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |