Method of casting monocrystalline metal parts

Abstract

A foundry method of casting monocrystalline metal parts, the method including at least casting a molten alloy into a cavity of a mold through at least one casting channel in the mold, subjecting the alloy to heat treatment, and removing the mold, and wherein the heat treatment is performed before an end of mold removal.

Claims

1. A foundry method of casting monocrystalline metal parts, the method comprising: casting a molten alloy into a cavity of a mold through at least one casting channel in the mold, wherein the cavity is shaped for molding a final metal part; subjecting the alloy to heat treatment; and removing the mold; wherein the heat treatment is performed after the alloy has solidified in the mold and before an end of mold removal, wherein the casting channel includes at least one transition zone adjacent to the cavity, and presents, in the transition zone, relative to an upstream section of the casting channel in a flow direction of the molten alloy, a cross-section that is enlarged in a direction of a main axis of a section of the cavity in a plane that is perpendicular to the casting channel, wherein, after the casting, the transition zone forms, adjacent to the final metal part formed by the cavity, an enlarged section, a central rod formed by the casting channel upstream from the enlarged section, and at least one metal web connected to the central rod and the enlarged section, the at least one metal web being thinner than the central rod, wherein the metal part is a turbine engine blade, and wherein the enlarged section is adjacent to a blade tip of the turbine blade.

2. A foundry method according to claim 1, wherein the removal of the mold comprises a first removal by hammering and a subsequent removal by water jet, the heat treatment being performed at least before the removal by water jet.

3. A foundry method according to claim 1, wherein the transition zone has a rounded portion of radius not less than 0.3 mm between the casting channel and the cavity.

4. A foundry method according to claim 1, wherein, after the casting, the transition zone forms at least one metal web on each of two opposite sides of the central rod, which at least one metal web is thinner than the central rod.

5. A foundry method according to claim 1, wherein the mold includes at least one core penetrating into and protruding from the cavity and occupying a space adjacent to the casting channel to form a cavity in the final metal part.

6. A foundry method according to claim 5, wherein, after casting, the transition zone forms at least one metal web adjacent to the core on each of two opposite sides of the core.

7. A foundry method according to claim 1, wherein the mold includes a plurality of cavities arranged as a bunch to mold a plurality of metal parts simultaneously.

8. A monocrystalline metal part produced by a foundry method according to claim 1.

9. A foundry method of casting monocrystalline metal parts, the method comprising: casting a molten alloy into a cavity of a mold through at least one casting channel in the mold, wherein the cavity is shaped for molding a final metal part; subjecting the alloy to heat treatment; and removing the mold; wherein the casting channel includes at least one transition zone adjacent to the cavity, and presents, in the transition zone, relative to an upstream section of the casting channel in a flow direction of the molten alloy, a cross-section that is enlarged in a direction of a main axis of a section of the cavity in a plane that is perpendicular to the casting channel, wherein, after the casting, the transition zone forms, adjacent to the final metal part formed by the cavity, an enlarged section, a central rod formed by the casting channel upstream from the enlarged section, and at least one metal web connected to the central rod and the enlarged section, the at least one metal web being thinner than the central rod, wherein the metal part is a turbine engine blade, and wherein the enlarged section is adjacent to a blade tip of the turbine blade.

10. A foundry method of casting monocrystalline parts according to claim 9, wherein, after the casting, the transition zone forms at least one metal web on each of two opposite sides of the central rod, which at least one metal web is thinner than the central rod.

11. A foundry method of casting monocrystalline metal parts according to claim 9, wherein the mold includes at least one core penetrating into and protruding from the cavity and occupying a space adjacent to the casting channel to form a cavity in the final metal part.

12. A foundry method of casting monocrystalline metal parts according to claim 11, wherein the metal web adjacent to the core presents an outer edge following a substantially concave line adjacent on a surface of the core.

13. A foundry method of casting monocrystalline metal parts according to claim 11, wherein, alter casting, the transition zone forms at least one metal web adjacent to the core on each of two opposite sides of the core.

14. A foundry method of casting monocrystalline metal parts according to claim 13, wherein the metal webs adjacent to the core present outer edges that join together at ends to surround the core.

15. A foundry method of casting monocrystalline metal parts according to claim 9, wherein the transition zone has a rounded portion of radius not less than 0.3 mm between the casting channel and the cavity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention can be well understood and its advantages appear better on reading the following detailed description of an implementation given by way of non-limiting example. The description refers to the accompanying drawings, in which:

(2) FIG. 1 shows a prior art foundry method;

(3) FIG. 2 shows a foundry method in an implementation of the present invention;

(4) FIG. 3 shows the connection between a casting channel and a molding cavity in a prior art mold;

(5) FIG. 4 is a perspective view of a metal part produced using the method of FIG. 2; and

(6) FIG. 5 is a cross-section on plane V-V of the metal part shown in FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

(7) A conventional foundry method, e.g. as used in the production of turbine engine blades and more particularly high pressure turbine blades is shown in FIG. 1. In a first step, a ceramic mold 150 is produced, typically by the lost wax method, although other conventional methods could alternatively be used. The ceramic mold 150 has a plurality of cavities 151 connected by means of casting channels 152 to an external orifice 153 of the mold 150. Each cavity 151 is shaped to mold a metal part that is to be produced. Under such circumstances, since the parts to be produced are hollow, the mold 150 also includes cores 155 penetrating into each of the cavities 151. After this first step, in a casting step, a molten alloy 154 is poured into the orifice 153 in order to fill the cavities 151 via the casting channels 152.

(8) After the alloy has solidified, in a third step, initial removal of the mold 150 is performed by hammering in order to release the metal parts 156 united as a bunch 157 from the mold 150. In order to eliminate the last remains of the mold 150, an additional step is then performed of removal by water jet. In the following step S105, the individual parts 156 are cut away from the bunch 157. The cores 155 are then removed from each of the parts 156 in the following step, and the parts 156 are finally subjected to heat treatment. By way of example, this heat treatment may be quenching, in which the parts 156 are briefly heated and then cooled rapidly in order to harden the alloy of the part.

(9) The alloys that can be used in this method include in particular so-called “monocrystalline” alloys that enable a part to be formed as a single crystal grain, or “monocrystal”. Nevertheless, in that prior art method, the heat treatment for the purpose of homogenizing the γ and γ′ phases of the monocrystal can trigger recrystallization phenomena that weaken the parts locally. In order to avoid that drawback, in a foundry method in an implementation of the invention as shown in FIG. 2, the order of the operations is modified by performing the heat treatment step earlier.

(10) Thus, in this method shown in FIG. 2, the first step is likewise producing a ceramic mold 250. As in the prior art, the ceramic mold 250 may also be produced by the lost wax method, or by some alternative method selected from those known to the person skilled in the art. In addition, and as in the prior art, the ceramic mold 250 has a plurality of cavities 251 connected by casting channels 252 to an external orifice 253 of the mold 250. Each cavity 251 is also shaped for molding a metal part that is to be produced. In addition, since the parts to be produced are also hollow, the mold 250 also includes cores 255 penetrating into each of the cavities 251.

(11) After the first step, and still as in the prior art, a molten alloy 254 is cast into the orifice 253 during a casting step in order to fill the cavities 251 via the casting channel 252. After the alloy has solidified, in a third step, initial removal of the mold 250 by hammering is likewise performed in order to release the metal parts 256 united as a bunch 257 from the mold 250. Nevertheless, in this method, after this initial removal, the heat treatment step is performed directly. During the heat treatment, the metal parts 256, still constituting a bunch 257 and still together with remaining pieces of the mold 250 are subjected directly to quenching, for example, in which the parts 256 are briefly heated and then rapidly cooled.

(12) In order to eliminate the last remains of the mold 250, it is possible in the following step to then proceed with removal by water jet. Finally, the individual parts 256 are cut away from the bunch 257 and the cores 255 are then removed from each of the parts 256, which parts have already been subjected to heat treatment before removal by water jet.

(13) Because the heat treatment step is performed earlier, it is possible to reduce recrystallization phenomena during this step. Nevertheless, in order to reduce this recrystallization even more completely and above all in order to do so reliably, it is also appropriate to give the casting channels 252 an appropriate shape. In FIG. 3, there can be seen the connection between a casting channel 152 and a mold cavity 151 in the prior art mold 150. This connection forms very sharp bends between the channel 152 and the cavity 151, which bends can lead to recrystallization zones 160 forming during the heat treatment.

(14) In the mold 250 of the method shown in FIG. 2, in order to avoid forming such recrystallization zones in each part 256 around the casting channels 252, the channels 252 may include transition zones adjacent to the cavities 251. In a transition zone, the casting channel 252 becomes progressively enlarged towards a main axis X of a section S of the cavity 251 in a plane A that is perpendicular to the casting channel in such a manner that the radius of the rounded portion between the casting channel 252 and the cavity 251 is not less than 0.3 mm. In particular, in the implementation shown, in which the mold 250 also includes a core 255 adjacent to the casting channel 252, this transition zone enlarges on either side of the core 255, and also away from the core 255. When the cavity 251 and the channel 252 are filled with metal, the metal thus forms a web 261 away from the core 255 and two webs 262 and 263 that are adjacent to the core 255, one on either side of the core 255, as shown in FIGS. 4 and 5. Perpendicularly to the axis X, these webs 261, 262, and 263 are substantially thinner than is the casting channel 252 upstream from the transition zone.

(15) During the casting step, the presence of the transition zone thus makes it possible to distribute the flow of molten alloy substantially throughout the width of the cavity 251, thus avoiding subsequent formation of recrystallization zones.

(16) The monocrystalline part 256 shown in FIG. 4 is a turbine blade. It is shown in its rough state after unmolding, i.e. with the metal that has solidified outside the part in the casting channel 252. This metal thus forms a central rod 275, webs 261, 262, and 263, and an enlarged section 276 adjacent to the blade tip 265. During casting, the molten alloy flows from the blade tip 265, through the blade root 266 and on to a casting channel 252 connected to another cavity 251 further downstream. The flow of molten alloy thus follows substantially the direction of the main axis Z of the blade. The web 261 that extends towards the trailing edge 267 of the blade presents an outer edge 268 with a concave upstream segment and a convex downstream segment. In cross-section, this outer edge 268 has a radius of curvature R that varies only very gradually from the central rod 275 to the enlarged section 276. The webs 262 and 263 that extend towards the leading edge 269 of the blade on either side of the core 255 present respective outer edges 270 and 271 that are substantially concave and that run along the core 255. These outer edges 270 and 271 join together via their ends above the core 255 and in front of it, thereby forming two connections 272, 273 so as to surround the core 255. In cross-section, the webs 262, 263 present radii of curvature R′ and R″ on the surfaces adjacent to the outer edges 270, 271 so as to avoid seeding undesirable metallurgical defects in the proximity of the core 255. The transition surfaces 277 of the webs 261, 262, and 263 and of the rod 275 at the enlarged section 276 are likewise rounded to avoid seeding such defects.

(17) Among the alloys that can be used in this method, there are in particular monocrystalline alloys of nickel, such as in particular AM1 and AM3 from Snecma, and also others such as CMSX-2®, CMSX-4®, CMSX-6®, and CMSX-10® from C-M Group, René® N5 and N6 from General Electric, RR2000 and SRR99 from Rolls-Royce, and PWA 1480, 1484, and 1487 from Pratt & Whitney, among others. Table 1 gives the compositions of these alloys.

(18) TABLE-US-00001 TABLE 1 Compositions of monocrystalline nickel alloys in weight % Alloy Cr Co Mo W Al Ti Ta Nb Re Hf C B Ni CMSX-2 8.0 5.0 0.6 8.0 5.6 1.0 6.0 — — — — — Bal CMSX-4 6.5 9.6 0.6 6.4 5.6 1.0 6.5 — 3.0 0.1 — — Bal CMSX-6 10.0 5.0 3.0 — 4.8 4.7 6.0 — — 0.1 — — Bal CMSX-10 2.0 3.0 0.4 5.0 5.7 0.2 8.0 — 6.0 0.03 — — Bal René N5 7.0 8.0 2.0 5.0 6.2 — 7.0 — 3.0 0.2 — — Bal René N6 4.2 12.5 1.4 6.0 5.75 — 7.2 — 5.4 0.15 0.05 0.004 Bal RR2000 10.0 15.0 3.0 — 5.5 4.0 — — — — — — Bal SRR99 8.0 5.0 — 10.0  5.5 2.2 12.0  — — — — — Bal PWA1480 10.0 5.0 — 4.0 5.0 1.5 12.0  — — — 0.07 — Bal PWA1484 5.0 10.0 2.0 6.0 5.6 — 9.0 — 3.0 0.1 — — Bal PWA1487 5.0 10.0 1.9 5.9 5.6 — 8.4 — 3.0 0.25 — — Bal AM1 7.0 8.0 2.0 5.0 5.0 1.8 8.0 1.0 — — — — Bal AM3 8.0 5.5  2.25 5.0 6.0 2.0 3.5 — — — — — Bal

(19) Although the present invention is described with reference to a specific implementation, it is clear that various modifications and changes may be made to that implementation without going beyond the general scope of the invention as defined by the claims. For example, in an alternative implementation, the heat treatment could be performed even before initial removal of the mold. In addition, the individual characteristics of the various implementations of the method may be combined in additional implementations. Consequently, the description and the drawings should be considered in an illustrative sense rather than in a restrictive sense.