US20060249231A1

US20060249231A1 - Solder comprising elemental powder

Info

Publication number: US20060249231A1
Application number: US11/413,840
Authority: US
Inventors: Patricia Bezerra; Michael Ott
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2005-04-28
Filing date: 2006-04-28
Publication date: 2006-11-09
Also published as: EP1716965A1; CN1853843A

Abstract

Solders contain at least one agent for lowering the melting point, but these agents lead to a deterioration in the properties of the component to which the solder is applied. The solder according to the invention has a composition which is identical or similar to that of a solder according to the prior art, but in this case the elements which form a compound with the agent for lowering the melting point are at least partially added in powder form.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/675,819, filed on Apr. 28, 2005 and is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to a solder.

BACKGROUND OF THE INVENTION

Solders are used, for example, to join components to one another or to fill recesses. The latter situation arises, for example, if a component had a crack or pore which has been machined out and is then refilled with a solder. This is done in particular for turbine components for a steam or gas turbine. Only a refurbished turbine blade or vane of this type can be used again.
The solder contains at least one agent for lowering the melting point, but this agent is undesirable after the soldering process, since it forms undesirable foreign phases which lead to a reduction in the ductility of the base material of the component.

SUMMARY OF THE INVENTION

Therefore, it is an object of the invention to provide a solder which overcomes the above problem.
The object is achieved by a solder in accordance with the claims.
The subclaims list further advantageous measures which can be combined with one another in advantageous ways.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing:
FIGS. 1, 2 show a solder,
FIG. 3 shows a list of compositions of superalloys,
FIGS. 4, 5 show components which can be treated by means of the solder according to the invention, and
FIG. 6 shows a gas turbine.

DETAILED DESCRIPTION OF THE INVENTION

The components which are treated, in particular repaired, with the solder according to the invention consist, for example, of iron-base, nickel-base and/or cobalt-base superalloys as listed in FIG. 3. However, the solder according to the invention can also be used to treat components made from other alloys or metals.
Examples of these components include a turbine blade or vane 120, 130 (FIG. 4) or heat shield elements 155 (FIG. 5) or housing parts 138 (FIG. 6) of a gas turbine.
When producing these components new, it may also be necessary for a recess formed during the casting process to be filled, even if there were no cracks present. Soldering is therefore not just used to repair damage after the components have been used.
The solder represents a metallic alloy composed of a plurality of alloying elements and contains at least one agent for lowering the melting point. Two-element solder alloys can also be realized in accordance with the invention.
The solder used may, for example, be a known superalloy (e.g. FIG. 3), in which case, however, at least one agent for lowering the melting point, such as for example boron (B), silicon (Si), zirconium (Zr), hafnium (Hf), titanium (Ti), is used, so that the solder melts at a temperature which is lower than the melting point of the superalloy and can be joined to the material of the component. It is preferable to use one or two agents for lowering the melting point: either B or Si or B and Si.
At least one alloying element of the solder, a foreign phase-forming alloying element, which during the soldering phase forms a foreign phase with the at least one agent which lowers the melting point, according to the invention is at least partially present as an additional powder in powder form, in particular as a nanopowder. FIGS. 1, 2 show a solder of this type. The solder as a whole, i.e. including its base material, is preferably in powder form and has a large number of grains. Most of the grains consist of an alloy, for example: Me1_xMe2_YMe3_Zor Me1_xMe2_YMe₃Me4_w-a(both of which are to be understood as base materials in the present context). Some grains Me4 consisting of the foreign phase-forming alloying element, according to the invention, are in elemental metallic form as additional powder. The at least one agent for lowering the melting point may likewise be in powder form. The term nanopowders is to be understood as meaning powders in the grain size range of <500 nm, in particular <300 nm or <100 nm. The additional powder preferably has grain sizes of between 300 nm and 500 nm, between 100 nm and 500 nm or preferably between 100 nm and 300 nm.
The base alloy of the solder therefore includes at least two alloying elements, one of which forms the matrix. During soldering or during use at high temperatures, an alloying element forms a foreign phase, which is, for example, brittle and in any event has an adverse effect on the mechanical properties, with the agent for lowering the melting point which is added to the alloy; consequently, the said alloying element is referred to as a foreign phase-forming element. Both the element which represents the matrix of the alloy and the further alloying constituent(s) may form a foreign phase with the agent for lowering the melting point.
The solder base material preferably consists of at least two, three or more alloying elements, and the foreign phase-forming alloying element(s) do not generally form the matrix.
The solder may be based on nickel, cobalt or iron as matrix and include at least one element selected from the group consisting of chromium, nickel, cobalt, aluminum, tungsten, tantalum, zirconium, titanium, manganese, carbon or iron.

Exemplary Embodiment

The known solder according to the prior art for an iron, nickel or cobalt superalloy includes, by way of example, at least the alloying elements tungsten, chromium, nickel, aluminum, tantalum, nickel or cobalt base, and in this case also comprises, for example, boron as the only agent for lowering the melting point. The boron forms borides with the foreign phase-forming alloying elements tungsten and chromium. Therefore, the foreign phase-forming alloying elements tungsten and/or chromium are added to the known solder at least partially in powder form, the grains in this case preferably being in nanopowder form. It is preferable for only chromium to be used as additional powder.
A solder according to the prior art (PA) has, for example, the following empirical formula: Me1_xMe2_YMe3_ZMe4_w. The solder according to the invention can then be described as follows (FIG. 1): Me1_xMe2_YMe3_Z+_wMe4 (Me4=foreign phase-forming alloying element).
The solder as a whole may, of course, also be in powder form, in which case the individual grains of the base material of the solder form an alloy and the foreign phase-forming alloying elements are admixed in powder form with the solder, i.e. the base powder of the solder.
It is also possible to reduce the level of foreign phase-forming alloying elements which form undesirable phases with the agent for lowering the melting point after the soldering process in a solder composition (substoichiometric solder), in which case the level of foreign phase-forming elements is then restored by the addition of elemental powder (FIG. 2):
Solder (1): Me1_xMe2_YMe3_ZMe4_W;
Solder (2)=Me1_xMe2_YMe3_ZMe4_w-a+aMe4.
According to the prior art, a cobalt-based solder alloy consists, for example, of 23% by weight of chromium, 3.5% by weight of tantalum, 10% by weight of nickel, 7.0% by weight of tungsten, 0.5% by weight of zirconium, 0.2% by weight of titanium, 0.1% by weight of manganese, 0.4% by weight of silicon, 0.6% by weight of carbon, 3.0% by weight of boron and 1.5% by weight of iron. The additional powder may form 1% by weight, 2% by weight, 3% by weight or 4% by weight. Ranges between 1% by weight and 3% by weight, 2% by weight and 4% by weight, 1% by weight and 2% by weight, 2% by weight and 3% by weight or 3% by weight and 4% by weight are likewise advantageous. 1 to 4% by weight of the foreign phase-forming element, i.e., for example, chromium and/or tungsten, is added to this powder, since in this solder boron, which forms borides with the foreign phase-forming alloying elements chromium and tungsten, is used as agent for lowering the melting point.
Alternatively, the level of tungsten and chromium can be reduced in the abovementioned cobalt-base solder alloy or in other known solder alloys of the prior art (substoichiometric solder), with the original stoichiometry being restored by adding elemental tungsten and/or cobalt in powder form.
The solder may be applied in the form of a paste, a strip or in some other form.
Further examples of a solder (overall composition) are:
20% by weight of chromium, 20% by weight of cobalt, 3% by weight of boron, 3% by weight of tantalum, remainder nickel
or
13.5% by weight of chromium, 9.5% by weight of cobalt, 2.5% by weight of boron, 3% by weight of tantalum, 4% by weight of aluminum, remainder nickel
or
14% by weight of chromium, 10% by weight of cobalt, 2.7% by weight of boron, 2.5% by weight of tantalum, 3.5% by weight of aluminum, remainder nickel
or
21% by weight of nickel, 22% by weight of chromium, 2% by weight of boron, 3.5% by weight of tantalum, remainder cobalt
or
15% by weight of chromium, 3.5% by weight of boron, remainder nickel
or
9% by weight of chromium, 8% by weight of cobalt, 3% by weight of boron, 2% by weight of aluminum, remainder nickel.
The solder according to the invention results in a more uniform and finer distribution of the precipitations, in particular when using fine-grained powders or nanopowders, so that the negative influence of precipitations does not manifest itself so strongly. In particular when using nanopowders, more precipitations (e.g. defects) occur, but they are mostly small. Since the susceptibility to cracking increases with the defect size, the susceptibility to cracking is lowered as a result. Moreover, there is a local drop in the concentration of the agent for lowering the melting point, which then may no longer form precipitations, but rather is dissolved in the lattice of the matrix, so that it only constitutes a minor disturbance in the lattice.
FIG. 4 shows a perspective view of a rotor blade 120 or guide vane 130 of a turbomachine, which extends along a longitudinal axis 121.
The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor.
The blade or vane 120, 130 has a securing region 400, an adjoining blade or vane platform 403 and a main blade or main part 406 in succession along the longitudinal axis 121. As guide vane 130, the vane 130 may have a further platform (not shown) at its vane tip 415.
A blade or vane root 183, which is used to secure the rotor blades 120, 130 to a shaft or disk (not shown), is formed in the securing region 400. The blade or vane root 183 is designed, for example, in hammerhead form. Other configurations, such as fir-tree or dovetail root, are also possible. The blade or vane 120, 130 has a leading edge 409 and a trailing edge 412 for a medium which flows past the main blade or vane part 406.
In the case of conventional blades or vanes 120, 130, by way of example, solid metallic materials, in particular superalloys, are used in all regions 400, 403, 406 of the blade or vane 120, 130. Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949; these documents form part of the present disclosure with regard to the chemical composition of the alloy. The blade or vane 120, 130 may in this case be produced by a casting process, also by means of directional solidification, by a forging process, by a milling process or combinations thereof.
Workpieces with a single-crystal structure or structures are used as components for machines which are exposed to high mechanical, thermal and/or chemical loads during operation. Single-crystal workpieces of this type are produced, for example, by directional solidification from the melt. This involves casting processes in which the liquid metallic alloy is solidified to form the single-crystal structure, i.e. the single-crystal workpiece, i.e. directionally. In the process, dendritic crystals are formed in the direction of the heat flux and form either a columnar-crystalline grain structure (i.e. with grains which run over the entire length of the workpiece and are referred to in this context, in accordance with the standard terminology, as directionally solidified) or a single-crystal structure, i.e. the entire workpiece consists of a single crystal. In this process, the transition to globular (polycrystalline) solidification needs to be avoided, since non-directional growth inevitably leads to the formation of transverse and longitudinal grain boundaries, which negate the good properties of the directionally solidified or single-crystal component. Where directionally solidified microstructures are referred to in general, this is to be understood as encompassing both single crystals, which do not have any grain boundaries or at most have small-angle grain boundaries, and columnar crystal structures, which do have grain boundaries running in the longitudinal direction, but do not have any transverse grain boundaries. In the case of these latter crystalline structures, it is also possible to refer to directionally solidified microstructures (directionally solidified structures). Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1; these documents form part of the present disclosure.
The blades or vanes 120, 130 may also have coatings protecting against corrosion or oxidation, e.g. (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon and/or at least one rare earth element, or hafnium (Hf)). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1, which are intended to form part of the present disclosure with regard to the chemical composition of the alloy.
It is also possible for a thermal barrier coating consisting, for example, of ZrO₂, Y₂O₄—ZrO₂, i.e. which is not, is partially or is completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, to be present on the MCrAlX. Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD).
The term refurbishment means that protective layers may have to be removed from components 120, 130 after they have been used (for example by sandblasting). Then, the corrosion and/or oxidation layers or products are removed. If necessary, cracks in the component 120, 130 are also repaired using the solder according to the invention. This is followed by recoating of the component 120, 130, after which the component 120, 130 can be used again.
The blade or vane 120, 130 may be of solid or hollow design. If the blade or vane 120, 130 is to be cooled, it is hollow and may also include film cooling holes 418 (indicated by dashed lines).
FIG. 5 shows a combustion chamber 110 of a gas turbine 100 (FIG. 6).
The combustion chamber 110 is configured, for example, as what is known as an annular combustion chamber, in which a multiplicity of burners 107, which are arranged around an axis of rotation 102 in the circumferential direction, open out into a common combustion chamber space 154, with the burners 107 producing flames 156. For this purpose, the combustion chamber 110 overall is of annular configuration, positioned around the axis of rotation 102.
To achieve a relatively high efficiency, the combustion chamber 110 is designed for a relatively high temperature of the working medium M of approximately 1000° C. to 1600° C. To allow a relatively long operating time even with these operating parameters, which are unfavorable for the materials, the combustion chamber wall 153 is provided with an inner lining formed from heat shield elements 155 on its side facing the working medium M. Each heat shield element 155 made from an alloy is equipped on the working medium side with a particularly heat-resistant protective layer (MCrAlX layer and/or ceramic coating) or is made from material that is able to withstand high temperatures (solid ceramic bricks). These protective layers may be similar to the turbine blades or vanes, i.e. meaning for example MCrAlX: M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon and/or at least one rare earth element, or hafnium (Hf). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1, which are intended to form part of the present disclosure with regard to the chemical composition of the alloy.
It is also possible for a, for example, ceramic thermal barrier coating to be present on the MCrAlX, consisting, for example, of ZrO₂, Y₂O₄—ZrO₂, i.e. it is not, is partially or is completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide.
Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EP-PVD).
The term refurbishment means that protective layers may have to be removed from heat shield elements 155 after they have been used (for example by sandblasting). Then, the corrosion and/or oxidation layers or products are removed. If necessary, cracks in the heat shield element 155 are also repaired using the solder according to the invention. This is followed by recoating of the heat shield elements 155, after which the heat shield elements 155 can be used again.
Moreover, on account of the high temperatures in the interior of the combustion chamber 110, it is possible for a cooling system to be provided for the heat shield elements 155 and/or for their holding elements. The heat shield elements 155 are in this case, for example, hollow and may also include film cooling holes (not shown) which open out into the combustion chamber space 154.
FIG. 6 shows, by way of example, a gas turbine 100 in the form of a longitudinal part section. In its interior, the gas turbine 100 has a rotor 103, which is mounted such that it can rotate about an axis of rotation 102 and has a shaft 101, also known as the turbine rotor. An intake housing 104, a compressor 105 a, for example toroidal, combustion chamber 110, in particular an annular combustion chamber, with a plurality of coaxially arranged burners 107, a turbine 108 and the exhaust casing 109 follow one another along the rotor 103. The annular combustion chamber 110 is in communication with a, for example annular, hot-gas duct 111 where, for example, four successive turbine stages 112 form the turbine 108.
Each turbine stage 112 is formed, for example, from two blade or vane rings. As seen in the direction of flow of a working medium 113, a row 125 formed from rotor blades 120 follows a row 115 of guide vanes in the hot-gas duct 111.
The guide vanes 130 are secured to an inner housing 138 of a stator 143, whereas the rotor blades 120 of a row 125 are fitted to the rotor 103, for example by means of a turbine disk 133. A generator or machine (not shown) is coupled to the rotor 103.
When the gas turbine 100 is operating, the compressor 105 sucks in air 135 through the intake housing 104 and compresses it. The compressed air which is provided at the turbine-side end of the compressor 105 is passed to the burners 107, where it is mixed with a fuel. The mixture is then burnt in the combustion chamber 110 to form the working medium 133. From there, the working medium 133 flows along the hot-gas duct 111 past the guide vanes 130 and the rotor blades 120. The working medium 113 expands at the rotor blades 120, transferring its momentum, so that the rotor blades 120 drive the rotor 103 and the rotor drives the machine coupled to it.
When the gas turbine 100 is operating, the components which are exposed to the hot working medium 113 are subject to thermal loads. The guide vanes 130 and rotor blades 120 of the first turbine stage 112, as seen in the direction of flow of the working medium 113, together with the heat shield elements which line the annular combustion chamber 110, are subject to the highest thermal loads. To withstand the temperatures prevailing there, these components can be cooled by means of a coolant.
It is likewise possible for substrates of the components to have a directional structure, i.e. they are in single-crystal form (SX structure) or include only longitudinally directed grains (DS structure). By way of example, iron-base, nickel-base or cobalt-base superalloys are used as material for the components, in particular for the turbine blades and vanes 120, 130 and components of the combustion chamber 110. Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949; these documents form part of the present disclosure with regard to the chemical composition of the alloys.
The blades and vanes 120, 130 may likewise have coatings to protect against corrosion (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon and/or at least one of the rare earth elements or hafnium). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1, which are intended to form part of the present disclosure with regard to the chemical composition.
A thermal barrier coating consisting, for example, of ZrO₂, Y₂O₄—ZrO₂, i.e. it is not, is partially or is completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, may also be present on the MCrAlX. Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD).
The guide vane 130 has a guide vane root (not shown here) facing the inner housing 138 of the turbine 108 and a guide vane head on the opposite side from the guide vane root. The guide vane head faces the rotor 103 and is fixed to a securing ring 140 of the stator 143.

Claims

1. A solder for repairing a nickel, cobalt or iron based super alloy component, comprising:

a base alloy made from a plurality of alloying elements; and

an agent that lowers the melting temperature of the solder and forms a foreign phase-forming alloying element in the solder during soldering or during use of the component wherein the foreign phase-forming alloying element in the solder is at least partially in the form of elemental metallic additional powder.

2. The solder as claimed in claim 1, wherein the solder contains alloying elements selected from the group consisting of: chromium, aluminum, tantalum and tungsten.

3. The solder as claimed in claim 2, wherein the solder comprises a single agent for lowering the melting point.

4. The solder as claimed in claim 3, wherein the agent for lowering the melting point is boron.

5. The solder as claimed in claim 3, wherein the solder includes two agents for lowering the melting point.

6. The solder as claimed in claim 3, wherein the agent for lowering the melting point is silicon.

7. The solder as claimed in claim 1, wherein the foreign phase-forming alloying element is tungsten or chromium.

8. The solder as claimed in claim 1, wherein the foreign phase-forming alloying element is tungsten and chromium.

9. The solder as claimed in claim 1, wherein the foreign phase-forming alloying element is from 1 to 4% by weight of tungsten or chromium in powder form.

10. The solder as claimed in claim 1, wherein the foreign phase-forming alloying element is from 1 to 4% by weight of tungsten and chromium in powder form.

11. The solder as claimed in claim 1, wherein the additional powder has a grain sizes of less than 500 nm.

12. The solder as claimed in claim 1 1, wherein the additional powder has a grain sizes of less than 300 nm.

13. The solder as claimed in claim 12, wherein the additional powder has a grain sizes of less than 100 nm.

14. The solder as claimed in claim 11, wherein in the foreign phase-forming alloying element in powder form is added to a solder having the composition Me1Me2_YMe3_ZMe4_wwherein Me is an alloying element.

15. The solder as claimed in claim 14, wherein the solder stoichiometry is restored to an initial solder stoichiometry by the addition of the at least one foreign phase-forming alloying element in powder form.

16. The solder as claimed in claim 15, wherein the alloyed base material of the solder is in powder form.

17. The solder as claimed in claim 1, wherein the solder consists essentially of:

23% by weight of chromium,

3.5% by weight of tantalum,

10% by weight of nickel,

7.0% by weight of tungsten,

0.5% by weight of zirconium,

0.2% by weight of titanium,

0.1% by weight of manganese,

0.4% by weight of silicon,

0.6% by weight of carbon,

3.0% by weight of boron,

1.5% by weight of iron, and

remainder cobalt.

18. The solder as claimed in claim 1, wherein the solder consists essentially of:

20% by weight of chromium,

20% by weight of cobalt,

3% by weight of boron,

3% by weight of tantalum, and

remainder nickel.

19. The solder as claimed in claim 1, wherein the solder consists essentially of:

14% by weight of chromium,

10% by weight of cobalt,

2.7% by weight of boron,

2.5% by weight of tantalum,

3.5% by weight of aluminum, and

remainder nickel.

20. The solder as claimed in claim 1, wherein the solder consists essentially of:

21% by weight of nickel,

22% by weight of chromium,

2% by weight of boron,

3.5% by weight of tantalum; and

remainder cobalt.