| Conventional nitriding of AerMet100 steel will lead to the low wear andcorrosion resistances of the nitrided surface layer and nitriding cannot beperformed directly on AZ91D magnesium alloy. Thus, in this paper, magnetronsputtering and pulse plasma nitriding were carried out on AerMet100 steel andAZ91D magnesium alloy to solve these problems. The microstructure, phasestructure and element distribution in deposited/nitrided surface layers werecharacterized by OM, SEM, TEM observations and XRD, EDS analyses. Inaddition, the microhardness, wear and corrosion resistances of the layers weretested.The OM and SEM observation results show that nitrogen element cannotdiffuses into substrate through the titanium film when the thickness of titaniumsputtered on the AerMet100 steel is larger than 1μm. Intermetallics are very easyto form at the interface of Ti film and substrate through interdiffusion, which willblock the diffusions of nitrogen and carbon into the substrate. Nitrogen candiffuse into the substrate when the thickness of Ti film is samller than 500nm,which will enhance the adhesion between the substrate and Ti film and improvethe properties of surface.The results from XRD, TEM and EDS show that a mixture of nanostructureand amorphous films is produced in the surface of AerMet100 steel when themagnetron sputtered titanium film with a thickness of 450nm was plasma nitridedat 460℃for 4h. The surface phase is mainly composed of Ti and TiN compound.A diffusion layer with a thickness about 1μm is formed by the interdiffusion ofTi and substrate elements. The results of mechanical and corrosive propertiesindicate that the wear and corrosion resistances are improved after the duplextreatment of magnetron sputtering and plasma nitriding. The friction coefficientof the surface layer of AerMet 100 steel deposited by magnetron sputtering oftitanium with the thickness of 450nm and then plasma nitrided at 460℃isobviously desecended up to 0.4. The deposited/nitrided layer is worn out whenthe sliding time is about 200s. At the same time, the friction coefficient isbasically equal to that of the untreated sample. The scar width decreases from 500μm of the original sample to 400μm and the wear rate decreasres from1.32×10-6g/(m-1·N-1) to 6.4×10-7g/(m-1·N-1). The corrosion potential of duplextreated sample moved to a noble direction from -0.464V to -0.300V of theuntreated sample and the corrosion density decreases from 6.7×10-6A/cm2 to5.7×10-7A/cm2.The interdiffusions of Ti, Al and Mg are very intense when AZ91Dmagnesium alloy deposited by titanium and aluminum films is plasma nitrided.And the thickess of diffusion layer is about 8μm. The surface phases of duplextreated AerMet100 steel consist mainly of Mg17Al12 and Ti2AlN ternaryccompound, which will enhance the hardness of the steel. The surface hardnessincreases from 44.1HV0.001, which is the hardness of original sample, to123HV0.001 in which AZ91D is deposited of titanium and aluminium films andthen plasma nitrided at 380℃. The corrosion potential increases from -1.5 to -1.1V after duplex treated, though the corrent density increases a bit. |
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