JPH10102227A - Powder material for thermal spraying excellent in high temperature corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder material for thermal spraying having sufficient corrosion resistance to sulfur, vanadium, sodium or the like promoting corrosion in an environment of high temp. use, in a gas turbine using heavy oil of low quality, by forming it of specified ratios of chromium, aluminum, zirconium, cobalt and iron. SOLUTION: This powder material for thermal spraying is composed of one or more kinds among, by weight, 40 to 60% Cr, 5 to 15% Al, 0.5 to 15% Zr, and the balance one or more kinds of Co and Fe. In the case the contents of Cr and Al respectively exceed the upper limits, the ductility of coating at a high temp. can not be obtd., its thermal shock resistance also deteriorates, and cracking and the peeling of coating are made easy to occur in the use, and in the case they fall below the lower limits, its corrosion resistance in a high temp. corrosive environment is made insufficient. Zr easily forms extra-thin oxidized coating of Zr under low oxygen partial pressure, and the one having more excellent corrosion resistance can be obtd., but, in the case it falls below the lower limit, the effect can not be recognized, and in the case it exceeds the upper limit, the ductility of the coating deteriorates, and it is formed into the one poor in thermal impact resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder material for thermal spraying applied to a coating excellent in high-temperature corrosion resistance for moving and stationary blades of a gas turbine. More specifically, the present invention relates to a thermal spraying powder material applied to a coating having excellent resistance to high-temperature corrosion, such as a burner diffuser for a boiler.

[0002]

2. Description of the Related Art Recently, from the viewpoint of resource saving and reduction of fuel cost, development of a gas turbine using low-quality heavy oil as fuel has been attempted. However, since such low-quality heavy oil contains many components that promote corrosion of metals such as sulfur, vanadium, and sodium, the moving and stationary blades of gas turbines, which are high-temperature components, are extremely harsh in corrosive environments. Exposed below. Under such an environment, sufficient corrosion resistance cannot be obtained only with the conventional base materials of heat-resistant steel and heat-resistant alloy. Therefore, a Ni-50Cr-based, MCrAlY
(M = Co, Ni, Fe, etc.)
Corrosion resistance is improved by plasma spraying to about 0 to 400 μm. As a coating method, a low-pressure plasma spraying method is generally used.

[0003]

However, recently, lower quality fuels (such as heavy fuel oil C) have been used, and metal parts have been exposed to an environment that further increases corrosion. Therefore, in the thermal spray coating using the conventional material, sufficient corrosion resistance cannot be obtained, so that the performance of the gas turbine is reduced, and the function as a protective coating cannot be sufficiently maintained. Under these circumstances, there has been a demand for a powder material for thermal spraying that can provide a thermal spray coating having better corrosion resistance and thermal shock resistance at higher temperatures than conventional materials such as Ni-50Cr and MCrAlY.

Accordingly, the present invention relates to a gas turbine using low-quality heavy oil as a fuel, in which a conventional Ni-50Cr-based material is used against sulfur, vanadium, sodium, etc., which are components that promote corrosion in a high-temperature use environment. , MCrAlY, and the like.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned object, and the gist of the invention is that the chemical composition is such that, by weight, 40 to 60% chromium and 5 to 15% A thermal spraying powder material comprising aluminum, 0.5 to 15% of zirconium, and one or two elements selected from the group consisting of cobalt and iron, and the balance comprising unavoidable impurities. With such a material, a sprayed coating having high corrosion resistance to sulfur, vanadium, and sodium, which are components that promote corrosion in a high-temperature use environment, can be obtained.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have limited the composition of the following chemical components as a thermal spray powder material having corrosion resistance at high temperatures with respect to components which promote corrosion such as sulfur, vanadium and sodium. Chromium (Cr) is an element indispensable for maintaining high-temperature corrosion resistance together with aluminum (Al), and a composite oxide of Cr and Al works as a protective film to improve corrosion resistance. Therefore Cr and A
Unless either one of l is used, sufficient corrosion resistance cannot be obtained.

However, when Cr and Al are used as the protective coating, the amounts of Cr and Al in the chemical composition are 6 by weight, respectively.
If the content exceeds the upper limits of 0% and 15%, ductility of the coating is lost, ductility at a high temperature cannot be obtained, and thermal shock resistance is reduced, and cracks and coating peeling are likely to occur during use. And
When the amounts of Cr and Al in the chemical composition are below the lower limits of 40% and 5% by weight, respectively, the problem of a decrease in thermal shock resistance is eliminated, but a material having insufficient corrosion resistance in a high-temperature corrosive environment cannot be obtained. . Therefore, the amounts of Cr and Al in the thermal spraying material are preferably in the range of 40 to 60% and 5 to 15% by weight, more preferably about 45% and about 8%.

On the other hand, zirconium (Zr) has a remarkably low free energy of formation of oxide of Zr, and therefore, when coated, it is easy to form an ultrathin oxide film of Zr under a low oxygen partial pressure. A more excellent corrosion resistance can be obtained than the improvement of corrosion resistance by forming only a film of Al and Al.

However, if the amount of Zr added is 0.5% or less, the effect of adding Zr is not recognized, so that 0.5%
It is desirable to add above. Further, the addition amount of Zr is 1
On the other hand, when the content is 5% or more, the ductility of the thermal sprayed coating is reduced, and the thermal shock resistance is poor. Therefore, the amount of Zr to be added is desirably 0.5 to 15% by weight, preferably about 5%. Further, the balance is cobalt (Co) or iron (F
e) or Co and Fe. Co or Fe is
It is an important element for forming this thermal spray coating, and is also necessary for obtaining heat resistance during long-term use at high temperatures. Co and Fe are nickel (Ni)
As compared with, the formation of sulfide is remarkably small, so that it shows excellent corrosion resistance in a high-temperature corrosive environment. It is desirable that the unavoidable impurities be as small as possible. The particle size of the thermal spraying powder material according to the present invention can be appropriately selected according to the thermal spraying method, the thickness of the coating, and the like, and is not particularly limited, but is preferably about 10 to 100 μm on average.

[0010]

EXAMPLES The chemical compositions shown in Table 1 (where Co and Fe
“Bal.” Indicates the remainder. Hereinafter, the same applies to Table 2. ) Was melted in vacuum and sprayed with argon gas. The obtained powder is classified and the particle size is 10 to 4
The thickness was set to 5 μm.

[0011]

[Table 1]

In order to examine the characteristics of the thermal spraying powder material used for this coating, a coating test was performed on a Ni-base heat-resistant alloy (IN738LC) and a Co-base heat-resistant alloy (ECY768), which are often used for the moving and stationary blade materials of a gas turbine. One piece of the base material was used. IN738LC used as this substrate
And the chemical composition of ECY768 is as shown in Table 2.

[0013]

[Table 2]

As a coating test piece, a round rod of a base material (particle diameter 10 mm × length 65 mm, coating part length 30
mm) was used. And it melt | dissolved in vacuum using the powder which has the same chemical composition as a base material, and sprayed using argon gas. Then, the obtained spherical powder is classified, and the particle size is 10
The thickness was set to about 0 to 300 μm. Using this spherical metal blast material, the outer peripheral portion of the round bar was blasted for several minutes.

Thereafter, the base material of the round bar after the pretreatment was mounted in a low-pressure plasma spraying container and sprayed under the conditions shown in Table 3. The film thickness coated by low-pressure plasma spraying using the material having the chemical composition shown in Table 1 was set to be 500 μm to 1000 μm in consideration of maintaining corrosion resistance. Further, the coated test piece was subjected to 115
A heat treatment at 0 ° C. × 2 hours was performed to improve the adhesion to the substrate.

[0016]

[Table 3]

A high-temperature corrosion test and a high-temperature thermal shock test were performed to confirm the film properties of the coated test piece. Table 4 shows the results.

[0018]

[Table 4]

The high-temperature corrosion test was performed using a molten salt (composition: 60 V ₂
The specimen was immersed in a magnetic alumina crucible containing O ₅ -40Na ₂ SO ₄ ), and this crucible was inserted into an electric furnace.
With the gas turbine combustion simulation gas flowing, 900
After holding at 100 ° C. × 100 hours, the specimen is taken out, washed with hot water and pickled (boiling with an aqueous solution of 18 wt% NaOH + 3 wt% KMnO ₄ and a 10% ammonium citrate aqueous solution for 1 hour) to remove an oxide film on the surface of the specimen. did. Thereafter, the weight of the specimen was measured to determine the weight loss of corrosion, and the cross-sectional structure was observed to measure the thickness of the coating damaged by corrosion. In the high temperature thermal shock test, the specimen was rapidly heated to 990 ° C. in about 180 seconds as shown in FIG.
Thereafter, the operation of cooling to 60 ° C. in about 240 seconds by wiping the alumina powder as a refrigerant was repeated. Thereafter, the presence or absence of cracking and peeling of the coating due to thermal stress was evaluated. Here, the maximum number of repetitions is 1000
Times. This value is a value set in order to clear the number of times of starting and stopping repeated by the end of the life of the actual gas turbine blade.

As shown in Table 4, in a high-temperature corrosion test using a coating test piece obtained by using a thermal spray powder material having the chemical composition of the present invention, the coating material has excellent corrosion resistance as compared with the conventional material. When the target value of the corrosion loss was set to 100 mg / cm ² or less and the target value of the maximum corrosion loss was set to 50 μm or less, it was possible to obtain values that sufficiently satisfied these target values. In addition, in the high-temperature thermal shock test, as in the case of the conventional material, the maximum number of repetitions was 1,000, and the coating was free of cracks and peeling. Also in this case, if the target condition is a state without cracking and peeling,
The material of the present invention was able to satisfy this target condition. Table 4
The circles in the column of "Evaluation" indicate that both the target value of the high-temperature corrosion test and the target conditions of the high-temperature thermal shock test were satisfied, and the cross mark did not.

On the other hand, the comparative material and the conventional material did not satisfy at least one of the above target values and target conditions. Therefore, it can be said that the material of the present invention has excellent corrosion resistance at high temperatures.

[0022]

As described in detail above, according to the present invention,
A thermal spray powder material having excellent corrosion resistance at high temperatures and excellent corrosion resistance to sulfur, vanadium, and sodium can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the temperature and heating time of a test piece in a high-temperature thermal shock test.

Claims (1)

[Claims] 1. The chemical composition by weight of 40-60% chromium, 5-15% aluminum, 0.5-15%
And zirconium, and one or two elements selected from the group consisting of cobalt and iron, and the balance comprising unavoidable impurities.