Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Coating – specific composition or characteristic
Reexamination Certificate
1999-04-27
2002-06-04
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Coating, specific composition or characteristic
Reexamination Certificate
active
06398503
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a technique concerning a high temperature component used under a high temperature corrosive or oxidative atmosphere in a gas turbine, a jet engine or the like. In particular, the present invention relates to a high temperature component and a gas turbine high temperature component which can improve a thermal barrier performance by subjecting a surface of a metal base material to a thermal barrier coating (TBC) and also relates to a method of manufacturing the same.
In order to improve a heat efficiency, research and development for high temperature (a rise of working gas temperature) have been earnestly made in a prime mover such as a gas turbine, a jet engine or the like. In view of materials for high temperature, there is a tendency for a component material to be exposed to a sever working environment such as high temperature. Therefore, in gas turbine components, in particular, in a movable blade, a stationary blade and components directly exposed to a combustion gas of a combustor, the following two matters have been studied so that these components can provide an durability under a high temperature improve a cooling characteristic and to improve a heat resistant temperature of materials.
First, the following is a description on a study for improving the cooling characteristic in order to reduce a temperature of component materials.
In order to improve the cooling characteristic, it is effective to use a gas having a high heat capacity or to increase a cooling gas flow rate in principle. However, according to the method of using a high heat capacity gas or the method of increasing a cooling gas flow rate, a combustion gas temperature is reduced, and conversely, there are many cases where a heat efficiency lowers. In view of such circumstances, the following methods are employed as a method of improving a cooling performance without lowering a combustion gas temperature. More specifically, there are provided a method of increasing a heat conductivity between a material and a cooling gas and a method of increasing a contact area of the material and the cooling gas.
Film cooling or impinge cooling will be listed up as a a typical example of the method of increasing a heat conductivity between a material and a cooling gas. Moreover, a return flow structure of a blade cooling passage is mentioned as a typical example of the method of increasing a contact area of the material and the cooling gas. As described above, a heat is effectively eliminated as occasion demands. However, in any case of using these methods, a structure of equipments is made into a large size, and the component structure becomes complicated. For this reason, a manufacturing cost of equipments is increased and the system becomes complicated.
Next, the following is a description on a study for improving a heat resistant temperature of the material.
Conventionally, as a heat resisting structural material, a unidirectionally solidified or monocrystalized superalloy has been developed. The superalloy uses any one of Ni-base, Co-base or Fe-base material as a main component. On the other hand, there has been developed an intermetallic compound which is excellent in oxidation resistance by adding Nb- and Mo-base element or the like, and thereby, a trial of further improving a strength to a high temperature is made. However, in the unidirectionally solidified or monocrystalized superalloy, a usable critical temperature is 1000° C. at most in view of a melting point of the superalloy. Moreover, in the case of the superalloy to which Nb- and Mo-base element are added in order to improve an oxidation resistance, there is a problem that a workability is made worse and the manufacturing cost thereof becomes high.
Moreover, there has been developed a method of improving a heat resistance of a high temperature component by applying a ceramic material, which has a high melting point and is excellent in an oxidation resistance and in a corrosion resistance, to the high temperature component. In fact, a SiC- and Si
3
N
4
-base ceramic is applied as the high temperature component. However, the ceramic has a weak toughness in comparison with a metallic material, and there is therefore provided a problem that a workability is made worse, and an involved cost becomes high. For this reason, many problems have caused in order to realize a high temperature resisting strength and cost decreasing to widely use the ceramic as a structural material of the high temperature component.
On the other hand, there is a method of using a metallic material having an excellent toughness as a base material of the high temperature component, and subjecting a surface of the metal base material to the thermal barrier coating (TBC), and thus, improving a heat resistance of the high temperature component. The thermal barrier coating is an oxide-base ceramic layer having a low heat conductivity, and a heat is cut off by forming the thermal barrier coating on the surface of the metal base material so as to prevent a rise of the temperature of a metal base material.
For example, as disclosed in Japanese Patent Laid-open Publication No. SHO-62-211387, there has been proposed a method of forming a thermal barrier ceramic layer having a thickness of a few hundred &mgr;m on the surface of a metal base material so that a rise of the temperature on the surface of the metal base material can be reduced by several tens of degree (° C.). According to this method, it is possible to restrain the rise of the temperature on the surface of the metal base material. Therefore, a gas turbine can be made high temperature, and that is, in the thermal barrier coating, the thicker the thickness of the thermal barrier ceramic layer is, the more a thermal barrier performance is excellent, and thereby, it is possible to reduce a temperature of the metal base material. Further, by subjecting the surface of the metal base material to thermal barrier coating, a heat flux from a combustion gas side to a cooling air side becomes small. Thus, a cooling gas flow rate can be reduced.
However, in the thermal barrier ceramic layer, to which the aforesaid coating is subjected, a crack and peeling from the base material constitute the great problem. For this reason, various research and development have been made in the prior art in order to solve the problem of the peeling.
A two-layer structure is representative of the thermal barrier coating for solving the problem of peeling. The two-layer structure is formed by coating the following two layers, that is, a MCrAlY alloy layer (M is Fe, Co or Ni) coated on the surface of the metal base material, and an oxide-base ceramic layer having a low heat conductivity coated on a surface of the MCrAlY alloy layer. In this case, a zirconia-base ceramic is used as the oxide-base ceramic layer.
The thermal barrier coating having the two-layer structure is usually formed by a thermal spray process. However, in the case where coating is carried out in an atmospheric air, the thermal barrier coating layer becomes porous, and for this reason, there is a problem that an adhesive strength to the metal base material lowers, or corrosion resistance and oxidation resistance are deteriorated. In order to solve such problems, in recent years, there has been developed a method of carrying out a plasma spraying in a low pressure inert gas atmosphere substantially excluding an air (which is generally called as a low pressure plasma spraying) and thereby, a durability of the thermal barrier coating has been greatly improved.
Various studies about a material for forming the thermal barrier ceramic layer have been made.
More specifically, in zirconia (ZrO
2
), a phase transformation takes place in the vicinity of 1200° C.; for this reason, an improvement in a phase stabilization and heat cycle characteristic is achieved by adding an additive for stabilizing the zirconia.
Moreover, in the case of forming the thermal barrier ceramic layer, a thermal barrier coating layer having a columnar structure is formed w
Itoh Masayuki
Koga Akinori
Matsumoto Kazuhide
Saitou Masahiro
Takahashi Masashi
Foley & Lardner
Kabushiki Kaisha Toshiba
Lazo Thomas E.
Look Edward K.
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