Patent Application
20140272467
The present invention is directed to thermal barrier coatings and methods of forming thermal barrier coatings. More specifically, the present invention is directed to calcium-magnesium-aluminosilicate (CMAS) resistant thermal barrier coatings and methods of forming CMAS resistant thermal barrier coatings.
Gas turbines are continuously exposed to increasing operating temperatures in order to enhance efficiency and performance. In order to withstand the increasing temperatures, components of the gas turbines are coated with thermal barrier coatings (TBC). The TBCs provide low thermal conductivity and ultra low thermal conductivity coatings for the gas turbine components.
During operation of the gas turbine, the TBCs can become damaged and/or degraded. The damage and/or degradation of the TBC may expose the gas turbine component to temperatures which damage the component. Often, the damage and/or degradation of the TBC are due to the atmospheric and operational conditions of the gas turbine.
For example, at the high operating temperatures of the gas turbine, environmentally ingested contaminants, such as airborne sand/ash particles, melt on the hot TBC surfaces and form calcium-magnesium-aluminosilicate (CMAS) glass deposits. The CMAS glass penetrates the TBC and leads to loss of strain tolerance and TBC failure.
A thermal barrier coating and method of forming a thermal barrier coating not suffering from the above drawbacks would be desirable in the art.
In an exemplary embodiment, a process of forming a calcium-magnesium-aluminosilicate penetration resistant coating includes providing a thermal barrier coating having a dopant, and exposing the thermal barrier coating to calcium-magnesium-aluminosilicate and gas turbine operating conditions. The exposing forms a calcium-magnesium-aluminosilicate penetration resistant layer.
In another exemplary embodiment, a calcium-magnesium-aluminosilicate penetration resistant thermal barrier coating includes a thermal barrier coating composition comprising a dopant. The dopant is selected from the group consisting of rare earth elements, non-rare earth element solutes, and combinations thereof.
In another exemplary embodiment, a calcium-magnesium-aluminosilicate penetration resistant thermal barrier coating includes a thermal barrier coating and an impermeable barrier layer or a washable sacrificial layer positioned on an outer surface of the thermal barrier coating.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts.
Provided is an exemplary calcium-magnesium-aluminosilicate (CMAS) resistant coating and a process of forming a calcium-magnesium-aluminosilicate (CMAS) resistant coating. Embodiments of the present disclosure, in comparison to processes not utilizing one or more features disclosed herein, lower thermal conductivity, increase resistance to CMAS, shift crystallization rate and/or crystallization temperature, form washable CMAS penetration resistant sacrificial layers, increase diopside formation, increase melting point, reduce wetting of surfaces, increase CMAS viscosity, or a combination thereof.
Suitable TBC compositions 108 include, but are not limited to, compositions having low thermal conductivity (low K), compositions having ultra low thermal conductivity (ultra low K), and compositions having thermal conductivity between low K and ultra low K, as effected or not effected by inclusion of the dopant 112. As used herein, “low K” refers to having a thermal conductivity that is about 30% of 7YSZ. As used herein, “ultra low K” refers to having a thermal conductivity that is about 50% of 7YSZ. A 30% decrease in the thermal conductivity produces a 0.1% increase in efficiency for a combined cycle, while a 50% decrease in the thermal conductivity produces a 0.2% increase in efficiency for a combined cycle. In one embodiment, the TBC composition 108 includes YSZ, for example, having a coefficient of thermal expansion (CTE) of about 10.5×10−6/° C. In one embodiment, the TBC composition 108 includes Al2O3, for example, having a CTE of about 7×10−6/° C. In one embodiment, the TBC composition 108 includes MgO, for example, having a CTE of about 12.8×10−6/° C. In one embodiment, the TBC composition 108 includes MgO and Al2O3, for example, having a CTE that is closer to that of YSZ. A lowering of the thermal conductivity of the TBC 110 increases efficiency of a system and increases an expected life of the substrate 111.
According to the process 101, the doped TBC 110 is exposed to CMAS 114 (step 103) and operational temperatures or other conditions, for example, of a turbine system (not shown), such as, a power generation system or a turbine engine. Suitable operational temperatures and/or material surface temperatures include, but are not limited to, at least about 1100° C., at least about 1200° C., at least about 1300° C., at least about 1400° C., at least about 1600° C., between about 1100° C. and about 1600° C., between about 1200° C. and about 1600° C., between about 1300° C. and about 1400° C., between about 1400° C. and about 1600° C., between about 1100° C. and about 1400° C., between about 1200° C. and about 1400° C., or any suitable combination, sub-combination, range, or sub-range thereof. Suitable operational durations include, but are not limited to, about 1,000 hours, about 5,000 hours, about 10,000 hours, about 15,000 hours, about 20,000 hours, about 25,000 hours, or any suitable combination, sub-combination, range, or sub-range therein.
The dopant 112 in the doped TBC 110 forms the CMAS penetration resistant layer 201 (step 105) when exposed to the CMAS 114 and the operational temperatures. In one embodiment, the CMAS penetration resistant layer 201 is a dense sealant reaction layer, such as an impermeable barrier layer, formed between a CMAS melt 214 and the thermal barrier coating 110. The impermeable barrier layer arrests ingression of the CMAS 114 into the TBC 110. In one embodiment, the impermeable barrier layer includes, but is not limited to, oxides such as SiOxNy (having a melting point greater than 1420° C.), HfO2, Ta2O5, TiO2, and combinations thereof. In one embodiment, the impermeable barrier layer includes, but is not limited to, non-oxides such as carbides, nitrides, silicides and combinations thereof.
As represented by
The dopant 112 is any suitable rare earth material capable of the shifting (step 203), for example, the dopant 112 in the TBC 110 being selected from the group consisting of, but not limited to, rare earth elements such as Ti, Al, La, Yb, Sm, and suitable combinations thereof. In a suitable embodiment, the dopant 112 has a thermal conductivity of approximately 1 W/mk, between approximately 0.1 W/mk and approximately 1 W/mk, between approximately 0.5 W/mk and approximately 1 W/mk, between approximately 0.5 W/mk and approximately 0.75 W/mk, between approximately 0.75 W/mk and approximately 1 W/mk, or any suitable combination, sub-combination, range, or sub-range thereof. In one embodiment, the dopant 112 in the TBC 110 is any suitable solute for incorporation in the TBC 110 formation, such as, but not limited to, InFeZnO4, mischmetal oxides, zirconia (ZrO2) doped with oxides (such as Yb2O3, La2O3, Sm2O3, TiO2, and Al2O3), and suitable combinations thereof.
The dopant 112 concentration controls the rate of the formation (step 105) of the CMAS penetration resistant layer 201. For example, in one embodiment, the dopant 112 concentration is, by weight, between about 30% and about 60%, between about 50% and about 80%, between about 60% and about 85%, between about 45% and about 65%, between about 50% and about 60%, between about 45% and about 55%, between about 55% and about 65%, or any suitable combination or sub-combination thereof. An increase in the concentration of the dopant 112 increases the CMAS penetration resistant layer 201 formation, regardless of the dopants 112 composition.
In one embodiment, the TBC 110 includes multiple layers. One or more of the multiple layers includes the dopant 112. In one embodiment, the dopant 112 has the same composition and/or concentration for at least two of the multiple layers. In one embodiment, the dopant 112 has a different composition and/or concentration for at least two of the multiple layers.
During the process 101, in one embodiment, an outer face 116 of a layer most distal from the substrate 111 is exposed (step 103) to the CMAS 114. The formation (step 105) of the CMAS penetration resistant layer 201 is on the outer face 116. The formation (step 105) of the CMAS penetration resistant layer 201 prevents one or more layers between the outer face 116 and the substrate 111 from being exposed to the CMAS 114.
As shown in
Referring to
V2O5+3MgO→Mg3(VO4)2 Mg3(VO4)2+SO3→Mg2V2O7+MgSO4
As will be appreciated by those skilled in the art, in general, the process 101 is dependent upon the composition of the CMAS 114. In one embodiment, the composition of the CMAS 114 is controlled, predicted, monitored, or a combination thereof. Depending upon the composition of the CMAS 114, the TBC 110, the dopant 112, or other materials used in the process 101, the melting point of the CMAS 114 is capable of being increased or decreased, the crystallization rate of the CMAS 114 is capable of being increased or decreased (for example, by increasing or decreasing the crystallization temperature), the wettability of the CMAS 114 is capable of being increased or decreased, or a combination thereof.
Suitable compositions for the CMAS 114 include, but are not limited to, environmental contaminant compositions including oxides, such as, Ca, Mg, Al, Si, Fe, Ni, Ti, Cr, and combinations thereof. In specific embodiments, the composition of the CMAS 114 is selected from those shown below in Table 1 and combinations, sub-combinations, ranges, and sub-ranges based upon those shown below:
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
