WO2017077801A1

WO2017077801A1 - Engine compressor blade with corrosion resistant coating and coating method therefor

Info

Publication number: WO2017077801A1
Application number: PCT/JP2016/079400
Authority: WO
Inventors: 荒木　隆人; 勇太田中; 和彦柿沼; 馬場　正信; 一生大寺; 直紀坂本; 杉山　裕一
Original assignee: 株式会社Ihi
Priority date: 2015-11-06
Filing date: 2016-10-04
Publication date: 2017-05-11
Also published as: JP2017088937A

Abstract

A coating method for coating an engine compressor blade comprises: introducing a nitrogen-containing working gas in a chamber of an arc ion plating device; generating an electric discharge inside the chamber with a titanium aluminum alloy as the cathode; and applying an initial bias voltage of −32 to −42 V compared to the cathode on a compressor blade substrate that has been introduced into the chamber to form a coating.

Description

Compressor blade for engine having corrosion resistant coating and coating method thereof

The following disclosure relates to compressor blades for aircraft jet engines or gas turbine engines, and more particularly to compressor blades with a corrosion resistant coating such as TiAlN and methods of coating.

In an aircraft jet engine or gas turbine engine, a combustor generates high-speed high-temperature gas, the turbine extracts energy from the high-temperature gas, and the compressor is driven with a part of the energy. The compressor sucks outside air, compresses it, and supplies it to the combustor. When air is compressed adiabatically in the compressor, a high temperature of, for example, about 400 to 700 ° C. is generated.

The outside air contains various dusts, sand, and, in some cases, volcanic ash, which inevitably flows into the compressor. They hit the compressor blades at high speed and erode or stick to them. The outside air also contains moisture, sulfate, sulfite, chloride, carbonate, etc. in the form of gas or fine droplets, which can also adhere to the compressor blades.

Compressor blades are constantly exposed to high temperatures and foreign substances as described above. Coating techniques have been proposed to protect compressor blades from harsh environments. Patent Documents 1 and 2 disclose related techniques.

Japanese Patent Application Publication No. 2013-019051 Japanese Patent Application Publication No. 2011-080149

Some coating materials, such as TiAlN, are considered to be suitable for protecting compressor blades because they have excellent properties in both erosion resistance and corrosion resistance. However, according to the study by the present inventors, it has been found that even the same material has a difference in the corrosion resistance especially depending on the coating method.

An object of the present disclosure is to provide a method for forming a coating exhibiting particularly excellent corrosion resistance for TiAlN, and a compressor blade having a coating formed by such a method.

A coating method for coating a compressor blade for an engine is as follows. A working gas containing nitrogen is introduced into a chamber of an arc ion plating apparatus, a discharge is generated using a titanium aluminum alloy as a cathode in the chamber, and the discharge is introduced into the chamber. The film is formed by applying an initial bias voltage of −32 to −42 V to the base of the compressor blade as compared with the cathode.

Preferably, the film is grown by changing the bias voltage from −48 to −84 V stepwise from the initial bias voltage. Alternatively, preferably, the bias voltage is changed from −48 to −63V stepwise from the initial bias voltage to grow the film, and the bias voltage changed from −48 to −63V is further changed to −64 to −84V. Change to grow the grown film further. More preferably, prior to the step of generating the discharge, the base is shielded from the discharge leaving the blade surface and the platform portion or the inner band portion and the outer band portion so as to limit the coating to the blade surface and the platform portion. To do. More preferably, in the step of forming the coating film, the pressure of the working gas is maintained in the range of 8.5 ± 4.0 Pa. Still preferably, in the step of forming the film and the step of growing the film, the cathode current flowing between the substrate and the cathode is in the range of 120 to 150A.

Exceptional corrosion resistance is imparted to compressor blades provided with a coating made of TiAlN.

FIG. 1 is a schematic diagram of an ion plating apparatus used in one embodiment. FIG. 2 is a schematic cross-sectional view of a compressor blade having a coating formed according to the embodiment. FIG. 3 is a schematic diagram of a cross section of the compressor blade after the corrosion test.

Several embodiments will be described below with reference to the accompanying drawings.

This embodiment uses a known arc ion plating method and its apparatus. Referring to FIG. 1, an arc ion plating apparatus 1 generally includes a chamber 3, a gas supply device 5, a vacuum pump 7, an evaporation source 9, a holder 11 installed in the chamber 3, and a discharge device. A power source 13 and a bias power source 17 are included.

The chamber 3 is hermetically configured so that the inside thereof is controlled to an atmosphere corresponding to the target film and a vacuum of about 0.1 to 10 Pa can be maintained. In order to control the internal atmosphere, a gas supply device 5 is connected to the chamber 3 and supplies a working gas to the chamber 3. The gas supply device 5 may be composed of a plurality of cylinders and valves each supplying pure gas, or may supply premixed gas. In this embodiment, for example, a mixed gas atmosphere of argon and nitrogen is used. Argon is exclusively for maintaining the discharge, and nitrogen is to form nitrides.

A vacuum pump 7 is further connected to the chamber 3. Due to the balance between the gas supply amount and the exhaust speed of the vacuum pump 7, the inside of the chamber 3 is maintained at a desired pressure.

The evaporation source 15 is connected to an evaporation source 15 installed in the chamber 3, and an external discharge power source 13 is connected in a direction of a negative potential with respect to the chamber 3. Preferably the chamber 3 is grounded. Arc discharge occurs with the evaporation source 9 as a cathode (cathode), and the raw material becomes vapor from the evaporation raw material 15. Further, the arc ion plating apparatus 1 can include a plurality of sets of evaporation sources 9 and evaporation raw materials 15.

The base B to be coated is coupled to the holder 11. The holder 11 has a structure suitable for coupling with the base B. For example, when the base B is a moving blade, the holder 11 has a shape complementary to the dovetail portion so as to be coupled using the dovetail portion. The shaft of the holder 11 is pulled out of the chamber 3 and connected to a bias power source 17 in a direction that is a negative potential with respect to the chamber 3. The holder 11 including the shaft is usually made of metal so that the bias voltage reaches the base B.

The holder 11 is normally rotatable, and a driving device 19 is coupled to give the rotation R. Forming the film while applying the rotation R promotes uniformization of the film.

Although not shown, the arc ion plating apparatus 1 can further include a heater for preheating the substrate B, a discharge device for cleaning the chamber, a trigger for starting discharge, and the like.

According to the present embodiment, the film is formed as follows.

The base B is a compressor blade for an aircraft jet engine or a gas turbine engine, and may be either a moving blade or a stationary blade. After closing the gas supply device 5 and the vacuum pump 7, the chamber 3 is opened to the outside air, and the evaporation raw material 15 and the substrate B are introduced into the chamber 3.

The evaporation raw material 15 is a titanium aluminum alloy ingot. The composition is selected according to the desired composition in the coating. The ratio of titanium and aluminum in the ingot is almost reflected in the ratio in the coating.

As already described, when the base B is a moving blade, the base B is coupled to the holder 11 by inserting the dovetail portion into the holder 11. This serves not only for electrical coupling, but also for shielding the dovetail portion from the discharge by the holder 11 and thus limiting the portion where the film is formed. That is, the formation of the coating is limited to the blade surface and platform surface of the moving blade that are not shielded. In the case of a stationary blade, a structure outside the outer band part or inside the inner band part is used. Due to the shielding by the holder, the formation of the coating is limited to the blade surface of the stationary blade, the outer band portion, and the inner band portion. By limiting the formation of the coating film, it is possible to prevent the hard surface from unintentionally damaging surrounding members.

The chamber 3 is hermetically closed, the vacuum pump 7 is operated, and the chamber 3 is communicated with the chamber 3 so that the chamber 3 is evacuated to a vacuum. This is useful for eliminating impurities, and for example, exhaustion is continued with a vacuum degree of about 0.01 Pa as a guide.

The holder 11 is rotated by the driving device 19 while the exhaust is continued, and the preheating of the base B is started. The rotation speed is, for example, about 1 to 10 rpm. While continuing the exhaust, the valve of the gas supply device 5 is opened to introduce argon and nitrogen, and the pressure in the chamber 3 is adjusted by adjusting the opening of the valve and / or the capacity of the vacuum pump 7. The pressure is, for example, 2 to 10 Pa.

The discharge power supply 13 applies a voltage between the evaporation source 9 and the chamber 3 to start the discharge, and at the same time, the bias power supply 17 applies a bias voltage having a negative potential to the chamber 3 to the substrate B. Titanium aluminum alloy, which is an evaporation raw material, becomes a cathode and discharge is generated. Titanium and aluminum are vaporized, partly ionized and accelerated toward the base B by a bias voltage, and react with nitrogen in the gas phase. As a result, a TiAlN coating 100 is formed on the substrate B as shown in FIG.

During the film formation, the bias voltage may be kept constant, but can be changed stepwise or continuously. For example, a relatively small bias voltage can be applied at the initial stage of film formation. Applying a relatively small initial bias voltage contributes to reducing defects at the interface between the substrate and the film, at the expense of film formation speed. The film can then be grown by increasing the bias voltage stepwise or continuously from the initial bias voltage. This contributes to an increase in the deposition rate. On the other hand, the cathode current can also be kept constant, or may be changed stepwise or continuously.

As already described, no film is formed on the portion shielded by the holder 11, but the gas phase particles are attracted by the bias electric field, so that the entire surface exposed on the substrate B is circulated, and in principle, all of the film is coated. 100 is formed. That is, the coating 100 covers and is limited to all surfaces that are not shielded.

The bias voltage, cathode current, and film formation time are appropriately adjusted in view of the required film thickness. The thickness of the coating 100 is not always uniform throughout the substrate B. Usually, the electric field concentrates on a convex surface such as an edge, resulting in a thicker film than an open plane, and conversely, the film is thinner on a concave surface such as the blade-platform boundary. From the viewpoint of corrosion resistance, the film thickness is required to be about 2 μm from experience. That is, in view of the shape of the substrate B, the bias voltage, the cathode current, and the film formation time are adjusted so that a film thickness of 2 μm can be secured even in the portion where the film 100 is thinnest.

There is a significant difference in corrosion resistance depending on the conditions of film formation. Particularly when the bias voltage is limited to a specific range, a film having excellent corrosion resistance is formed. Details will be described below with reference to several examples.

The ingot having the composition shown in Table 1 was adopted as the evaporation raw material.

A TiAlN film was formed under each bias voltage shown in Table 2 and each cathode current shown in Table 3. In the series of examples shown in Table 2, the cathode current is the same as the example of the symbol d in Table 3 (150 A), and in the series of examples shown in Table 3, the bias voltage is the same as the example of the symbol d in Table 2. The bias voltage was changed in three stages at the initial stage, the middle stage, and the latter stage of film formation. For example, in the case of the symbol d, the initial bias was −40 V, the intermediate bias was −60 V, and the bias described later was −80 V. The film formation time was 20 minutes in the initial period, 90 minutes in the middle period, and 50 minutes in the latter period. The surface temperature of the substrate B during film formation was in the range of 300 to 600 ° C., and the pressure was controlled in the range of 8.5 ± 4.0 Pa.

Specimens were cut out from each substrate, and appearance observation and coating component analysis were performed. Appearance observation was performed with the naked eye and a scanning electron microscope (SEM), and component analysis was performed with an electron probe microanalysis (EPMA).

In the observation with the naked eye, the coating of any sample is smooth and uniform, but in the observation with the SEM, the non-uniform portion seen as droplets is found in various places on the surface. Observed as far as the SEM sample stage can move, if there are almost no droplets, “Good”. If droplets are seen from several to several tens, “Droplets are noticeable”. These are shown in Tables 2 and 3.

Furthermore, the cut sample was washed with ethanol and dried, and a corrosion test was performed. The corrosion test was performed by burying each test piece in a crucible filled with a powder composed of calcium sulfate and the balance of an inert substance, and maintaining the temperature at 760 ° C. for 100 hours or more.

After the corrosion test, the presence / absence and number of corrosion sites of each test piece were observed with a laser microscope. Further, as shown in FIG. 3, the corrosion P proceeds so as to erode toward the base B from the interface between the base B and the coating 100. The distance d from the interface to the deepest point of the corrosion P was defined as the maximum corrosion depth and measured by a laser microscope. The results are summarized in Tables 2 and 3.

As understood from Table 2, the samples a, b, c, d, and e obtained under the condition where the bias voltage does not exceed −84V have good coating appearance, and the initial bias voltage is −32 to −40V. Samples a, b, c, and d obtained in the range have a relatively small maximum corrosion depth and good corrosion resistance. Furthermore, samples b, c, and d obtained with an initial bias voltage in the range of −36 to −40 V have fewer corrosion points and better corrosion resistance.

As understood from Table 3, under the bias voltage condition corresponding to the symbol d, a good coating appearance can be obtained when the cathode current is in the range of 120 to 150A. In particular, when the cathode current is in the range of 135 to 150 A, the maximum corrosion depth is smaller and the corrosion resistance is better.

According to the arc ion plating method, a coating made of TiAlN is formed under various conditions. Under any condition, it is difficult to find a clear difference in the structure of the coating and the characteristics other than the corrosion resistance, but as will be understood from the above, there is a clear difference in the corrosion resistance. The above disclosure provides coatings that exhibit excellent corrosion resistance under specific manufacturing conditions based on the arc ion plating method.

Although several embodiments have been described, those having ordinary skill in the art can modify or change the embodiments based on the above disclosure.

Compressor blades for engines with high corrosion resistance are provided.

Claims

A coating method for coating an engine compressor blade,
Introducing a working gas containing nitrogen into the chamber of the arc ion plating device,
In the chamber, a discharge is generated using a titanium aluminum alloy as a cathode,
An initial bias voltage of −32 to −42 V is applied to the base of the compressor blade introduced into the chamber as compared with the cathode to form a film.
A method consisting of things.
The method of claim 1, further comprising:
Changing the bias voltage stepwise from −48 to −84V from the initial bias voltage to grow the film.
The method of claim 1, further comprising:
The film is grown by changing the bias voltage stepwise from −48 to −63V from the initial bias voltage,
Changing the bias voltage changed from -48 to -63V to -64 to -84V to further grow the grown film.
4. The method according to any one of claims 1 to 3, further comprising:
Prior to the step of generating the discharge, in order to limit the coating to the blade surface and the platform portion, the base body is shielded from the discharge leaving the blade surface and the platform portion or the inner band portion and the outer band portion. Including methods.
4. The method according to any one of claims 1 to 3, wherein the pressure of the working gas is maintained in a range of 8.5 ± 4.0 Pa in the step of forming the coating film.
The method according to any one of claims 1 to 3, wherein in the step of forming the film and the step of growing the film, the cathode current flowing between the substrate and the cathode is in the range of 120 to 150A. There is a way.