Preparation method of micro-cantilever sample with precracks for testing fracture toughness of micro-nano material
By adjusting the energy parameters of the ion beam to control the prefabricated crack morphology of microcantilever beams, the problem of uncontrollable prefabricated crack morphology in the preparation of microcantilever beam samples is solved, and a fracture toughness test with high repeatability and reliability is achieved.
Patent Information
- Application Number
- CN202510632506.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-16
- Publication Date
- 2025-08-05
AI Technical Summary
In the preparation process of micro-cantilever beam samples in the prior art, the morphology of prefabricated cracks is uncontrollable, the morphology is characterized blind spots, and the dependence of equipment status results leads to poor repetition and comparableity of test results, making it difficult to achieve high-reliability fracture toughness testing.
By adjusting the ion beam energy parameters under the focused ion beam system, controlling the tip radius, opening and depth of prefabricated cracks, establishing a mapping relationship between process parameters and crack morphology, ensuring the repeatability and consistency of prefabricated crack morphology.
The repeatability of prefabricated crack morphology of micro-cantilever beam specimens is significantly improved, and the standard deviation of slope of elastic segment of the load-displacement curve is reduced to σ≤0.4, which improves the reliability and repeatability of fracture toughness tests.
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Figure CN120427341A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for preparing a micro-cantilever beam sample with pre-cracks for testing the fracture toughness of micro-nano materials, and belongs to the technical field of micro-nano materials. Background Art
[0002] The core principle of microcantilever technology is to induce pre-existing crack propagation by applying a controllable load to a micron-sized cantilever beam, and then calculate the fracture toughness of the material using fracture mechanics theory. This precise method for measuring fracture toughness is suitable for small samples at the micron or nanometer scale and has been widely applied in various fields, particularly in materials science, microelectronics, and advanced manufacturing.
[0003] Currently, there is no research on the preparation of microcantilever beams with pre-cracks. In microcantilever beam testing, the accuracy of mechanical performance parameters such as fracture toughness is highly dependent on the morphology of the pre-crack. Studies have shown that when multiple groups of microcantilever beam specimens with pre-cracks are prepared using focused ion beam (FIB) equipment with different ion sources, there are significant differences in the fracture toughness test results. This is mainly attributed to the difference in the pre-crack tip radius r caused by the differences in sputtering yield and beam density of different ion sources. t However, in the existing sample preparation process, crack morphology control has the following technical defects:
[0004] (1) Morphology uncontrollability: Under the same ion source and fixed parameters, it is sometimes impossible to completely reproduce the prefabricated crack morphology.
[0005] (2) Blind spot of morphology characterization: When using FIB to prepare pre-cracks on the sample surface, the crack size can only be indirectly evaluated through the surface morphology, but it is impossible to monitor and directly evaluate the crack morphology in real time.
[0006] (3) Equipment state dependence: Factors such as ion source stability and beam calibration accuracy lead to increased discreteness of crack morphology in different equipment or under different working conditions of the same equipment, which seriously reduces the repeatability and comparability of test results.
[0007] During microcantilever specimen preparation, the actual beam current can vary somewhat from the set value. This results in poor repeatability even when using the same equipment. Current processes attempt to standardize pre-fabricated cracks by fixing FIB sample preparation parameters or reproducing the actual beam current. However, data from repeated experiments show significant differences in the slope of the elastic segment of the load-displacement curve between the pre-test and the repeated experiment. Summary of the Invention
[0008] In view of this, the object of the present invention is to provide a method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials.
[0009] To achieve the above objectives, the technical solutions of the present invention are as follows.
[0010] A method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials, the method comprising the following steps:
[0011] (1) Under the focused ion beam system, the surface of the micro-nano material sample is cut to obtain a micro-cantilever beam with a target prefabricated crack, and the morphological parameters of the target prefabricated crack are obtained, including the target crack tip radius r t , target crack opening w and target crack depth a;
[0012] (2) Changing the ion beam energy parameters to perform multiple wire cuttings on the surface of the sample to be reproduced to form a reproduced pre-crack, and obtaining the morphological parameters of each reproduced pre-crack, including the radius of the reproduced crack tip r t ', the recurring crack opening w' and the recurring crack depth a';
[0013] (3) Calculate the deviations between the morphological parameters of the target prefabricated crack and the morphological parameters of each reproduced prefabricated crack, and prepare a microcantilever beam with a prefabricated crack on the sample to be reproduced using the ion beam energy parameter with the minimum deviation.
[0014] Furthermore, in step (1), under a focused ion beam system, the sample surface is first cut to obtain a sheet-like positioning piece with a smooth surface and a thickness greater than the target thickness on the sample; then, a wire cutting is performed on one end of the positioning piece close to the sample to obtain a positioning piece with a prefabricated crack; finally, the positioning piece with the prefabricated crack is cut according to the set size of the cantilever beam to obtain a micro cantilever beam with a target prefabricated crack.
[0015] Furthermore, the focused ion beam system uses Ga as the ion source, with an ion beam acceleration voltage of 25-30 keV. When cutting sheet-shaped spacers, the beam current decreases gradually over time from 20-25 nA to 2-2.5 nA. Using a high beam current early in the process improves cutting efficiency, while using a low beam current later in the process facilitates cross-section correction, ensuring a smooth surface.
[0016] Furthermore, the thickness of the sheet-shaped positioning sheet is 4 to 5 μm greater than the target thickness.
[0017] Furthermore, the distance between the prefabricated crack on the positioning piece and the sample substrate is 1 to 2 μm.
[0018] Furthermore, in step (2), the ion beam energy parameters include acceleration voltage V, beam current I and irradiation time t.
[0019] Furthermore, the acceleration voltage V varies in the range of 5 to 30 keV, the beam current I varies in the range of 5 pA to 0.1 nA, and the irradiation time t varies in the range of 20 to 60 s.
[0020] Furthermore, the sample in step (1) and the sample to be reproduced in step (2) are respectively made of metal or alloy materials. The two can be made of the same material, in which case the morphology and performance of the prefabricated crack can be repeated to obtain a cantilever beam sample with high performance and morphology repeatability, which can then be used to characterize different properties of the sample. The two can also be made of different materials, in which case a cantilever beam sample with a small deviation in the morphology of the prefabricated crack can be obtained.
[0021] Furthermore, in step (3), the calculation formula of the deviation Δ is as follows:
[0022]
[0023] Furthermore, in step (3), the deviation is less than 10.
[0024] Beneficial effects
[0025] This invention provides a method for preparing pre-cracked microcantilever beam specimens for testing the fracture toughness of micro-nanomaterials. The method characterizes the specific crack morphology by measuring the tip radius, crack opening, and crack depth. Ion beam parameters are then varied to control the pre-crack morphology. This ensures similar crack morphology and sample characteristics between repeated and verified tests, resulting in highly reproducible fracture toughness values obtained from microcantilever fracture testing. The core principle is to systematically adjust ion beam energy parameters, combine quantitative characterization of crack cross-sectional morphology (tip radius, crack opening, and crack depth) with parameter matching, establish a "process parameter-crack morphology" mapping, and select a parameter combination that reproduces the target crack morphology. Ultimately, a microcantilever beam with a smaller pre-crack morphology is produced.
[0026] The method described in this paper can reduce the repeatability of the prefabricated crack tip radius from ~50% to <10%, and the relative errors of crack opening and crack depth from >10% and >30% to <5%, respectively. It also ensures that the standard deviation (σ) of the slope of the elastic segment of the load-displacement curve satisfies σ ≤ 0.4, significantly improving the repeatability of prefabricated crack morphology in microcantilever beams and the reliability of test results. The method is simple to operate and suitable for application in fields such as materials science, microelectronics, and advanced manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 This is a scanning electron microscope image of the surface after the positioning plate is cut using a high-energy focused ion beam in step (2) of Example 1.
[0028] Figure 2 This is a scanning electron microscope image of the separation of one end of the positioning plate from the substrate in step (3) of Example 1.
[0029] Figure 3In step (5) of Example 1, a scanning electron microscope image of a positioning plate with a pre-crack of target thickness was prepared using a high-energy focused ion beam at a sample stage tilt angle of 52 degrees.
[0030] Figure 4 This is an ion beam imaging image of the bottom edge of the positioning plate cut using a high-energy focused ion beam at step (6) of Example 1 at a sample stage tilt angle of 7 degrees.
[0031] Figure 5 The microcantilever sample was finally prepared in step (6) of Example 1 using a high-energy focused ion beam at a sample stage tilt angle of 52 degrees.
[0032] Figure 6 The morphology of the prefabricated cracks in step (1) of Example 2 is repeated.
[0033] Figure 7 Cross-sectional morphology monitoring of the multi-morphological prefabricated cracks in step (3) of Example 2 was performed.
[0034] Figure 8 The repeatability of the slope of the elastic section of the load-displacement curve (a) and the fracture toughness of the linear elastic deformation analysis (b) measured between the repeated and repeated experiments in Example 2. DETAILED DESCRIPTION
[0035] The present invention will be further described in detail below with reference to specific examples. The methods described are conventional methods unless otherwise specified, and the raw materials described can be obtained from public commercial channels unless otherwise specified.
[0036] In the following examples, the equipment used is the American FEI / Thermo Fisher FIB dual-beam scanning electron microscope Helios G4.
[0037] Example 1
[0038] (1) Use conductive tape to stick the back of the sample to be tested on the inclined surface of the SEM sample stage without tilt angle, and place it on the mechanical platform of the dual-beam electron microscope.
[0039] (2) The mechanical platform of the dual-beam electron microscope is tilted 52 degrees so that the high-energy focused ion beam is perpendicular to the sample surface on the sample stage. Then, two grooves are symmetrically cut on the sample surface using the high-energy focused ion beam, and a sheet structure with a thickness of about 10 μm and a length of about 20 μm and two flat surface positioning pieces are formed between the two grooves, such as Figure 1 The process conditions for high-energy focused ion beam cutting of the positioning piece are as follows: ion source Ga, ion beam acceleration voltage of 30keV, and beam current of 21nA.
[0040] (3) Cut one end of the positioning piece so that the end is separated from the substrate and cut to the target length of 10 μm, as shown in FIG. Figure 2 The process conditions for high-energy focused ion beam cutting are as follows: Ga ion source, 30 keV ion beam acceleration voltage, and beam current between 9.3 nA and 2.5 nA. The beam current decreases gradually with increasing cutting time. Using a high beam current in the early stages improves cutting efficiency, while using a low beam current in the later stages facilitates cross-section correction and ensures a smooth surface for the positioning piece.
[0041] (4) Under the set parameters, a 10 μm long wire cutting is performed on the positioning piece at a distance of 1-2 μm from the substrate to perform pre-crack cutting, and a high-energy focused ion beam is used to cut the positioning piece symmetrically on both sides, flatten the positioning piece cross section and cut the positioning piece to the target thickness, i.e., 2 μm. Figure 3 The process conditions for high-energy focused ion beam cutting are as follows: ion source Ga, ion beam acceleration voltage 30keV, and beam current 2.5-0.23nA.
[0042] (5) Tilt the mechanical platform of the dual-beam electron microscope to 7 degrees and use a high-energy ion beam to cut the bottom edge of the positioning piece, such as Figure 4 Then tilted to 52 degrees, cutting to form a single-sided micro cantilever beam sample with a pentagonal cross section of 10 μm in length, 2 μm in width, 2.5 μm in height and a pre-crack depth of 700 nm, as shown Figure 5 As shown; wherein, the process conditions for high-energy focused ion beam cutting the shape and size of the cantilever are as follows: ion source Ga, ion beam acceleration voltage is 30keV, and beam current is 0.79nA-80pA.
[0043] Example 2
[0044] In this embodiment, the sample to be tested is pure vanadium (V).
[0045] The cantilever beam sample was prepared in the same manner as in Example 1, wherein, in step (4), a pre-crack cutting was first performed at V = 30 keV, I = 40 pA, and t = 45 s. The pre-crack characteristics were: rt0 was 30 nm, a0 was 642.6 nm, and w0 was 91.31 nm. Figure 6 shown.
[0046] Then, the morphology of the prefabricated cracks during repeated testing is monitored at locations near the positioning piece with similar material properties (such as grain orientation):
[0047] Under the condition of focused ion beam V=30keV, the following ion beam parameters were adjusted to cut out three kinds of prefabricated cracks. The details are as follows.
[0048] Parameter 1: I = 7.7 pA, t = 43 s;
[0049] Parameter 2: I = 24 pA, t = 41 s;
[0050] Parameter 3: I = 40 pA, t = 45 s;
[0051] Three types of prefabricated cracks, such as Figure 7 As shown. By monitoring the cross-sectional morphology, we can know the characteristics of the prefabricated cracks prepared with different parameters. The details are as follows:
[0052] The prefabricated crack characteristics obtained with parameter 1 are: rt' is 25 nm, a' is 632.1 nm, and w' is 83.01 nm;
[0053] The pre-crack characteristics obtained with parameter 2 are: rt' is 29 nm, a' is 646.1 nm, and w' is 97.28 nm;
[0054] The pre-crack characteristics obtained with parameter 3 are: rt' is 39 nm, a' is 658.4 nm, and w' is 117.01 nm;
[0055] Calculate the deviations between the three characteristics of the prefabricated cracks (rt', a', w') and the characteristics of the prefabricated cracks to be repeated (rt0, a0, w0) in (1). The details are as follows:
[0056] Δ parameter 1 = 14.28; Δ parameter 2 = 6.99; Δ parameter 3 = 31.48.
[0057] It is determined that under parameter 2 (30keV, I = 24pA, t = 41s), a sample with a pre-crack repetition deviation of less than 10 can be prepared. Therefore, this parameter is selected to prepare the pre-crack in the micro cantilever beam specimen, as shown in the following example. Figure 8 The slope of the load-displacement curve measured between the replicate and the repeated experiment and the fracture toughness KQ,LFEM obtained by analyzing the linear elastic deformation differ by 0.77 and 0.21, respectively, which are 10% and 14% of the replicate experiment itself.
[0058] Example 3
[0059] In this embodiment, the samples to be tested are Nb-O1 with an oxygen content of 1500 ppm and Nb-O2 with an oxygen content of 3700 ppm.
[0060] Referring to the method of Example 2, micro cantilever beams with similar morphology of pre-cracks were prepared on Nb-O1 and Nb-O2 respectively.
[0061] Among them, the pre-crack cutting parameters are as follows:
[0062] Nb-O1 parameters: V = 30keV, I = 40pA, t = 55s;
[0063] Nb-O2 parameters: V = 30keV, I = 40pA, t = 60s;
[0064] By monitoring the cross-sectional morphology of the pre-crack, the details are as follows:
[0065] The pre-crack characteristics obtained for Nb-O1 are: rt0 is 20 nm, a0 is 503.1 nm, and w0 is 83.01 nm;
[0066] The pre-crack characteristics obtained for Nb-O2 are: rt' is 25nm, a' is 53nm, and w' is 95.21nm;
[0067] The calculated deviation between the Nb-O1 and Nb-O2 pre-cracks is Δ = 5.21, indicating that the pre-crack characteristics are well repeated.
[0068] In summary, the invention includes but is not limited to the above embodiments. Any equivalent replacement or partial improvement made under the spirit and principle of the present invention shall be deemed to be within the scope of protection of the present invention.
Claims
1. A method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials, characterized by: The method steps include: (1) Under the focused ion beam system, the surface of the micro-nano material sample is cut to obtain a micro-cantilever beam with a target prefabricated crack, and the morphological parameters of the target prefabricated crack are obtained, including the target crack tip radius r t , target crack opening w and target crack depth a; (2) Changing the ion beam energy parameters to perform multiple wire cuttings on the surface of the sample to be reproduced to form a reproduced pre-crack, and obtaining the morphological parameters of each reproduced pre-crack, including the radius of the reproduced crack tip r t ', the recurring crack opening w' and the recurring crack depth a'; (3) Calculate the deviations between the morphological parameters of the target prefabricated crack and the morphological parameters of each reproduced prefabricated crack, and prepare a microcantilever beam with a prefabricated crack on the sample to be reproduced using the ion beam energy parameter with the minimum deviation.
2. The method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials according to claim 1, characterized in that: In step (1), under a focused ion beam system, the sample surface is first cut to obtain a sheet-like positioning piece with a smooth surface and a thickness greater than the target thickness on the sample; then, a linear cutting is performed on one end of the positioning piece close to the sample to obtain a positioning piece with a prefabricated crack; finally, the positioning piece with the prefabricated crack is cut according to the set size of the cantilever beam to obtain a micro cantilever beam with a target prefabricated crack.
3. The method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials according to claim 2, characterized in that: The focused ion beam system uses Ga as the ion source, with an accelerating voltage of 25-30 keV. When cutting sheet-shaped spacers, the beam current decreases gradually over time from 20-25 nA to 2-2.5 nA. Using a high beam current early in the process improves cutting efficiency, while using a low beam current later in the process facilitates cross-section correction and ensures a smooth surface.
4. The method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials according to claim 2, characterized in that: The thickness of the sheet-shaped positioning sheet is 4 to 5 μm greater than the target thickness.
5. The method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials according to claim 2, characterized in that: The distance between the prefabricated crack on the positioning piece and the sample substrate is 1 to 2 μm.
6. The method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials according to claim 1, characterized in that: In step (2), the ion beam energy parameters include acceleration voltage V, beam current I and irradiation time t.
7. The method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials according to claim 6, characterized in that: The acceleration voltage V varies in the range of 5 to 30 keV, the beam current I varies in the range of 5 pA to 0.1 nA, and the irradiation time t varies in the range of 20 to 60 s.
8. The method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials according to claim 1, characterized in that: The sample in step (1) and the sample to be reproduced in step (2) are respectively metal or alloy materials.
9. The method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials according to claim 1, characterized in that: In step (3), the calculation formula of the deviation Δ is as follows:
10. The method for preparing a micro-cantilever beam specimen with a pre-crack for testing the fracture toughness of micro-nano materials according to claim 9, characterized in that: In step (3), the deviation is less than 10.