Study On Failure Behavior Of Marine Steel And Diamond-Like Carbon Films Under Microbial Action

Because of the harsh service environment,marine engineering steel will suffer from the dual erosion of corrosive media and marine microorganisms in seawater,which will lead to failure and damage,thus reducing the service life of marine engineering steel and eventually leading to serious economic losses and safety accidents.Therefore,how to improve the service life of marine engineering steel in the marine microbial environment is one of the problems that need to be solved urgently and the key to China’s strategy of going marine.In this thesis,diamond-like carbon（DLC）films were prepared on the surfaces of HP13Cr stainless steel and AH32 steel by plasma-enhanced chemical vapor deposition（PECVD）technology,and the microbial corrosion behaviors of the matrix materials and DLC films in sulfate-reducing bacteria（SRB）and Chlorella were studied.In addition,the corrosion behaviors of the two materials and DLC films on their surfaces in dynamic and static biological environments were characterized by dynamic cycling devices.The micro-morphology and composition characteristics of DLC film,biofilm and corrosion product film on the surface of HP13Cr stainless steel and AH32 steel were characterized by AFM,SEM and FTIR.Through the potentiodynamic polarization curve,EIS and other electrochemical accelerated corrosion experiments combined with corrosion thermodynamics,the failure behavior and related mechanism of marine HP13Cr stainless steel,AH32 steel and DLC film under the action of SRB,Chlorella and other microorganisms were explored.The main achievements of this thesis are as follows:Ionization voltage has a significant effect on the mechanical properties of DLC films on HP13Cr stainless steel.DLC films prepared at 100 V voltage have high hardness and modulus.When the voltage is too high,the ionized high-energy plasma will destroy the integrity of DLC films,increase the number of internal defects in the films,and cause the mechanical properties of DLC films to be destroyed.After coating,the corrosion resistance of HP13Cr stainless steel is improved.The corrosion current density of DLC films prepared at 1800V voltage is 6.43×10^-9A/cm²,which is one order of magnitude lower than that of HP13Cr substrate,and the corrosion resistance is the best.There is no obvious corrosion of DLC film on the surface of HP13Cr stainless steel at the initial stage of immersion in SRB-containing solution.With the prolongation of soaking time,DLC films around SRB are consumed and damaged,which eventually leads to local corrosion.After the soaking time reaches 7days,the continuous and dense metabolite film plays a very good role in protecting the HP13Cr stainless steel matrix and DLC film and slows down corrosion.After AH32 offshore steel was soaked in the electrolyte containing Chlorella for3 days,Chlorella formed a biofilm on its surface which could inhibit corrosion,and its corrosion potential increased from-491.4 m V to-381.2 m V.When DLC film on the surface of AH32 steel is soaked in the electrolyte containing Chlorella,the biofilm will also be formed on the surface,but the formation speed is much lower than that of Chlorella on the surface of AH32 offshore steel.The corrosion resistance of HP13Cr stainless steel in the environment containing SRB dynamic electrolyte gradually decreases with the increase of soaking time.The growth trend of SRB in the dynamic environment is weaker than that in the static environment,which makes SRB enter the decline period ahead of time,and it is difficult to form a biofilm that can slow down corrosion.The corrosion resistance of AH32 marine steel in the dynamic electrolyte environment containing Chlorella decreases gradually with the increase of soaking time,and the impedance value is stable at about 6.6×10²Ω·cm² after 3 days.The growth trend of Chlorella is stronger than that of a static environment,which increases the reproduction number of Chlorella and forms a biofilm on the surface that can slow down corrosion.