Detection method for coating binding force and detection sample

Abstract

The invention discloses a detection method for coating binding force and a detection sample, two samples are bonded through a coating surface in a bonding manner, an adhesive is directly bonded on a coating, the bonding strength is determined by measuring the critical stress of interface cracking of the coating and a matrix, and the coating binding force is calculated according to the test condition. According to the method, the bonding strength of the coating and the matrix interface can be visually and accurately given, the coating quality and the matching between the coating and the environment can be better evaluated according to calculated data, the use quality of subsequent workpieces is improved, the service life of the workpieces is prolonged, and flight faults in use are avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of coating adhesion detection, and relates to a detection method and a detection specimen for coating adhesion. Background Art

[0002] Traditional coating adhesion is characterized by qualitative methods. For example, according to the requirements of GB / T 5270-2005 "Review of Test Methods for Adhesion of Metallic Coatings Electrodeposited and Chemically Deposited on Metallic Substrates", the characterization methods of coating adhesion include cross-cut test, thermal shock test and bending test, etc. In the cross-cut test, a sharp blade at 30° is used to cut squares with a distance of about 1-2 mm, and it is observed whether the coating in the observation area has peeling phenomenon; in the thermal shock test, the specimen is heated to an appropriate temperature in the furnace and kept for a period of time, and then taken out and quenched in cold water. If the coating does not show phenomena such as bubbling and peeling and separation from the substrate, it is considered qualified. This method is applicable when the thermal expansion coefficients between the coating and the substrate metal are significantly different; while in the bending test, the specimen is bent until it breaks under certain conditions, and the separation situation between the coating and the substrate at the fracture port is observed to judge the quality of the adhesion. These methods can only qualitatively reflect whether the coating adhesion is qualified, and cannot quantitatively express the coating adhesion by numerical values. Moreover, in actual production, some detection methods, such as the cross-cut test, require that the cross-cut be deep enough to reach the substrate surface. These operations are affected by the operator's control of force and experience, resulting in uncertainty in the detection results.

[0003] In recent years, with the development of aero-engines towards high temperature rise, high power and high thrust-to-weight ratio, higher and higher requirements have been put forward for the coating quality of components. For example, during the development of a certain engine, silver plating was applied to the tenon part of the titanium alloy blade. After the engine test run, the silver layer repeatedly showed poor adhesion phenomena such as bubbling and peeling, while the part passed the adhesion tests according to the cross-cut test, thermal shock test and bending test during production and processing. This also reflects that qualitative detection methods such as the cross-cut test, thermal shock test and bending test cannot meet the requirements for coating adhesion detection during the engine operation.

[0004] Titanium alloy belongs to a kind of high-strength light alloy. Due to its high strength, good plasticity and corrosion resistance, it has been widely used in aeroengines. The disadvantage of titanium alloy materials is poor wear resistance and easy to "seize", resulting in easy wear problems of titanium alloy parts during assembly and disassembly. To avoid wear or adhesion of titanium alloy parts during assembly and disassembly, it is necessary to apply lubricating coatings such as silver plating and copper plating on the assembly surface to reduce wear, avoid the "seizing" phenomenon and improve the service life. Since the assembly of engine components is relatively complex and precise, if the coating adhesion cannot meet the requirements of the working environment and peeling occurs during use, abrasion will occur at the assembly part, which will affect the working life of the engine to a lesser extent and cause the fracture of the load-bearing part and lead to flight failures in severe cases. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem that in the prior art, the coating adhesion cannot be quantitatively analyzed, resulting in the inability to better verify the practical matching of the coating during application, and the workpiece is prone to peeling during use, causing abrasion at the assembly part and leading to flight failures, and to provide a detection method and a detection specimen for coating adhesion.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A detection method for coating adhesion includes the following steps:

[0008] Form a coating layer on one end of the specimen to form a coated surface, bond two adjacent specimens to form a specimen group;

[0009] After clamping and fixing the specimen group, cure and cool it in sequence;

[0010] Conduct a tensile test on the cooled specimen group until the specimens break and separate, record the fracture load and fracture form of each specimen, judge whether the test is valid according to the fracture form. If it is valid, measure the end area of the specimen, and calculate the coating adhesion according to the end area and the fracture load. If the test is invalid, conduct the test again.

[0011] A further improvement of the present invention lies in:

[0012] The step of forming a coating layer on one end of the specimen to form a coated surface and bonding two adjacent specimens through the coated surface to form a specimen group includes:

[0013] One end of the specimen is an adhesive surface, and the other end is a thread. Coat the adhesive surface to form a coated surface;

[0014] Clean the coated surface, bond two adjacent specimens through an adhesive sheet to form a specimen group.

[0015] The roughness Ra of the bonding surface is ≤ 3.2 μm.

[0016] It also includes sandblasting the bonding surface:

[0017] Sandblasting is carried out in a dry sandblasting method;

[0018] When sandblasting, the abrasive grains are alumina with a mesh size of 60 - 120, and the sandblasting pressure is 0.3 - 0.5 Mpa;

[0019] Within two hours after the sandblasting ends, specimen bonding is carried out.

[0020] The bonding of two adjacent specimens with an adhesive sheet includes:

[0021] Use an FM - 1000 adhesive sheet to bond the coatings of two adjacent specimens together.

[0022] After clamping and fixing the specimen group, curing and cooling are carried out in sequence, including:

[0023] Put the bonded specimen group into a curing fixture, and put the curing fixture and the specimen group into an air - circulation furnace for curing. After curing, it is air - cooled in the furnace.

[0024] When curing, the temperature is 150 - 200 °C, and the time is more than 2 h.

[0025] The judgment of whether the test is valid according to the fracture form includes:

[0026] When fracturing, if the coating fractures from the specimen, the test is valid, and subsequent calculation processes are carried out. If the fracture occurs on the adhesive sheet, the fracture area of the coating surface is less than 50% of the total coating area, or the tensile bonding strength of the adhesive itself is less than 50 MPa, the test is invalid.

[0027] The calculation of the bonding strength of the coating according to the end area and the fracture load includes:

[0028]

[0029] Among them, σb represents the bonding strength of a single effective coating; F represents the failure load of a single effective specimen; A represents the end face area of the specimen.

[0030] A specimen for detecting the bonding force of a coating, which is used for the detection method described in any one of the present invention.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention discloses a method for detecting the bonding strength of a coating. Two specimens are bonded through an adhesive sheet by an adhesive bonding method, and the adhesive is directly bonded to the coating. The critical stress at which the interface between the coating and the substrate cracks is measured to determine its bonding strength. The bonding strength of the coating and the substrate interface can be calculated intuitively and accurately according to the test conditions. Based on the calculated data, the quality of the coating and the matching between the coating and the environment can be better evaluated, improving the service quality of subsequent workpieces, extending the lifespan of the workpieces, and avoiding flight failures during use.

[0033] Furthermore, in the specimens disclosed in the present invention, adjacent specimens are connected through the coating surface by an adhesive sheet, ensuring that fracture preferentially occurs at the coating-substrate interface rather than the adhesive layer, making the test more effective and the results more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0035] Figure 1 It is a schematic diagram of a typical specimen in the present invention.

[0036] Figure 2 It is a schematic diagram of a curing fixture in the present invention.

[0037] Figure 3 It is a schematic diagram of the loading of a tensile testing machine in the present invention.

[0038] Wherein: 1 - First loading fixture; 2 - Coating; 3 - Adhesive; 4 - Second loading fixture. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0040] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0041] It should be noted that like reference numerals and letters denote like items in the following figures, and thus, once an item is defined in one figure, it is not necessary to further define and explain it in subsequent figures.

[0042] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship in which the invention product is customarily placed during use, it is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, terms such as "first", "second", etc. are only used for distinguishing descriptions and cannot be construed as indicating or implying relative importance.

[0043] In addition, if the term "horizontal" appears, it does not mean that the component is required to be absolutely horizontal, but it can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but it can be slightly inclined.

[0044] In the description of the embodiments of the present invention, it should also be noted that unless otherwise clearly specified and limited, if terms such as "arranged", "installed", "connected", "coupled" are understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0045] The present invention will be further described in detail below with reference to the accompanying drawings:

[0046] See Figure 1 , an embodiment of the present invention discloses a method for detecting the coating adhesion force, which is used in the field of evaluating the coating adhesion force of titanium alloy blades of aeroengines. By determining an adhesive with a bonding strength greater than that of the coating, bonding it to a specimen with a coating that is convenient for applying a load, and determining its bonding strength by measuring the critical stress at which the interface between the coating and the substrate cracks, the method specifically includes the following steps:

[0047] Step 1: Specimen preparation

[0048] Step 1.1: Shape and size of the specimen

[0049] Each specimen consists of two loading fixtures, and the material of the fixture is the same as that of the part. The diameter of the fixture surface is φ25mm, and the fixture size is φ25mm×50mm. One end of the fixture is the bonding surface, and the other end has an M24 thread with a thread length of about 20mm. See the typical specimen. Figure 1 shown.

[0050] The roughness of all machined surfaces of the specimen is Ra≤3.2μm, the coaxiality of the loading fixture and the thread of the loading fixture is less than 0.08mm, the verticality of the two end faces of the loading fixture and the loading fixture is less than 0.08mm, and the coaxiality of the assembled specimen is less than 0.38mm.

[0051] Step: 1.2 Electroplating of the sample

[0052] Each test is conducted in groups of 3. Each sample is subjected to surface treatment on the bonding surface by selecting one of the loading fixtures. The specific operation method is to electroplate the sample alone or in the same tank with the part according to the part processing technology.

[0053] Step: 1.3 Specimen bonding

[0054] Steps: 1.3.1 Sand blasting

[0055] The bonding surface of the loading fixture of each sample that has not been surface treated is sandblasted, and the threads are protected before sandblasting.

[0056] Specifically, the sand blowing adopts dry sand blowing, the sand particles are 60-120 mesh aluminum oxide sand particles, the sand blowing pressure is 0.3-0.5Mpa, and the entire bonding surface after sand blowing should be a uniform gray sand blowing surface without metallic luster. Over-blowing to the side of the sample is allowed, and under-blowing is not allowed. The bonding should be completed within 2 hours after sand blowing, otherwise the sand blowing should be repeated.

[0057] Step: 1.3.2 Bonding

[0058] Step 1: Cleaning

[0059] Use acetone to clean the bonding surface of the sample. This is not necessary if the fresh sandblasted surface is not contaminated.

[0060] Step 2: Glue

[0061] Use FM-1000 adhesive sheet to stick on the bonding surface of the two loading fixtures, and place it on the curing fixture. The curing fixture has an inclination angle of 45 to 60°. For specific structure, see Figure 2 shown.

[0062] Furthermore, main components of the FM-1000 adhesive sheet include polyamide and epoxy resin.

[0063] Step 3: Curing

[0064] Put the bonded specimen together with the curing fixture into an air circulation furnace for curing. The specimen and the fixture are heated to 200 °C with the furnace and held for more than 2 h, and then air-cooled with the furnace.

[0065] Step 4: Cleaning

[0066] Take out the cured specimen and remove the residual binder around the specimen with sandpaper.

[0067] Step 2: Testing

[0068] Step 2.1: Tensile test of specimen

[0069] Put the bonded specimen on Figure 3 mount it on the tensile fixture. Both the first loading fixture 1 and the second loading fixture 4 are connected to the tensile testing machine. There is a coating 2 on the end face of the first loading fixture 1 close to the second loading fixture 4. The first loading fixture 1 and the second loading fixture 4 are connected by an adhesive 3.

[0070] Furthermore, after centering and placing it well on the tensile testing machine, conduct the tensile test. The tensile testing machine should be equipped with a universal joint that can automatically adjust the coaxiality, and the accuracy of the testing machine is ±1%. The tensile rate is 1 mm / min. After the specimen breaks, record the fracture load and fracture condition of each specimen.

[0071] Step 2.2: Result evaluation

[0072] The judgment basis for the effective fracture form is:

[0073] If the entire coating breaks away from the substrate, the tensile test is valid.

[0074] If there is an interlayer fracture in the coating, specifically observe:

[0075] If there is at least one specimen with a non-effective fracture between the adhesives, specifically: fracture occurs on the bonding sheet, and the fracture area of the coating layer is less than 50% of the total area of the coating layer, then the test is invalid.

[0076] If the tensile bonding strength of the adhesive itself is less than the corresponding required value, the test result is invalid, specifically when the tensile bonding strength of the adhesive itself is less than 50 MPa.

[0077] Step 3: Calculation

[0078] Step 3.1: Coating bonding strength of a single effective specimen:

[0079] The bonding strength of a single effective specimen is calculated according to Equation (1):

[0080]

[0081] In Equation 1:

[0082] σb represents the effective bonding strength of a single coating, in megapascals (MPa);

[0083] F represents the breaking load of a single valid specimen, in Newton (N);

[0084] A represents the end surface area of the sample, in square millimeters (mm2).

[0085] The method disclosed in the embodiment of the present invention can intuitively and accurately give the bonding strength of the interface between the coating and the substrate, which is of great significance for evaluating the quality of the coating, optimizing the electroplating process and evaluating the compatibility of the coating with the engine use environment.

[0086] It should be noted that the sample in this embodiment is the loading fixture.

[0087] The present invention discloses a specific embodiment:

[0088] The titanium alloy silver-plated blade of a certain machine, after the silver plating was qualified and delivered, the silver layer fell off many times during the engine test. In order to avoid the problem of silver layer falling off again, it is intended to perform sand blowing before silver plating. In order to verify the influence of dry sand blowing and wet sand blowing on the bonding strength of the silver layer, the bonding strength of the silver layer after dry sand blowing and wet sand blowing is tested according to the method disclosed in the present invention, which specifically includes the following steps:

[0089] Step 1: Sample preparation

[0090] Step 1.1 Specimen shape and size

[0091] Each specimen is composed of two loading fixtures, and the material of the fixtures is in the same state and material as the parts.

[0092] Specifically, the diameter of the fixture surface is φ25mm, the fixture size is φ25mm×50mm, one end of the fixture is the bonding surface, and the other end has an M24 thread with a thread length of about 20mm. Figure 1 shown.

[0093] Furthermore, the roughness of all machined surfaces of the sample is Ra≤3.2μm, the coaxiality of the loading fixture and the thread of the loading fixture is less than 0.08mm, the verticality of the two end faces of the loading fixture and the loading fixture is less than 0.08mm, and the coaxiality of the assembled sample is less than 0.38mm.

[0094] Step 1.2: Surface preparation of the specimen

[0095] Three samples form a group for each test, and two groups of samples are prepared, of which the first group is dry sandblasting and the second group is wet sandblasting. Each sample selects one of the loading fixtures to perform surface treatment on the bonding surface. Specific operation method:

[0096] (1) Thread protection

[0097] Use insulating tape to protect the threads.

[0098] (2) Blasting

[0099] Perform dry blasting on the first group of specimens. The abrasive grains are alumina abrasive grains with a mesh size of 120 - 220, and the blasting pressure is 0.2 - 0.3 MPa.

[0100] Perform wet blasting on the second group of specimens. The abrasive grains are alumina abrasive grains with a mesh size of 120 - 220, the blasting pressure is 0.2 - 0.3 MPa, and the ratio of abrasive to water is ≥2 Kg : 10 L.

[0101] (3) Silver plating

[0102] Silver plate the blasted loading fixtures according to the part processing technological process. The main technological parameters for silver plating are shown in Table 1.

[0103] Table 1 Main technological parameters for silver plating

[0104]

[0105] Step 1.3: Specimen bonding

[0106] Step 1.3.1: Blasting

[0107] Blast the bonding surface of the loading fixture of each specimen that has not been surface - treated. Protect the threads before blasting.

[0108] Use dry blasting. The abrasive grains are alumina abrasive grains with a mesh size of 60 - 120, the blasting pressure is 0.3 - 0.5 Mpa. After blasting, the entire bonding surface should be a uniformly gray blasted surface that has lost its metallic luster. Over - blasting to the side of the specimen is allowed, but under - blasting is not allowed. Bonding should be completed within 2 hours after blasting. Otherwise, re - blasting is required.

[0109] Step 1.3.2: Bonding

[0110] (1) Cleaning

[0111] Clean the bonding surface of the specimen with acetone. If the freshly blasted surface is not contaminated, this step can be omitted.

[0112] (2) Gluing

[0113] Use FM - 1000 adhesive sheets to stick on the bonding surfaces of the two loading fixtures, and place them on the curing fixture, as shown in Figure 2 Figure [figure number not provided]. The main components of the FM - 1000 adhesive sheets are polyamide and epoxy resin.

[0114] (3) Curing

[0115] Put the bonded specimen together with the curing fixture into an air circulation furnace for curing. The specimen and the fixture are heated in the furnace to 200 °C and kept at this temperature for more than 2 h, and then cooled in the furnace to room temperature.

[0116] (4) Cleaning

[0117] Take out the cured specimen and remove the residual binder around the specimen with sandpaper.

[0118] Step 2: Testing

[0119] Step: 2.1 Tensile test of the specimen

[0120] Place the bonded specimen on the tensile fixture. After centering it on the tensile testing machine, conduct the tensile test. The tensile testing machine should be equipped with a universal joint that can automatically adjust the coaxiality, and the accuracy of the testing machine is ±1%. The tensile rate is 1 mm / min. After the specimen breaks, record the breaking load and the failure mode of each specimen. Figure 3

[0121] Step: 2.2 Result evaluation

[0122] The criteria for judging the effective failure mode are as follows:

[0123] (1) If the coating breaks completely from the substrate, the test is valid.

[0124] (2) Interlayer fracture of the coating.

[0125] If there is at least one specimen with a non-effective failure between the adhesives, specifically: fracture occurs on the bonding sheet, and the fracture area of the coating layer is less than 50% of the total area of the coating layer, then the test is invalid.

[0126] If the tensile bonding strength of the adhesive itself is less than the corresponding required value, the test result is invalid, specifically when the tensile bonding strength of the adhesive itself is less than 50 MPa.

[0127] Evaluation result: All specimens break from the substrate, and the test is valid.

[0128] Furthermore, the calculated results of the bonding strength of a single effective specimen are as follows:

[0129] Group 1: 45 MPa, 47 MPa, 42 MPa;

[0130] Group 2: 35 MPa, 38 MPa, 19 MPa.

[0131] ​The numerical value of the coating adhesion can be quantified and used for optimizing the coating process and verifying the compatibility between the coating and the service environment. The fracture load is obtained through a tensile test, and the adhesion strength (σ = F / A) is calculated by combining with the end area, upgrading the traditional qualitative detection (such as the scratch method) to a quantitative evaluation. The obtained numerical indicators can establish a coating performance database to provide data support for process optimization. By using this method, unqualified products can be screened out in advance, reducing the risk of wear failure caused by coating spalling.

[0132] This embodiment also discloses a specimen for detecting the coating adhesion, which is used for the detection method described in any one of this embodiment.

[0133] The specimen disclosed in this embodiment connects two adjacent specimens through the coating surface by bonding, ensuring that fracture preferentially occurs at the coating-substrate interface rather than the adhesive layer, with higher test effectiveness and more accurate results.

[0134] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A detection method for the bonding strength of a coating, characterized in that, It includes the following steps: Form a plating layer at one end of the specimen, bond two adjacent specimens to form a specimen group; After clamping and fixing the specimen group, cure and cool it in sequence; Conduct a tensile test on the cooled specimen group until the specimens break and separate, record the fracture load and fracture mode of each specimen, judge whether the test is valid according to the fracture mode. If it is valid, measure the end area of the specimen, and calculate the bonding strength of the plating layer based on the end area and the fracture load. If the test is invalid, conduct the test again.

2. The detection method for coating adhesion according to claim 1, wherein, The step of forming a plating layer at one end of the specimen and bonding two adjacent specimens through the plating layer to form a specimen group includes: One end of the specimen is the bonding surface, and the other end is the thread. Plate the bonding surface to form a plating layer; Clean the plating layer, bond two adjacent specimens with an adhesive sheet to form a specimen group.

3. The detection method for coating adhesion according to claim 2, characterized in that, The roughness Ra of the bonding surface ≤ 3.2μm.

4. The detection method for coating adhesion according to claim 2, characterized in that, It also includes sandblasting the bonding surface: Conduct sandblasting in the dry sandblasting method; When sandblasting, the abrasive grains are aluminum oxide with 60 - 120 meshes, and the sandblasting pressure is 0.3 - 0.5 Mpa; Conduct specimen bonding within two hours after the sandblasting ends.

5. The detection method for coating adhesion according to claim 2, wherein, The step of bonding two adjacent specimens with an adhesive sheet includes: Use FM - 1000 adhesive sheet to bond the plating layers of two adjacent specimens together.

6. The detection method for coating adhesion according to claim 1, wherein, The step of clamping and fixing the specimen group and then curing and cooling it in sequence includes: Put the bonded specimen group into a curing fixture, put the curing fixture and the specimen group into an air circulation furnace for curing together, and then cool it in the furnace with the furnace when the curing ends.

7. A detection method for the bonding force of a plating layer according to claim 6, wherein When curing, the temperature is 150 - 200°C and the time is greater than 2h.

8. A detection method for the bonding force of a plating layer according to claim 1, wherein The step of judging whether the test is valid according to the fracture mode includes: When breaking, if the plating layer breaks from the specimen, the test is valid and the subsequent calculation process is carried out. If the break occurs on the adhesive sheet, the fracture area of the plating layer is less than 50% of the total area of the plating layer, or the tensile bonding strength of the adhesive itself is less than 50 MPa, the test is invalid.

9. A method for detecting the adhesion of a coating according to claim 1, characterized in that, The step of calculating the bonding strength of the plating layer based on the end area and the fracture load includes: Wherein, σb represents the bonding strength of a single effective coating; F represents the failure load of a single effective specimen; A represents the end area of the specimen.

10. A specimen for detecting the adhesion of a coating, characterized in that, For the detection method according to any one of claims 1 - 9.

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