CN117949292B - Metal surface crack testing device under tensile stress and hydrogen permeation conditions and application method thereof - Google Patents
Metal surface crack testing device under tensile stress and hydrogen permeation conditions and application method thereof Download PDFInfo
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- 229910052739 hydrogen Inorganic materials 0.000 title claims abstract description 84
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- 239000004696 Poly ether ether ketone Substances 0.000 claims description 4
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- UMGDCJDMYOKAJW-UHFFFAOYSA-N thiourea Chemical compound NC(N)=S UMGDCJDMYOKAJW-UHFFFAOYSA-N 0.000 description 2
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Abstract
The invention discloses a device for testing cracks on a metal surface under tensile stress and hydrogen permeation conditions and a use method thereof, comprising the following steps: the device comprises a tensile stress loading module, a hydrogen diffusion module and a surface potential in-situ measurement module, wherein the tensile stress loading module comprises: a tension drive assembly; stretching the clamping head; the tension sensor is used for sensing the tension and feeding back the tension to the control box of the tension driving assembly; the hydrogen diffusion module comprises an electrochemical workstation and an electrochemical cell, and the stretching chuck is positioned in the electrochemical cell; the surface potential in-situ measurement module comprises a Kelvin probe extending into the electrochemical cell, a Kelvin probe microscope test system, a sample stage for carrying the electrochemical cell and an optical microscopic positioning system. The invention has the beneficial effects that the crack state is measured by the surface potential in-situ measurement module under the conditions of tensile stress and hydrogen permeation, the crack growth condition is quickly and accurately observed in a longer time window, and the crack distribution and change condition are predicted.
Description
Technical Field
The invention relates to the field of metal material analysis and test, in particular to a device for testing metal surface cracks under the conditions of tensile stress and hydrogen permeation and a use method thereof.
Background
Metallic material service is typically in complex service environments, such as coupling of mechanical and chemical environments. Under the conditions of hydrogen-induced environment and tensile stress, hydrogen atoms in the metal material are diffused, so that the metal material part can be subjected to hydrogen embrittlement failure, and safety accidents and economic losses are caused. The hydrogen embrittlement phenomenon is widely applied to novel materials such as high-strength steel, nickel-based alloys, titanium alloys and the like, and the novel materials are widely applied to hydrogen storage tanks, hydrogen transmission pipelines, aerospace engine key parts and ocean engineering equipment. In order to ensure the service safety of novel materials such as high-strength steel, nickel-based alloy, titanium alloy and the like, the hydrogen embrittlement process needs to be studied intensively. Therefore, it is important to understand the diffusion process of hydrogen atoms and the hydrogen embrittlement mechanism to study the hydrogen diffusion process under the simulated actual conditions. During the processing, manufacturing and use of metallic materials, the occurrence of cracks is unavoidable. Material failure is also closely related to cracks, from initiation of a crack to crack propagation, and further material failure occurs. The crack initiation and propagation process is studied and mastered, the performance of the workpiece can be monitored at any time, the service life of the part is predicted, and the cost is reduced while the safety is ensured. In addition, the mechanism of the material breaking under different environments can be deduced by analyzing the existing micro-crack germination, and the micro-crack germination is reduced by optimizing the microstructure of the material, so that a direction is provided for further optimizing the performance of the material. Thirdly, by observing the expansion form (along the crystal/through crystal) of the crack on the microstructure, the toughness and brittleness of the material at the microscopic level can be better known, and the in-situ observation of the crack expansion of the material under the condition of charging hydrogen provides direct evidence for researching the hydrogen toughness and brittleness transition of the material.
The Chinese patent application publication No. CN112114168B discloses an in-situ test device and method for metal surface potential under the condition of stress and hydrogen permeation, wherein the device comprises a stress loading mechanism, a hydrogen permeation mechanism and a surface potential measuring mechanism, the stress loading mechanism comprises a base, a sample, a pressure head, a nut and a dial indicator, and the sample, the pressure head and the nut are all arranged in the base; the surface potential measuring mechanism comprises a KPFM testing system, a Kelvin probe and a sample platform, wherein the Kelvin probe is connected with the KPFM testing system and is used for detecting the surface potential of a sample, and the sample is connected with the sample platform through a wire; the hydrogen permeation mechanism comprises an electrochemical workstation, a hydrogen charging groove, a hydrogen charging solution, an auxiliary electrode and a reference electrode, wherein the hydrogen charging groove is arranged on the sample table, and the base is arranged in the hydrogen charging groove. The device can only be used for measuring the metal surface potential under the conditions of compressive stress and hydrogen permeation, and can only test the dry surface of the flat plate mechanism, and cannot realize full-size measurement and cannot measure crack conditions.
Disclosure of Invention
The invention aims to solve the technical problem that the existing metal material cannot accurately and rapidly measure the metal surface cracks under the conditions of tensile stress and hydrogen permeation, and provides a device for testing the metal surface cracks under the conditions of tensile stress and hydrogen permeation and a use method thereof.
The technical scheme of the invention is as follows: the device for testing the metal surface crack under the conditions of tensile stress and hydrogen permeation comprises: the device comprises a tensile stress loading module, a hydrogen diffusion module and a surface potential in-situ measurement module, wherein the tensile stress loading module comprises: a tension drive assembly; the stretching chuck comprises a movable stretching chuck and a fixed stretching chuck which are respectively connected with two ends of the sample, and the movable stretching chuck is driven by the stretching driving assembly to stretch the sample; the tension sensor is used for sensing the tension and feeding back the tension to the tension driving assembly; the hydrogen diffusion module comprises an electrochemical workstation and an electrochemical cell, the stretching chuck is positioned in the electrochemical cell, and a liquid inlet and a liquid outlet are formed in the side wall of the electrochemical cell; the surface potential in-situ measurement module comprises a Kelvin probe extending into the electrochemical cell, a Kelvin probe microscope test system, a sample stage for carrying the electrochemical cell and an optical microscopic positioning system.
In the scheme, the stretching chuck comprises a groove for accommodating the sample end, a gland for pressing the sample end and a limit column.
The improvement of the scheme is that the tensile stress loading module further comprises a control box for controlling the tensile force.
In the scheme, the cell body material of the electrochemical cell adopts polyether-ether-ketone.
In the above scheme, the hydrogen diffusion module adopts a three-electrode system, the sample is a working electrode, the reference electrode and the counter electrode are inserted from the top cover of the electrochemical cell, and the electrochemical workstation is connected with the three electrodes.
The tensile stress loading module and the hydrogen diffusion module are integrated on the base.
The application method of the metal surface crack testing device under the conditions of tensile stress and hydrogen permeation comprises the following steps: the tensile stress loading module applies stress to the sample and records a stress strain curve, the electrochemical workstation applies voltage to the sample, realizes a hydrogen charging process, regulates and controls the voltage and records the change process of electrochemical information, the surface potential in-situ measurement module performs surface potential measurement on the sample, the place with obvious surface potential difference is a crack area, and the distribution change condition of hydrogen atoms and cracks on the surface of the sample is obtained through analysis.
The invention has the beneficial effects that the crack state is measured by the surface potential in-situ measurement module under the conditions of tensile stress and hydrogen permeation, the crack growth condition is quickly and accurately observed in a longer time window, and the crack distribution and change condition are predicted.
Drawings
FIG. 1 is a schematic diagram of a device for testing cracks on a metal surface under tensile stress and hydrogen permeation conditions according to the present invention;
FIG. 2 is a side view of FIG. 1;
FIG. 3 is a schematic diagram of a tensile clamp mated with a hydrogen diffusion module;
FIG. 4 is a schematic diagram of a tensile chuck in combination with a hydrogen diffusion module and a sample surface potential in situ measurement module;
FIG. 5 is a schematic diagram of the control software and three modules of the in-situ test device for metal surface potential under conditions of stretching and hydrogen diffusion;
FIG. 6 is a graph of current and potential variations during hydrogen diffusion;
FIG. 7 is a stress-strain plot under 3500N loading force;
FIG. 8a is a surface topography of an in situ test micro-area scan of metal surface potential under tensile and hydrogen diffusion conditions;
FIG. 8b is a graph of potential change during in situ charging under tensile and hydrogen diffusion conditions;
FIG. 8c is a cross-sectional view of the resulting electrical potential along the AFM scan direction under conditions of stretching and hydrogen diffusion;
FIG. 9a is a surface topography of a sample before unloading and not switching on an electrochemical workstation;
FIG. 9b is a graph of potential change during in situ charging prior to unloading and switching on an electrochemical workstation;
FIGS. 9c1, 9c2, 9c3 are cross-sectional analysis views of FIG. 9 a;
FIGS. 9d1, 9d2, 9d3 are cross-sectional analyses of FIG. 9 b;
FIG. 10a is a graph of 3500N loading force, hydrogen diffusion condition metal surface topography;
FIG. 10b is a graph of 3500N loading force, hydrogen diffusion condition surface potential;
FIGS. 10c1, 10c2, 10c3 are cross-sectional analysis views of FIG. 10 a;
FIGS. 10d1, 10d2, 10d3 are cross-sectional analysis views of FIG. 10 b;
In the figure, 1, a stretching driving assembly, 2, a tension sensor, 3, a control box, 4, a movable stretching chuck, 5, a fixed stretching chuck, 6, a base, 7, a sample, 8, a roller, 9, a groove, 10, a gland, 11, a limit column, 12, a liquid inlet, 13, a liquid outlet, 14, a hydrogen diffusion module, 15, a Kelvin probe, 16, a sample stage, 17 and an optical microscopic positioning system.
Detailed Description
The invention will be further described with reference to the accompanying drawings and examples.
The scanning kelvin probe test technique is based on capacitors. The Kelvin probe/air/sample forms a capacitance that when the Kelvin probe is at a varying distance from the sample surface, a voltage is generated that can be measured, and the scanning Kelvin probe microscope "removes" the capacitance by applying a "removal voltage". The negative of the cancellation voltage is the work function difference between the probe and the sample. And (3) scanning and measuring each position of the sample through a Kelvin probe, finally obtaining a local work function distribution result, and analyzing to obtain the distribution change of hydrogen atoms on the surface of the sample. The current Kelvin probe testing technology is usually carried out in stress-free air, and a full-scale crack research analysis method for a hydrogen atom diffusion process in an in-situ stress loading and hydrogen-induced environment is very lacking. Therefore, a set of electrochemical in-situ hydrogen charging electrolytic cell device under the stretching condition which can monitor and record parameters such as stress-strain curve, hydrogen diffusion condition and the like is designed, and the electrochemical in-situ hydrogen charging electrolytic cell device is combined with a full-size scanning Kelvin probe research method, so that the electrochemical in-situ hydrogen charging electrolytic cell device has great significance for crack phenomenon research caused by hydrogen atom diffusion.
The device for testing the metal surface crack under the conditions of tensile stress and hydrogen permeation comprises: the device comprises a tensile stress loading module, a hydrogen diffusion module and a surface potential in-situ measurement module, wherein the tensile stress loading module comprises a tensile driving assembly 1; the stretching chuck comprises a movable stretching chuck 4 and a fixed stretching chuck 5 which are respectively connected with two ends of the sample, and the movable stretching chuck is driven by a stretching driving assembly to stretch the sample; a tension sensor 2 for sensing the tension and feeding back to a control box 3 of the tension driving assembly; the hydrogen diffusion module 14 comprises an electrochemical workstation and an electrochemical cell, the stretching chuck is positioned in the electrochemical cell, and a liquid inlet 12 and a liquid outlet 13 are formed in the side wall of the electrochemical cell; the surface potential in situ measurement module includes a Kelvin probe 15 extending into the cell, a Kelvin probe microscopy test system, a sample stage 16 for carrying the cell, and an optical microscopy positioning system 17.
The tensile stress loading module can realize program control through an external computer, achieves the function of reading mechanical data, and can record stress-strain curves. The tensile force of the tensile stress loading module is regulated within the range of 0-4900N.
In order to avoid that the deformation of the tensile clamp affects the overall performance of the surface potential in-situ test device, the clamp is designed to be reusable and also can be replaced integrally.
The design of the stretching chuck adopts the groove 9, the gland 10 and the limit column 11 of the chuck to fix a sample (i.e. a specimen) so as to ensure that the chuck can be repeatedly used under the condition of large tension and is not easy to damage or shift.
The hydrogen diffusion module 14 includes an electrochemical workstation, an electrochemical cell, a charging solution, electrodes, a solution inlet and a solution outlet, and can realize measurement of sample charging and electrochemical information. The electrochemical cell body material of the hydrogen diffusion module adopts polyether-ether-ketone (PEEK) with wide pH resistance range, and the bearable pH range is 1-14. The hydrogen diffusion module adopts a three-electrode system, the working electrode is a stretched sample, and the reference electrode and the counter electrode are fixed in a mode of being inserted from the top cover. The hydrogen charging solution flows into the electrochemical cell from the liquid inlet 12, fills the electrochemical cell and flows out from the liquid outlet 13. The liquid inlet is positioned below the liquid outlet, the electrochemical workstation is connected with three electrodes, and the electric signal is applied and the electrochemical information is recorded.
The surface potential measuring module comprises a scanning Kelvin probe microscope test system, a Kelvin probe 15, a sample stage 16 and an optical microscopic positioning system 17, and can realize the measurement of the surface potential of a sample, wherein the measurement range is from nanometer to centimeter. An atomic force microscope scanning Kelvin probe test system and corresponding Kelvin probe are selected according to the size range of the surface potential measurement. As shown in fig. 4, the combination of the metal surface potential in situ test device and the scanning kelvin probe is schematically shown. The metal surface potential in-situ testing device is connected through a screw hole of the atomic force microscope sample stage, and the whole testing device can move smoothly along with the movement of the sample stage.
The tensile stress loading module and the hydrogen diffusion module are integrated on the base 6, and the bottom of the tensile driving assembly is provided with rollers 8.
The interaction relationship among the tensile stress loading module, the hydrogen diffusion module and the surface potential in-situ measurement module of the metal surface potential in-situ test device under the condition of stretching and hydrogen diffusion is shown in fig. 5. The control system of the tensile stress loading module and the tensile stress loading module apply stress to the sample and record stress-strain curves, and process control is realized through the control system and software. The electrochemical workstation and the control software are connected with the hydrogen diffusion module, voltage is applied to the sample, the hydrogen charging process is realized, and the voltage is regulated and controlled by the control software, and the change process of electrochemical information is recorded. The surface potential of the sample is measured by the scanning Kelvin probe system and control software, and the distance between the Kelvin probe and the sample, the measurement accuracy and the surface potential distribution diagram of the sample are regulated by the control software.
The metal surface potential in-situ testing device under the conditions of stretching and hydrogen diffusion can also be applied to non-contact detection methods with sufficient cavity sizes such as Raman spectroscopy, surface profilometers, laser confocal microscopes, X-ray diffraction analyzers, industrial computer tomography, synchronous radiation and the like.
The application method of the metal surface crack testing device under the conditions of tensile stress and hydrogen permeation comprises the following steps: the tensile stress loading module applies stress to the sample and records a stress strain curve, the electrochemical workstation applies voltage to the sample, realizes a hydrogen charging process, regulates and controls the voltage and records the change process of electrochemical information, and the surface potential in-situ measurement module performs surface potential measurement on the sample, wherein the place with obvious surface potential difference is a crack area.
Example 1: pt is used as a counter electrode, an electrochemical solution is 0.1M sulfuric acid aqueous solution and 0.25g/L thiourea, a working electrode is made of titanium alloy, hydrogen charging reaction is carried out under the condition that the current density is 1-10mA/cm 2 under 3500N loading force, and surface potential in-situ scanning is carried out. The stress strain curve and the electrochemical parameters are shown in fig. 6 and 7.
Fig. 8a, 8b, 8c show surface topography, surface potential profile and cross-sectional analysis of surface potential during in situ charging. The surface topography and surface potential results before stretching and energizing are shown in fig. 8a and 8 b. The arrow in fig. 8b indicates the direction of the picture scan, the picture scan time is 17 minutes, the scale of color versus height in the figure is shown on the right side of the figure. 10a, 10b, 10c1, 10c2, 10c3, 10d1, 10d2, 10d3 are in-situ surface morphology and surface potential results under 3500N load at constant current, as shown in the middle black part of FIG. 10a, the morphology of the cracks in the morphology map is clearly visible, and the surface potential results of FIG. 10b show that the potential at the corresponding position of the cracks is lower, and that the potential also changes significantly compared with other areas where the cracks extend downward.
FIGS. 9a and 9c1, 9c2, 9c3 show that the surface topography shows scratches with a height difference of about 10nm, and FIGS. 9b and 9d1, 9d2, 9d3 show that the corresponding surface potentials have no significant potential difference, with a potential difference of about 0.2mV.
FIGS. 10a and 10c1, 10c2, 10c3 show that the surface topography showed cracks with a height difference of 90nm, and FIGS. 10b and 10d1, 10d2, 10d3 show that the corresponding surface potentials showed a difference of about 36mV. At the extension of the crack, the height difference was 12nm and the surface potential difference was 9mV.
The analysis process of the distribution change of hydrogen atoms and cracks on the surface of the sample is as follows: the work function is the minimum energy used by electrons to transition from the fermi level to the vacuum level, and electrons will spontaneously flow from the material with a low work function to the material with a low fermi level after conduction of the material with a different work function. As previously described, the kelvin probe/air/sample forms a capacitance that when the distance between the kelvin probe and the sample surface changes, a voltage that can be measured is generated, and the scanning kelvin probe microscope "cancels" the capacitance by applying an "cancellation voltage". The negative of the cancellation voltage is the work function difference between the probe and the sample. And scanning and measuring each position of the sample by a Kelvin probe, finally obtaining a local work function distribution result, and analyzing to obtain the distribution change of hydrogen atoms and cracks on the surface of the sample.
The potential difference between the two electrodes of the capacitor can be calculated by the following formula:
Where k is the electrostatic force constant, d is the probe-to-sample surface spacing, Q is the surface charge, ε r is the relative permittivity, and S is the probe area. In the test of the Kelvin probe microscope, the Kelvin probe and the sample are two poles of a capacitor. In order to eliminate the influence of factors such as the distance between the Kelvin probe and the sample, the area and the like on the electric potential, the same probe is used, and scanning is performed at the same distance. The specific process is that the morphology of the sample surface is collected firstly, and then the potential of the probe is raised according to a constant distance to test the surface, so that the influence of the distance between the probe and the sample surface and the area of the probe on the potential result is avoided.
The potential difference between the probe and the sample is calculated as follows:
Where Φ probe is the potential of the probe, Φ sample is the potential of the sample, W sample is the work function of the sample, W probe is the work function of the probe, e is the meta-charge, K is the electrostatic force constant, d is the distance between the probe and the surface of the sample, Q is the surface charge, epsilon r is the relative dielectric constant, and S is the probe area.
As can be seen from the results of fig. 9a, 9b, 9c1, 9c2, 9c3, 9d1, 9d2, 9d3, the surface potential of the crack generated without hydrogen charging and stretching is not significantly different, indicating that the work function at the crack is not significantly different from the substrate. The results in fig. 10a,10b,10 c1, 10c2, 10c3, 10d1, 10d2, 10d3 show that the cracks generated under hydrogen loading and stretching conditions have significant potential differences, indicating that there is a significant change in work function at the crack compared to the substrate, which should be a potential change due to enrichment of hydrogen elements. As shown in the above formula, the main cause of the potential difference in the test results is the change in work function in the sample.
In fig. 10a, 10b, 10c1, 10c2, 10c3, 10d1, 10d2, 10d3, the surface potential after hydrogen enrichment of the crack region is represented by the following formula,
V L is the surface potential of the crack region, V 0 is the surface potential before crack occurs, J is hydrogen flux, a is a constant, and the slope of the potential change during charging.
The hydrogen flux J can be calculated by the following formula
D L is the diffusion coefficient of a hydrogen atom in the lattice, C L is the concentration of a hydrogen atom in the lattice, V H is the partial molar volume of a hydrogen atom, R is the molar gas constant, which has a value of 8.314J/(mol.K), T is the temperature, sigma h is the hydrostatic stress, one third of the sum of the three stresses, i.e。
Therefore, the relationship between the surface potential and the hydrostatic stress is:
Stresses are in turn associated with cracks in many discrete ways, depending on the particular crack shape and manner of cracking. The specific cracking behavior prediction is mainly obtained by comparing stress intensity factors K and combining mathematical modeling.
For example, establishing a crack-centric polar coordinate system (r, θ), the stress intensity factor K I in mode I may be written as a function of σ h:
where v denotes poisson's ratio, r > r p,rp denotes the size of the plastic region, defined as the position where the elastic and pluronic fields coincide.
In this case, the relationship between the surface potential and the stress intensity factor K I can be obtained as follows:
Where a is a constant, is the slope of the potential change during charging, D L is the diffusion coefficient of hydrogen atoms in the lattice, C L is the concentration of hydrogen atoms in the lattice, V H is the partial molar volume of hydrogen atoms, R is the molar gas constant, which is 8.314J/(mol·k), T is the temperature, and V is the poisson ratio.
The mathematical relationship between the surface potential and the crack in the stretched state is thus obtained.
Claims (6)
1. The application method of the metal surface crack testing device under the conditions of tensile stress and hydrogen permeation is characterized by comprising the following steps: comprising the following steps: a tensile stress loading module, a hydrogen diffusion module (14), and a surface potential in situ measurement module, the tensile stress loading module comprising: a tension driving assembly (1); the stretching chuck comprises a movable stretching chuck (4) and a fixed stretching chuck (5) which are respectively connected with two ends of the sample (7), and the movable stretching chuck is driven by a stretching driving assembly to stretch the sample; the tension sensor (2) is used for sensing the tension and feeding back the tension to the tension driving assembly; the hydrogen diffusion module comprises an electrochemical workstation and an electrochemical cell, the stretching chuck is positioned in the electrochemical cell, and a liquid inlet (12) and a liquid outlet (13) are formed in the side wall of the electrochemical cell; the surface potential in-situ measurement module comprises a Kelvin probe (15) extending into the electrochemical cell, a Kelvin probe microscope test system, a sample stage (16) for bearing the electrochemical cell and an optical microscope positioning system (17); the using method comprises the following steps: the tensile stress loading module applies stress to the sample and records a stress strain curve, the electrochemical workstation applies voltage to the sample, realizes a charging process, regulates and controls the voltage and records the change process of electrochemical information, the surface potential in-situ measurement module performs surface potential measurement on the sample, the place with obvious surface potential difference is a crack area, a polar coordinate system (r, θ) taking the crack as the center is established, and the stress intensity factor K I is written as a function of sigma h:
Wherein v represents poisson's ratio, r > r p,rp represents the size of the plastic region, defined as the location where the elastic field and the pluronic field coincide; the relationship between the surface potential and the stress intensity factor K I is obtained as follows:
where a is a constant, which is the gradient of the potential change during the hydrogen charging process, D L is the diffusion coefficient of hydrogen atoms in the crystal lattice, C L is the concentration of hydrogen atoms in the crystal lattice, V H is the partial molar volume of hydrogen atoms, R is the molar gas constant, which is 8.314J/(mol·k), T is the temperature, V is the poisson ratio, and the distribution change of hydrogen atoms and cracks on the sample surface is analyzed.
2. The method for using the device for testing the metal surface crack under the conditions of tensile stress and hydrogen permeation according to claim 1, wherein the method comprises the following steps: the stretching chuck comprises a groove (9) for accommodating the sample end, a gland (10) for pressing the sample end and a limit column (11).
3. The method for using the device for testing the metal surface crack under the conditions of tensile stress and hydrogen permeation according to claim 1, wherein the method comprises the following steps: the tensile stress loading module further comprises a control box (3) for controlling the tensile force.
4. The method for using the device for testing the metal surface crack under the conditions of tensile stress and hydrogen permeation according to claim 1, wherein the method comprises the following steps: the electrochemical cell body is made of polyether-ether-ketone.
5. The method for using the device for testing the metal surface crack under the conditions of tensile stress and hydrogen permeation according to claim 1, wherein the method comprises the following steps: the hydrogen diffusion module adopts a three-electrode system, the sample is a working electrode, the reference electrode and the counter electrode are inserted from the top cover of the electrochemical cell, and the electrochemical workstation is connected with the three electrodes.
6. The method for using the device for testing the metal surface crack under the conditions of tensile stress and hydrogen permeation according to claim 1, wherein the method comprises the following steps: the tensile stress loading module and the hydrogen diffusion module are integrated on the base (6).
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