EP1837484A2 - Quasicrystalline bond coating and its use as a thermal barrier coating - Google Patents

Abstract

Compounds of formula: Al wCo xM yare new. M is Ni and/or Cr and at least 30 mass% of the compound has a quasi-crystalline structure. W = 70 - 76 and w + x + y = 100. Independent claims are included for: (A) coatings made form or containing the compounds; (B) coating systems containing a coating made from the compounds; (C) multi-layer coating systems containing two or more of the coating systems; (D) use of the compounds as heat-insulating coatings for components subjected to high temperature, especially turbine steam inlets (333) and blades (357); and (E) use of compounds containing aluminum and manganese, at least 30 mass% of the compound having a quasi-crystalline structure, for the same purpose.

Description

The present invention relates to a compound of the nominal atomic composition Al _w Co _x M _y , wherein M is at least one of the elements selected from the group consisting of Ni, Cr and at least 30 percent by mass of the compound as quasicrystalline structure or approximate, a coating consisting of Compound exists or contains a layer system comprising the coating and a metallic layer and the use of the compound as a thermal barrier coating for a component which is exposed to high temperatures.

When components are used at high temperatures and under corrosive conditions, it is often necessary to provide them with protective coatings. Thus, not only the life of the components can be increased by the use of thermal barrier coatings, but also partially the operating temperature can be raised, which leads to an efficiency control. This is especially true for components used in gas or steam turbines.

Normally zirconium oxides are used for such thermal barrier coatings, which are stabilized for example by yttrium oxides. Such ceramic thermal barrier coatings may be applied to a metallic substrate using techniques such as plasma spraying. However, since the ceramic layers do not sufficiently adhere to the metallic substrate, it is necessary to first apply a primer MCrAlY to the device, where M is at least one of iron, cobalt, nickel and Y is an active element and yttrium and or silicon and / or a rare earth element or hafnium.

It is laborious to apply two layers to the component to be protected, and therefore efforts are made to find alternative materials to the ceramic compounds. In this case, quasicrystalline materials have proven to be suitable because they have a high resistance to oxidation and corrosion, low thermal expansion, good processability to coatings and above all a low thermal conductivity.

Quasicrystals in the strict sense of the word are phases which have a 5, 10 or 12-fold rotational symmetry, which are incompatible with the symmetry of the translation lattice of classical crystal phases. As approximations of quasicrystals are termed translational periodic intermetallic compounds having diffraction patterns with 5, 8, 10 or 12-fold Absordesymmetrie.

Quasicrystalline alloys are roughly in the US 5,432,011 described. The alloys mentioned here are used inter alia for coatings, which in turn are used as thermal barrier coatings. However, the patent discloses a variety of possible alloys that can contain a wide variety of elements in a wide variety of compositions.

Also in the DE 103 58 813 A1 are called quasicrystalline alloys and their use as a coating. Here the state of the art to quasicrystalline alloys is comprehensively reviewed.

The quasicrystalline alloys described contain rare and above all expensive metals such as ruthenium, platinum or palladium. For the production of alloys, it is still problematic that in some cases more than six different metals are included, which complicates the exact weighing of the components and overall increases the effort. Not all cases also provide a sufficiently large proportion of the alloy in quasi-crystalline form or as an approximation, and the thermal conductivity is in some cases still too high for use as a thermal barrier coating.

Object of the present invention is to provide a compound which consists of a few favorable metallic constituents and is present at least 30 percent by mass as a quasi-crystalline structure or as an approximate. Another object of the invention is to develop a coating or a layer system using the compound and to use the compound as a thermal barrier coating for a component.

The object is achieved according to the invention by providing a compound of the nominal atomic composition Al _w Co _x M _y in which 70 ≦ w ≦ 76 and w + x + y = 100 and M represents one or two metals.

The basic idea of the invention is thus to provide a compound which consists of a maximum of three or four metallic elements, all of which are relatively inexpensive to acquire and in which aluminum is contained as a main constituent in a range between 70 and 76 atomic percent.

Three metallic elements

In one embodiment of the invention, M = Ni, 10 <x ≦ 15 and 10 <y ≦ 20. This compound consists of only three elements and, in addition, has very good heat resistance.

Experiments have also shown that a compound with particularly low thermal conductivity is obtained when M = Cr and 70 ≦ w ≦ 75, 10 ≦ x ≦ 15 and 10 ≦ y ≦ 20.

Four metallic elements

In another embodiment of the invention, in addition to aluminum and cobalt, a compound is composed of both chromium and nickel (M = Ni, Cr), where 70 ≦ w <75.

Coating and coating systems

The compound can be applied as a coating to a substrate. It may also be included as one of several components in a coating.

In addition, it is possible to form a layer system with the aid of the coating according to the invention. Preferably, a metallic layer is arranged under the coating of the compound according to the invention.
Here it has proved to be advantageous if the metallic layer contains nickel and aluminum, and this preferably in an atomic ratio of 95: 5.

The metallic layer may also be formed as a thin bonding layer, which improves the adhesion of the coating.

If the layer system consisting of coating and metallic layer is applied several times one above the other, a multilayer system is obtained which has particularly good corrosion resistance and low thermal conductivity.

The compound of the invention may also be used as a thermal barrier coating for a component 333, 357 (Figure 1) exposed to high temperatures.

In the same way, it is also possible to use a compound which contains aluminum and manganese and which is at least 30% by mass as a quasicrystalline structure or as an approximate.
The use according to the invention is particularly suitable for parts of turbines, in particular a steam turbine 300, 303, such as turbine blades 357 (FIG. 1).

FIG. 1 shows a steam turbine 300, 303 with a turbine shaft 309 extending along a rotation axis 306.

The steam turbine has a high-pressure turbine section 300 and a medium-pressure turbine section 303, each having an inner housing 312 and an outer housing 315 enclosing this. The high-pressure turbine part 300 is designed, for example, in Topfbauart. The medium-pressure turbine part 303 is designed, for example, double-flow. It is also possible for the medium-pressure turbine section 303 to be single-flow.

Along the axis of rotation 306, a bearing 318 is arranged between the high-pressure turbine section 300 and the medium-pressure turbine section 303, the turbine shaft 309 having a bearing region 321 in the bearing 318. The turbine shaft 309 is supported on another bearing 324 adjacent to the high pressure turbine sub 300. In the area of this bearing 324, the high-pressure turbine section 300 has a shaft seal 345. The turbine shaft 309 is sealed from the outer housing 315 of the medium-pressure turbine section 303 by two further shaft seals 345. Between a high-pressure steam inflow region 348 and a steam outlet region 351, the turbine shaft 309 in the high-pressure turbine section 300 has the high-pressure impeller blade 357, which preferably has the compound according to the invention as a coating. This high-pressure blading 357, together with the associated blades, not shown, represents a first blading region 360.

The medium-pressure turbine part 303 has a central steam inflow region 333, which preferably has a compound according to the invention as a coating. Associated with the steam inflow region 333, the turbine shaft 309 has a radially symmetrical shaft shield 363, a cover plate, on the one hand for dividing the steam flow into the two flows of the medium-pressure turbine section 303 and for preventing one direct contact of the hot steam with the turbine shaft 309 on. The turbine shaft 309 has a second blading area 366 with the medium-pressure rotor blades 354 in the medium-pressure turbine section 303. The hot steam flowing through the second blading area 366 flows out of the medium-pressure turbine section 303 from a discharge connection 369 to a downstream low-pressure turbine, not shown.

The turbine shaft 309 is composed for example of two partial turbine shafts 309a and 309b, which are fixedly connected to one another in the region of the bearing 318. Each turbine shaft 309a, 309b has a cooling line 372 formed as a central bore 372a along the axis of rotation 306. The cooling line 372 is connected to the steam outlet region 351 via an inflow line 375 having a radial bore 375a. In the medium-pressure turbine part 303, the coolant line 372 is connected to a cavity not shown below the shaft shield. The feed lines 375 are configured as a radial bore 375a, allowing "cold" steam from the high pressure turbine section 300 to flow into the central bore 372a. Via the discharge line 372, which is also designed in particular as a radially directed bore 375a, the vapor passes through the storage area 321 into the medium-pressure turbine section 303 and there to the mantle surface 330 of the turbine shaft 309 in the steam inflow area 333. The steam flowing through the cooling line has a significantly lower temperature as the reheated steam flowing into the Dampfeinströmbereich 333, so that an effective cooling of the first blade rows 342 of the medium-pressure turbine section 303 and the mantle surface 330 is ensured in the region of these blade rows 342.

Claims (15)

Connection of the nominal atomic composition:

Al _w Co _x M _y

where M is at least one of the elements selected from the group consisting of Ni, Cr and at least 30 percent by mass of the compound is present as a quasicrystalline structure or as an approximation,
characterized in that $$\mathrm{70}\mathrm{\le }\mathrm{w}\mathrm{\le }\mathrm{76}\mathrm{and\; w}\mathrm{+}\mathrm{x}\mathrm{+}\mathrm{y}\mathrm{=}\mathrm{100}\mathrm{is}\mathrm{,}$$

A compound according to claim 1,
characterized in that
M = Ni and 10 <x ≤ 15 and 10 <y ≤ 20,
in particular 11 ≤ x ≤ 14 and 12 ≤ y ≤ 18. A compound according to claim 1,
characterized in that
M = Cr and 70 ≦ w ≦ 75, 10 ≦ x ≦ 15 and 10 ≦ y ≦ 20
in particular 71 ≦ w 74, 11 ≦ x ≦ 14 and 12 ≦ y ≦ 18. A compound according to claim 1,
characterized in that
M = Cr and Ni and 70 ≦ w <75,
in particular 71 ≦ w ≦ 74. coating
which consists of or contains a compound according to any one of claims 1 to 4. layer system
with a coating according to claim 5. Layer system according to claim 6,
with another metallic layer. Layer system according to claim 7,
in which the metallic layer is arranged under the coating according to claim 5. Layer system according to claim 7,
wherein the metallic layer is disposed over the coating of claim 5. Layer system according to claim 7, 8 or 9,
in which the metallic layer contains Ni and Al, preferably in an atomic ratio of Ni = 95 and Al = 5. Layer system according to claim 7, 8 or 9,
in which the metallic layer is formed as a thin bonding layer. Multilayer system,
which consists of two or more successive layer systems according to one of claims 6 to 11. Use of a compound according to any one of claims 1 to 4
as a thermal barrier coating for a component (333, 357),
which is exposed to high temperatures. Using a connection,
which contains Al and Mn and of which at least 30 percent by mass are present as quasicrystalline structure or as approximate
as a thermal barrier coating for a component (333, 357), which is exposed to high temperatures. Use according to claim 13 or 14,
characterized in that
the component is a turbine blade (357), in particular a steam turbine (300, 303).

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