| N4 is a commercial pure nickel material with good mechanical properties and easy cold processing.It has good corrosion resistance under most acidic and alkaline conditions,so it is often used as an aerospace structural material.But,there is no many reports showed it corrosion in NaOH,NaCl solution.Therefore,in this paper,the corrosion behaviors of N4 in NaOH and NaCl were investigated for the purpose of studying the corrosion resistance of N4 under heat treatment temperature.Using scanning electron microscope(SEM)and Energy Disperse Spectroscopy(EDS)and electrochemical workstation PARSTAT 2273 technology,studied the N4 interchange material surface morphology and its electrochemical properties in NaOH,NaCl solution.The self-corrosion potential and point corrosion potential of the N4,which is without heat treatment,is-0.55V and 0.254V.These two values are both higher than the N4 after heat treatment.The corrosion reaction resistance and double layer resistance of N4 reaches its maximum under 200?heat treatment.Those two values are decrease under 300?heat treatment.When the heat treatment temperature reach 400?,those two values are reaches its minimum.Soaking in 3.5%NaCl solution for 15 days,not N4interchange when heat treatment is given priority to with pitting corrosion,along with the heat treatment temperature,the surface of the N4 interchange increase in the number of corrosion products generated,corrosion product morphology from the dendrite shape to flocculent,corrosion form by pitting corrosion gradually shift to local corrosion.With the increase of the soaking time of N4 in NaCl solution,the corrosion rate decreases gradually due to the accumulation of corrosion products on the surface of materials.The corrosion potential of N4 in 1%,3.5%and 5%NaCl solutions is from high to low,respectively-0.526 V,-0.640 V and-0.731 V.The corresponding concentration of NaCl was soaked in NaCl solution for 5 days,and the corrosion weight loss of N4 increased with the increase of NaCl concentration.Look from corrosion appearance,the higher the concentration of Cl~-,corrosion hole,the more the corrosion pore size,the greater the of 5%when the concentration of Cl~-metal interface was etched into a deep ditch.In NaOH solution,due to the existence of passive film,the corrosion rate of N4 at the initial stage of impingement was slow.With the extension of soaking time,the passive film broke down and the corrosion rate increased.With NaOH concentration increases,the Rp value is lower,N4 interchange in 5%,10%and 10%NaOH solution passive area wide,however,increases with the concentration of NaOH solution,N4interchange of pitting corrosion current density increased gradually,from 10~-3.3153.315 A/cm~2increases to 10~-2.9672.967 A/cm~2.N4 interchange of corrosion rate also increased as the NaOH solution concentration,the corrosion weight loss also increases with increased with the concentration of alkali solution soak for five days,by 5%NaOH solution in weightlessness about 13 mg to 15%solution of about 17 mg.N4 reverses typical point corrosion in NaOH solution.The higher the concentration of OH~-ion,the more corrosion pits and corrosion products on the surface of N4 materials.Compared with NaCl solution,N4 is more prone to surface passive in NaOH solution,and the same concentration of Cl~-is more suitable for N4 corrosion than OH~-.In 5%NaCl solution,there is no obvious passive region in the polarization curve of N4,and there are more corrosion holes on the surface of samples soaked for 15 days,and more deep holes and cracks in the parts.And in the process of polarization in 5%NaOH solution appeared obvious passive region,its surface anodic oxidation and formation of oxide film,immerse 15 days of the sample surface corrosion is not obvious,only a little residue is in the sample surface. |
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