A method for obtaining the brittle-plastic transition depth of two-phase composite materials

Abstract

This invention discloses a method for obtaining the brittle-plastic transition depth of a two-phase composite material. The method involves using a metallographic microscope to capture a microscopic image of the scratch surface morphology. The locations of the first small pit and the first large pit in the scratch are determined from this image. Then, the distances from these two locations to the scratch incision point are measured using a measuring scale. The three-dimensional morphology of the scratch groove is obtained by photographing it using a white light interferometer. Based on the distances obtained from the measuring scale, the starting point (first small pit) and the ending point (first large pit) of the brittle-plastic transition zone are determined. The cross-sectional profile curve of the scratch at these locations is then captured, and the groove depth is measured. This invention combines the microscopic morphology captured by a microscope with the three-dimensional morphology obtained by white light interferometry to accurately determine the location and depth of the brittle-plastic transition in the material. This avoids interference from defects in the two-phase composite material itself or surface impurities and dust, effectively improving the accuracy of the test results.

Description

Technical Field

[0001] This invention discloses a method for obtaining the brittle-plastic transition depth of two-phase composite materials, relating to the technical field of obtaining the brittle-plastic transition depth of two-phase composite materials. Background Technology

[0002] The brittle-plastic transition depth refers to the critical depth of cut during machining of brittle materials, where the material transitions from a state of plastic deformation to a state of brittle fracture. When the depth of cut is less than this critical value, material removal is achieved through plastic deformation. However, when the depth of cut is greater than this critical value, brittle fracture occurs during material removal. It is an important reference indicator for achieving plastic-domain machining of brittle materials.

[0003] Scratch testing is a common method for obtaining the brittle-plastic transition depth, with variable depth-of-cut scratch testing being particularly prevalent. The scratching tools used include Berkovich diamond tips, diamond tapers, and lathe inserts. Scratch experiments using Berkovich diamond tips can be performed on a nanoindenter, yielding relatively ideal brittle-plastic transition depths. Scratch experiments using diamond tapers and lathe inserts can be performed on various precision machine tools, with scratch speeds and tooling closely resembling actual machining conditions, and the scratch path can be straight or circular.

[0004] Obtaining an accurate result of the brittle-plastic transition depth is crucial for the success of an experiment; however, achieving accurate results in actual testing is quite difficult. On one hand, a steep change in cutting depth during testing results in a very small plastic cutting area on the scratch surface, making it difficult to observe and affecting the accurate measurement of the brittle-plastic transition depth. Conversely, a too gradual change in cutting depth can lead to inconspicuous changes in the scratch surface morphology, or even result in the cutting depth not reaching the brittle-plastic transition depth during testing. On the other hand, calculating the brittle-plastic transition depth using the geometric relationship between scratch width and maximum scratch depth fails to account for the unstable effects of the scratching process. Methods relying on white light interferometers or laser confocal microscopes to obtain the three-dimensional morphology of the scratch are easily affected by impurities or defects in the material itself.

[0005] In existing technologies, to specifically address the issue of tests being susceptible to the influence of impurities or material defects, a common approach is to use atomic force microscopy (AFM) to detect the three-dimensional and two-dimensional morphologies of scratches. While this method can locate brittle pit regions and accurately determine the brittle-plastic transition zone and obtain precise depth from the three-dimensional morphology image, AFM detection of scratch morphology requires extremely high precision and sensitivity. Furthermore, it is highly sensitive to AFM probe wear and failure, and the accuracy decreases with increasing test counts, leading to inaccurate results.

[0006] In summary, the existing technology suffers from inaccurate testing results of the brittle-plastic transition depth.

[0007] Content of this invention

[0008] The purpose of this invention is to provide a method for obtaining the brittle-plastic transition depth of two-phase composite materials, so as to achieve accurate acquisition of the brittle-plastic transition depth of two-phase composite materials.

[0009] To achieve the above-mentioned technical objectives and effects, the invention is implemented through the following technical solution:

[0010] A method for obtaining the brittle-plastic transition depth of a two-phase composite material, specifically: controlling the cutting depth of the tool to increase linearly from 0 to the maximum cutting depth as the scratch length increases during the scratching process, with a cutting speed of at least 100 mm / min;

[0011] The surface morphology of the scratch was photographed using a metallographic microscope. The location of the first small pit and the first large pit in the scratch was determined from the surface morphology of the scratch. Then, the distance between the two locations and the scratch incision location was measured with a measuring scale. The three-dimensional morphology of the scratch groove was obtained by photographing it with a white light interferometer.

[0012] The starting point (first small pit) and ending point (first large pit) of the brittle-plastic transition zone are determined based on the distance obtained from the measuring scale. The cross-sectional profile curve of the scratch at this location is taken and the groove depth is measured.

[0013] Furthermore, the surface of the sample to be subjected to the scratch test is pre-ground and polished to ensure that the surface flatness is good under visual observation and that the surface roughness of the sample is less than 0.1 μm.

[0014] Fix the force gauge on the machine tool worktable, use a clamp to fix the tool holder with the cutting tool on the force gauge, and ensure that the rake face of the cutting tool is perpendicular to the X or Y direction of the machine tool;

[0015] The force signal on the tool is tested when the tip of the tool just touches the surface of the sample.

[0016] Furthermore, the scratch path is set as a line segment along the X or Y direction, and the scratch path is divided into several equal parts with a length of 2 to 3 mm.

[0017] Furthermore, tool setting is performed at the starting point, each dividing point, and the ending point of the scratch, and the Z-coordinate of each point is recorded. At the same time, the Z-coordinate of the starting point of the scratch is set to zero, and the parallel line segments with a distance of 0.5 to 1 mm between the tool setting positions are used as the scratch path.

[0018] Furthermore, the cutting depth of each segment on the scratch path increases at the same rate as the scratch length increases. The tool's Z-axis coordinate at each dividing point on the scratch path is calculated during the scratching process, and the scratching speed of the tool is controlled by the given X-axis or Y-axis feed speed of the machine tool.

[0019] Furthermore, after removing the sample and ultrasonically cleaning to remove residual chips from the surface, a microscopic image of the surface morphology of the scratch was taken using a metallographic microscope at a magnification of 200 to 1000 times.

[0020] The characteristics of brittle pits on the surface during brittle removal of materials were analyzed. These characteristics include strip-shaped, sheet-shaped, granular with sharp edges, and multiple clustered pits.

[0021] Get and record the location where the first small dent appears and the location where the first large dent appears;

[0022] The term "small pit" refers to a depression that occurs within the scratch surface. The term "large pit" refers to a large, complete pit or a pit composed of multiple interconnected or contacting smaller pits. The term "large pit" refers to a pit whose width along the cross-sectional direction of the scratch is greater than 1 / 2 of the width of the scratch groove.

[0023] Furthermore, a measuring ruler was used to measure the distance between the location where the first small dent and the location where the large dent appeared and the location where the scratch cut in.

[0024] The location where the first small pit appears is taken as the starting point of the brittle-plastic transition zone, and the location where the first large pit appears is taken as the ending point of the brittle-plastic transition zone.

[0025] Furthermore, the feature is that a white light interferometer is used to photograph the scratched surface and obtain a three-dimensional topographic image of the scratch. Some obvious small pits can be seen from the three-dimensional topographic image. Based on the recorded positions of the first small pit and the first large pit, the corresponding target areas are determined on the three-dimensional topographic image.

[0026] Furthermore, the feature is that the coordinate data of the contour acquisition points on the cross-section of the scratch are extracted at the target area on the three-dimensional topography map, which are the x-coordinate along the extraction path direction of the cross-section and the z-coordinate along the depth direction.

[0027] Linear fitting is performed on the coordinate data of the collection points on both sides of the scratch edge. The fitted straight line is used as the baseline of the initial height on the cross section. Then, the maximum distance between the collection point on the inside of the scratch and the baseline is calculated, and the maximum distance is used as the cutting depth on the cross section.

[0028] Furthermore, the feature is that the formula for the distance between the sampling point within the scratch and the baseline is as follows:

[0029]

[0030] In the formula, d i x is the distance between any sampling point i within the scratch and the baseline; i and z i , respectively, are the x-coordinate of any acquisition point i within the scratch along the cross-section extraction path and the z-coordinate along the depth direction; k and b are the slope and intercept of the baseline expression, respectively.

[0031] Beneficial effects:

[0032] This invention analyzes the morphological characteristics of the start and end points of the brittle-plastic transition zone from microscopic images taken by a metallographic microscope, and measures the distances between the two locations and the scratch entry point. Based on the measured distances, the target region is determined from the three-dimensional morphology captured by a white light interferometer. This method reduces the subjectivity of determining the brittle-plastic transition location and improves the anti-interference and repeatability of the determination. It expands the brittle-plastic transition point of the material to the brittle-plastic transition zone, which is more in line with the complex characteristics of the brittle-plastic transition process of two-phase composite materials.

[0033] When measuring the depth of the brittle-plastic transition zone, the cutting depth is determined by calculating the maximum distance between the sampling point on the inside of the scratch and the fitted initial height baseline. This reduces the measurement error caused by the inconsistency in surface height on both sides of the scratch edge and effectively improves the accuracy of the test results.

[0034] Furthermore, by controlling the cutting speed, maintaining the linear relationship between the cutting depth and the advance position, and ensuring that the cutting position avoids the positioning position, the present invention avoids potential influences and improves the accuracy of test results from the cutting process.

[0035] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0036] Figure 1 This is a flowchart of a method for obtaining the depth of the brittle-plastic transition zone of a two-phase composite material according to the present invention;

[0037] Figure 2 Diagram of the experimental setup for variable depth scratching;

[0038] Figure 3 A schematic diagram illustrating the experimental principle of variable shear depth scratches on the sample surface;

[0039] Figure 4 This is a schematic diagram showing the tool setting position and the scratch path;

[0040] Figure 5a Microscopic image of the surface morphology of the scratch at the starting point of the brittle-plastic transition zone under a metallographic microscope;

[0041] Figure 5b This is a microscopic image of the surface morphology of the scratch at the endpoint of the brittle-plastic transition zone under a metallographic microscope.

[0042] Figure 6a A schematic diagram of the cross-section at the starting point of the brittle-plastic transition region in a three-dimensional topography image captured by a white light interferometer;

[0043] Figure 6b Schematic diagram of the cross section at the endpoint of the brittle-plastic transition region in a 3D topographic image captured by a white light interferometer;

[0044] Figure 7a A schematic diagram of the cutting depth on the cross-section 1 of the scratch at the starting point of the brittle-plastic transition zone;

[0045] Figure 7b A schematic diagram of the cutting depth on the cross-section 2 of the scratch at the end of the brittle-plastic transition zone;

[0046] Wherein: 1-machine tool spindle, 2-fixture, 3-tungsten alloy sample, 4-turning tool, 5-tool holder, 6-fixture, 7-force gauge, 8-machine tool worktable, 9-force gauge data acquisition and signal amplification system, 10-computer; Detailed Implementation

[0047] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.

[0048] Example 1

[0049] Existing research has shown that as the cutting depth increases, brittle materials undergo a transformation process from plastic removal to a transition zone between brittle and plastic, and then to brittle removal as the main process. During this process, the proportion of brittle removal gradually increases. Brittle removal as the main process indicates that there is still plastic removal in the material, but the proportion of brittle removal is larger and tends to be stable.

[0050] As the scratch depth increases, the material removal process can be divided into the following stages: plastic removal stage, brittle-plastic transition stage, and brittle removal stage. Using a metallographic microscope to photograph the scratch surface, it can be observed that as the cutting depth continuously increases, the surface morphology gradually changes from an initial smooth, crack-free, and pit-free characteristic to a characteristic of large-area pits and frequent coarse cracks. The brittle-plastic transition zone has a certain depth span; the starting point of the brittle-plastic transition zone is the location of the first small pit resulting from brittle fracture, and the ending point is the location of the first large pit resulting from brittle fracture.

[0051] Based on the aforementioned principles, the applicant discloses in this embodiment a method for obtaining the brittle-plastic transition depth of a two-phase composite material. Specifically, the cutting depth of the tool increases linearly from 0 to the maximum cutting depth as the scratch length increases during the scratching process, with a cutting speed of at least 100 mm / min.

[0052] The surface morphology of the scratch was photographed using a metallographic microscope. The location of the first small pit and the first large pit in the scratch was determined from the surface morphology of the scratch. Then, the distance between the two locations and the scratch incision location was measured with a measuring scale. The three-dimensional morphology of the scratch groove was obtained by photographing it with a white light interferometer.

[0053] The starting point (first small pit) and ending point (first large pit) of the brittle-plastic transition zone are determined based on the distance obtained from the measuring scale. The cross-sectional profile curve of the scratch at this location is taken and the groove depth is measured.

[0054] In the first specific embodiment, the surface of the sample to be subjected to the scratch test is pre-ground and polished to ensure that the surface flatness is good under visual observation, so that the surface roughness of the sample is less than 0.1 μm, and no obvious scratches are observed under a metallographic microscope.

[0055] Then, with the surface of the sample to be scratched facing outwards, it is fixed to the machine tool spindle 1 using clamps 2 and 6. The cutting tool is mounted on the tool holder 5. In order to accurately set the tool and collect the cutting force during the scratching process, the force gauge 7 is fixed on the machine tool worktable 8. The tool holder 5 with the cutting tool is fixed to the force gauge 7 using clamps 2 and 6, and it is ensured that the rake face of the cutting tool is perpendicular to the X or Y direction of the machine tool.

[0056] Finally, the force gauge 7 is turned on to collect the force data of the tool in real time, and the machine tool feed is controlled to perform the tool setting operation. When the tool tip just touches the sample surface, the increase in the tool force signal can be seen in the force gauge 7 software window.

[0057] Pretreatment of the material surface and initial calibration of the test can effectively improve the accuracy of the test.

[0058] In a second specific embodiment, the scratch path is set as a line segment along the X or Y direction. To reduce the adverse effect of the flatness of the sample surface on the control of the cutting depth, the scratch path is divided into several equal parts, each with a length of 2 to 3 mm. This embodiment can divide it into 2 to 4 equal parts to improve the straightness of the surface contour of each part on the scratch path.

[0059] In a preferred embodiment of this specific example, the cutting depth of the tool is controlled by a high-precision CNC device to achieve a more accurate acquisition of the brittle-plastic transition depth. The CNC device can precisely control the cutting depth of the tool at equal intervals along each scratch path, thereby avoiding measurement errors caused by insufficient flatness of the sample surface.

[0060] In another preferred embodiment, during the scratching process, each scratch path segment can be monitored in real time. For example, a laser displacement sensor or other high-precision measuring device can be used to measure the distance between the tool and the sample surface in real time. Thus, as the tool cuts to each segment, the cutting depth can be adjusted based on the real-time measurement data to achieve a more accurate acquisition of the brittle-plastic transition depth.

[0061] In another preferred embodiment, during the experiment, the optimal scratch parameters can be determined by repeating the scratching operation multiple times and comparing the results of each operation. This further improves the accuracy of obtaining the brittle-plastic transition depth.

[0062] Compared with the prior art, the preferred embodiment of the second specific embodiment can better solve the adverse effects of sample surface flatness on cutting depth control, thereby achieving more accurate acquisition of brittle-plastic transition depth.

[0063] In the third specific embodiment, tool setting is performed at the scratch start point, each dividing point, and the end point, and the Z-coordinate of each point is recorded. At the same time, the Z-coordinate of the scratch start point is set to zero.

[0064] To avoid the contact pressure between the tool and the sample during the tool setting process affecting the scratch morphology, and to ensure the validity of the tool setting data, a parallel line segment 0.5 to 1 mm away from the tool setting position in step 3 is used as the scratch path.

[0065] In a preferred embodiment of this specific example, the cutting tool can be pre-sharpened before the tool setting operation to ensure its sharpness and flatness. This helps reduce the friction between the tool and the sample, preventing unnecessary damage to the sample during the cutting process.

[0066] In a preferred embodiment, a closed-loop control system can be used during the scratching process to monitor the tool's motion in real time and adjust the tool based on the real-time data. This helps ensure that the tool maintains a constant cutting depth throughout the scratching process, thereby improving the stability of the brittle-plastic transition depth acquisition.

[0067] In a preferred embodiment, to prevent the cutting tool from being affected by vibration or other interference factors during the scratching process, anti-vibration measures, such as a suspended platform or anti-vibration pads, can be used to reduce the impact of the external environment on the scratching process. Simultaneously, the scratching equipment can be isolated to prevent interference from the operation of other equipment.

[0068] Based on the aforementioned preferred embodiments, multiple scratches can be performed during the scratching process, and the results of each scratch can be averaged to improve the stability and accuracy of the measurement results.

[0069] Compared with the prior art, the preferred embodiment of the third specific embodiment can effectively avoid the influence of the contact pressure between the tool and the sample on the scratch morphology while ensuring the validity of the tool setting data, thereby achieving a more accurate acquisition of the brittle-plastic transition depth.

[0070] In the fourth specific embodiment, the cutting depth of the tool increases linearly from 0 to the maximum cutting depth as the scratch length increases during the scratching process. Under the condition that the cutting depth of each equal part on the scratching path increases at the same rate as the scratch length increases, the Z-axis coordinate of the tool at each dividing point on the scratching path during the scratching process is calculated, and the CNC program is written based on the calculated coordinates. The scratching speed of the tool is achieved by setting the X-axis or Y-axis feed speed of the machine tool.

[0071] In some embodiments, a machine tool can be used to perform variable depth scratch experiments by running a CNC program.

[0072] By controlling the relationship between depth and scratch advancement, the scratch can be made to gradually become deeper, which meets the cutting conditions required in scratch experiments and can improve the accuracy of test results.

[0073] In the fifth specific embodiment, after removing the sample and performing ultrasonic cleaning to remove residual chips from the surface, a microscopic image of the surface morphology of the scratch was taken using a metallographic microscope at a magnification of 200 to 1000 times.

[0074] The characteristics of brittle pits on the surface during brittle removal of materials were analyzed. These characteristics include strip-shaped, sheet-shaped, granular with sharp edges, and multiple clustered pits.

[0075] Get and record the location where the first small dent appears and the location where the first large dent appears;

[0076] The term "small pit" refers to a depression that occurs within the scratch surface. The term "large pit" refers to a large, complete pit or a pit composed of multiple interconnected or contacting smaller pits. The term "large pit" refers to a pit whose width along the cross-sectional direction of the scratch is greater than 1 / 2 of the width of the scratch groove.

[0077] Specifically, after removing the sample and ultrasonically cleaning to remove residual chips, a metallographic microscope is used to photograph the surface morphology of the scratches at a magnification of 200–1000x. As the cutting depth gradually increases from 0, the changes in the smoothness, size, and number of pits on the scratched surface are observed. The fracture or breakage pits on the scratched surface of two-phase composite materials are complex and diverse. Therefore, it is necessary to first observe and analyze some characteristics of brittle surface pits during brittle removal using a metallographic microscope, such as elongated, thin-sheet, sharply angular granular, or multiple clustered pits. Then, starting from the scratch initiation point, the first small pit matching these characteristics is located and its position is recorded. The distance between the location of the first small pit and the scratch incision point can be measured using the software's measurement scale, or the morphology of the small pit can be recorded.

[0078] The brittle-plastic transition in composite materials is often not a rapid process. After the appearance of the first small pit, there is still a period of relatively good plastic removal, with pits of different shapes and sizes appearing randomly until the first series of large pits appear. After this point, the smoothness of the scratched surface begins to deteriorate further, and the plastic removal area significantly decreases. This length of scratched area is considered the brittle-plastic transition zone. Depending on the research requirements, the location of the first large pit can be recorded. The location of the first small pit is considered the starting point of the brittle-plastic transition zone, and the location of the first large pit is considered the ending point.

[0079] Based on the foregoing, in this implementation, a white light interferometer can be used to photograph the scratched surface and obtain a three-dimensional topographic image of the scratch. Some obvious small pits can be seen from the three-dimensional topographic image. Based on the recorded positions of the first small pit and the first large pit, the corresponding target areas are determined on the three-dimensional topographic image. This can be determined indirectly by the distance between the location of the pit and the cut-in position of the scratch, or it can be determined directly by comparing the topographic features of the pits.

[0080] Compared to existing technologies, this embodiment removes residual chips from the surface using ultrasonic cleaning, effectively reducing the impact of surface impurities on the measurement of the brittle-plastic transition depth and improving the accuracy of the measurement results. Metallurgical microscopy is used to capture microscopic images of the scratch surface morphology, and by analyzing the characteristics of the brittle pits, the start and end points of the brittle-plastic transition zone are more accurately located, thus precisely determining the brittle-plastic transition depth. Combined with three-dimensional morphology images captured by white light interferometer, the shape and location of the pits can be observed more intuitively, further improving the accuracy and reliability of obtaining the brittle-plastic transition depth. By recording the positions of the first small pit and the first large pit, the extent of the brittle-plastic transition zone can be more accurately reflected.

[0081] In summary, the fifth specific embodiment comprehensively utilizes metallurgical microscope and white light interferometer, enabling observation and analysis at different scales and angles during the acquisition of the brittle-plastic transition depth, thereby revealing the laws governing the brittle-plastic transition of composite materials more comprehensively.

[0082] In the sixth specific embodiment, a white light interferometer is used to photograph the scratched surface and obtain a three-dimensional topographic image of the scratch. Some obvious small pits can be seen from the three-dimensional topographic image. The positions of the first small pit and the first large pit are recorded, and the corresponding target areas are determined on the three-dimensional topographic image.

[0083] It should be understood that in this case, when a white light interferometer is used to photograph the scratched surface and obtain a three-dimensional topographic image of the scratch, only some of the deeper pits can be seen in the three-dimensional topographic image, and some shallow pits are difficult to see. Therefore, it is necessary to determine the target areas of the starting point and the ending point of the brittle-plastic transition zone in the three-dimensional topographic image, which effectively avoids misjudgment.

[0084] In the seventh specific embodiment, the coordinate data is imported into Origin, and the coordinate data of the collection points on both sides of the scratch edge are linearly fitted. The fitted straight line is used as the baseline of the initial height on the cross section. Then, the maximum distance between the collection point on the inside of the scratch and the baseline is calculated, and the maximum distance is used as the cutting depth on the cross section.

[0085] The cutting depths obtained in the target areas corresponding to the first small pit and the first large pit correspond to the starting depth and ending depth of the brittle-plastic transition zone of the material, respectively.

[0086] In this embodiment, the formula for the distance between the sampling point within the scratch and the baseline is as follows:

[0087]

[0088] In the formula, d i x is the distance between any sampling point i within the scratch and the baseline; i and z i , respectively, are the x-coordinate of any acquisition point i within the scratch along the cross-section extraction path and the z-coordinate along the depth direction; k and b are the slope and intercept of the baseline expression, respectively.

[0089] In summary, the effects achieved by this embodiment include:

[0090] 1. Lathe tools with different tip radii and rake angles can be used, and different scratching speeds can be used to conduct variable cutting depth scratching experiments to study the depth of the brittle-plastic transition zone of materials. The experimental procedure is simple and highly repeatable.

[0091] 2. The effect of grinding and polishing the sample before the experiment is only required to achieve a surface roughness of less than 0.1μm, good surface flatness observed by the naked eye, and no obvious scratches observed under a metallographic microscope. The sample preparation is simple.

[0092] 3. The variable depth scratch experiment can more precisely control the rate at which the cutting depth increases with the scratch length, thus allowing for the acquisition of plastic cutting zones of different lengths based on experience and experimental needs.

[0093] 4. Based on the morphological change law of the material from plastic removal to brittle removal and the characteristics of brittle pits, the starting and ending positions of the brittle-plastic transition zone are recorded in the images taken by the metallographic microscope. The target area is determined in the three-dimensional morphology taken by the white light interferometer based on the recorded positions. This method greatly reduces the subjectivity of determining the brittle-plastic transition position and improves the anti-interference and repeatability of the determination of the brittle-plastic transition position. In addition, it expands the brittle-plastic transition point of the material to the brittle-plastic transition zone, which is more in line with the complex characteristics of the brittle-plastic transition process of two-phase composite materials.

[0094] 5. When measuring the depth of the brittle-plastic transition zone, the cutting depth is determined by calculating the maximum distance between the sampling point on the inside of the scratch and the fitted initial height baseline. This can reduce the measurement error caused by the inconsistency of the surface height on both sides of the scratch edge, making the cutting depth measurement results more accurate.

[0095] 6. The cutting force of the entire scratching process is collected in real time by the force measuring instrument 7, which can provide a basis for subsequent research on the cutting force range of composite materials under different removal methods.

[0096] Example 2

[0097] Based on the test method in Example 1, the applicant conducted a specific scratch test in this example. The material tested in this example was a tungsten alloy sample 3, with dimensions of 12mm × 10mm × 5mm. Figure 1 This is a flowchart of a method for obtaining the depth of the brittle-plastic transition zone of a two-phase composite material according to the present invention, including:

[0098] S1: Sample preparation and experimental setup

[0099] The surface of the 12mm×10mm×5mm tungsten alloy sample 3 to be subjected to scratch test was ground and polished so that the surface flatness of the tungsten alloy sample 3 was good by visual observation, the surface roughness Ra≤0.1μm, and no obvious scratches were observed under a metallographic microscope.

[0100] like Figure 2As shown, the tungsten alloy sample 3, with the surface to be tested for scratching facing down, is fixed to the machine tool spindle 1 by the fixture 2. The turning tool 4 is mounted on the tool holder 5. In order to accurately set the tool and collect the cutting force during the scratching process, the force gauge 7 is fixed on the machine tool worktable 8. The tool holder 5 with the tool 4 is fixed on the force gauge 7 by the fixture 6, and the rake face of the tool 4 is ensured to be perpendicular to the Y direction of the machine tool.

[0101] S2: Perform a scratch test on the knife.

[0102] like Figure 3 As shown, a variable depth scratching experiment with a length of 6 mm, a cutting depth of 0–15 μm, and a scratching speed of 1000 mm / min will be performed on the sample. Before the experiment, the data acquisition and signal amplification system 9 of the force measuring instrument is turned on to collect the force data of the tool in real time and display it in real time in the force measuring instrument software of the computer 10, controlling the Z-axis feed and Y-axis feed of the machine tool for tool setting. When the tool tip just contacts the sample surface, the increase in the tool force signal can be seen in the force measuring instrument software window. Figure 4 As shown, the scratch path is set as a 6mm long line segment along the Y direction. To reduce the adverse effect of the sample surface flatness on the cutting depth control, the scratch path is divided into three equal parts to improve the straightness of the surface contour of each part. Tool setting is performed at the scratch start point, each dividing point, and the end point, and the Z-coordinate of each point is recorded. The Z-coordinate of the scratch start point is set to zero. To avoid the influence of the contact pressure between the tool and the sample on the scratch morphology during tool setting, and to ensure the validity of the tool setting data, a parallel line segment 0.5mm away from the tool setting position is used as the scratch path. Under the condition that the cutting depth of each part of the scratch path increases at a consistent rate with the scratch length, the tool Z-coordinate of each dividing point on the scratch path is calculated during the scratching process. A CNC program is written based on the calculated coordinates, and the tool scratching speed is achieved by setting the Y-axis feed speed of the machine tool. The machine tool conducts variable depth scratching experiments by running the CNC program.

[0103] S3: Characterize scratch morphology and determine the location of the brittle-plastic transition zone.

[0104] After removing the sample from the experimental setup and performing ultrasonic cleaning to remove residual chips, a microscopic image of the scratched surface morphology was captured using a metallographic microscope at a magnification of 200–1000x. For example... Figure 5aAs shown, as the cutting depth gradually increases from 0, the changes in the smoothness, size, and number of pits on the scratch surface are observed. The fracture or breakage pits on the scratch surface of tungsten alloy sample 3 are complex and diverse. Therefore, a metallographic microscope is used to first observe and analyze some characteristics of brittle surface pits during brittle removal, such as elongated, thin-plate, sharply angular granular, or multiple clustered pits. Then, starting from the scratch initiation point, the first small pit matching these characteristics is searched for and its position recorded. The recording method involves measuring the distance between the location of the first small pit and the scratch incision point using the software's measuring scale, or recording the morphology of the small pit. For example... Figure 5b As shown, the brittle-plastic transition of tungsten alloys is not completed quickly. After the first small pit appears, there is still a period of relatively good plastic removal, with pits of different shapes and sizes appearing randomly until the first series of large pits appears. After this point, the smoothness of the scratch surface begins to deteriorate further, and the plastic removal area significantly decreases. This length of scratch area is considered the brittle-plastic transition zone. Locate the first large pit and record its position. The location of the first small pit is taken as the starting point of the brittle-plastic transition zone, and the location of the first large pit is taken as the ending point.

[0105] S4: Obtain the depth of the brittle-plastic transition zone

[0106] A white light interferometer was used to photograph the scratched surface and obtain a three-dimensional morphology image of the scratch. Some obvious small pits can be seen in the 3D morphology image, such as... Figure 6a and Figure 6b As shown, based on the recorded positions of the first small and first large dents, the corresponding target areas are determined on the 3D topography map. This can be indirectly determined by the distance between the dent's location and the scratch's entry point, or directly determined by comparing the dent's shape. Then, the coordinate data of the contour acquisition points on the scratch cross-section are extracted at the target areas on the 3D topography map, namely the x-coordinate along the extraction path direction and the z-coordinate along the depth direction.

[0107] like Figure 7a and Figure 7b As shown, the coordinate data is imported into Origin, and linear fitting is performed on the coordinate data of the collection points on both sides of the scratch edge. The fitted straight line is used as the baseline for the initial height on the cross-section. Then, the maximum distance between the collection point on the inside of the scratch and the baseline is calculated, and the maximum distance is used as the cutting depth on the cross-section. The cutting depths obtained in the target areas corresponding to the first small pit and the first large pit correspond to the starting depth and ending depth of the brittle-plastic transition zone of the material, respectively.

[0108] The above are merely some of the embodiments of this application and are not intended to limit the application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments shall still fall within the scope of protection of the technical solution of this application.

Claims

1. A method for obtaining the brittle-plastic transition depth of a two-phase composite material, characterized in that, During the scribing process, the cutting depth of the tool increases linearly from 0 to the maximum cutting depth as the scribing length increases, and the cutting speed is at least 100 mm / min; The surface morphology of the scratch was photographed using a metallographic microscope. The location of the first small pit and the first large pit in the scratch was determined from the surface morphology of the scratch. Then, the distance between the two locations and the scratch incision location was measured with a measuring scale. The three-dimensional morphology of the scratch groove was obtained by photographing it with a white light interferometer. Determine the start and end points of the brittle-plastic transition zone based on the distance obtained from the measuring scale, take the cross-sectional profile curve of the scratch at the start and end points of the brittle-plastic transition zone and measure the groove depth; The starting point is specifically the first small pit, and the ending point is specifically the location of the first large pit; The surface of the sample to be subjected to scratch test is pre-ground and polished to ensure that the surface flatness is good under visual observation and that the surface roughness of the sample is less than 0.1 μm. Fix the force gauge on the machine tool worktable, use a clamp to fix the tool holder with the cutting tool on the force gauge, and ensure that the rake face of the cutting tool is perpendicular to the X or Y direction of the machine tool; The force signal on the tool is tested when the tip of the tool just touches the surface of the sample. The scratch path is set as a line segment along the X or Y direction, and the scratch path is divided into several equal parts with a length of 2~3mm. Tool setting is performed at the starting point, each dividing point, and the ending point of the scratch, and the Z-coordinate of each point is recorded. At the same time, the Z-coordinate of the starting point of the scratch is set to zero, and the parallel line segments with a distance of 0.5~1mm between the tool setting positions are used as the scratch path. The cutting depth of each segment on the scratch path increases at the same rate as the scratch length increases. The tool's Z-axis coordinate at each dividing point on the scratch path is calculated during the scratching process. The scratching speed of the tool is controlled by the given X-axis or Y-axis feed speed of the machine tool. After removing the sample and ultrasonically cleaning to remove residual chips from the surface, a metallographic microscope was used to take a microscopic image of the surface morphology of the scratches at a magnification of 200 to 1000 times. The characteristics of brittle pits on the surface during brittle removal of materials were analyzed. These characteristics include strip-shaped, sheet-shaped, granular with sharp edges, and multiple clustered pits. Get and record the location where the first small dent appears and the location where the first large dent appears; The small pit refers to the location of the depression that is produced in the scratch surface. The large pit is a single large-area continuous pit or a discontinuous pit composed of multiple smaller pits that are in contact with each other. The large pit is a pit whose width along the cross-sectional direction of the scratch is greater than 1 / 2 of the width of the scratch groove. A white light interferometer was used to photograph the scratched surface and obtain a three-dimensional topographic image of the scratch. Some obvious small pits can be seen from the three-dimensional topographic image. The positions of the first small pit and the first large pit were recorded, and the corresponding target areas were determined on the three-dimensional topographic image. The coordinate data of the contour acquisition points on the cross-section of the scratch are extracted in the target area of ​​the three-dimensional topography image, which are the x coordinates along the extraction path of the cross section and the z coordinates along the depth direction. Linear fitting is performed on the coordinate data of the collection points on both sides of the scratch edge. The fitted straight line is used as the baseline of the initial height on the cross section. Then, the maximum distance between the collection point on the inside of the scratch and the baseline is calculated, and the maximum distance is used as the cutting depth on the cross section. The formula for the distance between the sampling point within the scratch and the baseline is as follows: ； In the formula, It is the distance between any sampling point i within the scratch and the baseline; and , respectively, are the x-coordinate of any acquisition point i within the scratch along the cross-section extraction path and the z-coordinate along the depth direction; k and b are the slope and intercept of the baseline expression, respectively.

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