JP4986730B2 - Judgment method for coating deterioration of high temperature metal products - Google Patents

Description

  Non-destructive inspection of the degree of deterioration of metal coatings (hereinafter simply referred to as “coating”) of high-temperature metal products (hereinafter also referred to as “real machines”) having a metal coating on a heat-resistant alloy substrate The present invention relates to a determination method using the result of

  Here, typical high-temperature metal products (high-temperature parts) are gas turbines used in power plants and aircraft, and turbine blades in jet engines. Heat resistance and antioxidant properties are required as well as heat resistance at high temperatures (usually 600 ° C to 900 ° C or higher).

  The metal product for high temperature to which the present invention is applied is not limited to the turbine rotor blade. That is, it is not particularly limited as long as it is a high-temperature metal product provided with a metal coating on a heat-resistant alloy substrate, and can also be applied to turbine stationary blades, combustors, and other high-temperature metal products.

  In the following description, “part” and “%” indicating a blending unit mean a mass unit unless otherwise specified. In the present specification and claims, “X-ray” is expressed as “X-ray”.

  Hereinafter, turbine blades and stationary blades in a gas turbine will be mainly described as an example.

  1 (A) and 1 (B) are cross-sectional views with a cooling method added to the first stage moving blade and the first stage stationary blade, respectively.

  Turbine rotor blades and stationary blades have a Ni-base or Co-base super-heat-resistant alloy as a main body base material to ensure heat-resistant strength, and further have a coating on the main body base material from the viewpoint of heat-resistant oxidation prevention.

  As the coating material, what is called Mclary (MCrAlY) and a coating material for oxidation / high temperature corrosion resistance obtained by diffusing and dipping (packing) Al or the like in them are frequently used. Here, M means a metal element (single or combined) of Ni, Co, and Fe. Cr, Al, and Y are element symbols, meaning the elements indicated by each.

  However, when the coating is used in a harsh high temperature atmosphere for a long time, the coating is deteriorated or thinned by erosion caused by the oxidizing high-temperature combustion gas, so that the heat-resistant oxidation prevention function is hardly achieved. For this reason, periodic recoating is required.

  Proper determination of this re-coating time is critical from a maintenance management standpoint. That is, if the re-coating time (repair time) is too early, the maintenance efficiency is lowered. Conversely, if the time is too late and the time is lost, the main body substrate is damaged.

  Conventionally, a destructive inspection is performed in which a part of a part is sampled (sample extraction), the sample is destroyed, and a cross section is observed.

  However, parts destructive inspection is labor intensive and sample extraction, so when there are few samples, the repair time is often set early in consideration of variations, which also led to a decrease in maintenance efficiency. .

  Although it does not affect the patentability of the present invention, Patent Documents 1 and 2 can be cited as prior art documents related to the present invention.

  Patent Document 1 states that “the content of at least one of Ni and Co is measured by fluorescent X-ray analysis for a Ni-based or Co-based alloy product having an oxidation- and wear-resistant coating containing Al and Si on the surface. The metal coating thickness, the fluorescent X-ray analyzer, and the coating thickness corresponding to the measurement content are read from the relationship curve between the thickness and the measurement content obtained in advance in an experiment. "Measurement method of coating thickness on Ni-base or Co-base alloy" (Claim 1). That is, the present invention focuses on the fact that the detected intensity is proportional to the thickness of the coating when Ni and / or Co immediately below the coating is analyzed with a fluorescent X-ray analyzer via the coating (see paragraph 0021).

In Patent Document 2, in the estimated life of a gas turbine blade, the thickness of an intermetallic compound formed according to the operation time between the diffusion layer immediately below the coating layer and the base material is measured by ultrasonic thickness or the like. A technique is described in which the lifetime is estimated by measuring by means and substituting the thickness or the like into a predetermined formula.
JP-A-10-246619 JP 2005-344607

  An object of the present invention is to provide a method for determining the degree of coating deterioration of a high-temperature metal product by non-destructive inspection, which is not disclosed or suggested in the above prior art documents.

In order to solve the above-mentioned problems, the inventors conducted a thermal aging test on the test piece in the process of diligently developing and measuring each element content in the coating at a plurality of thermal aging times. As a result, it has been found that the relationship between the content (c) of the specific element (c) and the thermal aging time (t) is expressed by a stable function of c ² = at (a: proportional constant).

  Based on this knowledge, the inventors have come up with a method for determining the degree of coating deterioration of high-temperature metal products having the following structure.

A method for determining the degree of deterioration of a metal coating of a high-temperature metal product provided with a coating on a heat-resistant alloy substrate, using a result of nondestructive inspection,
The content rate of the specific element diffused from the heat-resistant alloy base material to the metal coating is measured by a fluorescent X-ray analyzer, and the coating deterioration degree of the actual machine is determined using the result.

  In the present invention, using a portable fluorescent X-ray analyzer and a detection amount master curve of a specific element (such as Mo) accompanying deterioration, a coating (usually, a Ni-based heat-resistant alloy substrate (component)) Nondestructive evaluation (inspection) can be performed on the deterioration state of representative components (Co, Ni, Cr, Al, Y, etc.). That is, it becomes possible to accurately evaluate the deterioration state of the coating without destroying all the individual parts, and it is possible to set the coating repair timing of the actual machine as optimal as possible.

  Hereinafter, desirable modes of the present invention will be described.

  The present invention relates to a method of determining the degree of deterioration of a coating of a high-temperature metal product (actual machine) provided with a coating on a heat-resistant alloy substrate, using the result of nondestructive inspection. Here, as an actual machine, the first stage moving blades and stationary blades of the power generation gas turbine as shown in FIG. 1 will be mainly described as an example.

  Here, examples of the heat resistant alloy base material include various Ni-based alloys and Co-based alloys. For example, the following material names can be used for power generation gas turbines.

For turbine blades: Inconel, IN-700 / 713C / 738LC / 792/939, Rene80, U-500 / 520, MAR-M247 (CC / DS), CM-247LC (DS), GTD111 ( CC / DS), MGA1400, CMSX-4 (SC), ReneN5 (SC), PWA1483 (SC); Ni-based alloys for turbine stationary blades ... X-40 / 45, FSX-414, MAR-M509, ECY -768, (CC / DS); Co-based alloy, CM-247LC (DS), GTD111 (CC / DS), MGA2400, MAR-M247, Rene108, CMSX-4 (SC), ReneN5 (SC); Base alloy, N-155, SCH-20; As described above, as the metal material for forming the iron-base alloy coating, the above-mentioned MCrAlY-based anti-oxidation / high-temperature corrosion-resistant coating material can be used.

  More specifically, the following material names (or compositions) can be exemplified.

  CoCrAlY, CoNiCrAlY, NiCrAlY, NiCoCrAlY, and those subjected to Al diffusion penetration treatment.

  The coating is usually formed by thermal spraying (usually plasma spraying), and the film thickness varies depending on the type of component, the heat-resistant alloy base material, and the type of thermal spray material.

  For example, when the component is the first stage blade, when the coating material is CoCrAlY or CoNiCrAlY, the thickness is set to 200 to 300 μm.

  And the feature of the present invention is the result of measuring the content of the specific element diffused from the heat-resistant alloy base material to the metal coating by the determination using the result of the non-destructive inspection of the deterioration degree of the coating by the fluorescent X-ray analysis. There is to do using.

  Here, fluorescent X-ray analysis refers to elemental analysis performed using fluorescent X-rays emitted when a substance is irradiated with X-rays according to the following principle.

  “With fluorescent X-ray analysis, it is possible to know the concentration analysis and content of all elements regardless of the chemical combination of substances. When a sample is irradiated with X-rays, the elements in the sample are excited and electrons are emitted. Play out.

  An element that has lost its stability due to electrons being ejected replenishes electrons from its outer shell to return to its original stable state. At this time, fluorescent X-rays (characteristic X-rays) specific to the element are generated. Elements can be identified by this intrinsic energy X-ray, and the intensity is proportional to the element concentration. X-ray fluorescence generated by this excitation enters a high-resolution proportional counter, is amplified by an amplifier circuit such as a preamplifier, and is decomposed and counted for each energy by a multichannel analyzer. If you specify the element to be measured, the energy window specific to that element is set and the concentration is calculated from the counted X-rays. ("Your Cyonics, X-ray fluorescence analysis" [May 9, 2007 search] Internet <URL: http://www.yuasa-ionics.co.jp/laser/index.html>).

Here, the specific element refers to an element showing a good correlation in which the relationship between the thermal aging time and the square value of the specific element content (c) is represented by c ² = at (a is a proportional constant). The inventors have found that the correlation also matches the actual operation time in the actual machine as described above (see Tables 1 and 2 and FIGS. 5 to 7). In addition, a specific element changes with combinations of a heat resistant alloy base material and coating.
For example, when the heat-resistant alloy substrate is a Ni-based or Co-based alloy and the coating is as follows, it is desirable that the specific element is as follows.
CoCrAlY (Al diffusion permeation treatment): Mo or Ni
CoNiCrAlY: Mo or Ti

  In addition, as a specific element, elements other than the above can be adopted as long as the above relational expression is satisfied. Usually, the initial content is a trace amount (0.01% or less). This is because a stable diffusion phenomenon can be expected without being affected by the elements contained in the initial coating (before use). In addition, elements that are not the main elements of the coating but have a small initial content (usually 8% or less) can be selected as specific elements if the amount of diffusion from the heat-resistant alloy substrate increases over time. is there.

  In particular, among these specific elements, CoCrAlY (Al diffusion permeation treatment) and NiCrAlY are desirable because Mo easily obtains a stable detection intensity in fluorescent X-ray analysis.

  Next, the master curve (determination graph) used in the present invention is obtained as follows.

    1) A set of test pieces in which the same specification coating is formed on the same base material (new) as the actual heat resistant alloy base material, with a number (for example, 5) corresponding to the set measurement time (thermal aging time) As such, the number of groups (for example, 4 groups) corresponding to each set test temperature is prepared.

  Then, the thickness of the initial interface diffusion layer is previously observed and measured with an optical microscope.

    2) For each set of test pieces, put them into each electric furnace adjusted to the set temperature, conduct a thermal aging test, and take out the test pieces for each set elapsed heat aging time (hereinafter referred to as “elapsed time”). The thickness of the interface diffusion layer is measured.

  At this time, the thickness of the interface diffusion layer 12 increases with each elapsed time as shown in FIG. In the illustrated example, 14 is a coating (layer), and 16 is an alloy substrate.

Here, the relationship between the thickness (L) of the interface diffusion layer and the thermal aging time (t) is
L ² = kt + L ₀ ² (where L _{0 is the} initial diffusion layer thickness, k is the diffusion coefficient) (1)
It is known that there is a relationship of

  For this reason, the relationship between the square value of the thickness of the interface diffusion layer and the actual machine equivalent thermal aging time (equivalent operation time) is linear (refer to FIG. 3).

Then, substituting k obtained in the above equation (1) into the Arrhenius equation (2), which is said to be applicable to diffusion,
k = k ₀ exp (−Q / RT) (2)
(K ₀ : constant, Q: activation energy, R: gas constant, T: absolute temperature)
It becomes.
When the above equation (2) is logarithmically modified, the relationship between In (k) and 1 / T becomes linear (primary equation) (see FIG. 4).

From this slope of the straight line, Q and k ₀ can be obtained.

  And the growth formula of the interface diffusion layer becomes the following formula (3) when formula (2) is substituted into formula (1).

d ² = k ₀ exp (−Q / RT) t + d ₀ ² (3)
By substituting the value of the interface diffusion layer measured (eg, cross-sectional inspection with an optical microscope) from the moving blade used in the actual machine into the equation (3), the internal temperature (T _a ) near the surface of the actual blade is estimated. it can.

And from the said estimated temperature, the correspondence of a test heat aging time and an equivalent real machine heat aging time can be calculated | required. That is, the diffusion coefficient in actual: k _a, test actual wings Temperature: When T _a, an In obtained in above (k) = - from A (A is a positive constant),
_{In (k) -In (k a} ) = Ink / k a = A (1 / T a -1 / T)
_{Thus, k / k a = exp (} A (1 / T a -1 / T)) = a T / T _a.

    3) At the same time as described above, the test piece of the thermal aging test having a predetermined set temperature (usually, the lowest set temperature is selected) is measured by the content of each element in each coating and fluorescent X-ray analysis. This is because the lower the set temperature, the closer the diffusion coefficient to the actual machine.

  And the content rate (c) of various elements and the analytical value of an element are plotted on a thermal aging time (refer FIG. 5).

Then, among the elements, an element placed on a graph of c ² = at (a: proportionality constant) in which the square value of the element content rate has a linear relationship with the thermal aging time is obtained.

And about the said specific element, let the relationship between the equivalent thermal aging time converted from the thermal aging time, and (specific element content) ² value be a master curve (judgment graph) (refer FIG. 6, 7).

  Using the determination graph thus obtained, the degree of coating deterioration is determined as follows.

  That is, after the actual machine operation time has elapsed, the content of the specific element in the coating of the actual machine blade is measured by a fluorescent X-ray analyzer.

  Then, the estimated equivalent thermal aging time corresponding to the content of the specific element is read from the determination graph. Then, the estimated equivalent thermal aging time is compared with the actual machine operating time.

  And, when the estimated equivalent thermal aging time is longer than the actual machine operating time exceeding a significant difference, it is determined that the thermal aging (thermal degradation) of the actual machine is progressing, and when the estimated equivalent thermal aging time is shorter than the significant difference, Judge that the thermal aging of the actual machine is not progressing.

  Here, the range of significant difference is usually around ± 5%.

  Examples that support the effects of the present invention will be described below. It was applied to 1100 ° C class gas turbine first stage blade damage assessment. In addition, the coating of the moving blade has been conventionally CoCrAlY (Al diffusion permeation treatment), but currently CoNiCrAlY is mainly used.

1) Estimation of operating temperature in actual machine (blade):
Here, the operating temperature of the actual machine was a value estimated as follows for a conventional CoCrAlY (Al diffusion permeation treatment) coated moving blade. The estimated temperature of the rotor blade is the same whether the coating is CoCrAlY (Al diffusion permeation treatment) or CoNiCrAlY. This is because the coating is thin and both have the same heat transfer coefficient.

  Three sets of five test pieces for thermal aging test were prepared.

  Each test piece was prepared by applying a coating material: CoCrAlY plasma sprayed film: 250 μm to a base material (Ni-based alloy base material): GTD111DS, which is the same as the moving blade, and then applying an Al diffusion permeation treatment: 80-90 μm.

  Table 1 shows the composition of the base material.

そして、各組の試験片を、３個の所定温度（950℃、1000℃、1070℃）に設定した電気炉中に置き各設定時間（100ｈ、300ｈ、500ｈ及び1000ｈ）ごとに、界面拡散層の厚さを測定した。その結果を図３に示す。

Then, each set of test pieces is placed in an electric furnace set at three predetermined temperatures (950 ° C, 1000 ° C, 1070 ° C), and the interface diffusion layer is set for each set time (100h, 300h, 500h and 1000h). The thickness of was measured. The result is shown in FIG.

Substituting the result into the Arrhenius equation,
k = k ₀ exp (−Q / RT) (2)
Taking the logarithm of both sides of the equation (2), a relationship graph between In (k) and 1 / T is obtained (see FIG. 4).

When Q and k ₀ are obtained from the slope of the straight line in this graph, the following growth formula for the interface diffusion layer is obtained.

d ² = 1.1 × 10 ¹⁴ exp (−328 × 10 ³ / RT) t + d ₀ ² (3)
Substituting the value of the interfacial diffusion layer measured from one of the actual moving blades after a predetermined operating time (2500 h) (for example, cross-sectional inspection with an optical microscope) into this equation (3), the estimated operating temperature ( The internal operating temperature near the surface) was determined. The result was 880 ° C.

2) Creating a master curve:
A test piece was prepared by applying a coating material: GT33incoat (CoNiCrAlY) plasma sprayed film: 250 μm to a base material (Ni-based alloy base material): GTD111DS, which is the same as the moving blade.

  In the above, with respect to a set of test pieces placed in an electric furnace at 1000 ° C., the contents (%) of all the elements contained in the coating at each set time (250 h, 500 h, 1000 h, 2000 h, 3000 h) are fluorescent. Measure with an X-ray analyzer. The results are shown in Table 2 and FIG.

なお、ＣｏＣｒＡｌＹ（Ａｌ拡散浸透処理）についても、同様に測定したので、その結果を、表３及び図５に示す。

Since CoCrAlY (Al diffusion permeation treatment) was measured in the same manner, the results are shown in Table 3 and FIG.

そして、これらの元素の中から、ｃ²＝ａｔのグラフ図に載る元素（本実施例では、Ｍｏ）を特定し、当該元素を特定元素として、ｃ²＝ａｔのグラフ図を、推定使用温度に相当する実機相当熱時効時間で表示したものをｔ軸として、マスターカーブ(判定グラフ)を作成する。

Then, among these elements, an element (Mo in this embodiment) listed in the graph of c ² = at is identified, and the graph of c ² = at is estimated using the element as the specific element. A master curve (judgment graph) is created using the t-axis as the actual machine equivalent thermal aging time equivalent to.

  The master curve is shown in FIGS. 6 and 7 (the master curves in FIGS. 6 and 7 are the same).

3) Degradation determination:
Then, the component analysis of Mo in the coating was performed on the actual machine (first stage moving blade: 10 sheets) after the following operation histories (a) and (b).

(a) Actual machine operation time: 17,196 hours, number of startups: 822 times
(b) Actual machine operation time: 32,460h Number of start-ups: 1,220 times Mo detection values were (a) 0.25 to 0.31% (average value: 0.28%) and (b) 0.34 to 0.50% (0.41%).

Accordingly, in (a), (Mo detection value average) ² = 0.0784, and the estimated equivalent thermal aging time from the master curve is 16000 h. The estimated equivalent thermal aging time is a “−7%” value of the actual machine operating time of 17196 h, and it can be determined that the thermal aging of the actual machine has not progressed beyond prediction.

In (b), (Mo detection value) ² = 0.1681, and the estimated equivalent thermal aging time from the master curve is 33620h. The estimated equivalent thermal aging time is a “+ 3.6%” value of the actual machine operating time of 32460 h, and it can be determined that the thermal aging of the actual machine is as predicted.

It is each model sectional drawing of the moving blade (A) and stationary blade (B) of the gas turbine for power generation which is an example of the application part of the metal coating degradation degree determination method of the high temperature product of this invention. It is model sectional drawing which shows the relationship between the heat aging time in a heating aging promotion test result, and Mo content rate in coating. It is a graph which shows the relationship between thermal aging time and the thickness of an interface diffused layer. FIG. 4 is a graph showing the relationship between In (k) and 1 / T obtained from the graph of FIG. 3. It is a graph which shows the relationship between Mo content rate measured with the fluorescent X ray in the coating in a thermal aging test, and thermal aging time. 6 is a graph illustrating the relationship between the square value of Mo content and the equivalent thermal aging time scale at the actual machine operating temperature in the relationship of FIG. 5, and is an explanatory diagram for determination when the actual machine operating time is 17196 h. Similarly, it is a determination explanatory diagram when the actual machine operating time is 32460h.

Claims (3)

Results of non-destructive inspection of the degree of coating deterioration of high-temperature metal products (hereinafter sometimes referred to as “actual machines”) having a metal-based coating (hereinafter simply referred to as “coating”) on a heat-resistant alloy substrate Is a method of determining using
A method of measuring the content of a specific element diffused from the heat-resistant alloy base material to the coating with a fluorescent X-ray analyzer, and using the result to determine a coating deterioration level of an actual machine ,
The heat-resistant alloy base material is a Ni-based alloy or a Co-based alloy, and the initial content of the specific element in the coating is a trace amount (0.01% or less),
When the coating is MCrAlY, the specific element is Mo. Judgment of the degree of coating deterioration based on a linear function (master curve) that is a relationship between a thermal aging time corresponding to an actual machine obtained by a thermal aging test using the fluorescent X-ray analyzer and a (specific element content) ^binary value The method for determining the degree of coating deterioration of a high-temperature metal product according to claim 1 . A maintenance method for a high-temperature metal product performed using the method for determining a coating deterioration level of a high-temperature metal product according to claim 2 , wherein the specific element content is determined from the high-temperature metal product after a predetermined time has elapsed since the actual operation time. as measured by a fluorescent X-ray analyzer, high temperature, characterized by determining the presence or absence of the coating repair by length compared with the estimated equivalent heat aging time on the master curve corresponding to the content and the actual operation time Maintenance method of metal products.

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