A method for measuring a scratch-induced metal surface layer plastic flow pattern based on DIC

Abstract

The application belongs to the technical field of metal material tribological performance test method, and particularly relates to a kind of based on DIC's scratch induced metal surface layer plastic rheological mode measurement method. Including the following steps: (1) preparing rectangular TA1 commercial pure titanium sample;(2) spraying spot on the sample observation surface;(3) the surface adjacent to the observation surface is taken as the scratch surface;(4) by friction testing machine, scratch is applied on the scratch surface, at the same time, high-speed camera is used to record video, and scratch video is obtained;(5) according to the scratch video, the strain size in the deformation zone is calculated;(6) the strain distribution curve of TA1 surface layer along the scratch direction is drawn;(7) the morphology of scratch TA1 surface under different loads is observed by scanning electron microscope;(8) the plastic rheological type is judged. The application provides a new idea for the dynamic formation process of microcracks and other damages in the scratch process, is relatively simple to operate, and has great application value.

Description

Technical Field

[0001] This invention belongs to the technical field of tribological property testing methods for metallic materials, specifically relating to a method for measuring the plastic rheological mode of scratch-induced metal surface based on DIC. Background Technology

[0002] Titanium and titanium alloys, as lightweight structural materials, possess excellent properties such as high toughness, low electrical conductivity, high specific strength, good corrosion resistance, and biocompatibility, making them indispensable materials in aerospace, automotive energy, biomedicine, and chemical industries. However, the relatively low strength and poor wear resistance of titanium alloys limit their application range to some extent. Currently, scratch testing is one of the most effective methods for studying the surface deformation behavior of metallic structural materials under high loads. Existing studies have shown that as the scratch-induced surface plastic rheological mode transforms from uniform laminar flow to chaotic eddy flow, significant material accumulation appears at the front of the wear mark, the wear mark surface is relatively rough, and there are numerous delamination and microcrack damages. Therefore, clarifying the strain field distribution and plastic rheological mode of scratch-induced metal surfaces is of great significance for revealing the friction and wear mechanism of alloys.

[0003] Imaging techniques, which utilize imaging equipment with appropriate exposure time and frame rate to intuitively capture and analyze information, are effective methods for studying strain distribution within plastic deformation zones. Particle Image Velocimetry (PIV) is one such effective technique for measuring strain fields. PIV is a transient, multi-point, non-contact fluid dynamics velocimetry method that indirectly measures the transient velocity distribution of a flow field by measuring the displacement of tracer particles over a known, extremely short time interval. PIV technology is often used to study the elastoplastic deformation behavior of materials during cutting and the chip formation mechanism. However, PIV technology requires laser illumination of the measured flow field area, demanding high laser energy. Insufficient laser pulse energy leads to inadequate exposure of the high-speed camera, resulting in unclear imaging of the tracer particles. Excessive laser energy produces strong laser reflection, also affecting measurement accuracy. For scratch strain analysis, in addition to errors caused by laser energy, the depth of surface scratch-induced strain is relatively small, and the displacement of tracer particles is not significant, leading to relatively insufficient accuracy of PIV technology and thus significant errors in friction strain measurement results. Summary of the Invention

[0004] The purpose of this invention is to provide a method for measuring plastic rheological modes introduced by metal scratching based on DIC (Dielectric-Induced Collision Diameter), including capturing the scratching process with a high-speed camera and performing strain analysis using DIC technology. Combined with the analysis of wear morphology on pure titanium surfaces, this method enables a more in-depth study of the friction and wear mechanism.

[0005] The technical solution to achieve the purpose of this invention is: a method for measuring the plastic rheological mode of scratch-induced metal surface based on DIC, comprising the following steps:

[0006] Step (1): Prepare rectangular TA1 commercial pure titanium samples;

[0007] Step (2): Spray a spot onto the sample observation surface;

[0008] Step (3) uses the surface adjacent to the observation surface as the rubbing surface;

[0009] Step (4): Apply scratching to the scratching surface using a friction testing machine, and simultaneously record the scratching video using a high-speed camera;

[0010] Step (5): Calculate the strain magnitude within the deformation zone based on the scratching video;

[0011] Step (6): Plot the strain distribution curve along the scratching direction in the TA1 surface layer;

[0012] Step (7): Observe the morphology of the scratches on the TA1 surface under different loads using a scanning electron microscope;

[0013] Step (8): Determine the type of plastic rheology.

[0014] Furthermore, the sample size in step (1) is 5±0.5mm×5±0.5mm×2±0.2mm.

[0015] Further, step (2) specifically involves: using a spray gun with a nozzle diameter of 0.5 mm to spray a layer of white paint on the surface so that the metallic luster of the sample is completely covered; then using a spray gun with a nozzle diameter of 0.18 mm to spray black paint spots on the surface, with the spots randomly distributed and the average diameter controlled below 20 μm, and the spots covering 80 ± 5% of the white paint area.

[0016] Furthermore, in step (4), the high-speed camera selects a 5x lens as the magnifying lens and a 100W LED light source as the illumination source.

[0017] Furthermore, the application of scratching in step (4) specifically involves using a conical diamond scratching head with a tip cone angle of 120° and a diameter of 0.2 mm, setting the scratching speed to 0.1 mm / s, the scratching distance to 1 mm, the loading time to 10 s, the holding time to 5 s, and the scratching time to 10 s.

[0018] Furthermore, in step (4), a high-speed camera is used to record the scratching video. Specifically, the following steps are taken: select loads of 2N, 10N, and 50N, set the image resolution to 2560×1920, the frame rate to 200fps, and the video saving time to 15s; start the friction machine, press the scratching head into the sample surface, and use the first 1s before it starts sliding as the starting point for shooting. Save the video after the 15s shooting time ends.

[0019] Further, step (5) specifically involves: sorting and organizing the scratching video and importing it into the DIC analysis program, selecting the strain change area within 100μm of the scratched surface, defining the starting point, and calculating the strain magnitude within the deformation zone.

[0020] Further, step (6) specifically involves: extracting the friction coefficients of rubbing under loads of 2N, 10N, and 50N from the friction testing machine; selecting a time point in the steady-state stage of strain, finding the strain magnitude directly below the indenter at the corresponding time in the DIC strain analysis, and plotting the strain distribution curve of the TA1 surface layer along the rubbing direction during that time.

[0021] Further, step (8) specifically means: within 200 μm in front of the indenter, when the strain difference between the maximum and minimum strain values ​​of the material surface is ≥15%, local strain concentration occurs, and the wear surface has peeling and crack damage. At this time, the plastic rheological type is eddy current; while when the strain difference of the material surface within 200 μm in front of the indenter is <15%, the strain distribution is relatively uniform, and there is no peeling phenomenon on the wear surface. At this time, the plastic rheological type is laminar flow.

[0022] This invention is achieved through the following technical solution: pure titanium is selected as the research object, and the scratching surface and the observation surface of pure titanium are polished; a thin layer of white primer is sprayed on the observation surface using a spray gun, and then randomly distributed black paint spots are sprayed; a series of images of the surface changes of the spray spots during the scratching process are captured and recorded by a high-speed camera, and DIC analysis is performed on the images to obtain the plastic rheological mode during the scratching process.

[0023] Results and benefits of the present invention:

[0024] (1) This patent provides a method for measuring the plastic rheological mode introduced by metal scratching based on DIC. By taking pictures with a high-speed camera and analyzing with DIC, the strain change of pure titanium surface under scratching stress can be observed in real time. Combined with the analysis of wear mark morphology, the plastic rheological mode in the scratching process under different loads can be obtained, which helps to analyze the surface deformation behavior and friction and wear mechanism of the material.

[0025] (2) This patent analyzes the strain changes under different scratch stresses and summarizes the strain field distribution, which is helpful for studying the surface modification process to improve the wear resistance of pure titanium surfaces.

[0026] (3) This patented technology is mature and relatively simple to operate. It provides a new idea for the study of the plastic rheological mode of pure titanium surface induced by scratching, and is of great significance for studying the initiation and propagation behavior of microcracks at stress concentration. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the scratched surface and the observation surface of the sample.

[0028] Figure 2 This diagram shows a high-speed camera, light source, and friction machine assembly.

[0029] Figure 3 The figures show the strain distribution diagrams of DIC analysis under different loads and the strain distribution curves of the rubbing surface along the rubbing direction at a certain time point in the steady-state stage. The strain values ​​directly below the rubbing indenter are circled in the figures for different loads at the selected time. Among them, (a1) is the strain distribution diagram at 5.5 seconds under 2N load, (a2) is the strain distribution curve at 5.5 seconds under 2N load, (b1) is the strain distribution diagram at 6 seconds under 10N load, (b2) is the strain distribution curve at 6 seconds under 10N load, (c1) is the strain distribution diagram at 8.5 seconds under 50N load, and (c2) is the strain distribution curve at 8.5 seconds under 50N load.

[0030] Figure 4 The wear marks under different loads are shown in (a) and (b) are the wear marks on the TA1 surface under a 2N load, and (c) are the wear marks on the TA1 surface under a 10N load. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings.

[0032] This invention provides a method for measuring the plastic rheological mode introduced by metal scratching based on DIC (Digital Injection Control). The method includes capturing images of the scratching process using a high-speed camera, performing strain analysis using DIC technology, and observing the wear mark morphology using SEM (Sequencing Electron Microscopy). A series of images of the surface spray pattern changes of pure titanium during the scratching process are captured by a high-speed camera. DIC analysis is then performed on these images to obtain the strain distribution during the scratching process. The wear mark morphology captured by SEM is then combined with the strain field distribution to determine whether the plastic rheological type introduced by scratching under different loads is laminar or eddy current. This patent allows for real-time observation of the strain changes on the surface of pure titanium under scratching stress, which helps in analyzing the surface deformation behavior and friction and wear mechanism of the material. This patented technology is mature and relatively simple to operate. It provides a new approach for analyzing the plastic rheological mode introduced by metal scratching and the dynamic strain distribution during the scratching process of pure titanium. It is of great significance for studying the surface deformation behavior of metallic structural materials under different loads and the friction and wear mechanism of alloys, and is beneficial for understanding the sliding flow field and deformation field in metals, thereby improving the functional properties of metal surfaces.

[0033] A method for measuring plastic rheological modes induced by metal scratching based on DIC (Diverterless Induction) is proposed. A series of images of surface spray changes during scratching under different loads are captured and recorded using a high-speed camera. DIC analysis is performed on these images to obtain the strain distribution during the scratching process. The morphology of the scratch is observed using SEM (Sequencing Electron Microscopy) and correlated with the strain field distribution to determine the type of plastic rheology (eddy current, laminar flow) induced by scratching under different loads.

[0034] The average diameter of the spray spots should be controlled below 20μm, and the distribution of the spots should be controlled to cover about 80% of the white paint area. Use a spray gun with a nozzle diameter of 0.5mm to spray white paint and a spray gun with a nozzle diameter of 0.18mm to spray black paint.

[0035] The high-speed camera uses a 5x zoom lens and a 100W LED light source for illumination. The image resolution is 2560×1920, and the frame rate is 200fps.

[0036] The strain analysis region of the titanium alloy surface layer is within a 100 μm thickness below the wear track. As the load increases, the strain non-uniformity intensifies, and the strain directly below the indenter increases with the load. Within a 200 μm range in front of the indenter, when the strain difference between the maximum and minimum strain values ​​on the material surface is ≥15%, local strain concentration occurs, and spalling and crack damage appear on the wear track surface. The plastic rheological type introduced at this time is eddy current. Conversely, when the strain difference on the material surface within a 200 μm range in front of the indenter is <15%, the strain distribution is relatively uniform, and there is no spalling on the wear track surface. The plastic rheological type introduced at this time is laminar flow.

[0037] Example

[0038] (1) TA1 commercial pure titanium was cut into samples with dimensions of 5mm×5mm×2mm as experimental objects.

[0039] (2) Spray spots on the observation plane of the sample. First, use a spray gun with a nozzle diameter of 0.5 mm to spray a thin layer of white paint on the surface to achieve the effect of completely covering the metallic luster of the sample; then use a spray gun with a nozzle diameter of 0.18 mm to spray black paint spots on the surface. The spots are randomly distributed, with an average diameter controlled below 20 μm, and the spots cover about 80% of the white paint area.

[0040] (3) Assemble a high-speed camera, select a 5x lens as the magnifying lens, a 100W LED light source as the illumination source, adjust the position of the camera and the friction test machine, change the focal length of the camera and the exposure time of the shot until a clear and magnified image appears.

[0041] (4) Use a conical diamond rubbing head with a tip cone angle of 120° and a diameter of 0.2 mm. Set the rubbing speed to 0.1 mm / s, the rubbing distance to 1 mm, the loading time to 10 s, the holding time to 5 s, and the rubbing time to 10 s.

[0042] (5) Select loads of 2N, 10N, and 50N, set the image resolution to 2560×1920, the frame rate to 200fps, and the video save time to 15s. Start the friction machine, press the rubbing head into the sample surface, and use the first 1s before it starts sliding as the starting point for shooting. Save the video after the 15s shooting time ends.

[0043] (6) Export the saved video file as a TIFF image, sort and organize it, then import it into the DIC analysis software. Select the strain change area within 100 μm of the scratched surface, define the starting point, and calculate the strain magnitude in the deformation zone.

[0044] (7) Derive the coefficient of friction (COF) under loads of 2N, 10N, and 50N from the friction testing machine. Select a time point during the steady-state strain stage, such as... Figure 3 As shown, the 5.5th second was selected for the 2N load, the 6th second for the 10N load, and the 8.5th second for the 50N load. During the DIC strain analysis, the strain magnitude directly below the indenter at the corresponding time was determined, and the strain distribution curve along the scratch direction in the TA1 surface layer was plotted for that time.

[0045] (8) The morphology and structure of the surface scratches on TA1 surfaces subjected to 2N, 10N, and 50N loads were observed and analyzed using a scanning electron microscope (SEM), such as... Figure 4 As shown.

[0046] (9) Summarize and analyze the scratch test results under different loads, explore the relationship between scratch morphology and load magnitude, and combine the DIC strain analysis results to determine the type of plastic rheology introduced by scratching under different loads based on the strain field distribution. Figure 3 , Figure 4 Analysis reveals that strain non-uniformity intensifies with increasing load, with strain directly beneath the indenter increasing with load. Within a 200 μm range in front of the indenter, when the strain difference between the maximum and minimum strain values ​​on the material surface is ≥15%, localized strain concentration occurs, resulting in spalling and crack damage on the wear track surface. The plastic rheological type introduced at this point is eddy current. Conversely, when the strain difference on the material surface within a 200 μm range in front of the indenter is <15%, the strain distribution is relatively uniform, and there is no spalling on the wear track surface. The plastic rheological type introduced at this point is laminar flow.

[0047] This invention successfully provides a novel measurement method for scratch-induced plastic rheological modes on metal surfaces. A high-speed camera is used to capture the scratching process of industrial pure titanium under different loads. Subsequently, DIC software is used to calculate and analyze the strain changes and stress field distribution within the deformation zone. The strain distribution is compared with the wear mark morphology observed by SEM to determine the type of plastic rheology induced by scratching under different loads. For example, a uniform strain distribution induces laminar flow, while localized strain concentration induces eddy currents. This provides a new understanding of the dynamic formation process of damage such as microcracks during scratching. The method is relatively simple to operate and has significant application value.

Claims

1. A method of measuring a scratch-induced metal surface layer plastic flow pattern based on DIC, characterized by, Comprising the following steps: Step (1): preparing a rectangular TA1 commercial pure titanium sample; Step (2): spraying spots on the sample observation surface; Step (3): taking the surface adjacent to the observation surface as the scratch surface; Step (4): applying scratches on the scratch surface by a friction tester while recording videos by a high-speed camera to obtain scratch videos; Step (5): calculating the strain size in the deformation zone according to the scratch videos; Step (6): drawing the strain distribution curve of the TA1 surface layer along the scratch direction; Step (7): observing the morphology of the scratch marks on the TA1 surface under different loads by a scanning electron microscope; Step (8): judging the plastic flow type; Step (2) specifically comprises: using a spray gun with a caliber of 0.5 mm to spray a layer of white paint on the surface so that the metallic luster of the sample is completely covered; then using a spray gun with a caliber of 0.18 mm to spray black paint spots on the surface, the spots are randomly distributed, the average diameter is controlled to be less than 20 μm, and the spot distribution accounts for 80±5% of the white paint area; In step (4), the scratch is applied specifically as follows: using a conical diamond scratch head with a tip cone angle of 120° and a diameter of 0.2 mm, setting the scratch speed to be 0.1 mm / s, the scratch distance to be 1 mm, the loading time to be 10 s, the holding time to be 5 s, and the scratch time to be 10 s; Step (5) specifically comprises: after sorting and arranging the scratch videos, importing them into a DIC analysis program, selecting the strain change area within 100 μm thickness from the scratch surface, defining the starting point, and calculating the strain size in the deformation zone; Step (8) specifically comprises: within the range of 200 μm in front of the indenter, when the strain difference between the maximum and minimum values of the material surface layer is ≥15%, local strain concentration occurs, and there are spalling and crack damage on the scratch surface, at this time, the plastic flow type is vortex flow; and when the strain difference within the range of 200 μm in front of the indenter is <15%, the strain distribution is relatively uniform, and there is no spalling phenomenon on the scratch surface, at this time, the plastic flow type is laminar flow.

2. The method of claim 1, wherein, In step (1), the sample size is 5±0.5 mm×5±0.5 mm×2±0.2 mm.

3. The method of claim 1, wherein, In step (4), the high-speed camera selects a five-times lens as the magnifying lens and a 100 W LED light source as the illumination light source.

4. The method of claim 1, wherein, In step (4), the scratch videos are obtained by recording videos using the high-speed camera specifically as follows: selecting loads of 2 N, 10 N and 50 N, setting the image resolution for shooting to be 2560×1920, the frame rate to be 200 fps, and the video saving time to be 15 s; Starting the friction tester, 1 s before the scratch head is pressed into the sample surface and starts to slide is taken as the starting point for shooting, and the video is saved after 15 s of shooting time.

5. The method of claim 1, wherein, Step (6) specifically comprises: the friction coefficients under the loads of 2 N, 10 N and 50 N are exported from the friction tester respectively; in the strain steady state stage, a time point is selected respectively, and the strain size directly below the indenter at the corresponding time is found out in the DIC strain analysis, and the strain distribution curve of the TA1 surface layer along the scratch direction within the time is drawn.

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