A type of C f Methods for determining the depth of cut in SiC ceramic matrix composites

Abstract

This invention relates to a C f The method for determining the cutting depth of SiC ceramic matrix composites first involves conducting nano-scraping tests to obtain the three-dimensional morphology, scratch depth, scratch force, and axial load variation curves of the nano-scratches along various directions with the scratch distance. Then, the scratch depth range corresponding to the microscopic brittle fracture domain is determined when scratching along a single direction. This process is repeated to obtain the scratch depth range corresponding to the microscopic brittle fracture domain along various directions. Finally, the depth of cut for SiC is determined. f When machining SiC ceramic matrix composites, the scratch direction is determined, and the corresponding scratch depth range corresponding to the microscopic brittle fracture domain is identified, which is then used as the cutting depth range. This invention controls the cutting depth within the scratch depth range corresponding to the microscopic brittle fracture domain, achieving material removal without causing excessive cutting forces, severe tool wear, or short tool life due to excessive cutting depth or the high hardness of the material.

Description

Technical Field

[0001] This invention belongs to the field of composite material processing and relates to a C f Methods for determining the cutting depth of SiC ceramic matrix composites. Background Technology

[0002] C f SiC ceramic matrix composites are primarily used as friction materials and high-temperature materials with short service lives. Due to increasingly stringent requirements for speed, load, and safety in vehicles, ordinary friction materials are prone to failure under braking conditions. f / SiC ceramic matrix composites possess a high and stable coefficient of friction, good wear resistance, excellent mechanical properties, are lightweight, have a high braking ratio, and a long service life. Therefore, C f / SiC ceramic matrix composites are considered the preferred choice for next-generation high-performance friction materials.

[0003] Cutting machining offers high precision and material removal rates, and the equipment used is relatively mature, making it widely used for large-scale material removal and the machining of high-precision, high-quality structures and surfaces. However, C f The high hardness, brittleness, anisotropy, and heterogeneity of SiC directly lead to low machining efficiency and poor machining quality, posing a significant challenge to the cutting process. In particular, the selection of the depth of cut directly affects the surface integrity and machining efficiency of the finished part. Therefore, the selection of the depth of cut is crucial for SiC... f / SiC cutting is crucial.

[0004] Existing research mainly determines C through parametric experiments. f The method for determining the depth of cut in SiC can only optimize from among alternative parameters; a depth of cut that achieves better machining quality, higher machining efficiency, and less tool wear has not yet been obtained. For example, the literature "Experimental study on milling performance of 2D C"... f / SiCcomposites using polycrystalline diamond tools” Explores two-dimensional braiding C using PCD tools f The study investigated the effects of milling parameters on cutting force, surface integrity, and machining defects in the slot milling of SiC composite materials. While pre-setting smaller depths of cut (0.01 mm, 0.02 mm) was used to improve machining quality, defects still occurred, along with low machining efficiency and tool wear. Therefore, C... f The method for determining the cutting depth of SiC ceramic matrix composites is crucial. Summary of the Invention

[0005] The purpose of this invention is to solve the problems existing in the prior art and provide a C f Methods for determining the cutting depth of SiC ceramic matrix composites.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A type of C f The method for determining the cutting depth of SiC ceramic matrix composites is as follows:

[0008] (1) Determine C f / SiC ceramic matrix composites;

[0009] C f The fibers in the SiC ceramic matrix composite are parallel to each other;

[0010] (2) Conduct nano-scratch tests to obtain the three-dimensional morphology, scratch depth, scratch force and axial load of nano-scratch as a function of scratch distance when scratching in various directions; each direction is along the fiber cross section, along the direction perpendicular to the fiber and along the fiber direction.

[0011] (3) Determine the range of scratch depth corresponding to the microscopic brittle fracture domain when scratching in a single direction;

[0012] (3.1) Select representative positions on the scratch. The representative positions are any three positions selected on the scratch before the scratch depth changes by 20% from the start of loading.

[0013] (3.2) The three-dimensional morphology of the nano-scratches is processed to obtain the cross-sectional profiles corresponding to each representative position, and the cross-sectional area is calculated by the cross-sectional profiles.

[0014] Simultaneously, based on the three-dimensional morphology, scratch depth, scratch force, and axial load variation curves of the nano-scratches with scratch distance, the scratch depth and scratch force corresponding to each representative location were obtained; the scratch specific energy corresponding to each representative location was calculated using the following formula:

[0015] μ s =Fs / S;

[0016] In the formula, μ s Fs represents the scratch energy, S represents the scratch force, and S represents the cross-sectional area.

[0017] (3.3) The scratch depth and scratch energy corresponding to each representative position are processed to obtain a scatter plot of the scratch energy as a function of scratch depth when scratching in a single direction.

[0018] (3.4) Obtain the microstructure of carbon fiber under different material removal mechanisms when scratching in a single direction; the different material removal mechanisms are ductile, ductile-brittle, micro-brittle fracture or micro-macro-brittle fracture transformation;

[0019] (3.5) Obtain the carbon fiber microstructure at each representative location when scratching along a single direction, and compare it with the carbon fiber microstructure under different material removal mechanisms when scratching along a single direction to determine the material removal mechanism corresponding to each representative location; in the scatter plot of the scratch specific energy changing with the scratch depth when scratching along a single direction, circle the points corresponding to the representative locations where the material removal mechanism is micro brittle fracture to obtain the micro brittle fracture domain, and then obtain the scratch depth range corresponding to the micro brittle fracture domain;

[0020] (4) Repeat step (3) to obtain the scratch depth range corresponding to the microscopic brittle fracture domain when scratching in each direction;

[0021] (5) Determine the relationship between C and C. f When machining SiC ceramic matrix composites, the scratch direction is used to find the scratch depth range corresponding to the microscopic brittle fracture domain. This range is then used as the cutting depth range, and the cutting depth is controlled within this range during subsequent machining processes.

[0022] As a preferred technical solution:

[0023] As described above, a type of C f The method for determining the cutting depth of SiC ceramic matrix composites, in step (1), C f The fibers in the / SiC ceramic matrix composite material are T300 carbon fibers, C f The volume fraction of T300 carbon fiber in the / SiC ceramic matrix composite is 42-47%.

[0024] As described above, a type of C f The method for determining the cutting depth of SiC ceramic matrix composites, step (2) is as follows:

[0025] (2.1) Before conducting the nano-scratch test, C f / SiC ceramic matrix composites are cut, cold-mounted, rough-ground, fine-ground and polished;

[0026] (2.2) Determine the indenter and nano-scratch instrument;

[0027] (2.3) Begin the nano-scratch experiment, targeting C f / SiC ceramic matrix composite material was scratched with varying depths in each direction; during the scratching process, the signals of displacement, axial load, scratch depth and scratching force were recorded in real time;

[0028] (2.4) After the scratch test, the three-dimensional morphology of the nano-scratches was measured using a KLA-Tencor-MicroXAM-800 non-contact optical profilometer.

[0029] As described above, a type of C f The method for determining the cutting depth of / SiC ceramic matrix composite material, in step (2.1), is to use a resin-bonded diamond saw blade for cutting.

[0030] As described above, a type of C f The method for determining the cutting depth of SiC ceramic matrix composites, in step (2.1), cold mounting, i.e., using resin to mount the cut C... f / SiC ceramic matrix composite material is cold-mounted.

[0031] As described above, a type of C f The method for determining the cutting depth of SiC ceramic matrix composites, in step (2.1), rough grinding, i.e., using a diamond grinding wheel to grind the cold-mounted C... f / SiC ceramic matrix composite material is coarsely ground.

[0032] As described above, a type of C f The method for determining the cutting depth of SiC ceramic matrix composites, in step (2.1), fine grinding and polishing, i.e., using diamond polishing fluid to polish the C after rough grinding. f / SiC ceramic matrix composites are finely ground and polished.

[0033] As described above, a type of C f The method for determining the cutting depth of / SiC ceramic matrix composite material, in step (2.2), the indenter is a cubic diamond indenter with a tip radius of 20nm; the nano-scratcher is an Agilent G200 nano-scratcher.

[0034] As described above, a type of C f The method for determining the cutting depth of SiC ceramic matrix composites, in step (2.3), the scratch distance is 700 μm and the scratching speed is 30 μm / s, which is a quasi-static loading process; during the scratching process, the indenter face is forward, and within the scratch distance range of 500 μm, the axial load increases linearly from 20 μN to 350 mN, and no axial load is applied within the scratch distance range of 500 to 700 μm, that is, the axial load is 0; the scratching test is repeated three times in each scratching direction.

[0035] As described above, a type of C f The method for determining the cutting depth of SiC ceramic matrix composites, in step (2.3), after the nano-scratching test, C f / SiC ceramic matrix composites were ultrasonically cleaned with acetone for 10 minutes to remove debris from the scratched surface and then dried.

[0036] Beneficial effects:

[0037] The most widely used continuous fiber reinforced silicon carbide ceramic matrix composites (FRCMCs-SiC) mainly include silicon carbide fiber reinforced (SiC) f / SiC) and carbon fiber reinforced (C f There are two types: FRCMCs-SiC and carbon fiber reinforced polymer (C-SiC). In existing scratch test studies of FRCMCs-SiC materials, the scratch depth is set much larger than the fiber diameter. Therefore, bending-induced fracture, compression-induced fracture, and shear-induced fracture are the fracture modes of the fiber, which is consistent with the fracture modes of carbon fiber reinforced polymer (C-SiC). f The fracture mode of carbon fibers in RP is consistent; however, the matrix of FRCMCs-SiC material is high-hardness CVI-SiC, which provides good support for the fibers. Therefore, when the scratch depth is small, the brittle fracture mode of the fibers will change. If the material removal mechanism of FRCMCs-SiC material is studied using existing scratch technology, the results may be one-sided or even inconsistent with reality. Therefore, this invention is based on variable load nano-scratching test (since this invention is nano-scratching, C... f Since the diameter of fibers is generally on the micrometer scale, the scratch depth is less than the diameter of the fibers. The results of the study on the variation of force and scratch ratio in different scratch directions during the variable depth scratching process, the fracture mechanism of fibers in FRCMCs-SiC and its variation with scratch depth, and the mechanism of damage behavior of materials in different scratch directions will be more accurate than the existing technology.

[0038] The variable load nano-scratching test according to the present invention can fully understand the material removal mechanism of FRCMCs-SiC. The material removal mechanism conclusions drawn from existing technologies are fiber bending-induced fracture, compression-induced fracture, and shear-induced fracture. However, based on the variable load nano-scratching test in this invention, the brittle domain of FRCMCs-SiC can be further subdivided into a micro-brittle fracture domain and a macro-brittle fracture domain. In the micro-brittle fracture domain, the material unit undergoing brittle fracture is the grain within the fiber; these micro-scale brittle fractures occur within the fiber. Under the extrusion action of the tool, microcracks initiate inside the fiber, and these microcracks... Grain propagation; a single fiber undergoes several brittle fractures during material removal; in the microscopic brittle fracture domain, the processed surface of the fiber is relatively rough and has residual microcracks on the surface and subsurface, but the fiber-matrix interface is almost undamaged, and the overall processed surface quality is good; in the macroscopic brittle fracture domain, the material unit that undergoes brittle fracture is the fiber, and a single fiber undergoes only one brittle fracture, in the form of bending fracture, shear fracture, or compression fracture; in the macroscopic brittle fracture domain, the fiber fracture surface or the processed surface of the fiber is smooth, but the fiber-matrix interface is severely damaged, the fiber fracture location is random, and the overall processed surface quality is poor;

[0039] A thorough understanding of the material removal mechanism of FRCMCs-SiC, combined with the scratch depth range corresponding to the microscopic brittle fracture domain, allows for control of the cutting depth and selection of more suitable processing techniques and parameters during subsequent manufacturing of this material, reducing process trial and error. As a result, manufacturers can achieve higher production efficiency, better surface finish, and longer tool life, ultimately resulting in cost reduction and efficiency improvement. Attached Figure Description

[0040] Figure 1 To obtain C f Microstructure diagram of the SiC ceramic matrix composite material; where (a) is the longitudinal fiber, (b) is the fiber cross section, (c) is the transmission electron microscope image, and (d) is the energy spectrum of the carbon fiber and SiC ceramic matrix.

[0041] Figure 2 C f A schematic diagram of nano-scratching test on SiC ceramic matrix composite material; where (a) is a schematic diagram of nano-scratching along the fiber cross section direction, (b) is a schematic diagram of nano-scratching along the perpendicular fiber direction, and (c) is a schematic diagram of nano-scratching along the fiber direction.

[0042] Figure 3 C f The graph shows the three-dimensional morphology, scratch depth, scratch force and axial load of nano-scratches on SiC ceramic matrix composites as a function of scratch distance; where (a) represents the direction along the fiber cross section, (b) represents the direction perpendicular to the fiber, and (c) represents the direction along the fiber.

[0043] Figure 4 C f Three-dimensional morphology and typical cross-sectional profile of nano-scratches on SiC ceramic matrix composites; where (a) is the three-dimensional morphology of nano-scratches, (b) is the cross-sectional profile at A-A', (c) is the cross-sectional profile at B-B', ① is the micro-brittle fracture in Figure (b), ② is the micro-brittle fracture in Figure (c), ③ is the debonding interface, and ④ is the fiber fracture surface.

[0044] Figure 5 C f The microstructure of carbon fibers in SiC ceramic matrix composites under different material removal mechanisms during scratching along the fiber cross-section; where (a) is the ductile domain, (b) is the ductile-brittle domain, (c) is the micro-brittle fracture domain, and (d) is the micro-macro-brittle fracture transition domain.

[0045] Figure 6 C f The microstructure of carbon fibers in SiC ceramic matrix composites under different material removal mechanisms when scratched along the direction perpendicular to the fiber; where (a) is the ductile domain, (b) is the micro-brittle fracture domain, (c) is the micro-to-macro-brittle fracture transition domain, and (d) is the macro-brittle fracture domain.

[0046] Figure 7 C f The microstructure of carbon fibers in SiC ceramic matrix composites under different material removal mechanisms during scratching along the fiber direction; where (a) is the ductile domain, (b) is the micro-brittle fracture domain, (c) is the micro-to-macro-brittle fracture transition domain, and (d) is the macro-brittle fracture domain.

[0047] Figure 8 C f Scatter plot of the scratch specific energy of SiC ceramic matrix composite material as a function of scratch depth when scratched along the fiber cross section; where ① is the ductile domain, ② is the ductile-brittle domain, ③ is the micro-brittle fracture domain, and ④ is the micro-macro-brittle fracture transition domain.

[0048] Figure 9 C f Scatter plot of the scratch specific energy of SiC ceramic matrix composite material as a function of scratch depth when scratched along the direction perpendicular to the fiber; where ① is the ductile domain, ② is the micro-brittle fracture domain, ③ is the micro-to-macro-brittle fracture transition domain, and ④ is the macro-brittle fracture transition domain.

[0049] Figure 10 C fScatter plot of the scratch specific energy of SiC ceramic matrix composite material as a function of scratch depth when scratched along the fiber direction; where ① is the ductile domain, ② is the micro-brittle fracture domain, ③ is the micro-to-macro-brittle fracture transition domain, and ④ is the macro-brittle fracture transition domain.

[0050] Figure 11 C f Simulation results of cutting SiC ceramic matrix composite material (cutting depth 5μm); where (a) is the fiber stress distribution, (b) is the machined surface and chip morphology, and (c) is the change of cutting force over time.

[0051] Figure 12 C f Simulation results of cutting SiC ceramic matrix composites (cutting depth 30μm); where (a) is the fiber stress distribution, (b) is the machined surface and chip morphology, and (c) is the change of cutting force over time.

[0052] Among them, 1 is variable depth nano-scratching, 2 is carbon fiber, 3 is SiC ceramic matrix, 4 is cubic diamond indenter, 5 is cutting tool, 6 is fiber, and 7 is chip. Detailed Implementation

[0053] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0054] A type of C f The method for determining the cutting depth of SiC ceramic matrix composites is as follows:

[0055] (1) Determine C f / SiC ceramic matrix composites;

[0056] C f The fibers in the SiC ceramic matrix composite are parallel to each other;

[0057] C f The fibers in the / SiC ceramic matrix composite material are T300 (6K) carbon fibers, C f The volume fraction of T300 carbon fiber in the SiC ceramic matrix composite is 42-47%; the material properties of T300 carbon fiber are shown in Table 1.

[0058] C f The preparation method for SiC ceramic matrix composites is chemical vapor infiltration (CVI), and the preparation process is as follows:

[0059] The carbon fibers are heat-treated in a sintering furnace to remove the binder on the fiber surface. Before SiC deposition, a 100 nm thick layer of pyrolytic carbon (PyC) is deposited on the carbon fiber surface in a CVI furnace by decomposing methane to form a weak interface phase. The deposition temperature is 1050℃ and the deposition time is 8-10 h.

[0060] Methyltrichlorosilane (MTS) is pyrolyzed in a CVI furnace to produce a silicon carbide ceramic matrix to fill the gaps between carbon fibers, thereby forming a densified material; wherein the deposition temperature of the silicon carbide ceramic matrix is ​​1000-1100℃, and the deposition time for each deposition is 80h.

[0061] After each deposition cycle on the silicon carbide ceramic substrate, the surface of the prepared sample is ground to remove surface silicon carbide ceramic that may cause blockage, allowing the MTS gas flow to continue entering the pores inside the sample. Deposition then continues to reduce porosity. This deposition process is repeated three times to obtain the final C... f / SiC ceramic matrix composites, to obtain C f The performance parameters of the / SiC ceramic matrix composite material are shown in Table 1;

[0062] Table 1

[0063]

[0064] C f The microstructure of SiC ceramic matrix composites is as follows: Figure 1 As shown; from Figure 1 As can be seen in (a) and (b), the material contains pores formed during the CVI process; layered SiC ceramic matrix is ​​deposited on the carbon fiber surface, and these CVI-SiCs are columnar crystal structures that grow radially along the fibers; from Figure 1 As can be seen in (c), there is a weak interface layer formed by PyC between the carbon fiber and the SiC ceramic matrix; from Figure 1 From (d), it can be determined that the position with only C element (EDS-1) is carbon fiber, and the position with Si and C elements in an approximately 1:1 ratio (EDS-2) is ceramic matrix;

[0065] (2) Conduct nano-scratch tests to obtain the three-dimensional morphology, scratch depth, scratch force and axial load of nano-scratch as a function of scratch distance when scratching in various directions;

[0066] (2.1) Before conducting the nano-scratch test, first use a resin-bonded diamond saw blade to apply C f / SiC ceramic matrix composites were cut into 6×20×10mm dimensions and bonded with resin (a material used for "cold mounting") to the SiC matrix. fCold mounting of SiC ceramic matrix composites was performed; a diamond grinding wheel was used to polish the cold-mounted SiC matrix composites with a diameter of Φ30mm. f The SiC ceramic matrix composite material was coarsely ground, then finely ground and polished using diamond polishing slurry; the ground and polished C f The surface roughness of the SiC ceramic matrix composite material is 80 nm, which meets the requirements of the nano-scratch test.

[0067] (2.2) Using a cubic diamond indenter on an Agilent G200 nano-scratch instrument to scratch C f Nano-scratch tests were conducted on SiC ceramic matrix composites using a cubic angular diamond indenter with a tip radius of 20 nm. Before the actual scratching, the indenter was pre-scanned on the sample surface with a load of 20 μN to measure the surface roughness of the sample in the scratched area.

[0068] (2.3) Begin the nano-scratch experiment, targeting C f / SiC ceramic matrix composites, such as Figure 2 As shown in (a), (b), and (c), a cubic angular diamond indenter 4 is used to perform variable-depth scratching along the fiber cross-section direction, along the direction perpendicular to the fiber, and along the fiber direction, respectively. The scratch distance is 700 μm, and the scratching speed is 30 μm / s, which is a quasi-static loading process (i.e., the scratching speed is very slow and the material strain rate is very small). During the scratching process, the indenter face is forward, and the actual loading zone is 500 μm (from 100 μm to 600 μm is the actual loading zone, and the 0-100 μm and 600-700 μm ranges are also considered). Within the scratch distance range (representing the pre-loading and unloading intervals), the axial load linearly increases from 20 μN to 350 mN. No axial load is applied within the scratch distance range of 500–700 μm, i.e., the axial load is 0. During the process, carbon fiber 2 and the SiC ceramic matrix 3 are scratched to varying degrees. Displacement, axial load, scratch depth, and scratch force signals are recorded in real time during the scratching process. The scratching test is repeated three times in each scratch direction, resulting in nine variable-depth nano-scratches 1. After the nano-scratching test, C… f / SiC ceramic matrix composite material was ultrasonically cleaned with acetone for 10 minutes to remove debris from the scratched surface and then dried.

[0069] (2.4) After the scratch test, the three-dimensional morphology of the nano-scratches was measured using a KLA-Tencor-MicroXAM-800 non-contact optical profilometer.

[0070] The curves showing the three-dimensional morphology, scratch depth, scratch force, and axial load of the nano-scratches as a function of scratch distance during rubbing along the fiber cross-section are as follows: Figure 3 As shown in (a); it can be seen from the figure that as the axial load increases from 20 μN to 350 mN, the scratch depth gradually increases to 8 μm;

[0071] The curves showing the variation of the three-dimensional morphology, scratch depth, scratch force, and axial load of the nano-scratches with scratch distance when scratched along a direction perpendicular to the fiber are as follows: Figure 3 As shown in (b), it can be seen from the figure that as the axial load increases from 20 μN to 350 mN, the scratch depth gradually increases to 18 μm. Since the radial elastic modulus and hardness of carbon fiber are less than the axial elastic modulus and hardness, under the same load, the indentation depth of the indenter in the radial direction of the fiber is greater than that in the axial direction of the fiber. In addition, the scratch damage width when scratching perpendicular to the fiber direction is much greater than that along the fiber cross section direction.

[0072] The curves showing the variation of the three-dimensional morphology, scratch depth, scratch force, and axial load of the nano-scratches with scratch distance during rubbing along the fiber direction are as follows: Figure 3 As shown in (c), it can be seen from the figure that as the axial load increases from 20μN to 350mN, the scratch depth gradually increases to 15μm. Whether scratching along the fiber direction or perpendicular to the fiber direction, the fiber radially bears the axial load, and the mechanical properties of the material are the same. Therefore, the scratch depth in these two directions is similar. When the indenter scratches along the fiber direction, the scratch damage width is much smaller than the scratch damage width when scratching perpendicular to the fiber direction.

[0073] (3) Determine the scratch depth range corresponding to the microscopic brittle fracture domain when scratching in a single direction;

[0074] (3.1) Select representative positions on the scratch. The representative positions are any three positions selected on the scratch before the scratch depth changes by 20% from the start of loading.

[0075] (3.2) The three-dimensional morphology of nano-scratches (e.g.) Figure 4 The cross-sectional profiles corresponding to each representative position are obtained by processing (as shown in (a)). Figure 4 In (b) and (c), the cross-sectional area is obtained by calculating the cross-sectional profile;

[0076] Simultaneously, based on the three-dimensional morphology, scratch depth, scratch force, and axial load variation curves of the nano-scratches with scratch distance, the scratch depth and scratch force corresponding to each representative location were obtained; the scratch specific energy corresponding to each representative location was calculated using the following formula:

[0077] μ s =Fs / S;

[0078] In the formula, μ s Fs represents the scratch energy, S represents the scratch force, and S represents the cross-sectional area.

[0079] (3.3) The scratch depth and scratch energy corresponding to each representative position are processed to obtain a scatter plot of the scratch energy as a function of scratch depth when scratching in a single direction.

[0080] (3.4) Obtain the microstructure of carbon fiber under different material removal mechanisms (ductility, ductility-brittleness, micro-brittle fracture, micro-macro-brittle fracture transition) when scratched along a single direction;

[0081] Figure 5 The image shows the microstructure of carbon fiber under different material removal mechanisms when scratched along the fiber cross-section. Since carbon fiber and CVI-SiC are typical brittle materials, no obvious elastic deformation of the material was observed in the image.

[0082] from Figure 5 As can be seen in (a), when the indenter begins to load, the carbon fiber and silicon carbide undergo plastic deformation; as the load increases, the ductile-brittle transition occurs during the material removal process.

[0083] from Figure 5 As can be seen in (b), CVI-SiC is crushed at this point, and the carbon fibers still undergo ductile removal, but there are a large number of conical cracks on both sides of the scratch; when scratching along the fiber cross-section, a ductile-brittle transition occurs when the scratch depth reaches 200 nm; as the scratch depth continues to increase, C f The removal mechanism of FRCMCs-SiC ceramic matrix composites transforms into brittle fracture. FRCMCs-SiC contains fibers and SiC, as well as a weak interface phase formed between them due to pyrolytic carbon. The fracture mechanism of this two-phase material in the brittle domain differs significantly from that of traditional single-phase materials. For layered CVI-SiC encapsulated on the fiber surface, the material removal mechanism in the brittle domain is blocky fragmentation, which remains essentially unchanged. The difference is caused by the fibers. Each fiber, as a whole, may experience micro-brittle fracture within a single fiber, or macro-brittle fracture (such as bending fracture, compression fracture, and shear fracture) as a whole fiber. Therefore, the brittle domain of FRCMCs-SiC can be further subdivided into micro-brittle fracture domains and macro-brittle fracture domains.

[0084] from Figure 5 As can be seen in (c), when the scratch depth is relatively small, several brittle fractures at the nanometer scale occur inside the carbon fiber; cracks initiate in the carbon fiber during the extrusion process; however, due to the insufficient scratch depth, the cracks only extend inside the fiber, causing the carbon fiber to be cut into small pieces; the surface of the carbon fiber after microscopic brittle fracture is relatively rough.

[0085] from Figure 5 As can be seen in (d), as the scratch depth increases to 5 μm, some carbon fibers undergo macroscopic brittle fracture; when scratched along the fiber cross-section, the macroscopic brittle fracture is mainly caused by the bending fracture of the entire fiber; the fracture surface of the macroscopic brittle fracture of carbon fiber is relatively smooth; however, due to the bending fracture, the position of the fiber fracture surface will be uneven.

[0086] Figure 6 The image shows the microstructure of carbon fiber under different material removal mechanisms when scratched perpendicular to the fiber direction;

[0087] like Figure 6 As shown in (a), the carbon fiber undergoes plastic deformation, producing plastic chips; the SiC matrix undergoes brittle fracture; as the load increases, the material removal changes from the ductile domain to the brittle domain; however, the ductile-brittle domain is very small in the scratches perpendicular to the fiber direction and is not clearly shown in the microstructure diagram.

[0088] like Figure 6 As shown in (b), when the scratch depth is still small, the fiber material is removed by micro-brittle fracture. The pressure head squeezes the fiber to produce scaly fragments. Each scaly fragment can be regarded as a micro-brittle fracture inside the fiber. There are residual conical cracks on the side of each scaly fragment. The scaly fragments produced by micro-brittle fracture have a rough surface and many cracks.

[0089] When the scratch depth increases to 3μm, some conical cracks can penetrate the carbon fiber under the drive of the indenter, such as Figure 6 As shown in (c), the fracture mode of carbon fiber changes from microscopic brittle fracture to macroscopic brittle fracture, that is, the entire fiber breaks and each fiber has only one fracture surface. However, this change is caused by the propagation of conical cracks.

[0090] As the scratch depth further increases, all C f The fibers on the surface of the SiC ceramic matrix composite material all underwent macroscopic brittle fracture, such as... Figure 6 As shown in (d), the surface fiber fracture is mainly bending fracture, and the fiber fracture surface is relatively smooth, but the distance between the fracture surface of each fiber and the center line of the scratch varies. For scratches perpendicular to the fiber direction, the damage width of the macroscopic brittle fracture domain exceeds 200 μm, which is much larger than that of scratches in other directions. In addition, when the surface fiber undergoes macroscopic brittle fracture, the indentation depth of the indenter is sufficient to scratch the subsurface fiber. However, the indentation depth of the indenter on the subsurface fiber is small, and the fiber debonding is difficult. Therefore, the subsurface fiber still undergoes microscopic brittle fracture.

[0091] Figure 7 The image shows the microstructure of carbon fiber under different material removal mechanisms when rubbed along the fiber direction;

[0092] like Figure 7 As shown in (a), carbon fibers undergo plastic deformation in the ductile region, producing plastic chips;

[0093] like Figure 7As shown in (b), similar to scratching perpendicular to the fiber direction, there is almost no ductile-brittle region when scratching along the fiber direction. After the ductile region, the carbon fiber directly undergoes scaly fracture as the scratch depth increases. The micro-brittle fracture caused by scaly fracture results in a rougher scratch surface and more surface cracks.

[0094] like Figure 7 As shown in (c), when the indentation depth of the indenter continues to increase, the resulting mid-center crack can penetrate the fiber, causing the fiber to fracture radially. At this point, the material is removed and enters the micro-to-macro brittle fracture transition domain. After the surface fiber fractures radially, it debonds and peels off from the silicon carbide matrix material under the drive of the indenter. However, the surface fiber is usually not a complete fiber. Therefore, in the micro-to-macro brittle fracture transition domain, radial fracture and scaly fragmentation of the carbon fiber occur alternately.

[0095] like Figure 7 As shown in (d), with the further increase of load, almost all the subsurface carbon fibers near the center line of the scratch underwent radial fracture and debonding. This indicates that the indenter depth at this point was sufficient to cause radial fracture and debonding of the intact carbon fibers from the matrix. Therefore, the material removal entered the macroscopic brittle fracture domain. However, microscopic brittle fracture still exists at the edge of the scratch due to the decrease in scratch depth. The surface formed by the macroscopic brittle fracture consists of intact axial fibers and SiC matrix. The carbon fiber surface is relatively smooth and intact, but the overall scratch surface has large undulations.

[0096] (3.5) Obtain the carbon fiber microstructure at each representative location when scratching along a single direction, and compare it with the carbon fiber microstructure under different material removal mechanisms when scratching along a single direction to determine the material removal mechanism corresponding to each representative location; in the scatter plot of the scratch specific energy changing with the scratch depth when scratching along a single direction, circle the points corresponding to the representative locations where the material removal mechanism is micro brittle fracture to obtain the micro brittle fracture domain, and then obtain the scratch depth range corresponding to the micro brittle fracture domain;

[0097] (4) Repeat step (3) to obtain the scratch depth range corresponding to the microscopic brittle fracture domain when scratching in each direction. The results are as follows: Figure 8-10 As shown;

[0098] (5) Determine the relationship between C and C. f When machining SiC ceramic matrix composites, the scratch direction is used to find the scratch depth range corresponding to the microscopic brittle fracture domain. This range is then used as the cutting depth range, and the cutting depth is controlled within this range during subsequent machining processes.

[0099] This invention controls the cutting depth within the scratch depth range corresponding to the microscopic brittle fracture domain, achieving the purpose of material removal without causing problems such as excessive cutting force, severe tool wear, and short tool life due to excessive cutting depth or high material hardness. A specific example will now be used to illustrate this:

[0100] Figure 11 The results shown are simulation results for a cutting depth of 5 μm; Figure 11 As shown in (a), the stress distribution area at the cutting edge of the fiber and the cutting tool 5 is mainly located in the cross-section of fiber 6; the machined surface of fiber 6 is a typical microscopic brittle fracture surface morphology; the stress distribution penetrating deep into the subsurface causes damage to fiber 6 at the subsurface; such as Figure 11 As shown in (b), the subsurface damage layer of fiber 6 reaches a depth of 27 μm; the chip 7 is powdery, and the surface roughness Rz of the machined fiber 6 is relatively small; due to the material removal method being in the microscopic brittle fracture domain, the cutting force is small, with a peak value of 0.4 N, as... Figure 11 As shown in (c);

[0101] Figure 12 The simulation results are shown for a cutting depth of 30 μm. When the cutting depth is 30 μm, fiber 6 undergoes macroscopic brittle fracture. When the cutting edge contacts fiber 6, fiber 6 exhibits significant bending deformation. Figure 12 As shown in (a), the stress distribution area in the contact zone between the fiber and the cutting edge of the tool 5 is relatively large, so the fracture location of the fiber 6 when it undergoes bending or compression fracture has an unavoidable randomness; from Figure 12 As can be seen in (b), when machining is performed in the macroscopic brittle fracture domain, the chips 7 are blocky with uneven cross-sections, and the fracture positions of the fibers 6 on the machined surface are random. This directly leads to a significant increase in the surface roughness Rz of the machined surface; and the subsurface damage layer depth of the fibers 6 also reaches 28 μm; due to the large cutting depth and wide stress distribution, the maximum cutting force reaches 1.5 N, such as Figure 12 As shown in (c).

[0102] Compare C f Simulation results for removing SiC from two different materials show that cutting in the microscopic brittle fracture domain can achieve better surface finish and lower cutting force, thereby reducing tool wear and extending tool life.

Claims

1. A type of C f A method for determining the cutting depth of SiC ceramic matrix composite materials, characterized in that... The steps are as follows: (1) Determine C f / SiC ceramic matrix composites; C f The fibers in the SiC ceramic matrix composite are parallel to each other; (2) Conduct nano-scratch tests to obtain the three-dimensional morphology, scratch depth, scratch force and axial load of nano-scratch as a function of scratch distance when scratching in various directions; each direction is along the fiber cross section, along the direction perpendicular to the fiber and along the fiber direction. (3) Determine the range of scratch depth corresponding to the microscopic brittle fracture domain when scratching in a single direction; (3.1) Select representative positions on the scratch. The representative positions are any three positions selected on the scratch before the scratch depth changes by 20% from the start of loading. (3.2) The three-dimensional morphology of the nano-scratches is processed to obtain the cross-sectional profiles corresponding to each representative position, and the cross-sectional area is calculated by the cross-sectional profiles. Meanwhile, based on the three-dimensional morphology, scratch depth, scratch force, and axial load of the nano-scratches as a function of scratch distance, the scratch depth and scratch force corresponding to each representative position were obtained. The scratch energy corresponding to each representative position can be calculated using the following formula: m s =Fs / S; In the formula, μ s Fs represents the scratch energy, S represents the scratch force, and S represents the cross-sectional area. (3.3) The scratch depth and scratch energy corresponding to each representative position are processed to obtain a scatter plot of the scratch energy as a function of scratch depth when scratching in a single direction. (3.4) Obtain the microstructure of carbon fiber under different material removal mechanisms when scratching in a single direction; the different material removal mechanisms are ductile, ductile-brittle, micro-brittle fracture or micro-macro-brittle fracture transformation; (3.5) Obtain the carbon fiber microstructure at each representative location when scratching in a single direction, compare it with the carbon fiber microstructure under different material removal mechanisms when scratching in a single direction, and determine the material removal mechanism corresponding to each representative location. In a scatter plot showing the change of scratch energy with scratch depth when scratching in a single direction, the points corresponding to the representative locations where the material removal mechanism is micro-brittle fracture are circled together to obtain the micro-brittle fracture domain, and then the scratch depth range corresponding to the micro-brittle fracture domain is obtained. (4) Repeat step (3) to obtain the scratch depth range corresponding to the microscopic brittle fracture domain when scratching in each direction; (5) Determine the relationship between C and C. f When machining SiC ceramic matrix composites, the scratch direction is used to find the scratch depth range corresponding to the microscopic brittle fracture domain, which is then used as the cutting depth range.

2. A C according to claim 1 f A method for determining the cutting depth of SiC ceramic matrix composite materials, characterized in that... In step (1), C f The fibers in the / SiC ceramic matrix composite material are T300 carbon fibers, C f The volume fraction of T300 carbon fiber in the / SiC ceramic matrix composite is 42-47%.

3. A C according to claim 1 f A method for determining the cutting depth of SiC ceramic matrix composite materials, characterized in that... Step (2) is as follows: (2.1) Before conducting the nano-scratch test, C f / SiC ceramic matrix composites are cut, cold-mounted, rough-ground, fine-ground and polished; (2.2) Determine the indenter and nano-scratch instrument; (2.3) Begin the nano-scratch experiment, targeting C f / SiC ceramic matrix composite material was scratched with varying depths in each direction; during the scratching process, the signals of displacement, axial load, scratch depth and scratching force were recorded in real time; (2.4) After the scratch test, the three-dimensional morphology of the nano-scratches was measured using a KLA-Tencor-MicroXAM-800 non-contact optical profilometer.

4. A C according to claim 3 f A method for determining the cutting depth of SiC ceramic matrix composite materials, characterized in that... In step (2.1), the cutting is performed using a resin-bonded diamond saw blade.

5. A C according to claim 4 f A method for determining the cutting depth of SiC ceramic matrix composite materials, characterized in that... In step (2.1), cold mounting involves using resin to mount the cut C... f / SiC ceramic matrix composite material is cold-mounted.

6. A C according to claim 5 f A method for determining the cutting depth of SiC ceramic matrix composite materials, characterized in that... In step (2.1), rough grinding involves using a diamond grinding wheel to grind the C after cold mounting. f / SiC ceramic matrix composite material is coarsely ground.

7. A C according to claim 6 f A method for determining the cutting depth of SiC ceramic matrix composite materials, characterized in that... In step (2.1), fine grinding and polishing involve using diamond polishing fluid to polish the C200 after rough grinding. f / SiC ceramic matrix composites are finely ground and polished.

8. A C according to claim 3 f A method for determining the cutting depth of SiC ceramic matrix composite materials, characterized in that... In step (2.2), the indenter is a cubic diamond indenter with a tip radius of 20 nm. The nano-scratch instrument is the Agilent G200 nano-scratch instrument.

9. A C according to claim 3 f A method for determining the cutting depth of SiC ceramic matrix composite materials, characterized in that... In step (2.3), the scratch distance is 700 μm and the scratching speed is 30 μm / s, which is a quasi-static loading process. During the scratching process, the indenter face is forward. Within the scratch distance range of 500 μm, the axial load increases linearly from 20 μN to 350 mN. No axial load is applied within the scratch distance range of 500 to 700 μm, i.e., the axial load is 0. The scratch test is repeated three times in each scratch direction.

10. A C according to claim 3 f A method for determining the cutting depth of SiC ceramic matrix composite materials, characterized in that... In step (2.3), after the nano-scratch test, C f / SiC ceramic matrix composites were ultrasonically cleaned with acetone to remove debris from scratched surfaces and then dried.

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