JPS62180026A - Low pressure turbine moving vane for steam turbine - Google Patents

Abstract

PURPOSE:To provide a low-pressure turbine moving vane for a steam turbine having excellent resistance to cavitation erosion by constituting the top end of the vane of a Ti alloy formed by dispersing >=1 kinds among a carbide, nitride, boride, and intermetallic compd. into a substrate. CONSTITUTION:The top end of the above-mentioned low-pressure turbine moving vane is constituted of the Ti alloy contg. >=1 kinds among the carbide, nitride, boride, and intermetallic compd. under the reduced pressure of gaseous Ar. For example, a roll method, etc., are used in order to uniformly disperse the above-mentioned carbide, nitride, etc., having the high hardness into the Ti alloy in this case. The melt of the above-mentioned alloy is quickly dropped onto the surface of a single roll or passed between twin rolls to obtain alloy foil. The Ti alloy foil is diffusively joined to the top end of the low-pressure turbine moving vane by hot hydrostatic press welding (HIP), by which the objective low-pressure turbine moving vane is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low-pressure turbine rotor blade for a steam turbine that has excellent cavitation and erosion resistance.

[Conventional technology]

Currently, 12Cr steel is used for the low-pressure turbine blades of steam turbines, but the practical application of Ti alloy blades is being considered domestically and internationally as a material to replace 12Cr 3fj.
Since i-alloy is lighter than l 2 Cr steel, it can contribute to increased efficiency with improved plant operating performance. Similarly to the 12CrfR turbine rotor blade, in the case of a Ti alloy blade, it is necessary to protect the tip of the blade in order to suppress cavitation caused by steam particles.

US Pat. No. 3,802,939 points out that a Ti-15Mo-5Z r-based alloy is suitable for improving the cavitation and erosion resistance of the tip of a Ti-based alloy rotor blade. However, since this Ti alloy does not contain hard particles such as carbides, nitrides, or borides, there is a problem in that the crushing corrosion resistance of the blade tips deteriorates during long-term operation.

To improve the cavitation and erosion resistance of metal materials, it is necessary to increase the strength and toughness of the matrix, and to achieve this, it is necessary to uniformly disperse a relatively large number of fine compounds with high hardness in a tough matrix. However, it is extremely difficult to significantly improve the corrosion resistance of Ti alloys using the normal melting → forging → processing → heat treatment process.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a blade tip portion with excellent cavitation and erosion resistance in a low-pressure turbine Ti-based alloy rotor blade for a steam turbine.

c) Means for Solving the Problems] In order to achieve the above object, the authors of the present invention have conducted a study and found that a Ti alloy film formed by plasma spraying as a molten metal rapid solidification method or a Ti alloy foil formed by a roll method is used. I remembered that cavitation resistance and two-lotion properties are improved when used on the wing tips.

In other words, in order to improve cavitation resistance and lotion resistance, high hardness carbides, nitrides,
It is necessary to disperse borides and intermetallic compounds in a relatively highly arsenic manner, but in the casting method, carbides, nitrides, borides, and intermetallic compounds that crystallize during solidification are limited due to constraints on alloy composition. Furthermore, these crystallized compounds have the disadvantage of agglomerating and growing to become large. On the other hand, alloy foil produced by the roll method is characterized in that the molten metal is produced by falling onto the surface of a single roll or passing between two rolls in a very short time, and the rolling speed is approximately 10 δ℃/sec or more. Since this is significantly higher than that in the case of the normal U-adic system, the resulting texture becomes finer.

Plasma spraying is a technology in which metal or compound powder is placed in a high-temperature plasma flame of several thousand degrees centigrade or more and melted, and the molten metal particles collide with a base material at high speed and are deposited to form a film. A feature of this technology is that various compounds can be dispersed finely and uniformly in a metal matrix with relative ease.In particular, in the present invention, the blade tips are formed directly on low-pressure turbine Ti alloy rotor blades by plasma spraying. It has the advantage of being able to

Compounds to be dispersed in the Ti alloy matrix include carbides,
Among nitrides, borides, and intermetallic compounds, one type is usually sufficient, but depending on the situation, these compounds can be selected as appropriate and two or more types of compounds can be dispersed. On the other hand, when Ti alloy foil obtained by solidifying molten metal is used for the blade tip, HI P (Hot 1st
Ti alloy foil can be diffusion bonded to the tip of the rotor blade by atic pressing (hot isostatic pressing).

According to the authors of the present invention, carbides, nitrides, and borides are contained in Ni-based or Co-based alloys as well as Ti alloys.

It has been found that when a plasma sprayed coating or alloy foil in which at least one type of intermetallic compound is dispersed is attached to a Ti alloy rotor blade, cavitation resistance and two-lotion properties are significantly improved.

It has also been revealed that forming a single film of carbide, nitride, or boride or a composite film of these by plasma spraying or ion beam treatment is also effective as a method of improving the crushing corrosion resistance of Ti alloys through surface treatment. Ta.

[Effect]

In order to improve the cavitation resistance and resistance of metal materials, it is important to finely and uniformly disperse a highly hard compound in a tough matrix. Although Ti alloy is basically a tough material.

Further improvement can be achieved if the crystal grains are made finer than those obtained by casting. To achieve this, it is effective to form a film by plasma spraying, which is characterized by rapid solidification, and to manufacture alloy foil by rapid cooling of the molten metal.These methods refine the crystal grains to a minimum of several micrometers and improve toughness. .

Carbides, nitrides and borides are suitable as toughness-enhancing compounds dispersed in the matrix. That is, the hardness of these compounds is high and is an important reinforcing factor for improving cavitation resistance and lotion resistance. Furthermore, intermetallic compounds with high hardness can also be used as dispersants.

Plasma spraying technology is characterized by injecting various metal and compound powders into a plasma flame, causing the molten metal particles to collide and deposit on the substrate at high speed to form a film. By relatively easily controlling the type and amount and adjusting its distribution state, it is possible to directly form a blade tip with excellent cavitation and two-lotion resistance. Plasma spraying can be performed in the atmosphere or under reduced pressure. In atmospheric plasma spraying, oxidation builds up on the surface of the molten metal particles heated in the plasma jet during thermal spraying, resulting in an oxide film being mixed into the coating, which tends to cause defects such as pores in the laminated thermal spray coating. Therefore, cavitation resistance and two-lotion properties deteriorate.

To overcome this drawback, plasma spraying can be performed using reduced pressure Ar gas (
50 to 300 Torn), oxide film-free molten metal particles are deposited on the base material, resulting in a dense film with almost no defects.

The alloy foil produced by rapid cooling of the molten metal is obtained by jetting the molten metal from a nozzle and letting it fall onto the surface of one roll or pass between two rolls to rapidly solidify it to a thickness of about 50 to 300 μm. The crystal grains of this alloy foil are fine and the crystallized compound is also fine.

Plasma sprayed coatings and alloy coatings of Ni-based alloys and Co-based alloys can also be produced in the same manner as in the case of Ti alloys described above, and can be used as the blade tips of Ti alloy rotor blades. If the plasma spray coating is directly sprayed onto the tip of the blade, the adhesion between the coating and the rotor blade will be good. In the case of alloy foil, it can be firmly diffusion bonded to the rotor blade by proper HIP treatment.

Plasma spraying and ion beam treatment are methods for forming a hard coating on a Ti alloy. In the case of plasma spraying, carbide, nitride, and boride films can be formed under reduced pressure of Ar gas. In the case of a carbide or boride film, these compound powders are put into an Ar high temperature plasma flame and melted, and high-speed molten metal particles are deposited on the Ti alloy base material. In the case of nitrides, the nitride powder is placed in an Ar Nz hot plasma flame.

In either case, if the thermal spraying conditions are set appropriately, a hard and dense coating can be obtained.

Ion planting is used as a surface treatment by ion beam treatment in the semi-filled industry, but ion beam mixing is an effective method for forming a film at high speed. In this method, an output ion beam from a high-power ion source is irradiated onto the material to be surface treated (in the present invention, a Ti alloy rotor blade) and injected into the base material. In this case, C, N, and B can be used as ion beams. Heat resistance and abrasion resistance can be improved by depositing various materials on the surface-treated material using an electron beam evaporation device and creating a certain type of alloy on the surface. That is, by using ion implantation and electron beam evaporation in combination, TiC, TiN and Tix
The hard coating of B is made of Ti alloy! It can be formed on the FII wing surface,
Cavitation resistance and lotion properties can be improved.

〔Example〕

Examples of the present invention will be described below.

[Example 1] A mixed powder having the composition (%+t10) shown in Table 1 was sprayed under reduced pressure to form a film of about 2 mm. The atmosphere for thermal spraying was Ar gas, the ambient pressure was 5QTorr, and the plasma was (Ar
+H2) gas and the plasma current is 800A. 3 at 1000℃ to remove the internal stress of the coating after thermal spraying.
It was heated for 0mln. As a result of observing the structure of the coating, it was revealed that the crystal grains were several μm in size, no oxide particles were observed, and the various compounds were approximately 1 μm in size and uniformly dispersed.

As a comparison material with the material of the present invention, the cavitation resistance and two-lotion properties of the Ti alloy of Comparative Example 1, which is currently used in the blade tips of low-pressure turbines, were also evaluated.

Cavitation/erosion resistance was evaluated using a magnetostrictive vibration type cavitation tester based on the weight loss after a 120-minute test under the conditions of 6.5 Hz, output 0.7 KW, amplitude 120 μm, and test temperature 25°C. Weight loss is also shown in Table 1.

As is clear from Table 1, the weight loss of Inventive Materials 1 to 10 is smaller than that of Comparative Example 1, and it can be seen that the cavitation resistance and lotion resistance are just 9.

[Example 2] After melting the alloy composition (wtlo) shown in Table 2 in a high-frequency melting furnace, alloy foil was produced by a twin roll method. The thickness of the obtained alloy foil is about 100 μm. Cavitation resistance
Samples for evaluation of lotion properties were prepared as follows. That is, 20 sheets of alloy foil for each composition were laminated and HI
A plate-shaped test piece having a thickness of approximately 1.5 to 1.7 mm was obtained by diffusion bonding using P, and was subjected to an evaluation test. The cavitation and erosion resistance test was the same as in Example 1.

As is clear from Table 2, the Ti-based, Co-based, and Ni-based gold foil cavitation resistance and lotion properties of Comparative Example 1
It can be seen that this is superior to the Ti alloy.

[Example 3] Ti alloy for low pressure turbine rotor blades (Ti-6, 3wt/.

Example 1 in which various coatings were formed on AΩ-3,9wt10V) by plasma spraying and ion beam mixing method.
Cavitation resistance and corrosion resistance were evaluated using the same method as in 2. This result is shown in the third problem.

It can be seen from Table 3 that the weight loss of the coating due to plasma spraying and ion mixing was smaller than that of Comparative Example 1, and the crushing corrosion resistance was excellent. The reason why the ion mixing coating has better cavitation and two-lotion resistance than the plasma sprayed coating is because the ion mixing coating is more dense than the plasma sprayed coating.

As is clear from the above examples, the cavitation and erosion resistance of the Ti-based alloy is significantly improved and can contribute to improving the reliability and operating rate of a steam turbine plant.

〔Effect of the invention〕

According to the present invention, the cavitation resistance and rotor resistance of the tip of the low-pressure turbine Ti-based alloy rotor blade of a steam turbine are improved, and the plant can be operated more efficiently. In the operation of a steam plant, low-pressure turbine rotor blades may come into contact with each other depending on the situation, causing wear and corrosion (fretting corrosion). To prevent this, fretting corrosion-resistant coatings are installed at the tips of the midspan of the rotor blades. Although it is necessary to use a material with excellent properties or to perform a surface hardening treatment, the various process techniques of the present invention are extremely effective as methods for greatly suppressing this fretting corrosion.

Claims (1)

[Claims] 1. In a low-pressure turbine rotor blade of a steam turbine, the blade tip is made of a Ti-based alloy in which at least one of carbides, nitrides, borides, and intermetallic compounds is dispersed in a matrix. A low-pressure turbine rotor blade for a steam turbine characterized by: 2. A low-pressure turbine rotor blade for a steam turbine according to claim 1, wherein the tip of the blade made of the Ti-based alloy is made of a thermally sprayed coating or an alloy foil. 3. A steam turbine according to claim 1, characterized in that a single film of carbide, nitride, or boride or a composite film of these is formed on the surface of the blade tip by plasma spraying or ion beam treatment. low pressure turbine rotor blades.