Method For Joining And/or Repairing Substrates Of Titanium Aluminide Alloys

Abstract

The present invention relates to a method of bonding at a faying surface two substrates of -titanium aluminide alloy having a -single phase region at elevated temperatures, comprising the steps of applying a braze material of a titanium alloy consisting of from 10 to 35 at. % aluminum, from 5 to 30 at. % iron and/or nickel, and optionally other alloying elements present in the substrate material in quantities (at. %) up to their content in the substrate material, the remainder being titanium, at the faying surface of the substrates, and subjecting the substrates and braze material to an elevated temperature in the -single phase region of the substrate, and joining the substrate at the crack interface by transient liquid phase bonding.

Claims

1. A method of bonding at a faying surface two substrates of -titanium aluminide alloy which has a composition within the range of Ti-(42-49) Al-(0.1-10) X (at. %), where X represents elements selected from Zr, V, Nb, Ta, Cr, Mo, W, Mn, Si, B, C or combinations thereof and which exhibits a -single phase region at elevated temperatures, comprising the steps of applying a braze material of a titanium alloy of the general composition Ti-(10-35)Al-(0-10)X-(5-30) Z (at. %), where X represents one or more elements selected from the group of Zr, V, Nb, Ta, Cr, Mo, W, Mn, Si, B, C, and Z represents one or more elements selected from the group of Fe and Ni, and wherein those alloying elements present in the substrate material other than titanium and aluminum are present in quantities (at. %) up to their content in the substrate material, the remainder being titanium, at the faying surface of the substrates, and subjecting the substrates and braze material to an elevated temperature in the -single phase region, and joining the substrates by transient liquid phase bonding.

2. A method for repairing a crack at a crack interface in a substrate of -titanium aluminide alloy which has a composition within the range of Ti-(42-49) Al-(0.1-10) X (at. %), where X represents elements selected from Zr, V, Nb, Ta, Cr, Mo, W, Mn, Si, B, C or combinations thereof and which exhibits a -single phase region at elevated temperatures, comprising the steps of applying a braze material of a titanium alloy of the general composition Ti-(10-35)Al-(0-10)X-(5-30) Z (at. %), where X represents one or more elements selected from the group of Zr, V, Nb, Ta, Cr, Mo, W, Mn, Si, B, C, and Z represents one or more elements selected from the group of Fe and Ni, and wherein those alloys present in the substrate material other than titanium and aluminum are present in quantities (at. %) up to their content in the substrate material, the remainder being titanium, and subjecting the substrate and braze material to an elevated temperature in the -single phase region of the substrate, and joining the substrate at the crack interface by transient liquid phase bonding.

3. The method of claim 1, wherein the elevated bonding temperature is chosen within the range between 1400 C. and 1475 C., provided the temperature is in the -single phase region of the -titanium aluminide alloy.

4. The method of claim 1, wherein the braze material is selected from titanium alloys of the composition Ti-20A1-20Fe (at. %), Ti-25Al-20Fe (at. %), Ti-20Al-20Ni (at. %) and Ti-30Al-18Ni (at. %).

5. The method of claim 1 wherein the titanium aluminide alloy of the substrate is an alloy of the composition Ti-45A1-(5-10)Nb(0-0.5)B(0-0.5)C(at. %).

6. The method of claim 1 wherein the titanium aluminide alloy of the substrate is selected from the group consisting of Ti-45Al-5Nb-0.2B-0.2C (TNB-V5), Ti-45Al-8Nb-0.2C (TNB-V2), and Ti-43.5Al-4Nb-lMo-0.1B (TNM).

7. The method of claim 1 wherein the braze material is a braze foil or a braze powder.

8. The method of claim 7, wherein the braze material is present in the form of a powder in admixture with an organic welding flux.

9. The method of claim 8 wherein the organic welding flux is selected from the group consisting of beeswax, paraffin wax, palm oil, olive oil, oleic acid and mixtures thereof.

10-11. (canceled)

12. The method of claim 2, wherein the elevated bonding temperature is chosen within the range between 1400 C. and 1475 C., provided the temperature is in the -single phase region of the -titanium aluminide alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0026] The titanium aluminide alloy from which the substrates are formed, is a titanium aluminide alloy of the general composition Ti-(42-49)Al-(0.1-10)X (at. %), where X represents one or more elements selected from the group of Zr, V, Nb, Ta, Cr, Mo, W, Mn, Si, B, C. Preferred alloys are e.g. commercially available alloys such as TNB-V5 with a composition of Ti-45Al-5Nb-0.2B-0.2C (at. %), TNB-V2 with a composition of Ti-45Al-8Nb-0.2C (at. %), or TNM with a composition of Ti-43.5Al-4Nb-1Mo-0.1B (at. %).

[0027] According to an aspect of the present invention the braze material useful for being applied in a method according to the present invention is a titanium aluminide alloy of the general composition Ti-(0-35)Al-(0-10)X-(5-30)Z (at. %), where X represents one or more elements selected from the group of Zr, V, Nb, Ta, Cr, Mo, W, Mn, Si, B, C, and Z represents one or more elements selected from the group of Fe and Ni. Preferred braze materials are of the general composition Ti-(10-35)Al-(0-9.5)X-(5-30)Z (at. %) or Ti-(0-35)Al-(0.1-10)X-(5-30)Z (at. %), such as Ti-(10-35)Al-(0.1-9.5)X-(10-25)Z (at. %), where X and Z are as defined above. Exemplary alloys are Ti-20Al-20Fe (at. %), Ti-25Al-20Fe (at. %), Ti-20Al-20Ni (at. %) and Ti-30Al-18Ni (at. %).

[0028] It is generally preferred that, with exception of elements Z, the braze alloy comprises the same elements as the alloy of the substrate. The contents of elements Al and X are advantageously either selected slightly below or equal to their content in the substrate. Alternatively, the contents of elements Al and/or X are selected slightly above their content in the substrate. In the former case no or nearly no diffusion based equilibration of these elements between braze zone and substrate is necessary. In the latter case especially by carefully selecting type and content of element X the presence of unordered phases in the braze zone, which allow faster diffusion, can be promoted.

[0029] The elevated temperature (bonding temperature), to which the substrate(s) and braze alloy are subjected, is chosen to a temperature within to an elevated temperature in the -single phase region of the substrate alloy. Preferably, the bonding temperature is chosen within the range between 1400 C. and 1475 C., provided the temperature is in the -single phase region of the -titanium aluminide alloy.

[0030] Preferably, the braze foil has a thickness of 5 m or more, preferably from 5 m to 500 m, more preferably from 10 m to 300 m, such as about 50 m, 100 m, 200 m or 300 m.

[0031] The joining is preferably performed in vacuum. The background vacuum can be chosen in a wide variety of pressures such as from 110.sup.3 Pa to 1 Pa, e.g. about 310.sup.3 Pa. The joining can also be performed at ambient pressure under a protective gas atmosphere. Preferred protective gases are selected among nitrogen and argon.

[0032] According to an embodiment the present invention relates to a method of bonding two substrates of titanium aluminide-base alloy of the TNB or TNM type, comprising the steps of applying a braze foil or a braze powder of a titanium alloy of the general composition Ti-(10-35 at. %)Al-(0-10 at. %)X-(5-30 at. %)Y, where X represents one or more elements selected from the group of Zr, V, Nb, Ta, Cr, Mo, W, Mn, Si, B, C, and Z represents one or more elements selected from the group of Fe and Ni, at the faying surface of the substrates, and subjecting the substrates and braze foil or braze powder to an elevated temperature in the -single phase region of the titanium aluminide-base alloy, and joining the substrates by transient liquid phase bonding. According to another embodiment, the present invention relates to a method of repairing a crack at a crack interface in a substrate of titanium aluminide-base alloy of the TNB or TNM type, comprising the steps of applying a braze foil or a braze powder of a titanium alloy of the general composition Ti-(10-35 at. %)Al-(0-10 at. %)X-(5-30 at. %)Z, where X represents one or more elements selected from the group of Zr, V, Nb, Ta, Cr, Mo, W, Mn, Si, B, C, and Z represents one or more elements selected from the group of Fe and Ni, into the crack interface, and subjecting the substrates and braze foil or braze powder to an elevated temperature in the -single phase region of the titanium aluminide-base alloy, and joining the substrates by transient liquid phase bonding.

[0033] Preferably, the titanium aluminide-base alloy is selected from the group consisting of TNB-V5 (Ti-45Al-5Nb-0.2B-0.2C) and TNB-V2 (Ti-45Al-8Nb-0.2C). More preferably, the titanium aluminide alloy is a TNM type alloy (Ti-43.5Al-4Nb-1Mo-0.1B).

[0034] Also in these embodiments, the braze foil preferably has a thickness of 5 m or more, preferably from 5 m to 500 m, more preferably from 10 m to 300 m, such as about 50 m, 100 m, 200 m or 300 m.

[0035] Also in these embodiments, the joining is preferably performed in vacuum. The background vacuum can be chosen in a wide variety of pressures such as from 110.sup.3 Pa to 1 Pa, e.g. about 310.sup.3 Pa. The joining can also be performed at ambient pressure under a protective gas atmosphere. Preferred protective gases are selected among nitrogen and argon.

[0036] Also in these embodiments, the heating and cooling rates may be kept at a constant rate of about 20 K min.sup.1. According to another embodiment the substrate may be subjected to an elevated temperature towards the end of the bonding process.

[0037] The present invention also relates to a braze alloy useful for transient liquid phase (TLP) bonding of a substrate of -titanium aluminide alloy, the braze alloy having the general composition Ti-(10-35)Al-(0.1-10)X-(5-30)Z (at. %), where X represents one or more elements selected from the group of Zr, V, Nb, Ta, Cr, Mo, W, Mn, Si, B, C, and Z represents one or more elements selected from the group of Fe and Ni. According to an embodiment of the present invention, the braze alloy may braze alloy be present in form of a foil or a powder, and if in the form of a powder, it may be present in admixture with an organic welding flux. The organic welding flux may be selected from the group consisting of beeswax, paraffin wax, palm oil, olive oil, oleic acid and mixtures thereof.

EXAMPLE

[0038] Two substrates of TNM were joined using a method according to the present invention, where a braze foil of a titanium alloy of the composition Ti-15Fe was applied at the faying surface of the substrates, and thereafter the substrates and braze foil were subjected to an elevated temperature of 1450 C. (i.e. in the -phase region) for 2 hours under vacuum, thereby joining the substrates by transient liquid phase bonding. Subsequently, the brazed specimen was cooled with a cooling rate of 20 K/min.

[0039] The microstructure of the produced joint is shown in FIG. 2. Surprisingly no visible difference in microstructure between the substrate material and the joint zone is visible in FIG. 2. The joint is marked by the arrows.