JPH0372706B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention provides superalloy matrix with NiCrAlY or
The present invention relates to a method of forming a NiCoCrAlY coating. [Prior art] A superalloy substrate is coated with NiCrAlY or NiCoCrAlY.
The protective function of the coating is obtained by the formation of a thin layer of alumina on the surface of the substrate. It is such an alumina layer that resists oxidation and hot corrosion. Oxygen active elements such as yttrium are added to the coating to improve the adhesion of the alumina and reduce its tendency to peel. In the early stages of superalloy development, superalloys were used in so-called equiaxed crystals, either uncoated or, if coated, with a simple coating such as an aluminide coating. It was used.
As performance requirements for superalloys have become more stringent, improvements have been made to the superalloys themselves and to their coatings. In the field of improving superalloys themselves, significant improvements have been made with the development of the so-called unidirectional solidification process, in which superalloys are solidified as elongated grains oriented in one direction crystallographically. Ta. This is described in commonly assigned US Pat. No. 3,260,505. Also, at about the same time, in the field of coating improvement, MCrAlY such as NiCrAlY or NiCoCrAlY
A mold coating was developed. This coating provides better protection than the previously used aluminide coating. U.S. Patent No. 3,542,530;
No. 3676085, No. 3754903, No. 3928026 are
It concerns MCrAlY coating. Although the unidirectional solidification method is promising, significant problems have arisen with regard to ductility in the transverse direction. It has been discovered that grain boundaries between unidirectionally oriented elongated grains are extremely weak in the direction perpendicular to the grain orientation axis. This problem can be solved in small amounts (0.5-2%) in alloys, as described in U.S. Pat. No. 3,711,337, also assigned to the same assignee.
was solved by adding hafnium. The development of the directionally solidified article, which improved the above-mentioned problem of directionality in strength by adding hafnium, and the development of the MCrAlY coating were carried out at almost the same time in the same laboratory. Of course, these were used in combination. Therefore, it is natural that in applications where strict demands are placed on both thermal and strength requirements, especially for first stage turbine blades,
Directly solidified substrate with added hafnium
An MCrAlY coating was applied. [Problem to be solved by the invention] However, when applying MCrAlY coating to a unidirectionally solidified columnar crystal matrix containing hafnium,
In order to optimize the composition of the MCrAlY coating, if its yttrium content is greater than about 0.5% or 0.7% by weight, undesirable low-melting phases (phases based on yttrium and hafnium) at the interface between the coating and the substrate
It was found that this occurs. The present invention uses MCrAlY, which is an important element for improving the adhesion and peeling resistance of coatings, for substrates such as unidirectionally solidified columnar crystal substrates in which hafnium is desired for improving strength properties. By focusing on the above-mentioned problem that has been found to occur when attempting to apply a coating, and by solving this problem, it is possible to coat a superalloy containing hafnium without forming the above-mentioned low melting point phase. By adding hafnium, the strength characteristics of the superalloy matrix itself can be sufficiently improved, and by containing yttrium in an optimal amount on the surface, the adhesion and peeling resistance can be improved. Provided is a method for obtaining a superalloy article coated with a sufficiently improved MCrAlY coating, which has excellent strength properties of the substrate itself and has excellent high temperature strength, and has high adhesion and peeling resistance. The challenge is to do so. [Means for solving the problem] According to the present invention, this problem can be solved by reducing Hf from 0.5 to 2
% containing 10 to 35% Cr, 8 to 20% Al, 1.1 to 3% Y, with the balance being substantially
Coating made of Ni or 10-35% Cr and 8-8% Al
Achieved by a method of obtaining a coated superalloy article by applying a coating containing 20% Co, 30% or less Co, 1.1 to 3% Y, and the remainder substantially Ni, by a plasma spray method. be done. [Function] When a MCrAlY type coating having the above composition is applied to a hafnium-containing superalloy substrate by a plasma spray method, when the coating material is sprayed onto the surface of the substrate by plasma spray, the surface of the substrate is Hafnium near the surface is
Under the high temperatures provided by the plasma, it is oxidized to hafnium oxide by the oxygen present in the coating as yttrium oxide and aluminum oxide. Once hafnium is oxidized, it is stable and does not form harmful low-melting phases.
The hafnium is thus oxidized before it reacts with yttrium to form a low-melting phase, thereby avoiding the formation of a low-melting phase and forming a MCrAlY-type coating on the yttrium-containing superalloy substrate. can do. [Example] According to the present invention, the amount of yttrium in the NiCoCrAlY coating is increased over the amount in the prior art,
More effective effects can be obtained in terms of adhesion and peeling resistance of the coating. Table 1 below shows the composition range of coatings applicable to the present invention.

[Table] Such a composition improves the oxidation resistance of the coating. Note that this composition is similar to the NiCoCrAlY coating composition described in US Pat. No. 3,928,026, except for the higher ythurium content. Such coating compositions are suitable for protecting nickel-based superalloys. It is known in the art that under certain circumstances it is useful to add other elements to the NiCoCrAlY coating. For example, U.S. Pat. No. 4,034,142 proposes adding silicon to MCrAlY coatings, and U.S. Pat. No. 3,918,139 proposes adding platinum and similar noble metals to NiCoCrAlY coatings. There is. The present invention may also be applied to the modified NiCoCrAlY coatings described in the above-mentioned US patents. In addition, tantalum (0-10%) is added to the coating used according to the invention in order to improve its properties without significantly adversely affecting the beneficial effects obtained by the high yttrium content. has a high yztrium content
It has been found that it may be added to NiCoCrAlY coatings. The attached drawings show NiCoCrAlY coating material and NiCoCrAlY modified by adding silicon.
It shows the influence of yttrium content on the oxidation life of +Si coating materials. The nominal composition of the NiCoCrAlY coating material is 22% Co, 18% Cr, 12.5% Al by weight,
The nominal composition of the NiCoCrAlY coating with varying amounts of Y, balance Ni, and silicon is 22% Co, by weight.
It consisted of 18% Cr, 12.5% Al, 1.5% Si, various amounts of Y, and the balance Ni. The test was conducted in a cyclic burner unit operated at a maximum temperature of 1149°C. The coating life measurements were corrected to reflect differences in coating thickness. It can be seen from the accompanying figures that increasing the yttrium content significantly increases the lifetime of the coating. For example, for the NiCoCrAlY coating, it can be seen that increasing the yttrium content from 1% to 2% increases the lifetime of the coating by more than 50%, from about 825 hours to about 1290 hours. Such a coating material was applied to a hafnium-containing substrate by plasma spraying. In this case, the hafnium in the substrate near the interface between the coating and the substrate is oxidized to stable hafnium oxide by the oxygen present in the coating as yttrium oxide and aluminum oxide, and the harmful low melting point phase is It was confirmed that no formation occurred.

[Brief explanation of drawings]

The accompanying drawing is a graph showing coating life as a function of yttrium content for two coatings: NiCoCrAlY and Si plus Si.

Claims (1)

[Claims] 1. Cr is applied on a superalloy matrix containing 0.5 to 2% Hf.
Contains 10-35%, Al 8-20%, Y 1.1-3%,
A method of obtaining a coated superalloy article by applying a coating with the balance essentially consisting of Ni by a plasma spray method. 2 Cr was applied onto a superalloy substrate containing 0.5 to 2% Hf.
10-35%, Al 8-20%, Co 30% or less, Y
1. A method for obtaining a coated superalloy article by applying a coating containing 1.1 to 3% Ni, the remainder consisting essentially of Ni, by a plasma spray method.