Basic Study On Carbon Steel/Stainless Steel Functionally Graded Materials Made By Electrodeposition(2)

With good performance,beautiful appearance,stainless steel material is widely used in various fields of manufacturing industry.The carbon steel/stainless steel gradient material was prepared by the methods of molten salt electrolysis and eletrodeposited from aqueous bath.The solubility of NiO,the mechanism of electrochemical reduction of Cr（Ⅲ）and Ni（Ⅱ）ions,the mechanism of electro crystallization were explored.EDS,XRD,SEM,and GDS were performed to characterized the microstructure and properties of the samples.The dissolution of NiO required 7h to reach saturation,the solubility of NiO increased with the increase of the contents of Cr₂O₃ and NaF and temperature.the dissolution mechanism of NiO in the molten salt system was pure physical dissolution.The electrochemical reduction process of Cr（Ⅲ）and Ni（Ⅱ）ions is a reversible process,in which,Cr（Ⅲ）is reduced by two steps as Cr³⁺+e→Cr³⁺,Cr³⁺+2e→Cr,Ni（Ⅱ）ion is directly reduced by one step as Ni³⁺+2e→Ni.The electrocrystallization mechanism of Cr,Ni were the nucleation and growth model and the continuous nucleation and growth model of the spherical three-dimensional crystal nucleus in the controlled by diffusion,respectively.Cathode is carbon steel and anode is nickel chromium alloy.Optimal conditions of obtaining the carbon steel/stainless steel gradient material with good surface morphology in the system are following.Molten salt compositions are X_NaCl:X_KCl:X_NaF:X_Cr2O₃:X_NiO=0.39:0.39:0.2:0.01:0.01;deposit temperature is 800 ℃;deposit time is 90 minutes current density is 90 m A/cm²;current waveform is bidirectional pulse.The diffusion coefficient increase as the temperature;diffusion mechanism of chromium in the Fe-30 Ni alloy with vacancy diffusion mechanism and atomic exchange mechanism;carbon steel / stainless steel gradient materials was prepared from carbon steel and its resistance to corrosive get significantly enhanced.