NiCoCrAlY-ALLOY, POWDER AND LAYER SYSTEM

Abstract

A metallic bond coat Ni16+/−1% Co15+/−1% Cr 8+/−0.5% Al2+/−0.2% Ta0.5+/−0.1% Y: Sicoat 2496 leads to a fusion barrier of titanium into the metallic bond coat so that a substrate is not depleted by titanium.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Application No. PCT/EP2017/070536, having a filing date of Aug. 14, 2017, which is based on Indian Application No. 201611031021, having a filing date of Sep. 12, 2016, the entire contents both of which are hereby incorporated by reference.

FIELD OF TECHNOLOGY

The following relates to a NiCoCrAly-Alloy, a powder and a layer system using this alloy.

BACKGROUND

Due to the high temperatures involved in the operation of modern gas turbines the titanium (Ti) from Ni— or Co-base material diffuses to a bond coat of NiCoCrAlY and forms spinels. These spinels subsequently lead to reduced creep resistance of the bond coat, thereby increasing the chances of failure.

In case of the older machines the operating temperatures were not so high and the problem of failure of the coating due to titanium spinels was not so prevalent. But with the relatively newer machines, in the pursuit of achieving higher efficiency the operating temperatures are increasing and this problem could become more prevalent.

SUMMARY

Instead of using a single bond coat layer, it is proposed to use a bi-layered bond coat system where the top layer is made of the usual metallic coating material while the bottom layer is made of a newly developed coating material which is richer in nickel (Ni) and has a reduced amount of cobalt (Co) as cobalt (Co) encourages the formation of spinels by destabilizing gamma prime state.

A new developed first layer NiCoCrAlY alloy coating comprises a gamma and gamma prime system whereas the gamma prime state has lower than 25 at % (Al, Ta) but a very high gamma/gamma prime transition temperature.

Titanium (Ti) will be caught because the free energy of formation of Ni₃Ti is more negative than that of Ni₃Al and it will be formed. Hence the titanium (Ti) cannot diffuse to the upper bond coat layer to form spinets.

The composition of the alloy or the new first layer coating comprises or consists or consists essentially of (in wt %):

16.0%+/−10% Co

15.0%+/−10% Cr

8.0%+/−10% Al

2.0%+/−10% Ta

0.5%+/−10% Y

base Nickel (Ni).
+/−10% has to be read as relative, e.g. 2%+/−10% means 1.8%-2.2%.

One inventive step is the addition of another metallic layer in the bond coat leading to a bi-layer bond coat system. Embodiments of the invention are expected to result in increased efficiency of the turbine because the blades will be able to withstand higher temperatures with a lesser probability of coating failure by Titanium (Ti).

BRIEF DESCRIPTION

The FIGURE shows a layer system 1.

DETAILED DESCRIPTION

The layer system 1 comprises at least a substrate 4, at least one metallic bond coat 7′, 7″ and an outer most ceramic layer 10.

The metallic substrate 4 is a nickel or a cobalt based super alloy which is used for turbine components, especially turbine blades, very especially for gas turbines.

Direct on this metallic substrate 4 a metallic bond coat 7′ is present, which acts as an oxidation and corrosion resistance for the metallic substrate and the bond coat for the used outer most ceramic layer 10.

This metallic bond coat 7′ is a NiCoCrAlY-alloy and could be also be a single layer made of the inventive alloy.

In a further embodiment of the invention there is a two layered metallic NiCoCrAlY layer 7′, 7″ with the underlying metallic layer 7′ according to the inventive alloy and on top a further but different NiCoCrAlY-alloy 7″.

For the top layer 7″ other coatings like (in wt %):

Ni-(24-26)Co-(11-14)Cr-(10-12)Al-(0.1-0.5)Y,

Ni-(24-26)Co-(23-25)Cr-(10-11)Al-(0.2-0.4)Y,

Ni-(24-26)Co-(14-17)Cr-(10-11)Al-(0.2-0.4)Y,

Ni-(24-26)Co-(14-17)Cr-(10-11)Al-(0.4-0.8)-(0.3-0.7)Ta,

Ni-(24-26)Co-(16-18)Cr-(10-11)Al-(1.0-2.0)Re-(0.1-0.5)Y,

Co-(29-31)Ni-(27-29)Cr-(7-8)Al-(0.5-0.7)Y(0.3-0.7)Si, are used.

Not shown but during coating with a ceramic layer or at least during operation a thermal crown oxide layer (TGO) is grown on top of the outermost metallic bond coat 7′ or 7″, which is responsible for oxidation resistance.

The ceramic layer 10 can be a zirconia-based layer as a single layer or as a double layer with an underlying partially stabilized zirconia and outer most fully stabilized zirconia layer or an outermost DVC layer or a two layered ceramic system with a pyrochlore layer as an outer most ceramic layer.

Although the invention has been illustrated and described in greater detail with reference to the preferred exemplary embodiment, the invention is not limited to the examples disclosed, and further variations can be inferred by a person skilled in the art, without departing from the scope of protection of the invention.

For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.

Claims

1. An alloy, at least comprising (in wt %):

Cobalt (Co) 16.0%+/−10%,

Chromium (Cr) 15.0%+/−10%,

Aluminum (Al) 8.0%+/−10%,

Tantalum (Ta) 2.0%+/−10%,

Yttrium (Y) 0.5%+/−10%; and

base nickel (Ni).

2. A powder comprising the alloy according to claim 1.

3. A layer system according to claim 2 comprising:

a metallic substrate, including a nickel- or a cobalt-based super alloy, at least one metallic layer made of the alloy or produced by using the powder and an outer most ceramic layer.

4. A ceramic layer system according to claim 3, wherein the ceramic layer is a two layered system, which comprises:

a partially stabilized zirconia layer and an outer most fully stabilized zirconia layer, or zirconia based ceramic layer with an outer most pyrochlore layer.

5. The layer system according to claim 3, wherein the metallic bond coat is a two layered metallic bond coat with an underlying metallic bond coat and an outer metallic bond coat, which especially selected from the compositions (in wt %):

Ni-(24-26)Co-(11-14)Cr-(10-12)Al-(0.1-0.5)Y,

Ni-(24-26)Co-(23-25)Cr-(10-11)Al-(0.2-0.4)Y,

Ni-(24-26)Co-(14-17)Cr-(10-11)Al-(0.2-0.4)Y,

Ni-(24-26)Co-(14-17)Cr-(10-11)Al-(0.4-0.8)-(0.3-0.7)Ta,

Ni-(24-26)Co-(16-18)Cr-(10-11)Al-(1.0-2.0)Re-(0.1-0.5), and

Co-(29-31)Ni-(27-29)Cr-(7-8)Al-(0.5-0.7)Y(0.3-0.7)Si.

6. The layer system according to claim 3, wherein only a single ceramic layer is present, said ceramic layer is made of zirconia.

7. An alloy, consisting of (in wt %):

Cobalt (Co) 16.0%+/−10%,

Chromium (Cr) 15.0%+/−10%,

Aluminum (Al) 8.0%+/−10%,

Tantalum (Ta) 2.0%+/−10%,

Yttrium (Y) 0.5%+/−10%, and

base nickel (Ni).

8. A powder consisting of the alloy according to claim 1.