In-situ synchronous measurement method for corrosion wear coupling damage of coating under corrosive atmosphere condition

Abstract

The invention discloses an in-situ synchronous measurement method for corrosion wear coupling damage of a coating under a corrosive atmosphere condition. No continuous liquid medium exists in the corrosive atmospheric environment, so that the problem of corrosive wear coupling damage in the corrosive atmospheric environment cannot be tested in situ by using a common electrochemical three-electrode system method. According to the method, a corrosive atmosphere corrosion friction testing machine and an electrochemical workstation are used as basic equipment, an electrochemical two-electrode system potentiostatic method is adopted, and the change rule of the current density along with time and the change rule of the friction coefficient and the abrasion depth along with time in the coating friction process under the corrosive atmosphere environment are synchronously measured. The change of the conductivity of the coating in the friction process is deduced according to the relation between the current density and the conductivity, and then the content change of the corrosion medium in the coating and the average diffusion rate of the corrosion medium in the friction process are deduced according to the corrosion medium and the inherent conductivity of the coating.

Description

Technical Field

[0001] The invention relates to an in-situ synchronous measurement method for coating corrosion and wear coupled damage under corrosive atmospheric conditions, belonging to the technical field of coating corrosion and wear coupled damage testing. Background Art

[0002] Generally, in open spaces and special operating conditions, solid lubricating coatings are applied to the surfaces of friction pairs to achieve the friction reduction and wear resistance of parts. In a corrosive atmosphere, due to the influence of the corrosive medium, the damage mechanism of the solid lubricating coating changes. Under the action of corrosion and wear coupling damage, the service life of the solid lubricating coating drops sharply. The corrosion and wear coupling damage action not only involves the synergistic effect of multiple fields, but the damage process also changes dynamically over time. Due to the complexity of the corrosion and wear coupling damage mechanism, there is currently no good in-situ synchronous testing method for solid lubricating coatings in a corrosive atmosphere. Therefore, designing an in-situ synchronous testing method for corrosion, friction and wear has important guiding significance for the design of solid lubricating coatings.

[0003] The corrosion and wear process mainly involves two aspects: friction and wear and electrochemistry. The main ways to detect friction and wear performance are friction testing machines, three-dimensional profilometers and other equipment. The most commonly used methods for electrochemical performance detection are AC impedance spectroscopy and polarization curves of electrochemical workstations. However, the above electrochemical tests need to be completed in a three-electrode system, that is, the reference electrode, counter electrode, and working electrode are in the same solution. There is no continuous corrosive medium in the corrosive atmosphere environment, and the ion transport channel is disconnected. Therefore, the three-electrode system is not suitable for measurements under corrosive atmospheric conditions. Based on the above problems, this method uses a two-electrode electrochemical system and uses a constant potential method to measure the change of coating conductivity during the friction process, and then deduce the change in the content of the corrosive medium in the coating, the penetration and diffusion, and the penetration time, to achieve in-situ synchronous measurement of corrosion and wear under corrosive atmospheric conditions. Summary of the invention

[0004] The present invention aims to provide an in-situ synchronous measurement method for the corrosion and wear coupled damage of coatings under corrosive atmospheric conditions.

[0005] The in-situ synchronous measurement method of the corrosion and wear coupling damage of the coating under the corrosive atmosphere condition of the present invention comprises the following steps: (1) Test sample clamping After the coating test sample is installed in the corrosion friction tester, the coating surface of the test sample is exposed to the corrosive atmosphere, and the metal substrate is completely isolated from the corrosive atmosphere to prevent the thin liquid film generated by the corrosive atmosphere from directly connecting the coating surface to the metal substrate; (2) Circuit connection between electrochemical workstation and friction and wear testing machine The metal substrate of the coating test sample is connected to the working electrode of the electrochemical workstation; the metal friction couple is connected to the counter electrode of the electrochemical workstation; the reference electrode of the electrochemical workstation is connected in series with the counter electrode, and the electrochemical workstation and the friction tester software use the same system time for synchronous measurement; (3) Test parameter setting The friction tester adopts the friction mode, and the electrochemical workstation selects the constant potential polarization test method. The parameter settings mainly include the potential size, test time, and acquisition frequency. The potential is preferably 0.2 V. Too large electrochemical polarization will occur, and too small will be easily affected by disturbances. The acquisition frequency of the workstation should not be less than the acquisition frequency of the friction tester. The acquisition frequency is 20Hz, and the test time is 2 hours. The test time is consistent with the friction tester. (4) Data collection First, turn on the corrosion atmosphere generating device of the corrosion friction tester to place the sample in a corrosion atmosphere environment, and then set the relevant parameters of the electrochemical workstation and the friction tester and start them synchronously; the electrochemical workstation and the friction tester use the same system time as the benchmark, the friction tester outputs the friction coefficient-time curve, and the electrochemical workstation outputs the current density-time curve; since the friction coefficient and the current density use the same time standard, the friction coefficient and current density curves are plotted simultaneously with time as the horizontal axis, so as to obtain the change of the friction coefficient with the current density; (5) Changes of the weight of corrosive media in the coating over time According to the current density-time curve, the coating conductivity σ can be obtained by using Ohm's law formula (1): total The law of change with time t, where J(t) is the current density and E is the electric field strength; each substance has a specific conductivity, assuming that the conductivity of the corrosive medium is σ cor , the conductivity of the coating is σ coat , the weight of the corrosive medium in the coating is χ cor , coating material weight is χ coat ; Combining formula (2) and formula (3) can obtain the weighted χ cor and χ coat , χ cor (t) is the function of the content of the corrosive medium in the coating as the friction process changes; (6) Calculation of the average penetration rate of corrosive media in the coating during friction In the current density-time curve, the current density at time t1 suddenly increases by more than three orders of magnitude. The reason for this phenomenon is that the corrosive medium penetrates from the coating into the metal matrix, causing the coating resistance to suddenly decrease. Therefore, time t1 is the time when the corrosive medium penetrates the coating. Assuming that the initial thickness of the coating is T and the wear depth at time t1 is d, the average diffusion rate v of the corrosive medium during the friction process can be calculated by formula (4): dif ; (4).

[0006] In summary, the present invention provides an in-situ synchronous measurement method for the coupled corrosion and wear damage of coatings under corrosive atmospheric conditions. The method uses a corrosive atmospheric corrosion friction tester and an electrochemical workstation as basic equipment, and adopts an electrochemical two-electrode system constant potential method to synchronously measure the change of current density over time during the friction process of the coating under the corrosive atmospheric environment, as well as the change of friction coefficient and wear depth over time. The change of conductivity of the coating during the friction process is deduced based on the relationship between current density and conductivity, and then the change of content of the corrosive medium in the coating and the average diffusion rate of the corrosive medium during the friction process are deduced based on the inherent conductivity of the corrosive medium and the coating. This solves the problem that the commonly used electrochemical three-electrode system method cannot be used for in-situ testing of the coupled corrosion and wear damage under the corrosive atmospheric environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is the clamping method of the coating sample; Figure 2 It is the friction coefficient-time curve; Figure 3 is the current density-time curve; Figure 4 It is the conductivity / friction coefficient vs time curve; Figure 5 This is a graph showing the weight of the corrosive medium versus time. DETAILED DESCRIPTION

[0008] The present invention will be further described below through specific implementation modes. Example

[0009] (1) Test sample clamping The test sample containing polyimide / polytetrafluoroethylene bonded solid lubricant coating was installed in the corrosion friction tester. The coating thickness was 21μm, and the sample substrate was made of Q235 carbon structural steel. The sample surface was wiped with acetone cotton balls to remove oil stains, sweat stains, etc. The coated metal substrate must be completely isolated from the corrosive atmosphere to prevent the thin liquid film generated by the corrosive atmosphere from directly connecting the coating surface to the metal substrate (such as Figure 1 ).

[0010] (2) Circuit connection between electrochemical workstation and friction and wear testing machine The metal substrate of the coating test sample is connected to the copper wire of the WE electrode of the electrochemical workstation; the metal friction couple is connected to the copper wire of the CE electrode of the electrochemical workstation; the RE electrode of the electrochemical workstation is connected in series with the CE electrode. The electrochemical workstation and the friction tester software use the same system time for synchronous measurement.

[0011] (3) Test parameter setting The friction tester uses the friction method, the friction ball is made of Gr15 bearing steel, the load is 5N, the amplitude is 2.5cm, and the frequency is 5Hz. The electrochemical workstation selects the constant potential polarization test method, the constant potential is set to 0.2V, the test time is 120min, the acquisition frequency is 20Hz, and the current density protection value is selected as the maximum value 2A / cm 2 , select current-time as the curve output form.

[0012] (4) Data collection: friction coefficient vs. time, current density vs. time Use 3.5% NaCl solution to create a salt spray atmosphere environment, turn on the corrosion atmosphere generator of the corrosion friction tester, and let the corrosion atmosphere enter the friction test box. Then turn on the electrochemical workstation and the friction tester simultaneously. The electrochemical workstation and the friction tester use the same system time as the benchmark, and the friction tester outputs the friction coefficient-time curve (such as Figure 2 As shown in the figure), the electrochemical workstation outputs the current density-time curve (as shown in the figure Figure 3 The variation of the weight of the corrosive medium in the coating over time According to the current density-time curve, the variation law of coating conductivity over time can be obtained through Ohm's law formula (1). Since the electrochemical test and friction test use the same time base, a conductivity / friction coefficient vs time curve can be drawn, such as Figure 4 According to the data, the conductivity of 3.5% NaCl salt water is 6.7S / m; the conductivity of the polyimide / PTFE coating is about 10 -10 S / m. From formula (2) and formula (3), χ can be calculated cor and χ coat , χ cor (t) is the changing law of the content of corrosive medium in the coating during the friction process, such as Figure 5 shown.

[0013] (5) Calculation of the average penetration rate of corrosive media in the coating during friction exist Figure 3It can be seen from the current density vs. time curve that at time t1, the current density suddenly increases across orders of magnitude. The reason for this phenomenon is that the corrosive medium penetrates from the coating into the metal matrix, causing the conductivity of the coating to suddenly increase. Therefore, the time it takes for the corrosive medium to penetrate the coating is t1. The initial thickness of the coating is 21.0 μm. The wear depth is measured by a three-dimensional profilometer. The wear depth at time t1 is 19.1 μm. The average diffusion rate v of the corrosive medium in the coating during the friction process is calculated by formula (4): dif 0.02μm / min; (4).

Claims

1. An in-situ synchronous measurement method for the coupled damage of corrosion and wear of coatings under corrosive atmospheric conditions. The following steps are involved: (1) Test sample clamping After the coating test sample is installed in the corrosion friction tester, the coating surface of the test sample is exposed to the corrosive atmosphere, and the metal substrate is completely isolated from the corrosive atmosphere to prevent the thin liquid film generated by the corrosive atmosphere from directly connecting the coating surface to the metal substrate; (2) Circuit connection between electrochemical workstation and friction and wear testing machine The metal substrate of the coating test sample is connected to the working electrode of the electrochemical workstation; the metal friction couple is connected to the counter electrode of the electrochemical workstation; the reference electrode of the electrochemical workstation is connected in series with the counter electrode, and the electrochemical workstation and the friction tester software use the same system time for synchronous measurement; (3) Test parameter setting The friction tester adopts the friction method, and the electrochemical workstation selects the constant potential polarization test method. The test time is consistent with that of the friction tester. (4) Data collection First, turn on the corrosion atmosphere generating device of the corrosion friction tester to place the sample in a corrosion atmosphere environment, and then set the relevant parameters of the electrochemical workstation and the friction tester and start them synchronously; the electrochemical workstation and the friction tester use the same system time as the benchmark, the friction tester outputs the friction coefficient-time curve, and the electrochemical workstation outputs the current density-time curve; since the friction coefficient and the current density use the same time standard, the friction coefficient and current density curves are plotted simultaneously with time as the horizontal axis, so as to obtain the change of the friction coefficient with the current density; (5) Changes of the weight of corrosive media in the coating over time According to the current density-time curve, the coating conductivity σ can be obtained by using Ohm's law formula (1): total The law of change with time t, where J(t) is the current density and E is the electric field strength; each substance has a specific conductivity, assuming that the conductivity of the corrosive medium is σ cor , the conductivity of the coating is σ coat , the weight of the corrosive medium in the coating is χ cor , coating material weight is χ coat ; Combining formula (2) and formula (3) can obtain the weighted χ cor and χ coat , χ cor (t) is the function of the content of the corrosive medium in the coating as the friction process changes; (6) Calculation of the average penetration rate of corrosive media in the coating during friction In the current density-time curve, t 1 At this moment, the current density will suddenly increase by more than three orders of magnitude. The reason for this phenomenon is that the corrosive medium penetrates from the coating into the metal matrix, causing the coating resistance value to suddenly decrease. Therefore, t 1 The time is the time when the corrosive medium penetrates the coating; Assuming the initial coating thickness is T, t 1 When the wear depth at time d is d, the average diffusion rate v of the corrosive medium during the friction process can be calculated by formula (4): dif ; （4）。 2. The in-situ synchronous measurement method for the corrosion and wear coupled damage of coatings under corrosive atmospheric conditions according to claim 1, Features: In the step (3) constant potential polarization test method, the constant potential is set to 0.2 V, the test time is 120 min, and the acquisition frequency is 20 Hz.

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