Chemical performance characteristics of nickel-based alloy (inconel625/NO6625)
Inconel 625 Introduction:
Alloy 625 has excellent corrosion and oxidation resistance. The alloy exhibits good tensile and fatigue properties whether in low temperature or high temperature environments of 980°C. In addition, it is resistant to stress corrosion under salt spray. Therefore, this material can be widely used in the manufacture of aerospace engine parts, spacecraft structural components, chemical equipment, and places that need to be in contact with seawater and withstand high mechanical stress.
1 Experimental materials and methods
The source of the test material Inconel625 surfacing layer comes from the 316L/In-conel625 composite pipe surfacing layer area. The weight loss sample size is 100mm×50mm×2mm, and the electrochemical test sample size is 10mm×10mm×2mm. The samples were ground and polished with 1200-grit sandpaper, ultrasonicated in an anhydrous ethanol solution for 5 minutes, dried in the air, and prepared for use. The test medium is natural seawater in Qingdao Sea, and the test temperature is controlled at 10°C to simulate the seawater temperature at a depth of 200m. The corrosion weight loss sampling nodes of the samples are 5d, 15d, 30d, 60d and 90d. After the samples are taken out, they are cleaned, the corrosion products are removed and then weighed to calculate the corrosion rate of the samples. The ACM-Gill6 electrochemical workstation was used to test the sample polarization curve and AC impedance spectrum. The 625 alloy overlay layer was used as the working electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the Pt sheet was used as the auxiliary electrode. The polarization test scanning potential starts from the open circuit potential and scans toward the cathode and anode at a scanning rate of 1mV/s; the AC impedance spectrum test frequency is 10⁵-10-²Hz, and is perturbed with an amplitude of 10mV near the open circuit potential. ZeissULTRA55 scanning electron microscope/energy spectrometer was used to observe the macroscopic and microscopic corrosion morphology of the sample surface.
2 Experimental results and discussion
The average corrosion rate of the Inconel625 alloy cladding layer after being immersed in seawater at 10°C for 90 days. According to the figure, the corrosion rate of the 625 alloy cladding layer immersed in seawater for 5 days is 0.0037 mm/year. Then the corrosion rate rapidly decreased to 0.001 mm/year, and as the immersion time increased, the corrosion rate of the surfacing layer further decreased. After 90 days of immersion, the corrosion rate of the sample was approximately 0.0004 mm per year.
3 Conclusion
(1) The corrosion rate of the 625 alloy cladding layer in seawater at 10°C was initially 0.0037mm/a, and then decreased to 0.0004mm/a.
(2) The 625 alloy surfacing layer corrodes uniformly in seawater, and no corrosion product layer or passivation layer is formed on the surface.
(3) The 625 alloy surfacing layer has stable corrosion resistance after being soaked in seawater for 90 days.
