WO2017134138A1 - Leachable ceramic materials for use in casting - Google Patents
Leachable ceramic materials for use in casting Download PDFInfo
- Publication number
- WO2017134138A1 WO2017134138A1 PCT/EP2017/052209 EP2017052209W WO2017134138A1 WO 2017134138 A1 WO2017134138 A1 WO 2017134138A1 EP 2017052209 W EP2017052209 W EP 2017052209W WO 2017134138 A1 WO2017134138 A1 WO 2017134138A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- phase
- alumina
- matrix
- silica
- sintered
- 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.)
- Ceased
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
Definitions
- This invention relates to leachable ceramic materials and to their use in investment casting.
- Investment casting is a process in which molten metals are poured into a refractory ceramic mould designed to create a duplicate of the desired part. Casting may be done around "cores". Ceramic materials used for such purposes include chemically bonded particles of materials such as silica, zircon, aluminium silicates (e.g. mullite), and alumina. Such materials are porous with low structural integrity and are simply required to resist the pressures and temperatures implicit in the casting process. After casting these materials are removed to leave the cast product remaining.
- core materials include those of US4073662, US4187266, US4837187, US5779809, GB1602027, and GB2126569. When making large items by investment casting it is frequently necessary to provide additional support to parts of the mould/core.
- Such supports it is conventional to use dense ceramics, for example such as quartz and alumina rods.
- Such rods may be of a variety of sizes, but typically range in diameter from 0.2 to 40mm. The present disclosure is not however limited to such ranges of diameter.
- Such supports need to be removed after the casting process and it is common to leach out the ceramic.
- Quartz is the traditional material of choice, since it can be leached out easily using strong aqueous solutions of hydroxides such as NaOH.
- Alumina is increasingly being used as it has a higher mechanical strength than quartz.
- alumina is chemically more inert to hydroxides, and typically leach cycle times are increased from one day (for quartz) to three days (for alumina) and requires the more aggressive KOH as a strong aqueous solution.
- This disclosure provides materials that are mechanically stronger than quartz, and yet chemically weaker than alumina, permitting shorter leach times in aqueous hydroxide solution than normal dense alumina without the strength limitation of quartz.
- alumina materials comprising:- ⁇ a mechanically supportive continuous matrix phase comprising alumina;
- the material preferably comprises at least lvol% of the at least one second phase, preferably more than 3vol%, and conveniently can comprise 5 ⁇ 3vol% or 5 ⁇ 2vol% or 5 ⁇ lvol%.
- the amount of the at least one second phase may be up to 10vol%, 20vol% or more.
- the present disclosure aims to use the mechanical strength of alumina to provide materials having a greater strength than quartz, but provides a second phase
- aluminas used as supports in investment casting are dense ceramics comprising very low amounts of other components (typically being 95% or more pure alumina). Typical modulus of rupture for such a material would be of the order of 550 MPa (80kpsi). Dissolution by KOH leachant is by attack at the surface.
- quartz used as supports in investment casting are glassy materials comprising essentially pure silica. Typical modulus of rupture for such a material would be of the order of 210 MPa (30kpsi). Dissolution by NaOH or KOH leachant is by attack at the surface, and quartz is attacked more vigorously than is alumina.
- the present disclosure provides an alumina containing matrix (that may incorporate other materials) and at least one second phase that interpenetrates the matrix and that provides a pathway for leachants.
- the second phase may comprise porosity (that enables penetration of the leachants below the surface); and may comprise a leachable phase that is more readily leachable than the matrix, so that preferential leaching of the leachable phase permits leachant to penetrate below the surface.
- the effect is to increase the area of the matrix phase that is exposed to the leachant above that of the outer surface of the support. This increased leachant contact permits quicker leaching of the material of the matrix.
- this invention contemplates materials having modulus of rupture above 250 MPa, above 300 MPa, and above 350 MPa.
- Example 1 porosity as second phase
- a 99.8% pure alumina powder [Grade 998E powder from Morgan Advanced Materials (from their Latrobe facility); a sub-micron powder with a d50 less than one micron] was pressed or extruded to form rods and other shapes which were fired at 1350°C with a ramp time 2.5 hours to 1350°C, soak for 1.5 to 2 hours , ramp down time of 0.5 to 1.5 hours with a total cycle time of 5-6 hours to provide porous sintered alumina shapes, including cylindrical rods having a cross section ranging from ⁇ 0.25mm to ⁇ 40mm (0.010" to 1.6"), and having a porosity in the range 5-7%.
- Example 2 - leachable material as second phase A 99.8% alumina powder [Grade 998E powder from Morgan Advanced Materials (from their Latrobe facility); a sub-micron powder with a d50 less than one micron] was mixed with sub-micron silica [Grade GP3i from Harbison Walker] in proportions to create a 97% alumina containing mixture.
- the mixture was pressed or extruded to form rods and other shapes which were fired at 1650°C with a ramp time of 14 hours to 1650°C, soak for 2 hours , ramp down time of 8 hours for a total cycle time of 24 hours to provide fully sintered alumino-silicate cylindrical shapes, including rods having a cross section ranging from ⁇ 0.25mm to ⁇ 40mm (0.010" to 1.6").
- Example 3 leachable material as second phase
- a 99.8% alumina powder [Grade 998E powder from Morgan Advanced Materials (from their Latrobe facility); a sub-micron powder with a d50 less than one micron] was mixed with sub-micron silica [Grade GP3i from Harbison Walker] in proportions to create a 95% alumina containing mixture.
- the mixture was pressed or extruded to form rods and other shapes which were fired at 1650°C with a ramp time of 14 hours to 1650°C, soak for 2 hours , ramp down time of 8 hours for a total cycle time of 24 hours to provide fully sintered alumino-silicate cylindrical shapes, including rods having a cross section ranging from ⁇ 0.25mm to ⁇ 40mm (0.010" to 1.6").
- Modulus of rupture of the rods of examples 1 to 3 were measured using a 3-point method [ASTM D790].
- the samples measured were ⁇ 35mm (1 3 ⁇ 4") sections cut from 0.79mm (0.031") diameter circular cross-section rods of material.
- silica used in manufacture of alumino-silicates in accordance with this invention should be fine materials to avoid excessive weakening of the structure of the support material.
- silicas with a d50 ⁇ l ⁇ m are used and good results may be achieved with d50 in the range 0.5 ⁇ 0.2 ⁇ or d50 in the range 0.5 ⁇ 0.1 ⁇ .
- the present invention is not limited to these particular ranges however.
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Compositions Of Oxide Ceramics (AREA)
- Mold Materials And Core Materials (AREA)
Abstract
A method of supporting mould parts and/or cores in investment casting comprises the use of supports comprising support material comprising a mechanically supportive continuous matrix phase comprising alumina; and at least one second phase interpenetrating the matrix phase and providing a pathway for leachants to penetrate into the material.
Description
Leachable ceramic materials for use in casting
This invention relates to leachable ceramic materials and to their use in investment casting. Investment casting
Investment casting is a process in which molten metals are poured into a refractory ceramic mould designed to create a duplicate of the desired part. Casting may be done around "cores". Ceramic materials used for such purposes include chemically bonded particles of materials such as silica, zircon, aluminium silicates (e.g. mullite), and alumina. Such materials are porous with low structural integrity and are simply required to resist the pressures and temperatures implicit in the casting process. After casting these materials are removed to leave the cast product remaining.
Examples of such "core" materials include those of US4073662, US4187266, US4837187, US5779809, GB1602027, and GB2126569. When making large items by investment casting it is frequently necessary to provide additional support to parts of the mould/core.
For such supports it is conventional to use dense ceramics, for example such as quartz and alumina rods. Such rods may be of a variety of sizes, but typically range in diameter from 0.2 to 40mm. The present disclosure is not however limited to such ranges of diameter.
Such supports need to be removed after the casting process and it is common to leach out the ceramic.
Comparison of quartz and alumina
Quartz and alumina both have low trace element presence which can be a requirement with casting some materials, but both represent compromises between mechanical strength and chemical resistance.
Quartz is the traditional material of choice, since it can be leached out easily using strong aqueous solutions of hydroxides such as NaOH.
Alumina is increasingly being used as it has a higher mechanical strength than quartz. However, alumina is chemically more inert to hydroxides, and typically leach cycle times are increased from one day (for quartz) to three days (for alumina) and requires the more aggressive KOH as a strong aqueous solution. The scope of disclosure
This disclosure provides materials that are mechanically stronger than quartz, and yet chemically weaker than alumina, permitting shorter leach times in aqueous hydroxide solution than normal dense alumina without the strength limitation of quartz.
This requirement has been met by providing alumina materials comprising:- · a mechanically supportive continuous matrix phase comprising alumina;
• at least one second phase interpenetrating the matrix phase and providing a pathway for leachants to penetrate into the material.
The material preferably comprises at least lvol% of the at least one second phase, preferably more than 3vol%, and conveniently can comprise 5±3vol% or 5±2vol% or 5±lvol%. The amount of the at least one second phase may be up to 10vol%, 20vol% or more. The scope of the invention is as set out in the claims, and in any new and inventive features described herein with reference to the following non-limitative description.
General disclosure The present disclosure aims to use the mechanical strength of alumina to provide materials having a greater strength than quartz, but provides a second phase
interpenetrating the quartz that permits easier access to leachants than is provided by dense alumina.
Conventional aluminas used as supports in investment casting are dense ceramics comprising very low amounts of other components (typically being 95% or more pure alumina). Typical modulus of rupture for such a material would be of the order of 550 MPa (80kpsi). Dissolution by KOH leachant is by attack at the surface.
Conventional quartz used as supports in investment casting are glassy materials comprising essentially pure silica. Typical modulus of rupture for such a material would
be of the order of 210 MPa (30kpsi). Dissolution by NaOH or KOH leachant is by attack at the surface, and quartz is attacked more vigorously than is alumina.
The present disclosure provides an alumina containing matrix (that may incorporate other materials) and at least one second phase that interpenetrates the matrix and that provides a pathway for leachants. The second phase may comprise porosity (that enables penetration of the leachants below the surface); and may comprise a leachable phase that is more readily leachable than the matrix, so that preferential leaching of the leachable phase permits leachant to penetrate below the surface.
In either case, the effect is to increase the area of the matrix phase that is exposed to the leachant above that of the outer surface of the support. This increased leachant contact permits quicker leaching of the material of the matrix.
In any event a modulus of rupture in excess of quarz is desired and (for example) this invention contemplates materials having modulus of rupture above 250 MPa, above 300 MPa, and above 350 MPa. Examples
Example 1 - porosity as second phase
A 99.8% pure alumina powder [Grade 998E powder from Morgan Advanced Materials (from their Latrobe facility); a sub-micron powder with a d50 less than one micron] was pressed or extruded to form rods and other shapes which were fired at 1350°C with a ramp time 2.5 hours to 1350°C, soak for 1.5 to 2 hours , ramp down time of 0.5 to 1.5 hours with a total cycle time of 5-6 hours to provide porous sintered alumina shapes, including cylindrical rods having a cross section ranging from ~0.25mm to ~40mm (0.010" to 1.6"), and having a porosity in the range 5-7%.
Example 2 - leachable material as second phase A 99.8% alumina powder [Grade 998E powder from Morgan Advanced Materials (from their Latrobe facility); a sub-micron powder with a d50 less than one micron] was mixed with sub-micron silica [Grade GP3i from Harbison Walker] in proportions to create a 97% alumina containing mixture.
The mixture was pressed or extruded to form rods and other shapes which were fired at 1650°C with a ramp time of 14 hours to 1650°C, soak for 2 hours , ramp down time of 8 hours for a total cycle time of 24 hours to provide fully sintered alumino-silicate cylindrical shapes, including rods having a cross section ranging from ~0.25mm to ~40mm (0.010" to 1.6").
Example 3 - leachable material as second phase
A 99.8% alumina powder [Grade 998E powder from Morgan Advanced Materials (from their Latrobe facility); a sub-micron powder with a d50 less than one micron] was mixed with sub-micron silica [Grade GP3i from Harbison Walker] in proportions to create a 95% alumina containing mixture.
The mixture was pressed or extruded to form rods and other shapes which were fired at 1650°C with a ramp time of 14 hours to 1650°C, soak for 2 hours , ramp down time of 8 hours for a total cycle time of 24 hours to provide fully sintered alumino-silicate cylindrical shapes, including rods having a cross section ranging from ~0.25mm to ~40mm (0.010" to 1.6").
Properties of examples
Modulus of rupture of the rods of examples 1 to 3 were measured using a 3-point method [ASTM D790]. The samples measured were ~35mm (1 ¾") sections cut from 0.79mm (0.031") diameter circular cross-section rods of material.
All examples showed a modulus of rupture significantly above that of quartz measured under the same conditions, and showed greater susceptibility to leaching than dense alumina.
It is to be noted that for best results the silica used in manufacture of alumino-silicates in accordance with this invention should be fine materials to avoid excessive weakening of the structure of the support material. Typically silicas with a d50<l^m are used and good results may be achieved with d50 in the range 0.5±0.2μιη or d50 in the range 0.5±0.1μιη. The present invention is not limited to these particular ranges however.
The above disclosure is illustrative and not limitative of the scope of the invention. Variants will readily occur to the person skilled in the art and be encompassed by the present invention. For example, the examples show only the use of porosity, or of a second material (leachable material) at grain boundaries of the matrix that is more readily attacked by leachants than the matrix. It will be apparent that both porosity and leachable material may be provided.
Claims
1. A method of supporting mould parts and/or cores in investment casting
comprising the use of supports comprising support material comprising:-
• a mechanically supportive continuous matrix phase comprising alumina; · at least one second phase interpenetrating the matrix phase and providing a pathway for leachants to penetrate into the material.
2. A method as claimed in Claim 1 , in which the support material comprises 1- 20vol% of the at least one second phase.
3. A method as claimed in Claim 1 or Claim 2 , in which the mechanically supportive matrix phase is a sintered ceramic.
4. A method as claimed in any of Claims 1 to 3, in which the second phase comprises open porosity in the matrix.
5. A method as claimed in any of Claims 1 to 4, in which the second phase comprises material at grain boundaries of the matrix that is more readily attacked by leachants than the matrix.
6. A method as claimed in Claim 4, in which the support structures comprise a
sintered aluminosilicate material, in which the matrix phase comprises a greater proportion of alumina than the second phase, and the second phase comprises a greater proportion of silica than the matrix phase.
7. A method as claimed in Claim 6, in which the sintered aluminosilicate material comprises 90-99wt% alumina.
8. A method as claimed in Claim 7, in which the sintered aluminosilicate material comprises 96±2wt% alumina.
9. A method as claims in any of Claims 6 to 8, in which the sintered aluminosilicate material comprises a sintered body formed from a mixture comprising alumina and silica.
10. A method as claimed in Claim 9, in which the silica in the mixture has a d50 of Ιμιη or less.
11. A method as claimed in Claim 10, in which the silica in the mixture has a d50 of 0.5±0.2μιη.
12. A method as claimed in Claim 11, in which the silica in the mixture has a d50 of 0.5±0.1μιη.
13. Supports, for use in the methods of any preceding claim, comprising support material comprising:-
• a mechanically supportive continuous matrix phase comprising alumina;
• at least one second phase interpenetrating the matrix phase and providing a pathway for leachants to penetrate into the material.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1800344.2A GB2553481A (en) | 2016-02-05 | 2017-02-02 | Leachable ceramic materials for use in casting |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US201662291858P | 2016-02-05 | 2016-02-05 | |
| US62/291,858 | 2016-02-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2017134138A1 true WO2017134138A1 (en) | 2017-08-10 |
Family
ID=57956306
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/EP2017/052209 Ceased WO2017134138A1 (en) | 2016-02-05 | 2017-02-02 | Leachable ceramic materials for use in casting |
Country Status (2)
| Country | Link |
|---|---|
| GB (1) | GB2553481A (en) |
| WO (1) | WO2017134138A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2019030025A1 (en) | 2017-08-08 | 2019-02-14 | Morgan Advanced Ceramics, Inc | Leachable ceramic materials for use in casting |
Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4073662A (en) | 1977-03-09 | 1978-02-14 | General Electric Company | Method for removing a magnesia doped alumina core material |
| US4187266A (en) | 1977-10-06 | 1980-02-05 | General Electric Company | Process for making a ceramic article having a dense integral outer barrier layer and a high degree of porosity and crushability characteristics |
| US4221594A (en) * | 1977-10-06 | 1980-09-09 | General Electric Company | Material composition for fired ceramic articles having a high degree of porosity and crushability characteristics |
| GB1602027A (en) | 1977-10-06 | 1981-11-04 | Gen Electric | Method for removing cores |
| GB2126569A (en) | 1982-09-04 | 1984-03-28 | Rolls Royce | Non-silica based ceramic cores for castings |
| US4837187A (en) | 1987-06-04 | 1989-06-06 | Howmet Corporation | Alumina-based core containing yttria |
| EP0539317A1 (en) * | 1991-09-20 | 1993-04-28 | United Technologies Corporation | Process for making cores used in investment casting |
| US5779809A (en) | 1995-12-26 | 1998-07-14 | General Electric Company | Method of dissolving or leaching ceramic cores in airfoils |
-
2017
- 2017-02-02 GB GB1800344.2A patent/GB2553481A/en not_active Withdrawn
- 2017-02-02 WO PCT/EP2017/052209 patent/WO2017134138A1/en not_active Ceased
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4073662A (en) | 1977-03-09 | 1978-02-14 | General Electric Company | Method for removing a magnesia doped alumina core material |
| US4187266A (en) | 1977-10-06 | 1980-02-05 | General Electric Company | Process for making a ceramic article having a dense integral outer barrier layer and a high degree of porosity and crushability characteristics |
| US4221594A (en) * | 1977-10-06 | 1980-09-09 | General Electric Company | Material composition for fired ceramic articles having a high degree of porosity and crushability characteristics |
| GB1602027A (en) | 1977-10-06 | 1981-11-04 | Gen Electric | Method for removing cores |
| GB2126569A (en) | 1982-09-04 | 1984-03-28 | Rolls Royce | Non-silica based ceramic cores for castings |
| US4837187A (en) | 1987-06-04 | 1989-06-06 | Howmet Corporation | Alumina-based core containing yttria |
| EP0539317A1 (en) * | 1991-09-20 | 1993-04-28 | United Technologies Corporation | Process for making cores used in investment casting |
| US5779809A (en) | 1995-12-26 | 1998-07-14 | General Electric Company | Method of dissolving or leaching ceramic cores in airfoils |
Non-Patent Citations (4)
| Title |
|---|
| ANONYMOUS: "Micro particles based on silicon dioxide size: 0.5 [mu]m | Sigma-Aldrich", 17 March 2017 (2017-03-17), XP055356664, Retrieved from the Internet <URL:http://www.sigmaaldrich.com/catalog/product/sigma/56796?lang=en ion=NL> [retrieved on 20170320] * |
| LI GE WANG ET AL: "Effect of SiO<sub>2</sub> Micro-Powders on the Properties of Alumina-Based Ceramic Core", ADVANCED MATERIALS RESEARCH, vol. 554-556, 1 January 2012 (2012-01-01), pages 731 - 735, XP055356525, DOI: 10.4028/www.scientific.net/AMR.554-556.731 * |
| QIN Y ET AL: "Effect of silica sol on the properties of alumina-based ceramic core composites", MATERIALS SCIENCE AND ENGINEERING: A, ELSEVIER, AMSTERDAM, NL, vol. 508, no. 1-2, 20 May 2009 (2009-05-20), pages 71 - 75, XP026074950, ISSN: 0921-5093, [retrieved on 20090327], DOI: 10.1016/J.MSEA.2008.12.016 * |
| YE XIA QIN ET AL: "Properties of <i>In Situ</i> Synthesized Alumina Ceramic Core Composites", KEY ENGINEERING MATERIALS, vol. 368-372, 1 January 2008 (2008-01-01), pages 724 - 725, XP055356522, DOI: 10.4028/www.scientific.net/KEM.368-372.724 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2019030025A1 (en) | 2017-08-08 | 2019-02-14 | Morgan Advanced Ceramics, Inc | Leachable ceramic materials for use in casting |
| US12390853B2 (en) | 2017-08-08 | 2025-08-19 | Morgan Advanced Ceramics, Inc. | Leachable ceramic materials for use in casting |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2553481A (en) | 2018-03-07 |
| GB201800344D0 (en) | 2018-02-21 |
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