GB2049644A - Silicon Carbide Bodies - Google Patents

Silicon Carbide Bodies Download PDF

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Publication number
GB2049644A
GB2049644A GB8013379A GB8013379A GB2049644A GB 2049644 A GB2049644 A GB 2049644A GB 8013379 A GB8013379 A GB 8013379A GB 8013379 A GB8013379 A GB 8013379A GB 2049644 A GB2049644 A GB 2049644A
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United Kingdom
Prior art keywords
silicon carbide
reaction
surface layer
silicon
sintered
Prior art date
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Granted
Application number
GB8013379A
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GB2049644B (en
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UK Atomic Energy Authority
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UK Atomic Energy Authority
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Filing date
Publication date
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Priority to GB8013379A priority Critical patent/GB2049644B/en
Publication of GB2049644A publication Critical patent/GB2049644A/en
Application granted granted Critical
Publication of GB2049644B publication Critical patent/GB2049644B/en
Expired legal-status Critical Current

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Classifications

    • 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
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/009—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone characterised by the material treated
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B18/00—Layered products essentially comprising ceramics, e.g. refractory products
    • 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
    • C04B35/56—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 carbides or oxycarbides
    • C04B35/565—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 carbides or oxycarbides based on silicon carbide
    • C04B35/573—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 carbides or oxycarbides based on silicon carbide obtained by reaction sintering or recrystallisation
    • 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
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/53—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone involving the removal of at least part of the materials of the treated article, e.g. etching, drying of hardened concrete
    • C04B41/5338—Etching
    • C04B41/5353—Wet etching, e.g. with etchants dissolved in organic solvents
    • 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
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
    • C04B41/91—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics involving the removal of part of the materials of the treated articles, e.g. etching
    • 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
    • F01D11/00—Preventing or minimising internal leakage of working-fluid, e.g. between stages
    • F01D11/08—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator
    • F01D11/12—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator using a rubstrip, e.g. erodible. deformable or resiliently-biased part
    • F01D11/122—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator using a rubstrip, e.g. erodible. deformable or resiliently-biased part with erodable or abradable material
    • 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
    • F01D5/12—Blades
    • F01D5/28—Selecting particular materials; Particular measures relating thereto; Measures against erosion or corrosion
    • F01D5/284—Selection of ceramic materials
    • 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
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
    • C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
    • C04B2235/6562—Heating rate
    • 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
    • C04B2237/00—Aspects relating to ceramic laminates or to joining of ceramic articles with other articles by heating
    • C04B2237/30—Composition of layers of ceramic laminates or of ceramic or metallic articles to be joined by heating, e.g. Si substrates
    • C04B2237/32—Ceramic
    • C04B2237/36—Non-oxidic
    • C04B2237/363—Carbon
    • 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
    • C04B2237/00—Aspects relating to ceramic laminates or to joining of ceramic articles with other articles by heating
    • C04B2237/30—Composition of layers of ceramic laminates or of ceramic or metallic articles to be joined by heating, e.g. Si substrates
    • C04B2237/32—Ceramic
    • C04B2237/36—Non-oxidic
    • C04B2237/365—Silicon carbide
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T50/00—Aeronautics or air transport
    • Y02T50/60—Efficient propulsion technologies, e.g. for aircraft

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Manufacturing & Machinery (AREA)
  • Ceramic Products (AREA)

Abstract

A reaction-sintered silicon carbide body having portions differing from each other in free silicon content and such a body with a surface layer rendered more readily abradable than the remainder of the body by the removal of free silicon from the surface layer, has a particular application in the provision of shrouds for gas turbines, which can be produced by slip-casting in two stages.

Description

SPECIFICATION Silicon Carbide Bodies and their Production This invention relates to silicon carbide bodies and their production. It is particularly concerned with silicon carbide bodies (hereinafter referred to as "reaction-sintered silicon carbide bodies") produced by the reaction sintering of green bodies formed from a coherent mixture of silicon carbide and carbon, in the presence of molten silicon. This reaction sintering process is hereinafter referred to as "siliconising". The production of such bodies is described, for example, in United States Patent Specification No. 3,495,939. They consist essentially of a substantially continuous matrix of silicon carbide particles bonded together and a substantially continuous free silicon phase.
One aspect of the present invention consists in a reaction-sintered silicon carbide body comprising a plurality of discrete portions differing from each other in free silicon content.
Another aspect of the present invention consists in a reaction-sintered silicon carbide body having a surface layer rendered more readily abraded than the remainder of the body by the removal of free silicon from the surface layer. This aspect of the invention finds a particular application in the production of tip shrouds for the rotor blades of gas turbine engines. It has been proposed that such shrouds should be provided with an inner surface which is readily abraded so that a rotor need not be matched to a particular shroud. Instead it can be used with any shroud and should wear its own track, establishing the necessary clearance.
The removal of free silicon from a surface layer is conveniently effected after siliconising by treatment of the surface layer with sodium hydroxide. To facilitate removal of free silicon in this way and for the residual surface layer to be readily abraded the surface layer should initially contain a relatively high proportion of free silicon, say 35% by volume, and a free silicon content up to about 50% by volume is desirable. This is to be contrasted with a preferred free silicon content of about 10% by volume for the reaction-sintered silicon carbide beneath the surface layer.
The proportion of free silicon to silicon carbide in reaction sintered silicon carbide bodies depends in part on the proportions of carbon to silicon carbide in the coherent mixture forming the green body. (It also depends on the porosity of the green body). Thus in general, the lower the proportion of carbon the higher the proportion of free silicon after siliconising. Hence to provide a surface layer which is to be more readily abraded after free silicon removal a relatively low proportion of carbon is most suitable in the initial coherent mixture. Such a surface layer may be provided on a body formed otherwise from a coherent mixture having a much higher proportion of carbon.
The surface layer may be conveniently formed by slip-casting and in a preferred embodiment of the invention the remainder of the body is also formed by slip-casting, the body being siliconised as a whole.
The following are examples of methods of producing a silicon carbide body in accordance with the invention.
Example 1 A mix containing carbon and silicon carbide powders in the ratio 0.25:1 is pressed at about 1 OOMN/m2 to form a base portion of green density 1 .97g/cc. This is re-pressed in contact with a mix containing carbon and silicon carbide powders in the ratio 0.1:1 at the same pressure and a second portion of density of 1.73g/cc. is formed as a layer or coating on the original base portion. On siliconsing the base material is converted to 90% dense silicon carbide containing 10% free silicon and the coating to 65% dense material containing 35% free silicon. If the siliconised component is then leached with sodium hydroxide solution at 1 0O0C the free silicon is removed from the coating but very little from the base material.
Example 2 A slip containing carbon and silicon carbide powders in the ratio of 0.4:1 is cast in a plaster mould to form a base portion of 'green' density 1 .73g/cc. A coating is then laid down upon the original component base using a slip containing carbon and silicon carbide powders in the ratio 0.1:1. On siliconising the component the base material is converted to 90% dense silicon carbide containing 10% free silicon and the coating to 51% dense silicon carbide containing 49% free silicon. The free silicon may be removed from the coating as in Example 1.
Example 3 A mix containing carbon and silicon carbide powders in the ratio 0.5:1 and sufficient plastic binder to provide 42% porosity in the fullyconsolidated body on removal of the binder is formed into a cylindrical pellet. Such a pellet contains no unfilled porosity. A second mix containing carbon and silicon carbide powders in the ratio 0.3:1 and sufficient plastic binder to provide a similar amount of porosity in the fully consolidated body on removal of the binder, is formed into an annular pellet, with an inner diameter the same as the outer diameter of the first pellet. Again the pellet contains no unfilled porosity. The cylindrical pellet is inserted in the annular peliet and the composite billet extruded to yield a rod with a surface layer having a different density from the core material.Also provided that the plasticities of the two mixes are matched, the ratio of the layer thickness to the core diameter is the same in the extrudate as in the original billet. On removing the binder and siliconising the extrudate the base portion is converted to 90% dense silicon carbide containing 1 0% free silicon and the coating to 80% dense silicon carbide containing 20% free silicon. The free silicon may be removed from the coating as in Example 1.
Example 4 A mix containing carbon and silicon carbide powders in the ratio 0.25:1 (and a binder) is pressed at about 100 MN/m2 to form a base portion of 'green' density, after removal of binder, of 1.97 g/cc. The base portion is 'green machined' if necessary and is heated in air up to 300 C to remove the binder. A coating is then laid down on the original pressed portion, or some feature is filled, using a slip containing carbon and silicon carbide in the ratio 0.2:1. On siliconising the base material is converted to 90% dense silicon carbide containing 10% free silicon and the coating to 64% dense silicon carbide containing 36% free silicon. The free silicon may be removed from the coating as in Example 1.
As an alternative to forming the base portion by the pressing it may be formed by extrusion e.g.
as in Example 3, the binder being removed at least in part before application of the coating by slip-casting.

Claims (9)

Claims
1. A reaction-sintered silicon carbide body comprising a plurality of discrete portions differing from each other in free silicon content.
2. A reaction-sintered silicon carbide body having a surface layer rendered more readily abraded than the remainder of the body by the removal of free silicon from the surface layer.
3. A reaction-sintered silicon carbide body according to claim 2 forming a tip shroud for the rotor blades of a gas turbine engine.
4. A reaction-sintered silicon carbide body according to claim 1 having a surface layer containing a substantially higher proportion of free silicon than the remainder of the body.
5. A reaction-sintered silicon carbide body according to claim 4 wherein the surface layer has a free silicon content of at least 35% by volume.
6. The production of a reaction-sintered silicon carbide body as claimed in claim 1 comprising the steps of compacting a first mix of carbon and silicon carbide to form a first portion, compacting a second mix of carbon and silicon carbide in contact with the first portion and in proportions differing from those of the first mix, to form a second portion and a green body comprising the first and second portions, and reaction-sintering the green body in the presence of molten silicon.
7. The production of a reaction-sintered silicon carbide body according to claim 6 having a surface layer differing in free silicon content from the remainder of the body comprising the steps of forming a green body by slip-casting a coherent mixture of silicon carbide and carbon on a second coherent mixture of silicon carbide and carbon in proportions differing from the proportions of silicon carbide and carbon in the slip-cast, and reaction-sintering the green body in the presence of molten silicon.
8. The production of a reaction-sintered silicon carbide body as claimed in claim 7 wherein the second coherent mixture is formed by slipcasting.
9. The production of a reaction-sintered silicon carbide body as claimed in claim 7 or claim 8 including the further step of treating the body to remove free silicon from the surface layer.
1 0. The production of a reaction-sintered silicon carbide body substantially as hereinbefore described in any of the Examples.
GB8013379A 1979-05-08 1980-04-23 Silicon carbide bodies Expired GB2049644B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8013379A GB2049644B (en) 1979-05-08 1980-04-23 Silicon carbide bodies

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB7915832 1979-05-08
GB8013379A GB2049644B (en) 1979-05-08 1980-04-23 Silicon carbide bodies

Publications (2)

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GB2049644A true GB2049644A (en) 1980-12-31
GB2049644B GB2049644B (en) 1982-12-08

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0242516A1 (en) * 1986-02-07 1987-10-28 Feodor Burgmann Dichtungswerke GmbH & Co. Device to bear and/or seal a shaft

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0242516A1 (en) * 1986-02-07 1987-10-28 Feodor Burgmann Dichtungswerke GmbH & Co. Device to bear and/or seal a shaft

Also Published As

Publication number Publication date
GB2049644B (en) 1982-12-08

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Legal Events

Date Code Title Description
732 Registration of transactions, instruments or events in the register (sect. 32/1977)
PCNP Patent ceased through non-payment of renewal fee