Method for rapidly determining technological parameters of medium carbon steel EBSD sample prepared through electrolytic polishing

Abstract

The invention relates to a method for rapidly determining technological parameters of a medium carbon steel EBSD sample prepared through electrolytic polishing. The technical problems that in mechanical polishing sample preparation, the preparation process is complex, and the influence of sample preparation quality on an EBSD detection result is large are mainly solved. According to the technical scheme, the method comprises the following steps that S1, a medium carbon steel material is cut into a square sample, the back face of the sample is connected with a wire, resin inlaying is conducted, and then the sample is polished to be flat from thick to thin through abrasive paper; s2, the sample is placed in an electrolytic polishing device, and the current-time relation and the anodic polarization curve of the material are measured; s3, after electrolysis is finished, measuring the surface roughness and the surface profile curve of the sample by using a surface roughness meter, and observing the surface of the sample by using a Tsai scanning electron microscope; and S4, based on the Jacquet mucous membrane model, a current-electrolysis time curve is drawn in combination with the current-time relation and the anodic polarization curve, the optimal electrolysis time is obtained, and therefore the optimal technological parameters of electrolytic polishing of the medium carbon steel used in the experiment are obtained.

Description

Technical Field

[0001] The invention relates to the technical field of surface treatment, and in particular to a method for quickly determining process parameters of a medium carbon steel EBSD sample prepared by electrolytic polishing. Background Art

[0002] Electron backscatter diffraction (EBSD) technology is a material microstructure characterization technology based on scanning electron microscopy. It can quantitatively analyze the grain structure, orientation, dislocation density, etc. of the sample, and perform microscale characterization of strain, orientation difference, grain orientation dispersion, and grain deformation ability. It has the advantages of large test area, fast data collection, and intuitive presentation, and is widely used in the field of materials science. However, its sample preparation is a complicated process, and the quality of sample preparation directly affects the feasibility of EBSD detection.

[0003] Mechanical polishing is a common sample preparation method in materials science and metallurgy. However, due to the effects of "cutting force" and "cutting heat", a plastic deformation layer will be generated on the surface of the workpiece during cutting, resulting in residual stress on the surface of the sample and poor quality of the Kikuchi line signal. Traditional electrolytic polishing often uses empirical trial and error methods to find sample preparation parameters suitable for a certain type of sample. The amount of experiments is large and there is a lack of theoretical basis. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problems that the preparation process of mechanical polishing sample is complicated and the sample preparation quality has a great influence on the EBSD detection result, and to provide a method for quickly determining the process parameters of electrolytic polishing medium carbon steel EBSD sample.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for quickly determining process parameters of electrolytic polishing of medium carbon steel EBSD specimens comprises the following steps:

[0007] S1: Cut the medium carbon steel material into a 10mm×10mm×10mm square specimen, grind off 1mm thickness of the specimen after the wire cutting, remove the cutting damage and oxide layer; connect the back of the specimen to one end of the wire, use the cold mounting method to embed the resin, let the wire pass through the resin, and test the conductivity; then use sandpaper to grind the specimen from coarse to fine, and then use 2.5μm and 1.5μm polishing paste to polish the specimen to a mirror surface, without visible scratches;

[0008] S2: Place the sample in an electrolytic polishing device. The sample is an anode material. The anode and cathode plates are 20 mm apart. The sample is cooled by a mixture of ice and water. The experiment is carried out at low temperature. A 10% analytical pure perchloric acid anhydrous ethanol solution is used as the electrolyte. The current-time relationship and the anode polarization curve of the material are measured.

[0009] S3: After the electrolysis, the surface roughness and surface profile curve of the sample were measured using an SJ-410 surface roughness meter to evaluate the electrolytic polishing effect. Three positions were selected for measurement on the same sample, and each position was measured three times. The error of each measurement result was less than 10% for valid data, and the final result was averaged. After the roughness measurement was completed, the sample surface was immediately observed using a Zeiss sigma300 scanning electron microscope secondary electron image (SEM) to prevent oxidation of the sample.

[0010] S4: Based on the Jacquet mucosal model, combined with the current-time relationship and anodic polarization curve of the material measured in step S2, the optimal voltage required for material electropolishing is obtained, the electropolishing experiment is carried out at this voltage, and the current-electrolysis time curve is plotted. The optimal electrolysis time at this voltage is obtained from the curve, thereby obtaining the optimal process parameters for electropolishing of medium carbon steel used in the experiment.

[0011] Furthermore, the low temperature in step S2 means that the temperature is controlled below 10° C.; and the cathode material is 304 stainless steel.

[0012] Furthermore, the measurement time of the anode polarization curve in step S2 is 45 seconds, during which a relatively stable current value can be obtained.

[0013] The beneficial effects of the present invention are:

[0014] Based on the Jacquet mucosal model, the present invention combines the current-time relationship and the anodic polarization curve of the material to electropolish the medium carbon steel, uses the SJ-410 surface roughness meter and the sigma300 scanning electron microscope secondary electron image (SEM) to measure the roughness and microscopic characterization, and quickly determines the optimal electrolytic process parameters of the medium carbon steel to prepare the EBSD sample. The technical problems of mechanical polishing sample preparation, such as the complex preparation process and the great influence of sample preparation quality on the EBSD test results, are solved. Compared with the background technology, the present invention has the advantages of high efficiency and high precision.

[0015] The surface roughness (Ra) of the sample prepared by the present invention reaches 0.021 μm, and the EBSD calibration rate is about 97%, which provides a reference for the electrolytic process parameters of other medium carbon steels. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of an electrolytic polishing device of the present invention,

[0017] In the figure: 1-wire, 2-thermometer, 3-mounting material, 4-sample, 5-cathode plate, 6-electrolyte, 7-ice-water mixture, 8-beaker;

[0018] Figure 21 is a schematic diagram of the electrolytic polishing principle of the present invention, in which: (a) no electrolysis; (b) activation zone; (c) passivation zone; (d) over-passivation zone;

[0019] Figure 3 is the anodic polarization curve of 42CrMo steel of the present invention;

[0020] Figure 4 It is the surface roughness profile curve diagram of the sample under different voltages of the present invention;

[0021] Figure 5 The microscopic morphology of the samples under different voltages of the present invention are shown in the figure: (a) 25V; (b) 30V; (c) 32V; (d) 36V;

[0022] Figure 6 It is the surface roughness profile curve diagram of the sample at different times of the present invention;

[0023] Figure 7 The microscopic morphology of the sample at different times of the present invention is shown in the figure: (a) 3s; (b) 5s; (c) 9s; (d) 20s;

[0024] Figure 8 It is a contrast diagram of the 42CrMo steel Kikuchi belt of the present invention. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0026] Example

[0027] A method for quickly determining process parameters of a medium carbon steel EBSD sample prepared by electrolytic polishing in this embodiment includes the following steps:

[0028] S1: Cut medium carbon steel (42CrMo) material into 10mm×10mm×10mm square specimens by wire cutting, and use sandpaper to grind the surface to be tested and the back of the specimen after wire cutting with a thickness of 1mm to remove cutting damage and oxide layer; connect the back of the specimen to one end of the wire, use cold mounting method to embed resin, let the wire pass through the resin, and test the conductivity; then use sandpaper to grind the surface to be tested from coarse to fine to make it flat, and then use 2.5μm and 1.5μm polishing paste to polish the surface to be tested of the medium carbon steel specimen to a mirror surface, without visible scratches;

[0029] S2: Place the medium carbon steel sample in Figure 1In the electrolytic polishing device shown, a medium carbon steel sample is placed in a beaker 8, which is then placed in a large beaker, and an ice-water mixture 7 is placed in the large beaker; the medium carbon steel sample is used as the anode material, 304 stainless steel is used as the cathode material, the two plates are 20 mm apart, and the experiment is cooled by an ice-water mixture to control the temperature below 10°C. According to YB / T4377-2014 "Electrolytic Polishing Method for Metal Samples", a 10% analytical pure perchloric acid anhydrous ethanol solution is selected as the electrolyte 6 and placed in the beaker 8, and the current-time relationship and the anodic polarization curve of the material are measured;

[0030] The electrolytic polishing principle is divided into four stages. The first stage is called the activation zone. As the electrolytic voltage increases, the current density continues to increase. At this time, the anode material is locally corroded under the action of acid and voltage, and a complete passivation film cannot be formed. Figure 2 (a) is shown; the second stage is called the transition zone. As the electrolysis voltage increases, the current density gradually changes from increasing to decreasing and then to a gentle trend. At this time, the anode is in an active dissolution state, the anode material dissolves rapidly, and the metal cations begin to form a passivation film in the depressions on the anode surface, such as Figure 2 (b) As shown; the third stage is called the passivation zone. As the electrolysis voltage increases, the current density remains stable, and the generation rate of cations and the generation rate of the passivation film reach a state of equilibrium. As the voltage increases, the passivation film continues to thicken and the resistance increases, so the current density will not continue to increase with the increase of voltage, as shown in Figure 2 (c) The fourth stage is called the over-passivation zone. As the electrolysis voltage increases, the current density increases rapidly and unstably. At this time, the voltage is enough to destroy the passivation film. As the voltage increases further, a large number of bubbles are generated on the surface of the sample. The bubbles leave the surface of the sample and diffuse outward. The passivation film is decomposed and destroyed. The surface of the sample dissolves rapidly, the polished surface is completely destroyed, and the electrolyte begins to boil. Figure 2 (d) as shown.

[0031] In order to reduce the error and maintain the steady state of the system, a time is selected during which the current can remain stable for a long time. The electrolysis adopts the static method in the constant potential method. The potential of the electrode to be measured is kept constant. The current change during the electrolysis process is measured. A relatively stable current value can be obtained when the electrolysis is carried out for 40 to 55 seconds. Therefore, the measurement time of the anode polarization curve is selected as 45 seconds. 16 groups of voltages are set: 16V, 18V, 20V, 22V, 24V, 26V, 28V, 29V, 30V, 31V, 32V, 33V, 34V, 35V, 36V, 38V. The electrolytic polishing experiment is carried out. The electrolysis time is 45 seconds. Three experiments are carried out for each group of voltages. The average value of the stable current is taken, and the current density is calculated and the anode polarization curve drawn is as shown Figure 3 .

[0032] according to Figure 3It can be seen that the passivation film begins to be destroyed at 33V, and the current density increases unstably. The straight line drawn through the slope of the rapid increase of the current density in the passivation zone intersects with the horizontal axis at 25V, and the theoretical minimum decomposition voltage is 25V. Therefore, the optimal electrolysis voltage of 42CrMo used in the experiment should be between 25V and 33V.

[0033] S3: After the electrolysis, the surface roughness and surface profile curve of the sample were measured using an SJ-410 surface roughness meter to evaluate the electrolytic polishing effect. Three positions were selected for measurement on the same sample, and each position was measured three times. The error of each measurement result was less than 10% for valid data, and the final result was averaged. After the roughness measurement was completed, the sample surface was immediately observed using a Zeiss sigma300 scanning electron microscope secondary electron image (SEM) to prevent oxidation of the sample.

[0034] In this embodiment, 25V, 30V, 32V, and 36V were selected for electrolytic polishing experiments, and the surface roughness was measured and the surface morphology was observed under a scanning electron microscope. The results are as follows: Figure 4 and Figure 5 (b) The curve is the smoothest at 30 V, with a roughness Ra of 0.021 μm. The sample surface is flat and smooth, with clear crystal features, and the grain boundaries can be clearly observed by SEM.

[0035] In this embodiment, the voltage was selected to be 30V, and the electrolytic polishing experiment was carried out for 3s, 5s, 9s, and 20s. The surface roughness was measured and the microscopic morphology of the surface was observed under a scanning electron microscope. The roughness profile curves of the polished surfaces of the samples are shown in Fig. Figure 6 As shown, the best surface quality is obtained at 5s, with a roughness Ra of 0.025μm. As time further increases, the surface roughness increases rapidly.

[0036] Figure 7 is the microscopic morphology of the samples at different times. Figure 7 As can be seen from (a), (b), (c) and (d), crystal features appeared locally at 3 s, and there were still a few pits. At 5 s, the sample surface was the smoothest and flattest. At 9 s, new pits had already appeared on the sample surface. When the time reached 20 s, the sample surface was full of pits and ripples formed by excessive electrolysis, and the polished surface was completely destroyed.

[0037] S4: Based on the Jacquet mucosal model, combined with the current-time relationship and anodic polarization curve of the material measured in step S2, the optimal voltage required for material electropolishing is obtained, the electropolishing experiment is carried out at this voltage, and the current-electrolysis time curve is plotted. The optimal electrolysis time at this voltage is obtained from the curve, thereby obtaining the optimal process parameters for electropolishing of 42CrMo steel used in the experiment.

[0038] The optimal electrolysis process parameters for 42CrMo steel in this embodiment are 30V-5s. The sample was prepared by this process and EBSD test was performed, and the calibration rate was about 97%. Figure 8 As shown in the figure, the grain morphology is clear, proving that the sample surface is smooth and flat, without stress deformation, and is an ideal EBSD sample. Other medium carbon steel conductive materials can use this method to find the optimal electrolytic polishing process value.

Claims

1. A method for quickly determining the process parameters of electrolytic polishing of medium carbon steel EBSD samples, characterized in that: The following steps are involved: S1: Cut the medium carbon steel material into a 10mm×10mm×10mm square specimen, grind off 1mm thickness of the specimen after the wire cutting, remove the cutting damage and oxide layer; connect the back of the specimen to one end of the wire, use the cold mounting method to embed the resin, let the wire pass through the resin, and test the conductivity; then use sandpaper to grind the specimen from coarse to fine, and then use 2.5μm and 1.5μm polishing paste to polish the specimen to a mirror surface, without visible scratches; S2: Place the sample in an electrolytic polishing device. The sample is an anode material. The anode and cathode plates are 20 mm apart. The sample is cooled by a mixture of ice and water. The experiment is carried out at low temperature. A 10% analytical pure perchloric acid anhydrous ethanol solution is used as the electrolyte. The current-time relationship and the anode polarization curve of the material are measured. S3: After the electrolysis, the surface roughness and surface profile curve of the sample were measured using an SJ-410 surface roughness meter to evaluate the electrolytic polishing effect. Three positions were selected for measurement on the same sample, and each position was measured three times. The error of each measurement result was less than 10% for valid data, and the final result was averaged. After the roughness measurement was completed, the secondary electron image of the Zeiss sigma300 scanning electron microscope was used to observe the sample surface immediately to prevent oxidation of the sample. S4: Based on the Jacquet mucosal model, combined with the current-time relationship and anodic polarization curve of the material measured in step S2, the optimal voltage required for material electropolishing is obtained, the electropolishing experiment is carried out at this voltage, and the current-electrolysis time curve is plotted. The optimal electrolysis time at this voltage is obtained from the curve, thereby obtaining the optimal process parameters for electropolishing of medium carbon steel used in the experiment.

2. A method for rapidly determining process parameters of electrolytic polishing of medium carbon steel EBSD samples according to claim 1, characterized in that: The low temperature in step S2 means that the temperature is controlled below 10° C.; the cathode material is 304 stainless steel.

3. A method for rapidly determining process parameters of electrolytic polishing of medium carbon steel EBSD samples according to claim 1, characterized in that: The measurement time of the anode polarization curve in step S2 is 45 seconds, during which a relatively stable current value is obtained.

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