Metal surface potential in-situ test device and method under stress and hydrogen permeation conditions
Technical Field
The invention belongs to the field of analysis and test of metal materials, and particularly relates to a metal surface potential in-situ test device and method under stress and hydrogen permeation conditions.
Background
The metal material is often accompanied by the action of working load and environmental stress in the service process. Acid gas, hydrogen-containing medium and the like in the atmospheric environment can cause generation, adsorption and permeation of atomic hydrogen into a metal matrix, and finally hydrogen embrittlement failure of the metal structure is induced. Particularly, under the condition of tensile stress, hydrogen is easy to interact with the material to cause hydrogen embrittlement of the material, and the service safety of the material is influenced. Therefore, hydrogen embrittlement type stress corrosion cracking behavior is an important safety concern when the metal is in service in atmospheric environments.
Kelvin Probe Force Microscope (KPFM) combines Kelvin technology with Atomic Force Microscope (AFM), realizes the characterization of sample surface potential and surface morphology, and is gradually applied to the field of metal material corrosion analysis and test in recent years. The hydrogen charging process usually adopts an electrochemical liquid-phase hydrogen permeation mode, and the submerged test of the Kelvin probe technology has a plurality of problems, so that the application of the Kelvin probe technology in the hydrogen permeation field is limited. In view of this, it is necessary to design a simple kelvin probe surface potential testing device that is more suitable for the stress and hydrogen permeation multi-field coupling condition of the real environment.
Disclosure of Invention
In view of the above, the present invention aims to provide a device and a method for in-situ testing of metal surface potential under stress and hydrogen permeation conditions, which solve the disadvantages of the existing surface potential testing device, can combine the stress loading with the hydrogen permeation process, and realize the parallel testing of hydrogen permeation and kelvin probe by adopting a sample bottom surface hydrogen charging mode, thereby completing the in-situ testing of the surface potential of the metal sample under the stress and hydrogen permeation coupling conditions.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a metal surface potential in-situ testing device under the conditions of stress and hydrogen permeation comprises a stress loading mechanism, a hydrogen permeation mechanism and a surface potential measuring mechanism, wherein the stress loading mechanism comprises a base, a sample, a pressure head, a nut and a dial indicator, the sample, the pressure head and the nut are all arranged in the base, a through hole is formed in the center of the bottom end of the base, two static supporting points are arranged on the inner wall of the top end of the base, the pressure head comprises a screw rod and two supporting plates which are parallel to each other, the bottom ends of the two supporting plates which are parallel to each other are fixedly connected with the screw rod, a movable supporting point is arranged at the top end of each supporting plate, the upper surface of the sample is in contact with the two static supporting points, the lower surface of the sample is in contact with the two movable supporting points, the screw rod extends into the through hole of the base, a limiting part which is matched with the screw rod and limits the circumferential rotation of the screw rod is arranged in the through hole, and the nut is matched with the screw rod and rotates to enable the end surface of the nut to be tightly attached to the inner wall of the bottom of the base, the dial indicator is used for detecting the surface stress of the sample;
the surface potential measuring mechanism comprises a KPFM testing system, a Kelvin probe and a sample stage, wherein the Kelvin probe is connected with the KPFM testing system through a lead, the Kelvin probe is used for detecting the surface potential of a sample, and the sample is connected with the sample stage through a lead;
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, the base is arranged in the hydrogen charging groove, the hydrogen charging solution is filled in the hydrogen charging groove, and the sample, the auxiliary electrode and the reference electrode are all connected with the electrochemical workstation through leads.
Furthermore, the screw rod is driven to load stress on the sample by rotating the nut, and the dial indicator measures the stress on the central area of the surface of the sample.
Further, the liquid level of the hydrogen charging solution contained in the hydrogen charging tank is over the lower surface of the sample, but the upper surface of the sample is kept dry.
Furthermore, an auxiliary electrode hole and a reference electrode hole are formed in one of the support plates, the auxiliary electrode penetrates through the auxiliary electrode hole, the reference electrode penetrates through the reference electrode hole and is arranged between the sample and the auxiliary electrode, and the sample, the auxiliary electrode, the reference electrode and the hydrogen-filled solution form a three-electrode system to realize hydrogen permeation on the sample from the lower surface of the sample.
Furthermore, limit structure is a plurality of spacing slide rails that evenly set firmly on the through-hole inner wall, and is corresponding, sets up the spacing spout with spacing slide rail complex on the screw rod.
Furthermore, the two movable supporting points contact the middle part of the sample, and the two static supporting points contact the two ends of the sample.
Further, the sample is of a flat plate type structure.
Furthermore, the base is made of PEEK.
A testing method of a metal surface potential in-situ testing device under stress and hydrogen permeation conditions comprises the following steps:
step S1, sample stress loading:
s11, calculating the strain quantity required by the static load required by the experiment;
s12, mounting the processed sample between a movable fulcrum and a static fulcrum;
s13, loading stress on the sample by rotating the nut, measuring the strain of the central area of the surface of the sample by using a dial indicator, and stopping loading when the reading of the dial indicator reaches the required strain of the sample;
step S2, hydrogen charge test preparation:
s21, horizontally placing the stress loading mechanism which is loaded in the step S1 in a hydrogen charging tank, and connecting the reference electrode, the auxiliary electrode and the sample with an electrochemical workstation;
s22, dropwise adding a hydrogen charging solution into the hydrogen charging groove until the liquid level just submerges the lower surface of the sample;
step S3, sample hydrogen charging:
s31, setting hydrogen charging experiment parameters, and charging hydrogen into the sample by using an electrochemical workstation;
s32, after the hydrogen charging process is finished, disconnecting the reference electrode, the auxiliary electrode and the sample from the electrochemical workstation;
step S4, testing the surface potential of the sample:
s41, connecting the sample with a sample table, operating a Kelvin probe to be close to the upper surface of the sample, and contacting the Kelvin probe with a micro-area to be detected in the middle of the sample;
s42, carrying out surface potential detection on the micro-area to be detected by using a KPFM test system and Kelvin probe force;
s43, after the surface potential measurement is finished, moving the Kelvin probe to be far away from the surface of the sample;
and S5, repeating the steps S3 and S4, and carrying out surface potential in-situ test on the selected micro-area to be detected until the designed parallel experiment is completed.
Compared with the prior art, the metal surface potential in-situ test device and method under the stress and hydrogen permeation conditions have the following advantages:
1. the manual adjusting nut is adopted, acting force is applied to the sample by the thread pair, transmission is stable, the thread pair has a self-locking effect, and the device can be conveniently stopped for reading without worrying about reading change, and the reading is accurate and convenient;
2. the sample is charged with hydrogen in a bottom surface charging mode, the hydrogen can permeate to the upper surface of the sample, and the upper surface of the sample can be kept dry, so that the Kelvin probe force test on the upper surface of the sample is facilitated;
3. the hydrogen filling parameters can be changed, a plurality of groups of parallel tests are designed, the surface potential change of the sample is subjected to in-situ test, the sample and the probe are always kept in the in-situ state, the test error caused by objective factors is reduced, and the test parallelism is better.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a schematic structural diagram of a metal surface potential in-situ testing device under stress and hydrogen permeation conditions according to an embodiment of the present invention;
FIG. 2 is a schematic perspective view of a sample holder according to an embodiment of the present invention;
FIG. 3 is a schematic view of a stress loading mechanism of the present invention.
Description of reference numerals:
the method comprises the following steps of 1-base, 2-sample, 3-pressure head, 4-nut, 5-dial indicator, 6-through hole, 7-static fulcrum, 8-screw, 9-support plate, 10-dynamic fulcrum, 11-electrochemical workstation, 12-hydrogen charging groove, 13-hydrogen charging solution, 14-auxiliary electrode, 15-reference electrode, 16-KPFM test system, 17-probe, 18-auxiliary electrode hole, 19-reference electrode hole, 20-sample table and 21-limit structure.
Detailed Description
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
As shown in fig. 1-3, a metal surface potential in-situ testing device under stress and hydrogen permeation conditions comprises a stress loading mechanism, a hydrogen permeation mechanism and a surface potential measuring mechanism, wherein the stress loading mechanism comprises a base 1, a sample 2, a pressure head 3, a nut 4 and a dial indicator 5, the sample 2 is of a flat plate type structure, the sample 2, the pressure head 3 and the nut 4 are all arranged in the base 1, a through hole 6 is arranged at the center of the bottom end of the base 1, two static fulcrums 7 are arranged on the inner wall of the top end of the base 1, the pressure head 3 comprises a screw rod 8 and two parallel support plates 9, the bottom ends of the two parallel support plates 9 are fixedly connected with the screw rod 8, a movable fulcrum 10 is arranged at the top end of each support plate 9, the upper surface of the sample 2 is in contact with the two static fulcrums 7, the lower surface is in contact with the two movable fulcrums 10, the screw rod 8 extends into the through hole 6 of the base 1, a limiting structure 21 which is matched with the screw 8 and used for limiting the circumferential rotation of the screw 8 is arranged in the through hole 6, the nut 4 is matched with the screw 8 and rotates the nut 4 to enable the end face of the nut to be tightly attached to the inner wall of the bottom of the base 1, and the dial indicator 5 is used for detecting the surface stress of the sample 2;
the surface potential measuring mechanism comprises a KPFM testing system 16, a Kelvin probe 17 and a sample stage 20, wherein the Kelvin probe 17 is connected with the KPFM testing system 16 through a lead, the Kelvin probe 17 is used for detecting the surface potential of the sample 2, and the sample 2 is connected with the sample stage 20 through a lead;
the hydrogen permeation mechanism comprises an electrochemical workstation 11, a hydrogen charging groove 12, a hydrogen charging solution 13, an auxiliary electrode 14 and a reference electrode 15, wherein the hydrogen charging groove 12 is arranged on a sample table 20, the base 1 is arranged in the hydrogen charging groove 12, the hydrogen charging solution 13 is filled in the hydrogen charging groove 12, and the sample 2, the auxiliary electrode 14 and the reference electrode 15 are all connected with the electrochemical workstation 11 through leads.
In the stress loading mechanism, the screw rod 8 is matched with the nut 4, the screw rod 8 is driven to load stress on the sample 2 by rotating the nut 4, and the dial indicator 5 measures the strain of the central area of the surface of the sample 2, so that the stress applied to the center of the sample 2 is calculated.
The surface level of the charging solution 13 contained in the charging tank 12 is submerged below the lower surface of the sample 2, but the upper surface of the sample 2 is kept dry, thereby facilitating the surface potential measurement of the upper surface of the sample 2 by the kelvin probe 17.
An auxiliary electrode hole and a reference electrode hole are formed in one of the support plates 9, the auxiliary electrode 14 penetrates through the auxiliary electrode hole, the reference electrode 15 penetrates through the reference electrode hole and is arranged between the sample 2 and the auxiliary electrode 14, the sample 2, the auxiliary electrode 14, the reference electrode 15 and the hydrogen charging solution 13 form a three-electrode system, and hydrogen permeation of the sample from the lower surface of the sample 2 is achieved.
The limiting structures 21 are a plurality of limiting slide rails uniformly fixed on the inner wall of the through hole 6, and correspondingly, limiting slide grooves matched with the limiting slide rails are formed in the screw rod 8.
The base 1 is made of high-strength insulating material, such as PEEK material.
The two movable supporting points 10 are in contact with the middle of the sample 2, and the two static supporting points 7 are in contact with the two ends of the sample 2, so that the force is transmitted uniformly, and the accuracy of a test result is facilitated.
A testing method of a metal surface potential in-situ testing device under stress and hydrogen permeation conditions comprises the following steps:
step S1, sample stress loading:
s11, calculating the strain quantity required by the static load required by the experiment;
s12, installing the processed sample 2 between the movable fulcrum 10 and the static fulcrum 7;
s13, loading stress on the sample 2 by rotating the nut 4, measuring the strain of the central area of the surface of the sample 2 by using the dial indicator 5, and stopping loading when the reading of the dial indicator 5 reaches the required sample strain;
step S2, hydrogen charge test preparation:
s21, horizontally placing the stress loading mechanism which is loaded in the step S1 in a hydrogen charging tank 12, and connecting the reference electrode 15, the auxiliary electrode 14 and the sample 2 with the electrochemical workstation 11;
s22, dropwise adding a hydrogen charging solution 13 into the hydrogen charging groove 12 until the liquid level just submerges the lower surface of the sample 2;
step S3, sample hydrogen charging:
s31, setting hydrogen charging experimental parameters, such as the magnitude of applied current during electrolysis or the duration of electrolysis, and charging the sample 2 by using the electrochemical workstation 11;
s32, after the hydrogen charging process is finished, disconnecting the reference electrode 15, the auxiliary electrode 14 and the sample 2 from the electrochemical workstation 11;
step S4, testing the surface potential of the sample:
s41, connecting the sample 2 with a sample table 20, operating the Kelvin probe 17 to be close to the upper surface of the sample 2, and contacting the Kelvin probe 17 with a micro-area to be detected in the middle of the sample 2;
s42, carrying out surface potential detection on the micro-area to be detected by using the KPFM test system 16 and the Kelvin probe 17;
s43, after the surface potential measurement is finished, moving the Kelvin probe 17 away from the surface of the sample 2;
and S5, repeating the steps S3 and S4, adjusting the hydrogen filling experiment parameters, and carrying out surface potential in-situ test on the selected micro-area to be detected until the designed parallel experiment is completed, and then finishing the step.
The in-situ test in the application refers to testing the same microscopic region of the same sample at different time nodes, the hydrogen charging can be carried out for multiple times under the condition that the sample does not move according to the step S2 and the step S3, then the Kelvin probe test is carried out on the same position on the surface of the sample, and therefore the influence of experiment parameters such as different hydrogen charging time, hydrogen charging current and the like on the surface potential of the sample can be observed, and thus, a parallel test formed by the Kelvin probe test after the hydrogen charging is carried out for multiple times is the in-situ test in the invention.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.