3. Results and discussion
3.1 Microstructural characterization
The Roman spectrum of Cr-DLC coating was shown in Fig.1. The overlapped D peak and G peaks located at 1363cm-1 and 1564cm-1 were obtained after fitted with Gaussian curves, respectively. It’s well known that the content of the graphite crystal was closely related to the value of ID/IG [22]. And the ratio of intensity between D peak and G peak (ID/IG) of Cr-DLC coating could be calculated by the fitted curve. The value of ID/IG was about 1.98, which meant the sizes of sp2 clusters were relatively large.
In order to analyze the chemical bond structure of Cr-DLC coating, the Cr2p and C1s XPS spectrum was showed in Fig.3. The Cr2p could be fitted into four peaks and each located at …show more content…
After a shorter running-in sliding distance of 50 m, the coefficient of friction in the deionized water was very close to that in seawater salinity of 32.37‰. The friction coefficient increased slightly in deionized water and was higher than that in salinity of 32.37‰. But for others, the friction coefficient gradually increased in a sliding distance of 150 m, the friction coefficient for salinity of 30.04‰ was similar to that salinity of 33.01‰ solution, whilst a higher coefficient of friction was presented in salinity of 29.84‰. The mean-steady friction coefficient of Cr-DLC/Si3N4 tribopairs in different salinity solutions was presented in Fig.4b. A lower coefficient of friction of 0.08 was obtained in deionized water. The friction coefficient decreased from 0.14 to 0.07 with an increase of salinity from 29.84‰ to 32.37‰ in seawater, while the friction coefficient increased to 0.12 in salinity of 33.01‰ solution. The specific wear rate of coatings was 3.0×10-6 mm3/Nm in deionized water, and then decreased to 1.8~5.5×10-7 mm3/Nm in seawater in Fig.4b. As compared with deionized water, the lowest wear rate of mating balls was 2.11×10-9 mm3/Nm in salinity of 29.84‰ solution, and then increased with increasing salinity. Though the friction coefficient was lower in deionized water, the corresponding wear rate was much higher than that in seawater. As seen in Fig.5, …show more content…
The values of each component of the equivalent circuit were fitted with the ZsimpWin3.10 software in Table.3. As seen in Fig.8, Rs represented the electrolyte resistance of the electrolyte solution in the equivalent circuit, Rpo was the pore resistance of coatings, indicating the equivalent resistance of coatings’ defects, and Rct was related to charge transfer resistance in the substrate/electrolyte interface. CPE1 and CPE2 were the double-layer capacitance of coating/ electrolyte and substrate/electrolyte interface separately. According to the definition of polarization, the polarization resistance was corresponding to the real part of the resistance when the frequency was zero. As seen in Fig.8, when the frequency was zero, the two constant phase elements (CPE1 and CPE2) were infinite value. Thus the circuit was equal to a series circuit of three equivalent resistances. In this case, the polarization resistance in the equivalent circuit was equal to the sum of the three equivalent resistances. The value of polarization resistance (Rs+Rpo+Rct) in different seawater’s salinity could be arranged as R30.04‰> R33.01‰> R29.84‰> R32.37‰. Usually, the smaller value of polarization resistance was, the larger corrosion current was, indicating the worse corrosion resistance of the coating. Therefore, the coating in seawater’s salinity of 30.04‰ showed the best anti-corrosion
3.1 Microstructural characterization
The Roman spectrum of Cr-DLC coating was shown in Fig.1. The overlapped D peak and G peaks located at 1363cm-1 and 1564cm-1 were obtained after fitted with Gaussian curves, respectively. It’s well known that the content of the graphite crystal was closely related to the value of ID/IG [22]. And the ratio of intensity between D peak and G peak (ID/IG) of Cr-DLC coating could be calculated by the fitted curve. The value of ID/IG was about 1.98, which meant the sizes of sp2 clusters were relatively large.
In order to analyze the chemical bond structure of Cr-DLC coating, the Cr2p and C1s XPS spectrum was showed in Fig.3. The Cr2p could be fitted into four peaks and each located at …show more content…
After a shorter running-in sliding distance of 50 m, the coefficient of friction in the deionized water was very close to that in seawater salinity of 32.37‰. The friction coefficient increased slightly in deionized water and was higher than that in salinity of 32.37‰. But for others, the friction coefficient gradually increased in a sliding distance of 150 m, the friction coefficient for salinity of 30.04‰ was similar to that salinity of 33.01‰ solution, whilst a higher coefficient of friction was presented in salinity of 29.84‰. The mean-steady friction coefficient of Cr-DLC/Si3N4 tribopairs in different salinity solutions was presented in Fig.4b. A lower coefficient of friction of 0.08 was obtained in deionized water. The friction coefficient decreased from 0.14 to 0.07 with an increase of salinity from 29.84‰ to 32.37‰ in seawater, while the friction coefficient increased to 0.12 in salinity of 33.01‰ solution. The specific wear rate of coatings was 3.0×10-6 mm3/Nm in deionized water, and then decreased to 1.8~5.5×10-7 mm3/Nm in seawater in Fig.4b. As compared with deionized water, the lowest wear rate of mating balls was 2.11×10-9 mm3/Nm in salinity of 29.84‰ solution, and then increased with increasing salinity. Though the friction coefficient was lower in deionized water, the corresponding wear rate was much higher than that in seawater. As seen in Fig.5, …show more content…
The values of each component of the equivalent circuit were fitted with the ZsimpWin3.10 software in Table.3. As seen in Fig.8, Rs represented the electrolyte resistance of the electrolyte solution in the equivalent circuit, Rpo was the pore resistance of coatings, indicating the equivalent resistance of coatings’ defects, and Rct was related to charge transfer resistance in the substrate/electrolyte interface. CPE1 and CPE2 were the double-layer capacitance of coating/ electrolyte and substrate/electrolyte interface separately. According to the definition of polarization, the polarization resistance was corresponding to the real part of the resistance when the frequency was zero. As seen in Fig.8, when the frequency was zero, the two constant phase elements (CPE1 and CPE2) were infinite value. Thus the circuit was equal to a series circuit of three equivalent resistances. In this case, the polarization resistance in the equivalent circuit was equal to the sum of the three equivalent resistances. The value of polarization resistance (Rs+Rpo+Rct) in different seawater’s salinity could be arranged as R30.04‰> R33.01‰> R29.84‰> R32.37‰. Usually, the smaller value of polarization resistance was, the larger corrosion current was, indicating the worse corrosion resistance of the coating. Therefore, the coating in seawater’s salinity of 30.04‰ showed the best anti-corrosion