A TURBINE ENGINE PART INCLUDING A TITANIUM-BASED ALLOY

Abstract

The present invention relates to a turbine engine part including a titanium-based alloy presenting a high level of work hardening, a high breaking load, and good ductility.

Claims

1. A turbine engine part including a titanium-based alloy in which one or more alloying elements are present, the alloy including at least one alloying element selected from the following list: Cr, Al, Sn, and V, and the alloy satisfying the following conditions: $4.10\le \frac{e}{a}\le 4.16;$ $10\le {\mathrm{Mo}}_{\mathrm{eq}}\le 14.5;$ $2.77\le \mathrm{Bo}\le 2.80;.Math.\mathrm{and}$ $2.34.Math..Math.\mathrm{eV}\le \mathrm{Md}\le 2.38.Math..Math.\mathrm{eV};$ where Mo.sub.eq designates the content by weight of beta-stabilizing elements in the alloy expressed as molybdenum equivalent, where $\frac{e}{a}=.Math..Math.\frac{e_i}{a_i}.Math.x_i,.Math.\mathrm{where}.Math..Math.\frac{e_i}{a_i}$ is the number of valence electrons of the element i and x.sub.i is the molar fraction of the element i in the alloy, the sum being performed over all of the elements present in the alloy; where Bo designates the mean bond order of covalent bonds between the titanium and the alloying elements; and where Md designates the mean energy level in eV of the d orbitals corresponding to the covalent bonds between the titanium and the alloying elements.

2. A part according to claim 1, wherein the alloy includes Cr and Al as alloying elements.

3. A part according to claim 1, wherein the alloy includes Cr and Sn as alloying elements.

4. A part according to claim 2, wherein the alloy constitutes a Ti—Cr—Al ternary alloy.

5. A part according to claim 3, wherein the alloy constitutes a Ti—Cr—Sn ternary alloy.

6. A part according to claim 2, wherein the content by weight of Cr in the alloy lies in the range 6% to 9%, and the content by weight of Al in the alloy lies in the range 1% to 3%.

7. A part according to claim 3, wherein the content by weight of Cr in the alloy lies in the range 6% to 9%, and the content by weight of Sn in the alloy lies in the range 1% to 5%.

8. A turbine engine part including a titanium-based alloy, the alloy being: a Ti—Cr—Al ternary alloy in which the content by weight of Cr in the alloy lies in the range 6% to 9% and the content by weight of Al in the alloy lies in the range 1% to 3%; or a Ti—Cr—Sn ternary alloy in which the content by weight of Cr in the alloy lies in the range 6% to 9% and the content by weight of Sn in the alloy lies in the range 1% to 5%.

9. A part according to claim 1, wherein the content by weight of Cr in the alloy lies in the range 7% to 9%.

10. A part according to claim 1, wherein the part constitutes a turbine engine casing.

11. A part according to claim 10, wherein the part constitutes a turbine engine retention casing.

12. A turbine engine including a part according to claim 1.

13. A part according to claim 8, wherein the content by weight of Cr in the alloy lies in the range 7% to 9%.

14. A part according to claim 8, wherein the part constitutes a turbine engine casing.

15. A part according to claim 14, wherein the part constitutes a turbine engine retention casing.

16. A turbine engine including a part according to claim 8.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Other characteristics and advantages of the invention appear from the following description of particular embodiments of the invention given as non-limiting examples and with reference to the accompanying drawings, in which:

[0040] FIGS. 1 and 2 are electronic diagrams showing the positioning of example alloys of the invention;

[0041] FIG. 3 shows the “TRIP” effect in which there is a phenomenon of a β phase transforming into an α″ phase in a Ti-8.5Cr-1.5Al alloy of the invention;

[0042] FIGS. 4A and 4B are photographs showing the twinning phenomenon in a Ti-8.5Cr-1.5Sn alloy of the invention; and

[0043] FIGS. 5 and 6 show the results of traction tests on alloys of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0044] FIGS. 1 and 2 are electronic diagrams with titanium alloys positioned thereon. These electronic diagrams show the deformation mechanisms that take place when the alloy is subjected to stress.

[0045] Bo is plotted up the ordinate axis of the electronic diagrams of FIGS. 1 and 2. As mentioned above, Bo quantifies the mean cohesive force of covalent bonds between titanium and the alloying elements.

[0046] Md is plotted along the abscissa axis of the electronic diagrams of FIGS. 1 and 2. As mentioned above, Md specifies the mean energy level of d orbitals corresponding to the covalent bonds that result from the interaction between titanium and the alloying elements.

[0047] The electronic diagrams provided in FIGS. 1 and 2 show various regions corresponding to different deformation mechanisms taking place: slip, twinning, and stress induced martensitic (SIM) transformation.

[0048] As shown, various example alloys of the invention are positioned on the electronic diagrams of FIGS. 1 and 2 in the zone corresponding to activating twinning phenomena. For example it is possible to have: 2.77≦Bo≦2.79 and 2.34 eV≦Md≦2.38 eV for alloys of the invention.

[0049] FIG. 3 is a photograph showing an α″ phase obtained in an alloy of the invention from a β phase (activation of the mechanism for transforming a β phase into an α″ phase when applying a stress). Activating such a phase transformation contributes advantageously to obtaining high ductility. FIGS. 4A and 4B show the activation of a twinning phenomenon obtained in an alloy of the invention, which also contributes to obtaining high ductility.

[0050] FIG. 5 shows the results of traction tests obtained for a Ti-8.5Cr-1.5Al alloy. For this alloy, e/a=4.129 and Mo.sub.eq=12.1. This alloy presents high ductility of the order of 40%, a breaking load of 1150 MPa, and conserves a high elastic limit. Similar results are obtained for the Ti-8.5Cr-1.5Sn alloy for which Mo.sub.eq=13.6 and e/a=4.16 (see FIG. 6). The traction tests were performed at ambient temperature with deformation at a rate of 10.sup.−3 s.sup.−1 on test pieces having a length of 50 millimeters (mm), a thickness of 0.5 mm, and a width of 5 mm.

Example

[0051] An ingot of Ti-8.5Cr-1.5Al alloy was fabricated by compacting titanium sponge elements, chromium grains, and aluminum powder, and then using the arc melting technique. In the compacted mixture, the following contents by weight were used: Ti 90% by weight, Cr 8.5% by weight, and Al 1.5% by weight. The ingot was then deformed in order to obtain a sheet having a thickness of 0.5 mm. The sheet was heat-treated at 900° C. in the beta domain followed by rapid cooling. Flat traction test pieces were cut out from the sheet and they were used in the context of the traction testing described above with reference to FIG. 5.

[0052] The term “including/containing a” should be understood as “including/containing at least one”.

[0053] The term “lying in the range . . . to . . . ” should be understood as including the bounds.