The process of pore initiation and development during anodizing of aluminium was studied using ultramicrotome sectioning allied with tran- smission electronmicroscopy.Based on the observations,ageometric model of the process of pore initiation and development,and a mathematic model of quasi-static electric field within the film during anodizing were pro- posed.The electric field distributions at differnt stages of pore initiation and development were calculated using finite elements method under sim- plified two dimensional conditions.The major role played by the electric field during the process was confirmed and the mechanism of the function of electric field was discussed.

The equivalent circuit and the relationship among parameters of an impedance with a single dispersing capacitive loop on Sluyters diagram were discussed.A method by which all the parameters of a single disper- sing capacitive loop impedance can be calculated rapidly was proposed, and a calculating process for estimating all seven parameters for impeda- nce with double dispersing capacitive loops was established.An applied software was made up to be used with Solartron 1096 Data-Management- System for processing impedance data.

An investigation on the features of electrochemical noises during pitting corrosion of aluminium,iron,carbon steel and two kinds of stainless steels in various passivating solutions with different concentrations of pas- sivators and Cl~- ion was carried out.All the electrochemical noises obser- ved are low frequency noises.The highest frequency f_c observed for a given solution usually increases with the increasing of Cl~- concentration.It seems that the higher the value of f_c is,the more easily the pit initiates,and that it is possible to evaluate the effectiveness of passivatorsor the resis- tance of metals against pitting corrosion by comparing f.Sometimes there is a maximum on the curve of f_c varying with Cl~- ion concentration, and pitting corrosion occurs before the maximum while general corrosion occurs after the maximum.All the spectral power densities measured show that the electrochemical noise is 1/(f~n) noise,though the value of n is somewhat different for different metals.A mathematical model for the spectral power density has been proposed.

The pit initiation process on commercially pure titanium in bromide solution was investigated by means of surface analysis.The results sho- wed that the titanium surface film formed by anodic polarization in bromide solution was mainly TiO_2.Prior to the pit initiation,Br- ions were adsorbed and accumulated on localized spots of the TiO_2 film forming Br nuclei containing mostly TiBr_4.The Br nuclei grew up into “critical nuclei”when the film was in the critical state of breaking down.The depth of the critical nuclei was equal to or less than 3nm. The concentration of Br in the critical nuclei was the critical surface concentration(CSC).It was the requisite condition for pit initiation that concentration of Br in Br nuclei reached CSC.In the system of titanium/bromide solution,the CSC(not measured in situ) was 25- 35wt% and was independent of the temperature and concentration of solution.

The anodic polarization behaviour and the initiation and propagation processes of pitting corrosion of TUP copper have been studied by electro- chemical method and surface analysis technique in mixed solution of low Cl~- and SO_4~(2-) but high HCO_3~- concentrations.Copper shows typical pitting characteristics in this mixed solution.The initiation of pitting corrosion of copper is due to Cl~- ions entering surface film and migrating to metal/ film interface,resulting in local breakdown of film.The main process of pitting propagation of copper is the formation and hydrolysis of CuCl, resulting in low pH value and Cl~- enrichment with autocatalytic effect in pitting process.

The response equation of the polarization of electrode under the condi- tion of galvanodynamic scanning in linear polarization region was derived from which another equation was obtained as follows: R_S=(△h)/(2i_0) ((i_0)/(△E))=(C/λ+1/(2R_p)) It is shown that based on this formula,plotted with (i_0)/(△E) against λ~(-1),a technique can be developed to measure the polarization resistance Rp and interracial capacitance C of the electrode without need of elimi- nating the influence of solution resistance R_S,and R_S can be determined as well.It is pointed out that this transient technique is very useful for those electrode systems with rather large time constants.Examples of its application are presented.

In this paper,a method was proposed to determine the critical pitting potential(φcb)which is obtained by extrapolating the curve of 1/φvsφ to 1/τ=0.A formula,φL=φ_(ε,o)+η_(co),was then derived to calculate the limit free corrosion potentials(φ)of practical passive systems. Finally,the boundary condition for prevention of practical passive sys- tems from pitting initiation was established.That is,if φ_(cb)>φfor a practical passive system,it is impossible for pitting nuclei to oc cur in the system,on the contrary,it is possible if φ_(cb)<φ■.

Flame sprayed welding with secondary remelting was adopted to improve the fatigue property of steel 45.The effect of the plasma sprayed Ni/Al coating on fatigue strength of steel 45 in air and in corrosive medium were compared with that of the flame sprayed welding Ni60.It was demonstrated that all the coatings reduced the fatigue limit in air,the plasma spraying (P.S)gave a reduction of 12% and the flame sprayed welding(F.S.W), 7%.On the contrary,thermal coating shows an advantageous effect on corrosion fatigue strength in 3.5%NaCl solution.F.S.W can increase over 70% in corrosion fatigue strength at 10~7 cycles and P.S can only increase 29%.It can be seen by fractographic analysis that fatigue cracks initiated at such places of coating which contain more defects,and the cracks grew more rapidly in cleavage or mixed mode through the Ni/Al or Ni60 coating. Occasionally,the interface between coating Ni/Al and matrix may be separated.It is found that coating Ni60 consisting of Ni-Cr solid solution and borides can decrease the passive current density.Obviously the micros- tructure and strength of the coating and bonding strength are related to the lifetimes of fatigue crack initiation.

Mn-Cu alloy is susceptible to SCC in sea water.A simulated occluded corrosion cell was used to study the chemical and electrochemical changes within corrosion cracks of Mn-Cu alloy in 3.5% NaCl solution.Under nature corrosion condition the potential within corrosion cracks always maintained 30-60mV more negative than the bulk potential.As anodic current (i_a=3.5mA/cm~2)passed through the occluded cell,the pH of solution decreased rapidly from 7to 3.5,and the Cl~=concentration increased 1.6 times.A linear relationship existed between Cl~= migration into occluded cell and time.When the bulk specimen was cathodically polarized at potential -0.85～0.95 V(vs.SCE),the potential within corrosion cracks is approximatelly equal to the bulk potential,and the pH in the occluded cell increased from 7to 8-9.Therefore SCC of Mn-Cu alloy can be prevented by cathodic protection.Control of the bulk potential range (-0.90～-0.95 V,vs.SCE)could prevent the initiation and propagation of cracks,

Electrodeposited Ni-P amorphous alloy was implanted with chromiu at 150 keV in dosage of(1,3,5)×10~(17)ions·cm~(=2). During implantation of Cr~+ ion,carbon from the residual gases in the vacuum chamber could reach the implanting layer assisted by absorption- diffusion and formed Ni-Cr-P-C layer on the surface of Ni-P. The distribution of Ni,Cr,P and C in the implanted layer was examined by means of SIMS.TEM observation proved that the surface Ni-Cr-P-C was amorphous. The modification of the corrosion properties of the amorphous surface alloys was studied by dynamic polarization in 1M H_2SO_4 and 1M HCl. The experimental results showed that Cr-implantation not only had beneficial effect on the active-passive behavior of electrodeposited Ni-P in 1M H_2SO_4,but also increased,the pitting resistance of the Ni-P in the 1M HCl solution.

Laser claddings of FeCrSiB alloy and NiCrSiB alloy have been done to A_3 steel with laser optical rotative mirror.It is shown that the corrosion resistance of the coatings has been significantly improved.