US20220048097A1 - Casting slurry for the production of shell molds - Google Patents
Casting slurry for the production of shell molds Download PDFInfo
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- US20220048097A1 US20220048097A1 US17/309,616 US201917309616A US2022048097A1 US 20220048097 A1 US20220048097 A1 US 20220048097A1 US 201917309616 A US201917309616 A US 201917309616A US 2022048097 A1 US2022048097 A1 US 2022048097A1
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- 239000002002 slurry Substances 0.000 title claims abstract description 110
- 238000005266 casting Methods 0.000 title claims abstract description 24
- 238000004519 manufacturing process Methods 0.000 title claims description 15
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 claims abstract description 32
- 239000002245 particle Substances 0.000 claims abstract description 25
- 239000000843 powder Substances 0.000 claims abstract description 24
- 229910002084 calcia-stabilized zirconia Inorganic materials 0.000 claims abstract description 22
- SIWVEOZUMHYXCS-UHFFFAOYSA-N oxo(oxoyttriooxy)yttrium Chemical compound O=[Y]O[Y]=O SIWVEOZUMHYXCS-UHFFFAOYSA-N 0.000 claims abstract description 22
- 239000011230 binding agent Substances 0.000 claims abstract description 21
- 229910001092 metal group alloy Inorganic materials 0.000 claims abstract description 6
- 229910052751 metal Inorganic materials 0.000 claims description 18
- 239000002184 metal Substances 0.000 claims description 18
- 238000000034 method Methods 0.000 claims description 18
- 230000008569 process Effects 0.000 claims description 18
- OQPDWFJSZHWILH-UHFFFAOYSA-N [Al].[Al].[Al].[Ti] Chemical compound [Al].[Al].[Al].[Ti] OQPDWFJSZHWILH-UHFFFAOYSA-N 0.000 claims description 13
- 229910021324 titanium aluminide Inorganic materials 0.000 claims description 13
- 230000002787 reinforcement Effects 0.000 claims description 11
- 239000004576 sand Substances 0.000 claims description 7
- 238000001035 drying Methods 0.000 claims description 6
- 238000005488 sandblasting Methods 0.000 claims description 6
- 239000000292 calcium oxide Substances 0.000 claims description 5
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium oxide Inorganic materials [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 claims description 5
- 238000007598 dipping method Methods 0.000 claims description 4
- BRPQOXSCLDDYGP-UHFFFAOYSA-N calcium oxide Chemical compound [O-2].[Ca+2] BRPQOXSCLDDYGP-UHFFFAOYSA-N 0.000 claims description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 12
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 7
- 239000000203 mixture Substances 0.000 description 6
- 230000009257 reactivity Effects 0.000 description 6
- 239000000654 additive Substances 0.000 description 5
- 229910045601 alloy Inorganic materials 0.000 description 4
- 239000000956 alloy Substances 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 239000002518 antifoaming agent Substances 0.000 description 3
- 239000003795 chemical substances by application Substances 0.000 description 3
- KZHJGOXRZJKJNY-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Si]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O KZHJGOXRZJKJNY-UHFFFAOYSA-N 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- 238000005495 investment casting Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229910052863 mullite Inorganic materials 0.000 description 3
- 239000000377 silicon dioxide Substances 0.000 description 3
- 239000000080 wetting agent Substances 0.000 description 3
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 3
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000004138 cluster model Methods 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 238000010304 firing Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 239000004115 Sodium Silicate Substances 0.000 description 1
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 description 1
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 1
- 239000002671 adjuvant Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 239000008119 colloidal silica Substances 0.000 description 1
- 239000000084 colloidal system Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 229910052593 corundum Inorganic materials 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000007730 finishing process Methods 0.000 description 1
- 235000013312 flour Nutrition 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 239000001995 intermetallic alloy Substances 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000005058 metal casting Methods 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 description 1
- 229910052911 sodium silicate Inorganic materials 0.000 description 1
- 239000003381 stabilizer Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 229910001845 yogo sapphire Inorganic materials 0.000 description 1
- 229910052845 zircon Inorganic materials 0.000 description 1
- GFQYVLUOOAAOGM-UHFFFAOYSA-N zirconium(iv) silicate Chemical compound [Zr+4].[O-][Si]([O-])([O-])[O-] GFQYVLUOOAAOGM-UHFFFAOYSA-N 0.000 description 1
Images
Classifications
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- 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
- B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
- B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
- B22C1/181—Cements, oxides or clays
-
- 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
- B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
- B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
- B22C1/165—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents in the manufacture of multilayered shell moulds
-
- 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
- B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
- B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
- B22C1/183—Sols, colloids or hydroxide gels
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/02—Sand moulds or like moulds for shaped castings
- B22C9/04—Use of lost patterns
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/12—Treating moulds or cores, e.g. drying, hardening
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
- B22D21/002—Castings of light metals
- B22D21/005—Castings of light metals with high melting point, e.g. Be 1280 degrees C, Ti 1725 degrees C
Definitions
- the present disclosure relates to the field of casting, in particular to investment (or lost-wax) casting processes, and more particularly to the slurries used in such processes, notably for the production of casting shell molds.
- Investment (or lost-wax or lost-mold) casting processes have been known, in and of themselves, since antiquity. Such a process is for example described in the document FR3031921. They are particularly suitable for the production of metal parts with complex shapes. Investment casting is used for the production of turbomachine blades or impeller sectors, for example.
- the first step is normally the production of a shell mold, which generally consists in creating a model made of a comparatively low melting point material, such as wax or resin, around which a refractory material shell is then made.
- a molten metal is poured into this mold in order to fill the cavity formed by the model inside the mold after its discharge. Once the metal cools and solidifies, the mold can be opened or destroyed to recover a metal part that conforms to the shape of the model.
- the wax model is generally dipped in a casting slurry, then coated with sands and dried. These operations can be repeated in order to form several layers and to obtain the desired thickness and mechanical strength of the shell mold.
- the first layer of slurry used plays a key role in the quality of the cast metal parts. Indeed, this contact slurry allows the internal surface of the shell mold to form, coming directly in contact with the metal of the metal part to be molded.
- the present disclosure relates to a casting slurry for producing shell molds for casting parts comprising a metal alloy, the slurry comprising powder particles and a binder, the binder comprising colloidal yttrium oxide, and the powder particles comprising calcia-stabilized zirconia.
- a casting slurry is a slurry suitable for use in the formation of a shell mold into which molten metal will be poured.
- a slurry comprises a binder, i.e., a compound ensuring cohesion between the powder particles and imparting mechanical strength to the shell mold during and after sintering.
- the binder can be inorganic.
- the powder particles can be sand particles (also known as “flour”), in particular refractory particles, generally having a diameter comprised between 1 micrometer and 100 micrometers.
- the casting slurry used in the present disclosure comprises a binder comprising colloidal yttrium oxide, and powder particles comprising zirconia.
- calcia-stabilized zirconia CSZ
- the viscosity of a slurry of the prior art for example a binder comprising colloidal yttrium oxide and powder particles comprising yttrium oxide
- a binder comprising colloidal yttrium oxide and powder particles comprising calcia-stabilized zirconia tends to increase over time, resulting in gelling of the slurry.
- the use of calcia-stabilized zirconia modifies the interaction between the binder and the powder particles to stabilize the slurry, while maintaining low reactivity with the metals to be molded, such as titanium aluminide (TiAl) alloys, and even lower reactivity than a slurry including an yttrium oxide powder and a binder comprising colloidal yttrium oxide.
- TiAl titanium aluminide
- the slurry thus obtained has a longer life and can be reused.
- the baths used can also be larger, without leading to loss.
- the slurry is a contact slurry configured to come into contact with the metal of the part to be molded.
- the first slurry used which comes into direct contact with the metal of the part at the time of molding, is called contact slurry, as opposed to subsequent slurries, which are called reinforcement slurries and cover the previous layers of the shell mold being formed.
- a contact slurry is configured to conform to the shape of the part and not alter it.
- a contact slurry is often retained for longer periods of time than a reinforcement slurry which is consumed more quickly, whence an increased need for stability in a contact slurry.
- the slurry according to the present disclosure is therefore particularly suitable for use as a contact slurry, due to its stability over time and its non-reactivity with certain metals such as TiAl.
- the mass content of calcium oxide in the calcia-stabilized zirconia is comprised between 1% and 30%, preferably between 3% and 20%, more preferably between 5% and 10%.
- a mass ratio of the calcia-stabilized zirconia in the slurry is comprised between 65% and 75%, preferably between 68% and 72%, more preferably equal to 70%.
- a mass ratio of the binder in the slurry is comprised between 20% and 40%, preferably between 25% and 35%, more preferably equal to 29.8%.
- a mass ratio of additives in the slurry is less than 10%, preferably between 0.1% and 5%, more preferably between 0.5% and 2%.
- the viscosity of the slurry is comprised between 0.1 and 2 Pa.s.
- the viscosity of the slurry is maintained at a value comprised between 0.1 and 2 Pa.s for a period of at least 24 hours.
- these values facilitate the accessibility of the slurry to certain narrow zones of the model.
- the casting slurry is configured for the production of shell molds for casting parts comprising a titanium aluminide-based metal alloy.
- the slurry according to the present disclosure is particularly suitable for use as a contact slurry, due to its stability over time and its non-reactivity with titanium aluminide (TiAl)-based metal alloys.
- the present disclosure also relates to the use of a casting slurry in accordance with any one of the preceding embodiments for the production of a shell mold.
- the present disclosure also relates to a process for producing a shell mold for casting parts, the process comprising the steps of:
- the reinforcement slurry comprises a binder and powder particles, the binder being selected from: ethyl silicate, sodium silicate or colloids including, in particular, colloidal silica, colloidal alumina, colloidal yttrium oxide or colloidal zirconia.
- the powder particles comprise at least one compound among alumina, mullite, zirconia, mullite-zirconia composites.
- the present disclosure also relates to a shell mold obtained by a process in accordance with any one of the preceding embodiments.
- the shell mold obtained by the process according to the present disclosure limits the oxygen-rich reaction layer that forms on the surface of a metal part, such as an aeronautical engine blade, cast in this shell mold.
- the reaction layer is defined here as the thickness at which the oxygen concentration is greater than at least twice the concentration measured in the base alloy. In particular, for an isothermal contact at 1600° C. for a duration of 5 min, this reaction layer remains less than 15 ⁇ m for the part thus obtained.
- FIG. 1 schematically represents the steps of a process for producing a shell mold for casting processes
- FIG. 2 is a graph showing change in the viscosity of a control slurry, and of the slurry of the present disclosure, as a function of shear stress.
- the process for producing aeronautical parts is a casting process.
- the various steps of this process are described for example in the document FR3031921.
- the first step of this process consists in creating a wax cluster model, also called ‘non-permanent cluster’.
- the shell mold is made from the wax cluster.
- the wax constituting the cluster model is removed from the mold. This wax removal is done by heating the shell mold in an autoclave (or the like) at a temperature greater than the melting temperature of the wax.
- the metal blade cluster is formed in the shell mold by pouring molten metal into the shell mold.
- the cluster is removed from the shell mold.
- each of the blades is separated from the rest of the cluster and finished by finishing processes such as machining.
- the invention relates in particular to the production of the shell mold in which the metal casting will be carried out, and more specifically to the contact slurry used for the production of this mold.
- the various steps of this process are illustrated in FIG. 1 .
- the first step comprises providing a model made of wax, or other equivalent material that can be easily discharged later, of the part.
- the wax model is dipped into a first slurry, the contact slurry (step S 2 ), comprising powder particles and a binder.
- Sandblasting i.e., deposition of sand particles called contact stucco, is then carried out, followed by a drying of the layer obtained (step S 3 ). This sandblasting step reinforces the layer and facilitates the adhesion of the next layer.
- step S 4 The layer thus obtained is then dipped in a second slurry, called reinforcement slurry (step S 4 ).
- a deposition of sand particles, called reinforcement stucco, is then carried out, followed by a drying of the layer obtained (step S 5 ).
- Steps S 4 and S 5 are repeated N times, until a determined thickness of shell mold is obtained.
- a dewaxing step consisting of removing the wax model from the model, followed by heat treatment, is performed (step S 6 ). After removal of the wax model, a ceramic shell mold whose cavity is a negative reproduction of all the details of the part to be molded is obtained.
- the heat treatment includes the firing of the mold obtained, the firing temperature preferably being comprised between 1000 and 1200° C.
- the slurries used are composed of particles of ceramic materials, in particular alumina, mullite, zirconia or others, with a mineral colloidal binder and, if need be, adjuvants such as wetting agents or antifoam agents.
- the contact slurry used in step S 2 comprises yttrium oxide.
- the contact stucco used in step S 3 may also comprise yttrium oxide.
- the reinforcement slurry and reinforcement stucco used in steps S 4 and S 5 may comprise mullite, alumina, silico-alumina, silica, zircon, zirconia or yttrium oxide, for example.
- the invention relates more particularly to the contact slurry used in step S 2 , and in particular to the presence of colloidal yttrium oxide and calcia-stabilized zirconia (CSZ) in the powder particles therein.
- CSZ calcia-stabilized zirconia
- Slurry A can have the following composition, expressed in percentages by mass:
- Slurry A does not contain CSZ.
- a slurry B which the inventors have determined exhibits similar reactivity with TiAl as slurry A, and whose powder particles comprise calcia-stabilized zirconia (CSZ), with CaO acting as a stabilizing agent.
- CSZ can be obtained for example by reactive sintering.
- the CaO content in mass percentage in the powder is comprised between 1% and 20% by weight.
- the slurry B thus obtained has the following mass percentages:
- Slurry B also includes unavoidable impurities.
- unavoidable impurities for example, mention may be made of silicon dioxide (SiO 2 ), titanium dioxide (TiO 2 ), iron oxide (Fe 2 O 3 ) or alumina (Al 2 O 3 ).
- Unavoidable impurities are defined as those elements which are not intentionally added to the composition and which are brought in with other elements.
- the curves shown in FIG. 2 illustrate the influence of the composition used for the contact slurry according to the present disclosure on its stability.
- This figure shows the change in the dynamic viscosity ⁇ in Pa.s of the slurry, as a function of a shear applied to this slurry.
- These measurements are performed using a rotary rheometer with coaxial cylindrical geometries, to apply to the slurry a shear comprised between 0.1 and 100 s ⁇ 1 .
- Curve (a) represents the viscosity of slurry A after 0.5 h
- curve (b) represents the viscosity of slurry A after 2 h
- curve (c) represents the viscosity of slurry A after 3.5 h
- curve (d) represents the viscosity of slurry B of the invention after 24 h.
- the above-mentioned times are determined from a time t 0 corresponding to the end of the production of the slurry.
- Curves (a) and (b) illustrating the viscosity of slurry A after 0.5 h and after 2 h are substantially coincident.
- the viscosity of slurry A is roughly equal to 4 Pa.s after 2 h. This viscosity then increases very rapidly with time, and reaches a value greater than 25 Pa.s after 3.5 h. In other words, the slurry quickly becomes very viscous, and tends to gel.
- curve (d) illustrating the viscosity of slurry B of the invention shows that the viscosity of slurry B remains less than 1 Pa.s after 24 h, regardless of the shear applied thereto.
- slurry B has increased stability compared with slurry A, and remains fluid by maintaining a low viscosity even 24 h after preparation of this slurry.
- the composition of slurry B maintains a low reactivity with TiAl alloys, equivalent or even lower than that of slurry A.
Abstract
Description
- The present disclosure relates to the field of casting, in particular to investment (or lost-wax) casting processes, and more particularly to the slurries used in such processes, notably for the production of casting shell molds.
- Investment (or lost-wax or lost-mold) casting processes have been known, in and of themselves, since antiquity. Such a process is for example described in the document FR3031921. They are particularly suitable for the production of metal parts with complex shapes. Investment casting is used for the production of turbomachine blades or impeller sectors, for example. In investment casting, the first step is normally the production of a shell mold, which generally consists in creating a model made of a comparatively low melting point material, such as wax or resin, around which a refractory material shell is then made. After the model has been destroyed, most commonly by discharging the model material from within the shell mold, which gives these processes their name, a molten metal is poured into this mold in order to fill the cavity formed by the model inside the mold after its discharge. Once the metal cools and solidifies, the mold can be opened or destroyed to recover a metal part that conforms to the shape of the model.
- To make the carapace mold, the wax model is generally dipped in a casting slurry, then coated with sands and dried. These operations can be repeated in order to form several layers and to obtain the desired thickness and mechanical strength of the shell mold. However, the first layer of slurry used, called contact slurry, plays a key role in the quality of the cast metal parts. Indeed, this contact slurry allows the internal surface of the shell mold to form, coming directly in contact with the metal of the metal part to be molded.
- In the aeronautical field, the production of parts such as turbine blades uses these investment casting processes. In particular, intermetallic alloys based on titanium aluminide (TiAl), due to their low density, are frequently used to produce these blades. This type of alloy has the particular feature of reacting easily with the constituents of the shell mold, the contact of this shell mold with the metal of the part being able to damage the surface finish of this part. To limit this effect, it is known to use a contact slurry including an yttrium oxide powder and a binder comprising colloidal yttrium oxide. However, this slurry has the disadvantage of being unstable. Indeed, contact slurry with this composition tends to gel quickly, after a few hours, for example after three or four hours. This disadvantage limits the industrial application of this type of slurry. Moreover, this type of slurry is expensive.
- Alternatively, certain additives could be used, but none of these additives was satisfactory insofar as the improvement of one parameter of the slurry was compensated by the unacceptable regression of another parameter.
- There is therefore a need for a new type of contact slurry, with increased stability over time.
- The present disclosure relates to a casting slurry for producing shell molds for casting parts comprising a metal alloy, the slurry comprising powder particles and a binder, the binder comprising colloidal yttrium oxide, and the powder particles comprising calcia-stabilized zirconia.
- A casting slurry is a slurry suitable for use in the formation of a shell mold into which molten metal will be poured. In particular, unlike any suspension, such a slurry comprises a binder, i.e., a compound ensuring cohesion between the powder particles and imparting mechanical strength to the shell mold during and after sintering. The binder can be inorganic. Conventionally, the powder particles can be sand particles (also known as “flour”), in particular refractory particles, generally having a diameter comprised between 1 micrometer and 100 micrometers.
- The casting slurry used in the present disclosure comprises a binder comprising colloidal yttrium oxide, and powder particles comprising zirconia.
- Surprisingly, it was observed by the inventors that the presence of calcia-stabilized zirconia (CSZ) in the powder particles significantly stabilized a slurry comprising yttrium oxide, and maintained sufficient fluidity, i.e., low viscosity. Conversely, the viscosity of a slurry of the prior art (for example a binder comprising colloidal yttrium oxide and powder particles comprising yttrium oxide) not having the composition of the present disclosure, i.e., a binder comprising colloidal yttrium oxide and powder particles comprising calcia-stabilized zirconia (CSZ), tends to increase over time, resulting in gelling of the slurry.
- In the slurry of the present disclosure, the use of calcia-stabilized zirconia modifies the interaction between the binder and the powder particles to stabilize the slurry, while maintaining low reactivity with the metals to be molded, such as titanium aluminide (TiAl) alloys, and even lower reactivity than a slurry including an yttrium oxide powder and a binder comprising colloidal yttrium oxide. The slurry thus obtained has a longer life and can be reused. The baths used can also be larger, without leading to loss.
- In some embodiments, the slurry is a contact slurry configured to come into contact with the metal of the part to be molded.
- The first slurry used, which comes into direct contact with the metal of the part at the time of molding, is called contact slurry, as opposed to subsequent slurries, which are called reinforcement slurries and cover the previous layers of the shell mold being formed. A contact slurry is configured to conform to the shape of the part and not alter it. A contact slurry is often retained for longer periods of time than a reinforcement slurry which is consumed more quickly, whence an increased need for stability in a contact slurry. The slurry according to the present disclosure is therefore particularly suitable for use as a contact slurry, due to its stability over time and its non-reactivity with certain metals such as TiAl.
- In certain embodiments, the mass content of calcium oxide in the calcia-stabilized zirconia is comprised between 1% and 30%, preferably between 3% and 20%, more preferably between 5% and 10%.
- In certain embodiments, a mass ratio of the calcia-stabilized zirconia in the slurry is comprised between 65% and 75%, preferably between 68% and 72%, more preferably equal to 70%.
- In certain embodiments, a mass ratio of the binder in the slurry is comprised between 20% and 40%, preferably between 25% and 35%, more preferably equal to 29.8%.
- In certain embodiments, a mass ratio of additives in the slurry is less than 10%, preferably between 0.1% and 5%, more preferably between 0.5% and 2%.
- In certain embodiments, the viscosity of the slurry is comprised between 0.1 and 2 Pa.s.
- More precisely, the viscosity of the slurry is maintained at a value comprised between 0.1 and 2 Pa.s for a period of at least 24 hours. In particular, these values facilitate the accessibility of the slurry to certain narrow zones of the model.
- In certain embodiments, the casting slurry is configured for the production of shell molds for casting parts comprising a titanium aluminide-based metal alloy.
- The slurry according to the present disclosure is particularly suitable for use as a contact slurry, due to its stability over time and its non-reactivity with titanium aluminide (TiAl)-based metal alloys.
- The present disclosure also relates to the use of a casting slurry in accordance with any one of the preceding embodiments for the production of a shell mold.
- The present disclosure also relates to a process for producing a shell mold for casting parts, the process comprising the steps of:
-
- providing a model of a part to be produced;
- dipping the model in a contact slurry in accordance with any of the preceding embodiments;
- sandblasting the dipped model in a contact sand comprising yttrium oxide;
- drying the layer obtained by the preceding steps;
- dipping the model in a reinforcement slurry, sandblasting the dipped model in a reinforcement sand, and drying the layer obtained, until a desired shell mold thickness is obtained;
- removing the part model.
- In certain embodiments, the reinforcement slurry comprises a binder and powder particles, the binder being selected from: ethyl silicate, sodium silicate or colloids including, in particular, colloidal silica, colloidal alumina, colloidal yttrium oxide or colloidal zirconia.
- In certain embodiments, the powder particles comprise at least one compound among alumina, mullite, zirconia, mullite-zirconia composites.
- The present disclosure also relates to a shell mold obtained by a process in accordance with any one of the preceding embodiments.
- The shell mold obtained by the process according to the present disclosure limits the oxygen-rich reaction layer that forms on the surface of a metal part, such as an aeronautical engine blade, cast in this shell mold. The reaction layer is defined here as the thickness at which the oxygen concentration is greater than at least twice the concentration measured in the base alloy. In particular, for an isothermal contact at 1600° C. for a duration of 5 min, this reaction layer remains less than 15 μm for the part thus obtained.
- The invention and its advantages will be better understood upon reading the detailed description below of various embodiments of the invention given by way of non-limiting examples. This description refers to the appended pages of figures, wherein:
-
FIG. 1 schematically represents the steps of a process for producing a shell mold for casting processes; -
FIG. 2 is a graph showing change in the viscosity of a control slurry, and of the slurry of the present disclosure, as a function of shear stress. - The process for producing aeronautical parts, in particular a turbine blade or a turbine blade cluster, is a casting process. The various steps of this process are described for example in the document FR3031921.
- The first step of this process consists in creating a wax cluster model, also called ‘non-permanent cluster’. In a second step, the shell mold is made from the wax cluster. At the end of this operation, the wax constituting the cluster model is removed from the mold. This wax removal is done by heating the shell mold in an autoclave (or the like) at a temperature greater than the melting temperature of the wax. In a third step, the metal blade cluster is formed in the shell mold by pouring molten metal into the shell mold. In a fourth step, after the metal has cooled and solidified in the shell mold, the cluster is removed from the shell mold. Finally, in a fifth step, each of the blades is separated from the rest of the cluster and finished by finishing processes such as machining.
- The invention relates in particular to the production of the shell mold in which the metal casting will be carried out, and more specifically to the contact slurry used for the production of this mold. The various steps of this process are illustrated in
FIG. 1 . - The first step (step S1) comprises providing a model made of wax, or other equivalent material that can be easily discharged later, of the part. In a second step, the wax model is dipped into a first slurry, the contact slurry (step S2), comprising powder particles and a binder. Sandblasting, i.e., deposition of sand particles called contact stucco, is then carried out, followed by a drying of the layer obtained (step S3). This sandblasting step reinforces the layer and facilitates the adhesion of the next layer.
- The layer thus obtained is then dipped in a second slurry, called reinforcement slurry (step S4). A deposition of sand particles, called reinforcement stucco, is then carried out, followed by a drying of the layer obtained (step S5). Steps S4 and S5 are repeated N times, until a determined thickness of shell mold is obtained. Finally, when the desired thickness is reached, a dewaxing step, consisting of removing the wax model from the model, followed by heat treatment, is performed (step S6). After removal of the wax model, a ceramic shell mold whose cavity is a negative reproduction of all the details of the part to be molded is obtained. The heat treatment includes the firing of the mold obtained, the firing temperature preferably being comprised between 1000 and 1200° C.
- The slurries used are composed of particles of ceramic materials, in particular alumina, mullite, zirconia or others, with a mineral colloidal binder and, if need be, adjuvants such as wetting agents or antifoam agents.
- In the context of the production of titanium aluminide (TiAl)-based aeronautical parts, the contact slurry used in step S2 comprises yttrium oxide.
- The contact stucco used in step S3 may also comprise yttrium oxide. The reinforcement slurry and reinforcement stucco used in steps S4 and S5 may comprise mullite, alumina, silico-alumina, silica, zircon, zirconia or yttrium oxide, for example.
- The invention relates more particularly to the contact slurry used in step S2, and in particular to the presence of colloidal yttrium oxide and calcia-stabilized zirconia (CSZ) in the powder particles therein.
- In order to appreciate the influence of the presence of CSZ in a contact slurry, the inventors first studied a control slurry, denoted slurry A, intended to be used as a contact slurry for the production of a shell mold. Slurry A can have the following composition, expressed in percentages by mass:
-
- binder (colloidal yttrium oxide): 24.5%;
- powder particles (yttrium oxide powder): 75%;
- wetting agent, antifoam agent and other additives: 0.5%.
- This mass distribution is given here by way of example, it being understood that a variation in mass distribution of up to 10% is possible. Slurry A does not contain CSZ.
- Furthermore, the inventors have studied a slurry B which the inventors have determined exhibits similar reactivity with TiAl as slurry A, and whose powder particles comprise calcia-stabilized zirconia (CSZ), with CaO acting as a stabilizing agent. CSZ can be obtained for example by reactive sintering. The CaO content in mass percentage in the powder is comprised between 1% and 20% by weight. The slurry B thus obtained has the following mass percentages:
-
- binder (colloidal yttrium oxide): 29.8%;
- powder particles (CSZ): 70%, including 5% CaO;
- wetting agent, antifoam agent and other additives: 0.2%.
- Similarly, this mass distribution is given here by way of example, it being understood that a variation of the mass distribution is possible in the ranges previously mentioned.
- Slurry B also includes unavoidable impurities. Among unavoidable impurities, for example, mention may be made of silicon dioxide (SiO2), titanium dioxide (TiO2), iron oxide (Fe2O3) or alumina (Al2O3). Unavoidable impurities are defined as those elements which are not intentionally added to the composition and which are brought in with other elements.
- The curves shown in
FIG. 2 illustrate the influence of the composition used for the contact slurry according to the present disclosure on its stability. This figure shows the change in the dynamic viscosity η in Pa.s of the slurry, as a function of a shear applied to this slurry. These measurements are performed using a rotary rheometer with coaxial cylindrical geometries, to apply to the slurry a shear comprised between 0.1 and 100 s−1. More precisely, the dynamic viscosity η can be calculated in a non-normalized manner from the shear stress T and a shear rate Ý, according to the relationship η=τ/Ý. Curve (a) represents the viscosity of slurry A after 0.5 h, curve (b) represents the viscosity of slurry A after 2 h, curve (c) represents the viscosity of slurry A after 3.5 h, and curve (d) represents the viscosity of slurry B of the invention after 24 h. The above-mentioned times are determined from a time t0 corresponding to the end of the production of the slurry. - Curves (a) and (b) illustrating the viscosity of slurry A after 0.5 h and after 2 h are substantially coincident. For a low shear, of the order of 0.1 s−1, the viscosity of slurry A is roughly equal to 4 Pa.s after 2 h. This viscosity then increases very rapidly with time, and reaches a value greater than 25 Pa.s after 3.5 h. In other words, the slurry quickly becomes very viscous, and tends to gel.
- Conversely, curve (d) illustrating the viscosity of slurry B of the invention shows that the viscosity of slurry B remains less than 1 Pa.s after 24 h, regardless of the shear applied thereto. Thus, slurry B has increased stability compared with slurry A, and remains fluid by maintaining a low viscosity even 24 h after preparation of this slurry. Furthermore, the composition of slurry B maintains a low reactivity with TiAl alloys, equivalent or even lower than that of slurry A.
- Although the present invention has been described with reference to specific example embodiments, it is obvious that modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated/mentioned embodiments may be combined in additional embodiments. Consequently, the description and drawings should be considered in an illustrative rather than restrictive sense.
- It is also obvious that all the features described with reference to a process are transposable, alone or in combination, to a device, and conversely, all the features described with reference to a device are transposable, alone or in combination, to a process.
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FR1872711A FR3089438B1 (en) | 2018-12-11 | 2018-12-11 | Improved foundry slurry for making shell molds |
FR1872711 | 2018-12-11 | ||
PCT/FR2019/052940 WO2020120882A1 (en) | 2018-12-11 | 2019-12-05 | Improved casting slurry for the production of shell molds |
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BR0013491A (en) * | 1999-08-25 | 2002-05-14 | Dentsply Int Inc | Die mold composition for precision casting, method for forming a die mold, and die mold |
US20060144556A1 (en) * | 2000-03-16 | 2006-07-06 | Wang Ming-Jong P | Shell mold binder composition and method |
PT103018A (en) * | 2003-09-12 | 2005-03-31 | Univ Do Minho | PROCESS FOR OBTAINING FISH IN G-TIAI BY FOUNDATION |
US7296616B2 (en) * | 2004-12-22 | 2007-11-20 | General Electric Company | Shell mold for casting niobium-silicide alloys, and related compositions and processes |
US7892343B2 (en) * | 2005-06-29 | 2011-02-22 | Nissan Chemical Industries, Ltd. | Method for manufacturing slurry and mold for precision casting |
EP1992430A1 (en) * | 2007-05-15 | 2008-11-19 | Treibacher Industrie AG | Yttria-based refractory composition |
US8122942B2 (en) * | 2009-05-29 | 2012-02-28 | General Electric Company | Casting processes and yttria-containing facecoat material therefor |
JP5455501B2 (en) * | 2009-08-07 | 2014-03-26 | 日揮触媒化成株式会社 | Dispersion of core-shell composite oxide fine particles, method for producing the dispersion, coating composition containing the core-shell composite oxide fine particles, curable coating, and substrate with curable coating |
CN102294436B (en) * | 2011-09-19 | 2013-01-02 | 哈尔滨实钛新材料科技发展有限公司 | Method for precisely casting titanium alloy and titanium aluminum alloy with low cost |
CN102601307B (en) * | 2012-04-13 | 2013-12-04 | 北京工业大学 | Preparation method of shell mold for investment casting of TiAl based alloy |
CN102873273B (en) * | 2012-10-29 | 2014-03-05 | 哈尔滨工业大学 | Method for producing oxide ceramic shell capable of improving TiAl alloy casting surface performances |
CN103071764B (en) * | 2012-11-30 | 2016-03-30 | 上海大学 | For the CaZrO of titanium or titanium alloy hot investment casting 3the preparation method of shell |
CN103949590B (en) * | 2014-05-12 | 2016-06-29 | 西北工业大学 | A kind of oxide doped and modified Y2O3The preparation method of+YSZ is high temperature resistant shell |
FR3031921B1 (en) | 2015-01-27 | 2017-02-10 | Snecma | METHOD AND DISCHARGE MACHINE FOR CLUSTERING LONG-MODEL FOUNDRY PARTS |
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