17 Very High-Cycle Fatigue Resistance of Shot Peened High-Strength Aluminium Alloys: Role of Surface Morphology 131 Fig. 17.3 Surface morphologies measured through optical profilometer. (a) As-received, (b) Z150 peened, (c) B120 peened, (d) B120 peened and tribofinished, (e) V40 peened, (f) V40 peened and tribofinished. The assessment area is 636 477 m2 Fig. 17.4 Microhardness profiles of the as-received and peened variants, obtained by averaging the results of five tests peening treatments are very superficial, the maximum hardness is within 60 m from the surface, the depth of the surface layer interested by the plastic deformation is about 100 m. The B120 treatment causes a more intense work hardening of the sub-superficial layers, and hence higher microhardness values, while the V40 treatment introduces higher microhardness values down to 40 m below the surface. The Z150 treatment induces a sub-superficial microhardness peak, where the Hertzian pressure is nearly maximal; the effect of shot peening vanishes at approximately 0.17 mm below the surface. The tribofinishing treatment slightly modifies the microhardness profiles, mainly due to the removal of the outer material layer without significantly altering the work-hardening state.
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