In Situ Monitoring Of Pitting Corrosion Of Stainless Steel With Digital Holographic Surface Imaging Technique

Materials corrosion will affect the national infrastructure construction,industrial and agricultural production,military defense construction and many other fields.The annual economic loss of materials corrosion accounts for 4% of GNP.The pitting of metal is one of the most significant forms of corrosion,which has been researched focus in the field of engineering materials.The acquisition of the dynamic changes information is the focus the study of pitting corrosion.Therefore,the development of new surface monitoring method is the key to study the pitting corrosion information of materials surface.In this paper,the exploitation of digital holographic surface imaging method in-situ monitoring the corrosion process of materials surface is aimed.Firstly,an optical test system is set up to monitor pitting corrosion of stainless steel in real based on Michelson interferometer.Taking the pitting process of stainless steel as an example,the interference fringe video images of the dynamic processes of stainless steel electrode pitting corrosion were collected and combining with digital image processing methods reconstruct the dynamic change of the object wave phase of interference fringe,which achieve the in-line measurement of dynamic change of electrode surface during stainless steel pitting.The pitting corrosion during the development,the solution concentration change of the stainless steel surface and the spatial distribution of the pitting corrosion were achieved,which combined with the traditional electrochemical methods and the SEM to analyze the pitting corrosion process,mechanism and morphological changes synchronously.This article mainly carries out the following four aspects of work.(1)Digital holographic surface imaging system has been designed.Based on Michelson interferometer,the holographic surface imaging system was designed,which in-situ monitored the dynamic process of stainless steel electrode surface,and the change of interference fringe pattern was recorded by industrial camera.Finally,the dynamic interference fringe pattern was analysis by MATLAB software,which combined with electrochemical workstation to observe stainless steel pitting process.(2)The interference fringes processing algorithm of suitable for electrode surface observation were designed.Reconstruct the phase change of object light caused by the change of ion concentration on the electrode surface solution.Through introduce carrier fringe and use Fourier transform to analysis of interference fringe images.Using adaptive bandpass filters achieve automatic image processing of interference fringes and obtain the higher phase measurement accuracy.It can be used to monitor the dissolution and self-healing process of the electrode surface film during stainless steel pitting.(3)The study of the dynamic process of electrode surface during the process of 304 stainless steel pitting corrosion use the above software and hardware system.Combined with conventional electrochemical measurement methods,the process of 304 stainless steel pitting corrosion in ferric chloride solution and sodium chloride solution was observed synchronously.The results indicate that the external magnetic field can restrain stainless steel pitting corrosion,which provides a reliable experimental basis to study the mechanism of stainless steel pitting corrosion.(4)The self-assembled film can significantly reduce 316 stainless steel pitting corrosion and the longer the assembly time,the lower the probability of 316 stainless steel pitting corrosion.Digital holographic surface imaging as an effective monitoring technique can monitor the dynamic process of 316 stainless steel pitting corrosion with the self-assembled film.