Residual Stress And Fatigue Behavior Of Surface Nanostructured Zr-3Alloy

Surface nanocrystallization (SNC) is a newly developed technique to form ananostrcutured surface layer on bulk materials, and the residual compressive stress and workhardening was generated on the surface, which can enhance the whole properties byimproving the surface structure. In this paper, the Zr-3with typical HCP structure wereselected as target specimens to be treated by surface mechanical attrition treatment(SMAT)technique. The microstruture and properties of nanostructured surface layer werecharacterized and analyzed, then the surface residual stress were represented along the depthdirection, and last the fatigue were researched of Zr-3by SNC. In order to study the propertiesof metal by SNC.The SMAT with different durations was applied of Zr-3alloy. The surface microhardness,tensile properties, and the surface roughness were determined of Zr-3samples by SMAT-ed.The surface organization and grain size were analyzed of Zr-3samples by surface mechanicalattrition treatment (SMAT) with different durations by X-ray diffraction(XRD), Opticalmicroscope(OM), transmission electron microscopy(TEM) and scanning electron microscope(SEM). And the macroscopic residual stress at different depth from surface were evaluated byXSTRESS3000X, the fatigue limit was determined of Zr-3samples by surface mechanicalattrition treatment with different durations by Four-point bending fatigue experiment. And thefatigue fracture characteristic was observed of samples.The results indicate that the Zr-3can be nanocrystallization by SMAT process, and thegrain size was refined nano size, and the TEM can be prove it. Twin and slip were main of itsdeformation mode, and the strengthening layer was formed on the surface.The macroscopic residual stress was compressive stress, and the surface residual compressive stress was increased at first and then decreased with depth from surface. thesurface residual compressive stress was enhanced with duration increased from15min to30min, and it decreased with the time increased further. the maximum residual compressivestress showed increment from-503MPa to-618MPa as the duration increased from15minto30min, and kept stable.The fatigue limit was improved obviously of SMAT samples, which was first increase andthen decrease with durations increase gradually, and compared with the CP samples, thefatigue limit was improved23%, the fatigue crack source was initiated subsurface about80μm form the surface, and the fatigue crack source are multivariant. The factors that improvethe fatigue limit was discussed in this paper of SMAT Zr-3, and the residual compressivestress is a importance factor.