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

Abstract

The present invention relates to a method of bonding two substrates of titanium aluminide alloy at a faying surface, 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 above the melting point of the braze material and below -solvus temperature of the -titanium aluminide alloy, and joining the substrates by transient liquid phase bonding.

Claims

1. A method of bonding at a faying surface two substrates of -titanium aluminide alloy having 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, comprising the steps of applying a braze material of a titanium-aluminde 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, at the faying surface of the substrates, and subjecting the substrates and braze material to an elevated temperature above the melting point of the braze material and below the -solvus temperature of the -titanium aluminide alloy, 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 having 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, 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, and subjecting the substrate and braze material to an elevated temperature above the melting point of the braze material and below the -solvus temperature of the -titanium aluminide alloy, 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 between 942 C. and 1250 C., provided that the temperature is above the melting point of the braze material and below the -solvus temperature of the -titanium aluminide alloy.

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

5. The method of claim 1 wherein the titanium aluminide alloy of the substrate is an alloy of the composition Ti-45Al-(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) and Ti-45Al-8Nb-0, 2C (TNB-V2).

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.

10-15. (canceled)

16. The method of claim 2, wherein the elevated bonding temperature is chosen between 942 C. and 1250 C., provided that the temperature is above the melting point of the braze material and below the -solvus temperature 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-(10-35)AC-(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-20Al-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 above the melting point of the braze alloy and below the -solvus temperature of the -titanium aluminide alloy which is far below the melting point of the substrate alloy.

[0030] Preferably, the bonding temperature is chosen within the range between 942 C. and 1250 C., provided the above temperature is above the melting point of the braze alloy and below -solvus temperature of the -titanium aluminide alloy.

[0031] 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.

[0032] 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.

[0033] According to an embodiment the present invention relates to a method of bonding two substrates of titanium aluminide-base alloy of the TNB 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 above the melting point of the braze foil or braze powder and below the -solvus temperature of the -titanium aluminide 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 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 above the melting point of the braze foil or braze powder and below the -solvus temperature of the -titanium aluminide alloy, and joining the substrates by transient liquid phase bonding.

[0034] 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).

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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 1

[0039] Two substrates of TNB-V5 were joined using a method according to the present invention, where a braze foil of a titanium alloy of the composition Ti-20Fe-20Al was applied at the faying surface of the substrates, and thereafter the substrates and braze foil were subjected to an elevated temperature of 1250 C. for 24 hours. The substrates were joined by transient liquid phase bonding. For comparative purposes a TNB-V5 substrate was also subjected to a temperature of 1250 C. for 24 hours.

[0040] The strain versus stress curves of a specimen of the joined substrates and of two different specimens of the TNB-V5 substrate were recorded respectively. The results are shown in FIG. 2. FIG. 2 shows that surprisingly an equal yield stress can be achieved, within the accuracy of the experiment. In addition a plastic ductility of nearly 0.5% is retained in the joined substrate.

EXAMPLE 2

[0041] Two substrates of TNB-V5 were joined using a method according to the present invention, where a braze foil of a titanium alloy of the composition Ti-24Ni was applied at the faying surface of the substrates, and thereafter the substrates and braze foil were subjected to an elevated temperature of 1110 C. for 24 hours, thereby joining the substrates by transient liquid phase bonding. For comparative purposes a TNB-V5 substrate was also subjected to a temperature of 1110 C. for 24 hours.

[0042] The strain versus stress curves of two different specimens of the joined substrates and of one specimen of the TNB-V5 substrate were recorded respectively. The results are shown in FIG. 3. FIG. 3 shows that a tensile strength only 10% below the yield stress of an untreated specimen can be achieved, within the accuracy of the experiment.