CN110528010B - Method for cleaning fracture of nickel-based high-temperature alloy - Google Patents

Abstract

A nickel-based superalloy fracture cleaning method, comprising the following steps: step 1) preparing a cleaning solution; step 2) completely immersing the alloy fracture in the cleaning solution, and boiling in a water bath to obtain a preliminarily cleaned fracture; step 3) Repeatedly pasting the fracture with tape until the tape no longer sticks to the dirt; step 4) brushing the fracture with a brush dipped in acetone solution; step 5) immersing the fracture completely in the HCl solution for ultrasonic cleaning; step 6) repeating steps 3) and Step 4); Step 7) The fracture is used as the cathode, the platinum electrode is used as the anode, and electrolytic cleaning is carried out in the HCl solution; Step 8) Repeat steps 3) and 4) until the magnification of 500 times to 1000 times under the scanning electron microscope, The dirt on the fracture is cleaned, and the characteristics of the fracture can be identified. The invention can effectively clean the oxides on the fracture of the nickel-based superalloy, avoid secondary damage to the fracture, and make preparations for sample preparation for finding the real cause of alloy service failure.

Description

A kind of nickel-based superalloy fracture cleaning method

technical field

The invention belongs to the field of general inhibition of corrosion or fouling of metal materials in the metallurgical industry, and particularly relates to a fracture cleaning method for nickel-based superalloy materials.

Background technique

Nickel-based superalloys (for example, grades GH6783, GH2984, GH3625) have been widely used in the manufacture of pressure valve bolts in ultra-supercritical power units in recent years, which are affected by vibration, high temperature around 650 ° C, water vapor and other external environments, Generally, fracture failure occurs between 20,000 and 50,000 hours of service.

alloy[J].Materials characterization,2005,54(2):149-155.)，这种电解液一般是为了去除断口表面的油脂和硅酸盐垢。The fracture faithfully records the irreversible deformation of the material before fracture and the whole process of crack initiation and propagation until fracture under the action of load and environment, and is the most important physical evidence for fracture failure analysis. At present, the commonly used fracture cleaning methods for steel parts with short service time mainly include: (1) organic solvent cleaning method, such as soaking or brushing with gasoline, acetone, alcohol, etc., which is suitable for cleaning the oil and other pollution attached to the fracture surface (2) Ultrasonic method, using ultrasonic cleaning machine for ultrasonic cleaning, which is suitable for cleaning off loose attachments attached to the surface; (3) Dry airflow or soft brush, which is suitable for removing loose particles attached to the surface; ( 4) Chemical etching method, a chemical etching solution is prepared from a variety of reagents, which is suitable for removing relatively dense oxides, the production process is relatively complex, and there is often a risk of excessive chemical reaction resulting in damage to the fracture morphology characteristics due to overwashing; (5) ) Electrochemical cleaning method, usually using an inert anode (such as carbon and platinum), and using the fracture sample to be cleaned as the cathode, the hydrogen bubbles generated on this sample mechanically remove surface debris and deposits, such as Ni -The electrolyte for fracture electrolysis of Cr-based superalloys is mostly composed of alkali and salt (for details, please refer to the literature: Lu YL, Brooks CR, Chen LJ, et al. A technique for the removal of oxides from the fracture surfaces of

alloy[J].Materials characterization,2005,54(2):149-155.), this electrolyte is generally used to remove grease and silicate scale on the fracture surface.

Corrosion in special working conditions of power plants (for example, humid atmosphere, corrosive gas/liquid environment, etc.) coupled with long service time, it is difficult to obtain timely protection of on-site fractures and rust occurs, so that the surface of fractured fractures is usually covered with oxides. Products, corrosion products and deposited scale, if the existence of such a covering is not cleaned properly, the objective and accurate electron microscopic appearance of the fracture will not be obtained. However, the above existing methods are not ideal for the fracture cleaning effect of the parts of the superalloy with a long service time, or the oxides and corrosion products on the fracture surface cannot be removed and the fracture morphology cannot be revealed, or the local cleaning is excessive and leads to damage. True fracture texture information.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies in the above-mentioned prior art, the present invention provides a method for cleaning the fracture of nickel-based superalloy, the specific steps are as follows:

Step 1) prepare cleaning solution;

Step 2) completely immersing the fracture of the nickel-based superalloy to be cleaned in the cleaning solution, and boiling in a water bath to obtain the fracture for preliminary cleaning;

Step 3) Repeatedly stick the fracture with tape until the tape no longer sticks the dirt;

Step 4) scrub the fracture with a brush dipped in acetone solution;

Step 5) Completely immerse the fracture in the HCl solution for ultrasonic cleaning;

Step 6) Repeat step 3) and step 4);

Step 7) The fracture is used as the cathode, the platinum electrode is used as the anode, and electrolytic cleaning is carried out in the HCl solution. In parts by weight, the components of the HCl solution are: 18-22 parts of HCl and 78-82 parts of H ₂ O, Electrolysis time is 1-5min;

Step 8) Repeat step 3) and step 4) until when magnified 500 times to 1000 times under the scanning electron microscope, the dirt on the fracture is cleaned, and the fracture characteristics can be identified.

Further, in the step 1), the cleaning solution is composed of the following parts by weight: 14-18 parts of NaOH, 4-8 parts of KMnO ₄ and 74-82 parts of H ₂ O.

Further, the time for boiling in the water bath in the step 2) is 100-140min.

Further, in the step 5), the HCl solution is composed of the following parts by weight: 18-22 parts of HCl and 78-82 parts of H ₂ O.

Further, in the step 5), the ultrasonic cleaning time is 1-5 minutes.

Further, in the step 7), during the electrolytic cleaning, the current density is 50-150A/m ² , and the electrolysis temperature is 30-50°C.

Compared with the prior art, the beneficial effects of the present invention are:

1. The preparation of the cleaning solution is simple and easy to obtain: the reagents used in the cleaning solution are all commonly used reagents, no special purchase is required, and there is no long-term toxicity, which poses less threat to the health of users.

2. After boiling in a water bath, the fracture was pasted with tape and brushed with acetone solution for many times to remove the oxide of Ni; then the oxide of Fe on the surface of the fracture was removed by pickling; the electrolyte for electrolysis with the fracture of Ni-Cr-based superalloy Compared with most alkalis and salts, the electrolyte of the present invention is an HCl solution, which not only has the effect of pickling, but also generates more hydrogen in the process of electrolysis, which physically impacts the remaining oxidation products, greatly reducing the long The damage to the fracture texture of stress corrosion and stress fatigue under the condition of time service, the fracture morphology is preserved to the greatest extent.

3. This method avoids the secondary damage to the fracture caused by improper cleaning, prepares samples for finding the real cause of the alloy fracture, and provides an important basis for judging the failure mode and prevention of the material. The design and prevention of experimental products are important.

The above description is only an overview of the technical solution of the present invention. In order to understand the technical means of the present invention more clearly, and implement it according to the content of the description, the preferred embodiments of the present invention are described in detail below with the accompanying drawings. Specific embodiments of the present invention are given in detail by the following examples and accompanying drawings.

Description of drawings

Fig. 1 is the step block diagram of the cleaning method of the present invention;

Fig. 2 is the schematic diagram of fracture morphology treated by the prior art (the oxalic acid and acetone ultrasonic cleaning are respectively used after the NaOH ₊ KMnO water bath is boiled);

Figure 3 is an uncleaned oxidized fracture;

Fig. 4 is the cleaning result of adopting the method of the present invention to oxidation fracture (Fig. 3);

Fig. 5 is the fresh unoxidized fracture of uncleaned;

Fig. 6 is the cleaning result of fresh unoxidized fracture (Fig. 5) using the method of the present invention.

Detailed ways

The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

In Example 1-2, the fracture of the GH6783 nickel-based superalloy that has been in service for 23,000 hours was cleaned. Example 3 The fracture of fresh unoxidized GH6783 nickel-based superalloy was cleaned.

Figure 2 shows the fracture of nickel-based superalloy after being boiled in a NaOH+KMnO ₄ water bath and ultrasonically cleaned with oxalic acid and acetone respectively. It can be seen from the figure that the oxides on the surface of the fracture have been relaxed, but most of the subsurface oxides remain, and the fracture characteristics are still heavily covered.

Example 1

Specific steps for fracture cleaning of GH6783 nickel-based superalloy that has been in service for 23,000 hours:

Step 1) prepare a cleaning solution, in parts by weight, mix 15 parts of NaOH, 5 parts of KMnO ₄ and 80 parts of H ₂ O evenly;

Step 2) The GH6783 alloy fracture is completely immersed and placed in the above-mentioned cleaning solution, boiled in a water bath, and the preliminarily cleaned fracture is obtained after 130 min, and dried;

Step 3) Repeatedly stick the fracture with tape until the tape no longer sticks the dirt;

Step 4) scrub the fracture with a brush dipped in acetone solution;

Step 5) The fracture was completely placed in the HCl solution of 19 parts by weight of HCl and 81 parts of H ₂ O, and ultrasonic cleaning was carried out for 4 minutes.

Step 6) Repeatedly paste the fracture with tape until the tape no longer sticks to the dirt, and brush the fracture with a brush dipped in acetone solution.

Step 7) Using the fracture as the cathode and the platinum electrode as the anode, electrolytic cleaning was carried out in HCl solution of 19 parts of HCl and 81 parts of H ₂ O for 4 minutes, the current density was 120A/m ² , and the electrolysis temperature was 42°C.

Step 8) Repeatedly stick the fracture with tape until the tape no longer sticks to the dirt, and brush the fracture with a brush dipped in acetone solution, until the dirt on the fracture is cleaned when magnified 500 times to 1000 times under the scanning electron microscope , the fracture characteristics can be identified.

The steps and operation methods of Examples 2 and 3 are the same as those of Example 1, and the specific cleaning solution, electrolyte ratio, water bath boiling time, and electrolysis conditions are shown in Table 1.

The cleaning method of table 1 embodiment 1-3

Comparison of fracture morphology before and after cleaning,

Example 2 Referring to Figure 3 (before cleaning) and Figure 4 (after cleaning), it can be seen that the method of the present invention can completely remove the oxides on the fracture surface, and rarely damage the fracture morphology, and the cleaning effect is good.

Embodiment 3 sees accompanying drawing 5 (before cleaning) and accompanying drawing 6 (after cleaning), it can be seen from the comparison that no serious corrosion traces are found in the fracture structure of the material before and after cleaning, and the dimple structure in the fracture has clear characteristics, thus it can be seen that the present invention has The above method will not damage or change the fracture morphology without long-term oxidation of the fracture, and the cleaning effect is better, which is helpful for fracture analysis.

In the present invention, the adhesion between the surface oxide and the substrate is first reduced by alkaline boiling, followed by repeated pasting and brushing to mechanically remove the oxides of the outer Ni, and then the oxides of Fe on the fracture surface are removed by pickling, and then the oxides of Fe on the fracture surface are removed by HCl cathode. The method of electrolysis removes the remaining oxides on the surface under the continuous scouring of acidic solution and cathode gas. Compared with pure pickling, the gas shock generated by electrolysis has a more obvious effect on the shedding of oxides. In practice, it is found that if the percentage of HCl is too high, the hydrogen ions in the electrolyte will increase, the pH value will decrease, the conductivity will increase, the electrolysis current will increase, and the electrolysis process will be too fast, which will easily corrode the substrate. The HCl percentage is too low to clean out the oxides. The high temperature of the electrolyte will increase the conductivity of the electrolyte and the heat energy consumption will be large, the solution will evaporate a lot, and the working environment will be deteriorated. After comprehensive consideration, the electrolysis time is 1-5min, the current density is 50-150A/m ² , and the electrolysis temperature is 30-50℃

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or change of the inventive concept thereof shall be included within the protection scope of the present invention.

Claims (3)

1. The method for cleaning the fracture of the nickel-based superalloy is characterized by comprising the following steps of:

step 1) preparing a cleaning solution, wherein the cleaning solution consists of the following components in parts by weight: NaOH 14-18 parts, KMnO₄4-8 parts and H₂O74-82 parts;

step 2) completely immersing the nickel-based high-temperature alloy fracture to be cleaned in cleaning liquid, and boiling in water bath to obtain a primarily cleaned fracture;

step 3) repeatedly sticking the fracture with the adhesive tape until the adhesive tape does not stick dirt any more;

step 4) brushing the fracture with a brush soaked with an acetone solution;

and 5) completely immersing the fracture into an HCl solution for ultrasonic cleaning, wherein the HCl solution comprises the following components in parts by weight: 18-22 parts of HCl and H₂78-82 parts of O;

step 6) repeating the step 3) and the step 4);

and 7) taking the fracture as a cathode and a platinum electrode as an anode, and carrying out electrolytic cleaning in an HCl solution, wherein the HCl solution comprises the following components in parts by weight: 18-22 parts of HCl and H₂O78-82 parts, the current density is 50-150A/m during electrolytic cleaning²The electrolysis temperature is 30-50 ℃, and the electrolysis time is 1-5 min; the HCl solution has the pickling effect, can generate more hydrogen in the electrolysis process, and physically impacts the residual oxidation products, so that the damage to the fracture textures of stress corrosion and stress fatigue under long-time service conditions is greatly reduced, and the fracture morphology is kept to the maximum extent;

and 8) repeating the step 3) and the step 4) until the dirt on the fracture is cleaned up when the fracture is amplified by 500-1000 times under a scanning electron microscope, so that the fracture characteristics can be identified.

2. The method for cleaning the nickel-based superalloy fracture as claimed in claim 1, wherein the method comprises the following steps: the time for boiling the water bath in the step 2) is 100-140 min.

3. The method for cleaning the nickel-based superalloy fracture as claimed in claim 1, wherein the method comprises the following steps: in the step 5), the ultrasonic cleaning time is 1-5 minutes.

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