Effect Of Electrolytic Plasma Nitrided Layer On Corrosion And Abrasion Resistance Of38CrMoAl Steel

In this paper, nitrided layer with different phase composition and differentthickness are fabricated on the surface of38CrMoAl advanced nitrinding steel bydifferent plasma electrolytic nitriding process. The phase composition, section andsurface morphology of nitrided layer are analyzed by a series of analysis measures,such as, XRD, OM, SEM. Salt fog, electrochemical polarization curves test and weartest are used to investigate the corrosion and wear behaviors of the nitrided layer withdifferent phase composition and different thickness.The experimental results shows,The different ratio of the active oxygen ions and the active hydrogen ions,different surface temperature can be formed on the surface of38CrMoAl steel bycontrol the electrolyte formula and voltage during electrolytic plasma nitrided process.With the different ratio and surface temperature, the ε-Fe2-3N, ε-Fe2-3N+FeO andε-Fe2-3N+Fe3O4phase nitrided layer are prepared on the surface of38CrMoAl steel.By control different processing time,37μm(17μm ε-Fe2-3N),70μm(23μm ε-Fe2-3N),110μm(34μm ε-Fe2-3N) nitrided layer are prepared. The formation mechanism ofsurface morphology is same during the electrolytic plasma nitrided process. Thedifferent phase composition and thickness of nitrided layer have basically the samesurface morphology, which perform volcanic group structure, flocculent structure andporosity characteristic. With the different phase composition nitrided layers,ε-Fe2-3N+FeO phase nitrided layer has the lowest volcano micro-area gap andminimum poriness; with the different thickness of nitrided layers,37μm thick nitridedlayer has the lowest volcano micro-area gap and minimum poriness;The result of salt fog shows, phase composition, thickness and surfacemorphology of the nitrided layer have great influence to the corrosion resistance ofnitrided layers. Different phase composition of nitrided layer are characterized bypitting corrosion. The nitrided layer which consist of ε-Fe2-3N and FeO has theminimum surface flaw, has the least tendency of pitting corrosion. The shape of itsetch pit exhibits as disc with the least depth. The etch pit does not penetrate thesurface compound layer and has the best protection for matrix; the singleε-Fe2-3Nnitrided layer has the minimum corrosion rate; with different thickness of nitridedlayer,70μm (23μm ε-Fe2-3N)thick nitrided layer has the best fit between the thicknessof nitrided layer and surface morphology,which performs best corrosion resistance;The result of electrochemical polarization curves test shows, with different phasecomposition of nitrided layer, the singleε-Fe2-3N nitrided layer has the highest corrosion potential and lowest corrosion current density, which performs bestcorrosion resistance; with different thickness of nitrided layer,70μm(23μm ε-Fe2-3N)thick nitrided layer has the highest corrosion potential and lowest corrosion currentdensity, which performs best corrosion resistance;Wear experimental results show, the ε-Fe2-3N nitrided layer has good initialadhesive and abrasive wear resisitance, which performs good wear resistance; theε-Fe2-3N+Fe3O4nitrided layer performs good wear resistance because the Fe3O4phasecan be as a solid lubricant during wear process;with the increase of nitrided layerthickness, the nitrided layer have more well initial adhesive and abrasive wearresisitance, which performs more well wear resistance.