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Öğe Analysing the Fatigue Behaviour and Residual Stress Relaxation of Gradient Nano-Structured 316L Steel Subjected to the Shot Peening via Deep Learning Approach(Korean Inst Metals Materials, 2022) Maleki, Erfan; Unal, Okan; Guagliano, Mario; Bagherifard, SaraIn this study, the effect of kinetic energy of the shot peening process on microstructure, mechanical properties, residual stress, fatigue behavior and residual stress relaxation under fatigue loading of AISI 316L stainless steel were investigated to figure out the mechanisms of fatigue crack initiation and failure. Varieties of experiments were applied to obtain the results including microstructural observations, measurements of hardness, roughness, induced residual stress and residual stress relaxation as well as axial fatigue test. Then deep learning approach through neural networks was used for modelling of mechanical properties and fatigue behavior of shot peened material. Comprehensive parametric analyses were performed to survey the effects of different key parameters. Afterward, according to the results of neural network analysis, further experiments were performed to optimize and experimentally validate the desirable parameters. Based on the obtained results the favorable range of shot peening coverage regarding improved mechanical properties and fatigue behavior was identified as no more than 1750% considering Almen intensity of 21 A (0.001 inch). Graphic abstractÖğe Assessing the efficacy of several impact-based mechanical techniques on fatigue behavior of additive manufactured AlSi10Mg(Elsevier Science Sa, 2023) Maleki, Erfan; Bagherifard, Sara; Unal, Okan; Shao, Shuai; Shamsaei, Nima; Guagliano, MarioPost-processing methods to reduce issues associated with the presence of internal and external anomalies are often necessary for obtaining adequate structural performance for additively manufactured products. However, the choice of the proper post-treatment and the corresponding parameters is still a challenge requiring adaption to the material type, geometry, size and undeniably costs. In this study, four different pure impact-based mechanical operations involving ultrasonic nanocrystal surface modification (UNSM), ultrasonic shot peening (USSP), severe shot peening (SSP), and severe vibratory peening (SVP) to investigate their efficacy on the fatigue behavior of hourglass AlSi10Mg specimens manufactured via laser powder bed fusion (LPBF) were considered. Experimental characterizations involving microstructural approach, porosity level and surface texture, hardness and residual stresses measurements, as well as tensile and fatigue testing, were conducted. The results exhibited considerable improvement in mechanical/physical performances leading to substantially enhanced fatigue performance of the mechanically treated specimens. Based on a cost-performance analysis, it was found that UNSM, while having reasonable cost, presented considerable improvement on fatigue behavior.Öğe Effects of Conventional and Severe Shot Peening on Residual Stress and Fatigue Strength of Steel AISI 1060 and Residual Stress Relaxation Due to Fatigue Loading: Experimental and Numerical Simulation(Korean Inst Metals Materials, 2021) Maleki, Erfan; Farrahi, Gholam Hossein; Reza Kashyzadeh, Kazem; Unal, Okan; Gugaliano, Mario; Bagherifard, SaraThis study investigates and compares the effects of different shot peening treatments including conventional and severe shot peening on microstructure, mechanical properties, fatigue behavior, and residual stress relaxation of AISI 1060 steel. Shot peening treatments were applied with two Almen intensities of 17 and 21 A and a wide ranges of coverage (100%-1500%). Various microstructural observations were carried out to analyze the evolution of microstructure. Microhardness, residual stress and surface roughness measurements and also axial fatigue test were performed. Moreover, the extent of the residual stress relaxation during cyclic loading was investigated by means of XRD measurements. Furthermore, numerical simulation of residual stress relaxation due to fatigue loading was carried out and validated against experimental investigations. The comparison indicated a good agreement for the surface residual stress relaxation up to 100 cycles. The experimental results indicated the efficiency of severe shot peening processes in obtaining nanostructured surface layer and achieving superior mechanical properties and fatigue behavior. Also, residual stress measurements revealed that stress relaxation started with a high rate at the initial stages of loading and gradually increased at higher number of cycles which was lower in the case of severely shot peened samples compared to the conventionally treated ones.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, MarioLaser 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.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, MarioInternal 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.Öğe The effects of shot peening, laser shock peening and ultrasonic nanocrystal surface modification on the fatigue strength of Inconel 718(Elsevier Science Sa, 2021) Maleki, Erfan; Unal, Okan; Guagliano, Mario; Bagherifard, SaraAs most of the failures in engineering components initiate from the surface layer, applying surface treatments can play a crucial role in controlling material performance and lifetime. In this study, different surface severe plastic deformation techniques including severe shot peening, laser shock peening and ultrasonic nanocrystal surface modification have been considered. The effects of process parameters and the kinetic energy of each treatment on the microstructure, mechanical properties and fatigue behavior of nickel-based super-alloy Inconel 718 have been investigated. The results revealed that using the proper parameters to increase the kinetic energy of the applied surface treatments, it is possible to effectively promote surface grain refinement and induce a deep compressive residual stress field in Inconel 718 samples. Among the applied treatments, ultrasonic nanocrystal surface modification was found to be the most efficient one in improving the mechanical properties as it led to the most significant fatigue performance, followed by severe shot peening and laser shock peening.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, MarioA 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.Öğe Fatigue performance of U-notched additively manufactured AlSi10Mg parts: The effects of chemical and thermal post-treatments(Elsevier, 2023) Maleki, Erfan; Bagherifard, Sara; Ahmad, Nabeel; Shao, Shuai; Unal, Okan; Guagliano, Mario; Shamsaei, NimaIn the current study, the effects of different post-processing methods, including heat treatment (HT) and electrochemical polishing (ECP) as well as their combination on the surface texture, porosity, microstructure, mechanical properties, and rotating bending fatigue behavior of U-notched laser powder bed fused AlSi10Mg specimens were comprehensively investigated. In addition, to better understand the effects of the applied post processing methods on the sensitivity of the notched specimen to surface and near-surface defects, finite element analysis was performed. Chemical treatment was found to be very influential on surface texture modification of the very narrow notched parts, for which the application of other treatments can be quite challenging. It was also found that the fatigue behavior of the notched specimens was more sensitive to the surface texture rather than to the near-surface defects. The hybrid treatment involving HT+ECP was the most effective for fatigue behavior improvement due to simultaneous homogenization of the microstructure, released tensile residual stresses, enhanced ductility and high surface texture modification.Öğe Hybrid Intelligence approach to study post-processing impact on the mechanical performance of notched additively manufactured AlSi10Mg(Elsevier, 2024-11-16) Maleki, Erfan; Bagherifard, Sara; Unal, Okan; Guagliano, MarioThis study introduces a Hybrid Intelligence approach to investigate the Process-Structure-Property-Performance (PSSP) relationship in additively manufactured (AM) materials, specifically focusing on V-notched laser powder bed fused (L-PBF) AlSi10Mg specimens. The Humen Intelligence (HI) component managed the design, manufacturing processes, post-processing, structural characterization, mechanical testing, and data collection. In parallel, Artificial Intelligence (AI), utilizing advanced machine learning (ML) algorithms, performed tasks related to prediction, sensitivity analysis, and parametric analysis. AI identified patterns and developed predictive models that provided deeper insights into how process parameters affect material properties and performance. This integration of HI and AI enabled a more thorough exploration of these relationships; data collected from our previous research were complemented with new experiments conducted to assess the effects of various heat treatments (HTs) and surface post-treatments (SPTs) on the fatigue behavior of the specimens. The techniques applied included stress relief (SR), T6 thermal treatments, sand blasting (SB), shot peening (SP), severe vibratory peening (SVP), laser shock peening (LSP), tumble finishing (TF), abrasive flow machining (AFM), chemical polishing (CP), electrochemical polishing (ECP), and chemical milling (CM), along with their combinations. A total of 54 different post-processing techniques were examined in this study. The experimental data, covering surface texture, microstructure, porosity, hardness, and residual stress, were used to develop an ML model that analyzed the fatigue behavior of the specimens. This approach represents a significant advancement toward integrated mechanistic and data-driven materials engineering, offering valuable insights for optimizing fatigue performance in practical applications.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, SaraMaterials 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.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, MarioShot 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.Öğe Mechanical characterization and interfacial enzymatic activity of AISI 316L stainless steel after surface nanocrystallization(Elsevier Science Sa, 2021) Maleki, Erfan; Maleki, Nasim; Fattahi, Alborz; Unal, Okan; Guagliano, Mario; Bagherifard, SaraShot peening is a well-known surface severe plastic deformation treatment widely used for improving the mechanical performance of metallic materials. It was revealed that applying severe shot peening, which is characterized by high kinetic energy, has an effective role in surface nanocrystallization of metallic materials. In this study, firstly the effects of different shot peening treatments using conventional and severe parameters were investigated on the mechanical properties and fatigue behavior of the 316L stainless steel. Microstructural analyses and measurements of grain size, microhardness, residual stresses, surface roughness, surface wettability as well as fatigue tests were performed. Then for the first time, the interfacial enzymatic activity of Laccase multicopper oxidoreductase enzyme was investigated on the nanostructured and rough surface of the shot peened samples. The surface nanostructured 316L samples exhibited considerable improvement in terms of mechanical properties and fatigue behavior and also showed increased enzymatic activity. These results can promote the application of surface nanocrystallized samples for biochemical and biomedical applications.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, MarioPost-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.Öğe Superior effects of hybrid laser shock peening and ultrasonic nanocrystalline surface modification on fatigue behavior of additive manufactured AlSi10Mg(Elsevier Science Sa, 2023) Maleki, Erfan; Bagherifard, Sara; Unal, Okan; Jam, Alireza; Shao, Shuai; Guagliano, Mario; Shamsaei, NimaThe surface texture of metallic parts produced by laser powder bed fusion (L-PBF) in the as-built condition detrimentally affects their mechanical properties, especially fatigue behavior. Accordingly, applying surface post-treatments has become an attractive approach to improve the mechanical performance of these materials. In the present study, both the individual and combined effects of post-processing methods, i.e., laser shock peening (LSP) and ultrasonic nanocrystalline surface modification (UNSM) with the same intensity of 10-12 A [0.001 in.], were systematically investigated on mechanical properties and fatigue behavior of L-PBF AlSi10Mg speci-mens. A wide range of experiments involving microstructural characterization, hardness and residual stresses measurements, porosity and surface texture analyses, tensile tests, and rotating bending fatigue tests were conducted. The results revealed that the hybrid LSP + UNSM process resulted in significant improvement in mechanical properties and fatigue behavior due to (i) sub-surface pores closure up to the depth of 517 mu m, (ii) 60 % surface hardness improvement, (iii) inducing-420 MPa surface compressive residual stresses, and (iv) surface roughness reduction up to 70 %. The fatigue life was improved up to 75, 56, and 35-fold compared to the as-built state after applying LSP + UNSM, UNSM, and LSP treatments, respectively.Öğe A systematic study on the effects of shot peening on a mild carbon steel: Microstructure, mechanical properties, and axial fatigue strength of smooth and notched specimens(Elsevier, 2021) Maleki, Erfan; Unal, Okan; Kashyzadeh, Kazem Reza; Bagherifard, Sara; Guagliano, MarioUsed with the right combination of parameters, shot peening process can be regarded as a severe plastic deformation method that can greatly enhance the strength of mechanical components by inducing surface grain refinement, increasing the hardness, and generating compressive residual stresses in the top surface layer. The present experimental study explores the effects of gradual rise of shot peening kinetic energy on microstructure, mechanical properties, and fatigue behavior of AISI 1045 carbon steel by changing the process parameters over a wide range of Almen intensity (20-32A) and surface coverages (100-3000%). Microstructural observations, X-ray diffraction, microhardness and residual stress measurements were carried out to analyze the effects of grain refinement as the kinetic energy of the peening process increased. In addition to compression-tension axial fatigue tests, fatigue crack growth measurements were also performed on specimens in both smooth and notched configurations. The results demonstrated that increasing the kinetic energy of the process is an effective technique to achieve nanostructured surface layer combined with superior mechanical properties. Severe shot peening treatment significantly improved the fatigue strength of the treated specimens, while the continuous growth of surface coverage proved to have detrimental effects on fatigue behaviour.
