The corrtest electrochemical test system can automatically carry out the electrochemical corrosion test and fit the test curve. Before the test, it is necessary to measure some parameters of the sample and prepare the working electrode containing the sample. Firstly, the edge of the as cast and nitrocarburized lzqt600-3, 1 / 2R Measure the surface area of the test surface with the core sample and record the density of the sample. Then use copper wire to make electrode around the side of the sample. Put the sample into the PVC pipe and stick it on the tape together. After the polyamide resin and epoxy resin with the ratio of 1:1.5 are dissolved at high temperature and evenly stirred, they are poured into the PVC pipe and sealed.
In the test, salt bridge and electrolyte also need to be prepared in advance. Agar powder (1-1.5 g) and potassium chloride (10 g) are mixed and poured into 30 ml distilled water to be heated to boiling. Lugin capillary tube is used to suck the solution into the tube under negative pressure. After cooling and solidification, the salt bridge is formed, as shown in the figure. The analytical pure sodium chloride (35 g) was poured into 965 ml distilled water and mixed evenly with a stirring rod to form a 3.5 wt.% NaCl electrolyte.
As a strengthening layer is formed on the surface of the sample after nitrocarburizing, the surface of the sample is only slightly polished before testing. After removing the oxide layer on the surface of the sample, it is put into the working electrode and inserted into the electrolytic cell. In addition, the reference electrode and auxiliary electrode are connected with the correct interface. Check whether the display value of open circuit potential in the software is reasonable. If it is reasonable, it can be tested.
(1) Open circuit potential
The corrosion form of the sample in the electrolyte can be clearly monitored by CS electrochemical workstation, and the change rule between time and natural corrosion potential can be obtained. The stable value of potential is the steady potential of the sample. This is a constantly changing process, the electrode will be from unstable state to stable state, and the sample in the electrolyte will also form a protective film on its surface to increase the material stability. The test parameters are as follows: the open circuit potential of as cast and nitrocarburized samples is measured for 4500 s.
(2) Electrochemical impedance spectroscopy
In order to obtain the electrochemical impedance spectroscopy (EIS) and obvious high-frequency corresponding characteristics of the material, the “field” mode was selected in the whole test process, and the test frequency was 0.01 Hz ~ 100 kHz, which did not damage the surface of the material.
(3) Potentiodynamic polarization curve
Finally, the potentiodynamic polarization curve of the sample is tested, which will corrode the surface of the material. The test parameters are: scanning potential range is + 0.25 V, scanning speed is 0.5 MV / s.