Yazar "Bandini, Michele" seçeneğine göre listele

Listeleniyor 1 - 6 / 6
  • Küçük Resim Yok
    Öğe
    Effects of different mechanical and chemical surface post-treatments on mechanical and surface properties of as-built laser powder bed fusion AlSi10Mg
    (Elsevier Science Sa, 2022) Maleki, Erfan; Bagherifard, Sara; Unal, Okan; Sabouri, Farshad; Bandini, Michele; Guagliano, Mario
    Laser powder bed fusion (LPBF) materials have various surface defects, which can detrimentally affect the mechanical properties and fatigue behavior of these materials. Surface post-processing can be crucial to reduce or eliminate these surface imperfections. In this study, the effects of different post-processing methods including shot peening, ultrasonic nanocrystalline surface modification and severe vibratory peening as well as electrochemical polishing and other hybrid treatments obtained from their combination were surveyed on microstructure, surface and mechanical properties of LPBF AlSi10Mg specimens. Two different processes with varying levels of kinetic energy were considered for each mechanical surface treatment. The results indicate that mechanical treatments can effectively modify the surface morphology, improve surface hardness and induce compressive residual stresses. In addition, electro-chemical polishing was highly efficient in surface roughness reduction and increasing the wettability of the hybrid mechanically and chemically treated specimens.
  • Küçük Resim Yok
    Öğe
    The effects of microstructural and chemical surface gradients on fatigue performance of laser powder bed fusion AlSi10Mg
    (Elsevier Science Sa, 2022) Maleki, Erfan; Bagherifard, Sara; Unal, Okan; Bandini, Michele; Guagliano, Mario
    Internal and surface imperfections are known to reduce the fatigue strength of parts fabricated by laser powder bed fusion (LPBF). Post-treatment can play a key role to ameliorate the adverse effects of these defects. In this study, severe vibratory peening, as a novel surface treatment based on severe plastic deformation, was applied for the first time on LPBF material. The effects of this mechanical surface treatment were investigated individ-ually and in combination with heat treatment on microstructural and mechanical properties of V-notched LPBF AlSi10Mg samples. The results revealed the simultaneous formation of microstructural and chemical gradients on the surface layer of the mechanically treated samples, resulting in remarkable mechanical properties' improvement. In addition, the hybrid thermal and mechanical post-treatment significantly improved the fatigue life compared to the as-built condition, through affecting multiple physical phenomena regarding surface and subsurface characteristics.
  • Küçük Resim Yok
    Öğe
    The efficiency of tumble finishing as a final post-treatment for fatigue enhancement of notched laser powder bed fusion AlSi10Mg
    (Nature Portfolio, 2023) Maleki, Erfan; Bagherifard, Sara; Unal, Okan; Revuru, Manoj; Bandini, Michele; Guagliano, Mario
    A hybrid post-treatment combining tumble finishing as a final step after shot peening and heat treatment was developed to alleviate the adverse effects of internal and surface defects on the fatigue performance of laser powder bed fusion AlSi10Mg samples. The effects of each post-treatment were investigated individually and synergistically on microstructure, surface morphology and roughness, hardness, residual stresses, porosity, and rotating bending fatigue behavior of V-notched AlSi10Mg samples. The results reveal that tumble finishing can highly reduce surface roughness by 28 and 32% compared to the as-built and heat-treated states while inducing extra surface layer hardening and compressive residual stresses. The hybrid post-treatment of heat treatment + shot peening + tumble finishing significantly increased the fatigue life of the samples by over 500 times higher compared to the as-built series.
  • Küçük Resim Yok
    Öğe
    Individual and synergistic effects of thermal and mechanical surface post-treatments on wear and corrosion behavior of laser powder bed fusion AlSi10Mg
    (Elsevier Science Sa, 2022) Maleki, Erfan; Unal, Okan; Bandini, Michele; Guagliano, Mario; Bagherifard, Sara
    Materials fabricated by laser powder bed fusion (LPBF) are generally characterized with internal defects, inhomogeneous microstructure and rough surface with multiple forms of irregularities in their as-built state. Post-treatments are needed to resolve the issues associated with these imperfections. In this study, the individual and synergistic effects of different post-treatments including heat treatment, shot peening and ultrasonic nanocrystalline surface modification on microstructure, surface morphology, roughness, mechanical, corrosion and tribological properties of LPBF AlSi10Mg specimens have been investigated. Two different sets of parameters were considered for the surface treatments, both with mechanical energy source. Apart from surface characteristics, various properties including microhardness and residual stresses as well as wear and corrosion behavior of post-processed specimens were analyzed and compared with those of the as-built condition. The results indicated that hybrid post-treatments have the highest positive effects on wear and corrosion resistance as their kinetic energy affected multiple physical aspects; these include the microstructure leading to surface grain refinement paired with deep compressive residual stress field and improved surface morphology offering a more regular surface.
  • Küçük Resim Yok
    Öğe
    Introducing gradient severe shot peening as a novel mechanical surface treatment
    (Nature Portfolio, 2021) Maleki, Erfan; Bagherifard, Sara; Unal, Okan; Bandini, Michele; Farrahi, Gholam Hossein; Guagliano, Mario
    Shot peening is widely used for improving mechanical properties especially fatigue behavior of metallic components by inducing surface hardening, compressive residual stresses and surface grain refinement. In air blast shot peening, projection pressure and surface coverage (an index of peening duration) have been considered as major controlling process parameters; the combination of these parameters plays a critical role in the beneficial effects of shot peening. Generally in severe shot peening aimed at obtaining surface grain refinement, constant values of pressure are considered with different peening durations. Considering very high peening duration, however, the phenomenon of over shot peening, which can be identified with the formation of surface defects could occur. The present study introduces a novel shot peening treatment, here called gradient severe shot peening (GSSP) that instead of using constant projection pressure, implements gradually increasing or decreasing pressures. The gradual increase of the projection pressure acts as a pre-hardening stage for the following higher projection pressure boosting the potential of the material to tolerate the sequential impacts and thus become less prone to the formation of surface defects. The results of the experiments indicate significant fatigue life improvement obtained for GSSP treated specimens compared to the standard treatment with constant pressure. GSSP avoids the detrimental effects of over-peening, while maintaining the beneficial effects of surface nano-crystallization, surface hardening and compressive residual stresses. The notable difference in fatigue strength enhancement for GSSP treated material can be also attributed to the modulated surface morphology with lower surface roughness compared to a standard shot peening treatment with the same exposure time.
  • Küçük Resim Yok
    Öğe
    On the effects of laser shock peening on fatigue behavior of V-notched AlSi10Mg manufactured by laser powder bed fusion
    (Elsevier Sci Ltd, 2022) Maleki, Erfan; Bagherifard, Sara; Unal, Okan; Bandini, Michele; Guagliano, Mario
    Post-processing methods can efficiently reduce the negative effects of the internal and surface defects in as-built laser powder bed fusion materials. In this study, the influence of different post-treatments including T6 thermal treatment and laser shock peening were investigated individually and synergistically together with electrochemical polishing on microstructure, surface morphology, roughness, hardness and residual stresses as well as rotating bending fatigue behavior of V-notched LPBF AlSi10Mg samples. The results indicated that laser shock peening has a high potential to close the sub-surface pores up to a depth of 390 and 420 mu m leading to an overall mean porosity reduction of 52% and 62% in the as-built and heat treated samples, respectively. In addition, the hybrid post-treatment of heat treatment + laser shock peening + electro-chemical polishing was found to remarkably improve the fatigue life up to 400 times longer compared to the as-built state.