CN115078086A - Method for measuring bonding force between metal matrix and oxide film by using SEM (scanning electron microscope) in-situ tensile instrument - Google Patents
Method for measuring bonding force between metal matrix and oxide film by using SEM (scanning electron microscope) in-situ tensile instrument Download PDFInfo
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Abstract
A method for measuring the bonding force of a metal matrix and an oxide film interface based on an SEM (scanning electron microscope) in-situ tensile instrument aims at providing an in-situ tensile method for quantitatively measuring the bonding force of the metal matrix and the oxide film, and the method can reveal the cracking process and mechanism analysis of a plastic metal matrix and brittle oxide film system. The method comprises the following steps: firstly, preparing and pretreating a sample; secondly, in-situ tensile experiment of the sample is carried out, and a displacement-tension curve and corresponding data are recorded; thirdly, measuring the stress-strain curve of the substrate material without the oxide film in the same temperature environment and recording data; fourthly, calculating the tensile strength sigma of the oxide film in the stable state of the crack density f (ii) a Fifth, substituting the parameters into the formula
Description
Technical Field
The invention relates to a method for measuring binding force based on SEM in-situ stretching, in particular to a method for measuring the binding force of a metal matrix and an oxide film interface by using an SEM in-situ stretching instrument.
Background
Improving energy conversion efficiency and reducing CO 2 Emissions have been a goal pursued by the energy and power industry. The temperature and the pressure of the main steam are improved, and the energy conversion efficiency can be effectively improved. However, the high temperature service performance of metal materials limits the development of advanced energy conversion systems, in which critical components of the high temperature boiler are supercritical CO at high temperature and high pressure 2 The problems of oxidation and carbonization corrosion of the environment are particularly critical, and the supercritical CO is directly influenced by overtemperature and tube explosion caused by the over-quick oxidation and peeling of the high-temperature heating surface pipeline of the boiler 2 The development of a novel power generation technology of the Brayton cycle. Therefore, the measurement of the bonding force of the oxide film and the matrix in the service environment of the unit can help to predict the peeling condition of the oxide skin of the high-temperature component, and can effectively reduce overtemperature and pipe explosion accidents caused by peeling.
Most of the existing measuring methods are qualitative measurement, the oxide film combination strength is defined by passing or failing, such as bending method, pressing method, scratch experiment and other methods, the methods can not give quantitative values, and the method has limited guiding significance to field engineering. Liu et al (H.Y.Liu, Y.G.Wei, L.H.Liang, X.H.Liu, Y.B.Wang, H.S.Ma.Damage characteristics model of ceramic coating system based on quantitative damage and bonding tests [ J ]. Ceramics International,2018,44(5):4807-4813.) disclose a method for constructing a ceramic coating system quantitative damage model based on a three-point bending method, which is limited in that it is only applicable to a weak interface system, and the method cannot effectively measure the interface bonding performance when the interface bonding strength of the film and the substrate is higher than the bonding strength of an adhesive. Song et Al (SONG Y N, XU B S, WANG H D, et Al. failure Process Analysis of Plasma Sprayed Coatings under Tip Load Based on Acoustic Emission Signals [ J ]. Surface Engineering,2014,30(9):675-682.) measured the interface binding strength by performing a Surface indentation test on 3 different binding strength Coatings, such as Al2O3, Al2O3-TiO2 and FeCrBSi, analyzing and extracting the distribution characteristics of the amplitude and energy of the Acoustic Emission signal during the test, and combining the indentation method with the Acoustic Emission technology. The bonding strength is measured by a pure press-in method, the press-in load is fixed, the critical load when the film is peeled off cannot be accurately obtained, and the added quality standard is divided into general systems, so that the method is only used as qualitative representation of the bonding strength of the film. Lu et al (Ping Lu, Humberto Gomez, Xingcheng Xiao, Michael Lukitsch, Delcie Durham, oil Sachde, Ashock Kumar, Kevin Chou, Coating thickness and interlayer effects on CVD-diamond film addition to coated treated CVD diamond films [ J ] Surface and Coatings Technology,2013,215:272 and 279.) have found that the interfacial bond strength obtained using the scratch method correlates approximately linearly with positive film thickness, i.e., increases with increasing film thickness. Therefore, the physical significance of the critical load measured by the scratching method is not clear, and even the scholars think that the critical load Lc of the scratching method has no definite relation with the interface bonding performance and only reflects the bearing capacity of the film-based system.
The matrix stretching method based on the SEM in-situ stretcher can not only adjust the moving speed of the stretching table and simulate the actual running temperature of the sample, but also reflect the condition of the oxide film on the surface of the sample in real time, and is beneficial to mastering the growth and the diffusion of the oxide film cracks at the target position under the actual working condition, so that the accuracy of the overall measurement is improved, and the final measurement result is more fit with the actual condition.
Disclosure of Invention
The invention provides a method for measuring the interface binding force of a metal matrix and an oxide film by utilizing an SEM (scanning electron microscope) in-situ stretching instrument, which can control the stretching rate and observe the cracking condition of a surface oxide layer in real time, and has the advantages of practical measurement result fitting and good accuracy.
A test method for measuring the bonding force of an interface of a metal matrix and an oxide film by utilizing an SEM in-situ tensile tester comprises the following specific implementation steps:
step 1: preparing in-situ stretched metal samples:
selecting strip-shaped plastic metal as a sample, wherein the specific shape is that two sides are wide and the middle is narrow, and U-shaped gaps are prefabricated at two sides of the center of the sample;
step 2: pretreatment of the sample:
grinding and polishing the sample to further level the surface; cleaning and drying the flat sample, and then carrying out a corrosion experiment to generate an oxide film;
and step 3: in-situ tensile experiments were performed:
fixing a test sample on a clamp of an in-situ stretching table, installing the in-situ stretching table in an SEM sample chamber after the fixing is finished, and observing the full appearance of a U-shaped notch through a scanning electron microscope when the test sample on the in-situ stretching table is installed in the SEM sample chamber;
and 4, step 4: carrying out data processing by carrying in parameters: firstly, the tensile strength sigma of the oxide film when the crack density reaches the steady state is calculated f Wherein it is calculated as
Wherein S 1 Is the cross-sectional area, S, of the oxide film with a thickness of delta 2 Is the cross-sectional area of the non-oxidized substrate, S 3 The cross-sectional area of the substrate material without the oxide film.
The invention also discloses a method for measuring the bonding force of the interface of the metal matrix and the oxide film by using the SEM in-situ tensile tester, which is applied to the design of the high-temperature heating surface pipeline of the boiler.
Has the advantages that:
the invention is based on an SEM in-situ tensile instrument, and utilizes an in-situ tensile sample with special size and shape to carry out a matrix tensile method, so as to test the bonding strength between the brittle oxide film and the plastic metal matrix.
By means of the real-time image of the scanning electron microscope and the specific stretching speed of the in-situ stretcher, the process from crack initiation to complete fracture of the brittle oxide film and the plastic metal matrix system can be clearly observed. Through the observation of a scanning electron microscope, the whole process that the surface crack of the brittle oxidation film of the oxidized sample is initiated, expanded and contracted until the system is completely broken in the stretching process is recorded by utilizing the real-time video recording function of the scanning electron microscope. Meanwhile, the stretching speed of the in-situ stretching table is controlled in real time through computer software, and a displacement-tension curve of the sample in the stretching process is obtained for subsequent analysis of the mechanical property of the sample. And (3) by integrating the microstructure observed by a scanning electron microscope and the displacement-tension curve characterization result recorded by software in the in-situ tensile experiment process, the splitting mechanism between the brittle oxidation film and the plastic metal matrix is disclosed, and a reference basis is provided for corrosion and failure of the material in a supercritical carbon dioxide environment. The method is suitable for measuring the interface bonding strength of all brittle oxide films and plastic metal matrix systems.
Drawings
FIG. 1 is a schematic flow chart of the present invention.
FIG. 2 is a schematic view of an SEM in-situ tensile specimen as set forth in step 1 of the present invention.
Fig. 3 is a displacement-tension curve obtained by performing an in-situ tensile test on a sample.
FIG. 4 shows the micro-morphology of the oxide film with an in-situ tensile rate of 0.769%.
FIG. 5 shows the micro-morphology of the oxide film with an in-situ elongation of 2.516%.
FIG. 6 shows the micro-morphology of the oxide film with an in-situ elongation of 3.422%.
Detailed Description
A test method for measuring the bonding force of the interface of a metal substrate and an oxide film by using an SEM in-situ tensile tester is characterized in that: the method comprises the following steps:
step 1: preparing an in-situ stretched metal sample;
selecting strip-shaped plastic metal as a sample, wherein the specific shape is that two sides are wide and the middle is narrow, and U-shaped gaps are prefabricated at two sides of the center of the sample;
total length L of the metal substrate 1 45mm, width W 1 The thickness H is 0.8mm, and the radius R of the four arc chamfers is 10 +/-0.1 mm;
the experimental area of the metal is a U-shaped notch with a length L 2 8mm, width W 2 2.5mm, thickness H is 0.8mm, and prefabricated U type breach degree of depth is transition fillet radius, and transition fillet radius R is 30 ± 0.1 mm.
The dimensions and the shape of the test specimen are shown in FIG. 2. The U-shaped notch is prefabricated to meet the requirement of an SEM observation visual field, other types of notches are selected to exceed the SEM observation range, and if cracks occur in the range exceeding the visual field in the stretching process, the cracks cannot be observed, so that errors occur in the stress-strain data records of the initial cracks. The sizes of the prefabricated metal matrix and the U-shaped notch are comprehensively considered by the size of the in-situ stretching table. If the length and the thickness are smaller, the clamp of the stretching table cannot firmly fix the sample, so that the sample falls under the stretching table in the stretching process, and the experiment fails; if the length and thickness are too large, the maximum dimension that the stretching table can fix and the stroke of the stretching table are exceeded, and the experiment cannot be performed. The data selected in the experiment is the moderate size selected on the basis of considering the SEM visual field, the size of a clamp of the stretching table and the stroke of the stretching table, so that the experiment can be ensured to be carried out smoothly, and the optimal observation visual field, the maximum stroke distance and the most stable fixation can be realized.
Step 2: pretreatment of the sample:
(1) grinding two sides of the sample by using 500#, 800#, 1000# and 1500# sandpaper, and then polishing by using diamond grinding paste with the particle size of 1 mu m to further level the surface;
(2) putting the operated sample into a beaker containing absolute ethyl alcohol, putting the beaker into an ultrasonic cleaning instrument to clean for 5 minutes, and taking out and drying;
(3) and putting the cleaned sample into a sealed high-pressure reaction kettle at 650 ℃ and 25Mpa in a supercritical carbon dioxide environment for 800-hour corrosion experiment to generate an oxide film.
The reason for selecting the type of sandpaper in (1) is: the surface of the processed sample is rough, and sand paper is needed for polishing so that a subsequent oxide film can be perfectly attached and observed in a square deformation manner; the selection of the 500# initial sand paper is to consider that the initial surface roughness of the sample is not very large, and the selection of the 500# initial sand paper is less than that of the 500# initial sand paper, so that deep scratches can be generated on the surface of the sample, and the later observation is not facilitated. The gradient polishing mode is adopted to gradually level the surface of the sample, and if the parameter difference of the abrasive paper is too large, scratches on the surface are difficult to level, so that the adhesion and observation of an oxide film are not facilitated.
And the absolute ethyl alcohol is selected for cleaning for 5 minutes, so that impurities generated by polishing on the surface can be washed, and compared with clear water, the absolute ethyl alcohol contains fewer impurities and cannot cause secondary residue of the impurities. Cleaning for 5 minutes is a reasonable time, and the time is increased again, so that the impurities are not obviously cleaned, and the efficiency is low.
The service environment of the supercritical carbon dioxide unit is mostly 650 ℃ and 25Mpa, and the corrosion in the environment can restore the real service environment to the maximum extent, so that the result has more confidence level. Considering the size of the sample, 800 hours is enough to generate a significant oxide film, the growth rate of the carbonized layer is extremely slow, and the thickness of the carbonized layer can be increased by continuously increasing the time, but the increase degree is small, and the influence on the experimental result can be small.
And step 3: in-situ tensile experiments were performed:
fixing the prepared sample on a clamp of an in-situ stretching table, installing the in-situ stretching table in an SEM sample chamber after the fixing is finished, and when the sample on the in-situ stretching table is installed in the SEM sample chamber, the full view of the U-shaped notch can be seen through a scanning electron microscope;
sealing the sample chamber and vacuumizing, heating the sample by using an electric heating mode after ensuring that the sample chamber is vacuum, setting the stretching speed of an in-situ stretching table to be 1 mu m/s after the target temperature is reached to 650 ℃, and starting stretching; the stretching speed of 1 mu m/s ensures that an observer can clearly catch the process of crack growth, and the efficiency and the effect are ensured;
in the in-situ stretching process, the growth and the expansion process of oxide film cracks are observed, the cracks are firstly initiated at the upper and lower boundaries of the oxide film, because the oxide film grown at the boundaries generates a large number of cavities due to the position limitation, the growth resistance of the cracks is reduced, and the cracks are expanded along the directions with many hole defectsAnd (6) unfolding. And recording a displacement-tension curve in real time, and collecting videos, pictures and the displacement-tension curve in the experimental process. The displacement-tension curve of the experiment is shown in figure 3, the displacement-tension curve reflects the relation between the tension applied to the sample and the deformation displacement of the sample, the tension is divided by the sectional area of the U-shaped notch to obtain the stress, and the sectional area is W 2 *L 2 (ii) a The strain can be obtained by dividing the displacement by the initial length of the U-shaped notch, wherein the initial length of the U-shaped notch is L 2 。
The change of the bonding strength between the metal substrate and the oxide film, fig. 4 shows the microstructure of the oxide film with an in-situ tensile rate of 0.769%, at this time, a crack just appears on the surface of the oxide film, it can be considered that the oxide film and the substrate begin to separate, the corresponding tensile force at this time of fig. 4 is 446.505N, that is, the stress is 22.325Mpa, the corresponding displacement is 345 μm, that is, the strain is 0.0431, and the stress and the strain at this time are recorded; FIG. 5 shows a microstructure of an oxide film with an in-situ tensile rate of 2.516%, wherein the tensile state is a strengthening stage, uniform plastic deformation occurs, whether new cracks are initiated or not needs to be noticed, and after the stage, a sample can quickly enter a local deformation stage, and the number of cracks is stable; fig. 6 shows the microstructure of the oxide film with an in-situ tensile rate of 3.422%, at this time, the oxide film is stressed to the top, the number of cracks is stable, the tensile force at this time is 596.731N, namely, the stress is 29.837Mpa, the corresponding displacement is 1539 μm, namely, the strain is 0.192, and the stress and the strain at this time are recorded.
And 4, step 4: carrying out data processing by carrying in parameters:
substituting into formulas based on collected data
And calculating the shearing force of the interface.
The formula is derived as follows: tensile stress σ (x) versus interfacial shear τ (x):
delta is the film thickness. Then for analysis, the interfacial shear force τ (x) is calculated as a sinusoidal distribution, then
λ 1 Is epsilon 1 Maximum crack spacing of time, σ f Is the tensile strength of the image layer,
wherein S 1 Is the cross-sectional area, S, of the oxide film having a thickness of delta 2 Is the cross-sectional area of the non-oxidized substrate, S 3 Is the cross-sectional area of the substrate material without oxide film, F 2 Amount of strain ε at which crack density reaches steady state 2 When the tension is applied, the corresponding tension is applied,
measuring the strain quantity epsilon of the base material without the oxide film in the same temperature environment 2 Corresponding tension. In order to research the integral interface bonding strength and make the research phenomenon more obvious, the strain is properly increased to epsilon in the experiment 2 The number of cracks at this time reaches a stable value, and therefore the above formula
Is modified into
λ 2 Strain epsilon at which crack density is stabilized 2 The corresponding maximum crack spacing.
The invention provides a method for measuring the interface binding force of a metal matrix and an oxide film by utilizing an SEM (scanning electron microscope) in-situ stretching instrument, which introduces the preparation, pretreatment and experimental processes of a sample required by the method in detail.
The invention is characterized in that the total length L is prepared in the early stage 1 45mm, width W 1 The thickness H is 0.8mm, the radius R of the four arc chamfers is 10 +/-0.1 mm, the experimental area is a U-shaped notch, and the length L is the same as the length of the notch 2 8mm, width W 2 The method comprises the following steps of grinding, polishing and cleaning a metal sample with the prefabricated U-shaped notch depth of transition fillet radius and the transition fillet radius R of 30 +/-0.1 mm at the temperature of 650 ℃ and under the pressure of 25MPa for 800 hours to obtain an oxide film, wherein the thickness H of the metal sample is 2.5mm, and the thickness H of the metal sample is 0.8 mm. Carrying out in-situ tensile experiment on the sample which finishes the earlier stage work to obtain a stress-strain curve, and substituting the stress-strain curve into a formula
The bonding force between the oxide film and the substrate can be calculated quantitatively. The problem that the traditional method can only give a conclusion qualitatively is solved, and the numerical value quantification effect is realized. The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are merely illustrative of the principles of the invention, but that various changes and modifications may be made without departing from the spirit and scope of the invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (8)
1. A test method for measuring the bonding force of an interface of a metal matrix and an oxide film by utilizing an SEM in-situ tensile instrument is characterized by comprising the following steps: the method comprises the following steps:
step 1: preparing in-situ stretched metal samples:
selecting a strip-shaped plastic metal base body as a sample, wherein the specific shape is that two sides are wide and the middle is narrow, and U-shaped notches are prefabricated at two sides of the center of the sample;
step 2: pretreatment of the sample: grinding and polishing the sample to further level the surface; cleaning and drying the flat sample, and then carrying out a corrosion experiment to generate an oxide film;
and step 3: in situ tensile experiments were performed:
fixing a test sample on a clamp of an in-situ stretching table, installing the in-situ stretching table in an SEM sample chamber after the fixing is finished, and observing the full appearance of the U-shaped notch through a scanning electron microscope when the test sample on the in-situ stretching table is installed in the SEM sample chamber;
and 4, step 4: carrying out data processing by carrying in parameters: firstly, calculating the tensile strength sigma of the oxide film when the crack density reaches the steady state f The calculation expression is
Wherein S 1 Is the cross-sectional area, S, of the oxide film with a thickness of delta 2 Is the cross-sectional area of the non-oxidized substrate, S 3 Is the cross-sectional area of the substrate material without the oxide film, F 2 Amount of strain ε at which crack density reaches steady state 2 The corresponding tension force is generated when the steel wire is pulled,
measuring the strain quantity epsilon of the base material without the oxide film in the same temperature environment 2 Corresponding tension.
2. The method for testing the bonding force of the interface between the metal substrate and the oxide film by using the SEM in-situ tensile tester as claimed in claim 1, wherein: the step 1 further comprises the following steps:
total length L of the metal substrate 1 45mm, width W 1 The thickness H is 0.8mm, the upper chamfer and the lower chamfer from the left edge to the transition area and the upper chamfer and the lower chamfer from the right edge to the transition area are four circular arc chamfers, and the radius R is 10 +/-0.1 mm;
the experimental area of the metal matrix is a U-shaped notch, and the length L of the notch 2 8mm, width W 2 2.5mm, thickness H is 0.8mm, and prefabricated U type breach degree of depth is transition fillet radius, and transition fillet radius R is 30 ± 0.1 mm.
3. The method for testing the bonding force of the interface between the metal substrate and the oxide film by using the SEM in-situ tensile tester as claimed in claim 1, wherein: the two sides of the metal sample were ground with 500#, 800#, 1000# and 1500# sandpaper in this order, and then polished with diamond paste having a particle size of 1 μm to further smooth the surface.
4. The method for testing the bonding force of the interface between the metal substrate and the oxide film by using the SEM in-situ tensile tester as claimed in claim 3, wherein: putting the operated sample into a beaker containing absolute ethyl alcohol, putting the beaker into an ultrasonic cleaning instrument to clean for 5 minutes, and taking out and drying; and putting the dried sample into a sealed high-pressure reaction kettle at 650 ℃ and 25Mpa in a supercritical carbon dioxide environment for 800-hour corrosion experiment to generate an oxide film.
5. The method for testing the bonding force of the interface between the metal substrate and the oxide film by using the SEM in-situ tensile tester as claimed in claim 1, wherein: the step 3 further comprises the following steps: and (3) sealing the sample chamber and vacuumizing, heating the sample by using an electric heating mode after ensuring the vacuum in the sample chamber, setting the stretching speed of the in-situ stretching table to be 1 mu m/s after the target temperature is reached, and starting to perform in-situ stretching.
6. The method for testing the bonding force of the interface between the metal substrate and the oxide film by using the SEM in-situ tensile tester as claimed in claim 5, wherein: in the in-situ stretching process, the growth and the expansion process of oxide film cracks are observed, a displacement-tension curve is recorded in real time, videos, pictures and the displacement-tension curve in the experimental process are collected, and the change condition of the bonding strength between the metal matrix and the oxide film is analyzed.
7. The method for testing the bonding force of the interface between the metal substrate and the oxide film by using the SEM in-situ tensile tester as claimed in claim 1, wherein: the step 4 further comprises the following steps: substituting the above expression into formula
Wherein tau is the shearing stress of the interface of the metal matrix and the oxide film and is the bonding force of the metal matrix and the oxide film; delta is the thickness of the oxide film; sigma f For oxidation ofTensile strength of the film, ε 1 E is the amount of strain at which cracks appear, and E is the elastic modulus of the oxide film; lambda [ alpha ] 1 To strain epsilon 1 Maximum crack spacing in time;
λ 2 strain epsilon to stabilize crack density 2 Maximum crack spacing of (d).
8. The method for testing the bonding force of the interface between the metal matrix and the oxide film by using the SEM in-situ tensile tester, which is disclosed by any one of claims 1 to 7, is applied to the design of a high-temperature heating surface pipeline of a boiler.
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| CN116793829B (en) * | 2023-03-17 | 2023-12-05 | 北京建筑大学 | Evaluation method for mechanical properties of brittle solid material in direct tensile fracture |
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