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    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, Sara
    In 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 abstract
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    Application of Deep Neural Network to Predict the High-Cycle Fatigue Life of AISI 1045 Steel Coated by Industrial Coatings
    (Mdpi, 2022) Maleki, Erfan; Unal, Okan; Seyedi Sahebari, Seyed Mahmoud; Reza Kashyzadeh, Kazem; Danilov, Igor
    In this study, deep learning approach was utilized for fatigue behavior prediction, analysis, and optimization of the coated AISI 1045 mild carbon steel with galvanization, hardened chromium, and nickel materials with different thicknesses of 13 and 19 mu m were used for coatings and afterward fatigue behavior of related specimens were achieved via rotating bending fatigue test. Experimental results revealed fatigue life improvement up to 60% after applying galvanization coat on untreated material. Obtained experimental data were used for developing a Deep Neural Network (DNN) modelling and accuracy of more than 99%.was achieved. Predicted results have a fine agreement with experiments. In addition, parametric analysis was carried out for optimization which indicated that coating thickness of 10-15 mu m had the highest effects on fatigue life improvement.
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    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, Mario
    Post-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.
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    Comprehensive analysis of pulsed plasma nitriding preconditions on the fatigue behavior of AISI 304 austenitic stainless steel
    (Springer, 2021) Unal, Okan; Maleki, Erfan; Varol, Remzi
    This study aims to draw an exact boundary for microstructural and mechanical behaviors in terms of pulsed plasma nitriding conditions. The pulsed plasma nitriding treatment was applied to AISI 304 austenitic stainless steel at different temperatures and durations. Results reveal that nitriding depth increased as process temperature and duration increase. The nitriding depth remarkably increased at 475 degrees C for 8 h and at 550 degrees C for 4 h. An austenite structure was transformed into a metastable nitrogen-oversaturated body-centered tetragonal expanded austenite (S-phase) during low-temperature plasma nitriding. The S-phase was converted to CrN precipitation at 475 degrees C for 8 h and at 550 degrees C for 4 h. Surface hardness and fatigue limit increased through plasma nitriding regardless of process conditions. The best surface hardness and fatigue limit were obtained at 550 degrees C for 4 h because of the occurrence of CrN precipitation.
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    A Critical Review on Improving the Fatigue Life and Corrosion Properties of Magnesium Alloys via the Technique of Adding Different Elements
    (Mdpi, 2023) Kashyzadeh, Kazem Reza; Amiri, Nima; Maleki, Erfan; Unal, Okan
    Magnesium is the eighth-most abundant element in the world and its alloys have a widespread application in various industries such as electronic and transport (i.e., air, land, and sea) engineering, due to their significant mechanical properties, excellent machinability, high strength to weight ratios, and low cost. Although monolithic Mg metal is known as the lightest industrial metal (magnesium density is 30% less than the density of the aluminum, and this unique property increases the attractiveness of its usage in the transportation industry), one of the significant limitations of magnesium, which affects on its applications in various industries, is very high reactivity of this metal (magnesium with an electronegativity of 31.1 can give electrons to almost all metals and corrodes quickly). To overcome this problem, scholars are trying to produce magnesium (Mg) alloys that are more resistant to a variety of loads and environmental conditions. In this regard, Mg alloys include well-known materials such as aluminum (Al), Zinc (Zn), Manganese (Mn), Silicon (Si), and Copper (Cu), etc., and their amount directly affects the properties of final products. In the present review paper, the authors attempted to present the latest achievements, methods, and influential factors (finish-rolling, pore defects, pH value, microstructure, and manufacturing processes, etc.) on the fatigue life and corrosion resistance of most significant Mg alloys, including AM50, AM60, AZ31, AZ61, AZ80, AZ91, ZK60, and WE43, under various conditions. The summarized results and practical hints presented in this paper can be very useful to enhance the reliability and quality of Mg-made structures.
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    Effect of combined shot peening and ultrasonic nanocrystal surface modification processes on the fatigue performance of AISI 304
    (Elsevier Science Sa, 2019) Amanov, Auezhan; Karimbaev, Ruslan; Maleki, Erfan; Unal, Okan; Pyun, Young-Sik; Amanov, Tileubay
    In this study, the fatigue performance of AISI 304 subjected to shot peening (SP), ultrasonic nanocrystal surface modification (UNSM) and the combination of SP + UNSM processes was systematically assessed by rotary bending fatigue (RBF) tester at different stress levels. The purpose of combining SP and UNSM processes is to find out whether SP following UNSM process can further improve the fatigue life of AISI 304 in comparison with the SP and UNSM processes alone. Interestingly, the fatigue strength of AISI 304 was deteriorated by the combination of SP + UNSM processes in comparison with the UNSM process alone, but the combination of SP + UNSM processes demonstrated a higher fatigue strength in comparison with the SP process alone.
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    Effect of severe shot peening and ultra-low temperature plasma nitriding on Ti-6Al-4V alloy
    (Pergamon-Elsevier Science Ltd, 2018) Unal, Okan; Maleki, Erfan; Varol, Remzi
    In this study, the fatigue behavior of Ti-6Al-4V alloy is tend to be improved by severe plastic deformation via shot peening and plasma nitriding. Shot peening with sub-branches: Conventional shot peening (A12-14), severe shot peening (A28-30 and A34-36) and repeening (N6-8) are exposed. Besides plasma nitriding is implemented at 500 degrees C, 550 degrees C and 600 degrees C with the durations of 4, 8 and 16 h. Due to utilization of shot peening as prior severe plastic deformation during diffusion of nitrogen, two methods are applied in sequence. Severe shot peening forms ultra-fine crystals and oriented grains by disintegrating of a and 13 phases just below the surface and increases surface roughness. Plasma nitriding temperature increase the compound layer thickness and the treatment leads to vanish of 13 particles through a certain line for diffusion layer. Prior severe plastic deformation by severe shot peening generally triggers the formation of thicker compound layer and emerges distinct diffusion depth with finer and oriented precipitation. The phase's intensity obtained from XRD peaks has been amplified by the application of prior shot peening. Each shot peening provides fatigue improvement on the other hand plasma nitriding application regardless of being pre or post treatments diminish the fatigue resistance. (C) 2018 Elsevier Ltd. All rights reserved.
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    Effect of severe vibratory peening on microstructural and tribological properties of hot rolled AISI 1020 mild steel
    (Elsevier Science Sa, 2020) Das, Turan; Erdogan, Azmi; Kursuncu, Bilal; Maleki, Erfan; Unal, Okan
    In this study, microstructural and mechanical performance of AISI 1020 were investigated after severe vibratory peening (SVP) for emerging the potential and performance of this novel treatment among surface severe plastic deformation (SSPD) methods. The specimens were subjected to SVP treatment of V1, V2, and V3 conditions at 20, 40 and 60 min. durations, respectively. Optical microscope (OM) and SEM images demonstrated two layered gradient structure. XRD analysis showed the oxide layer was completely vanished besides surface nanocrystallization by severe plastic deformation (SPD). The microhardness test revealed an average improvement of 48% compared to the untreated specimen. SVP caused raising of hardness from surface to a depth of approximately 900 mu m. In wear tests, the volume loss after SVP were less. The hardness improvement due to deformation overcame the negative effect caused by roughness increase. However, the friction coefficient of the unpeened specimen was the lowest at all loads.
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    Effects of constrained groove pressing, severe shot peening and ultrasonic nanocrystal surface modification on microstructure and mechanical behavior of S500MC high strength low alloy automotive steel
    (Elsevier, 2021) Karademir, Ibrahim; Celik, Mustafa B.; Husem, Fazil; Maleki, Erfan; Amanov, Auezhan; Unal, Okan
    S500MC high strength low alloy automotive steel is exposed to bulk severe plastic deformation (SPD) via constrained groove pressing (CGP) and surface severe plastic deformation (S2PD) via severe shot peening (SSP) and ultrasonic nanocrystal surface modification (UNSM). SSP and UNSM could create a nanocrystallization layer till 50-100 mu m away from outmost surface. EBSD investigations showed average nano-grain size obtained via SSP and UNSM was found to be below 100 nm regime. The strength was improved via 1st to 4th pass of CGP, but elongation percentage decreased abruptly. UNSM achieves both strength-ductility improvement with gradient structure. SSP improves the total elongation however a slight decrease on strength is observed. SSP and UNSM showed better wear and friction resistance particularly at lower loads compared to CGP and untreated specimens. Nevertheless, wear and friction behavior at higher loads showed better responses for Bulk-SPD applications regardless of pass numbers. The frictional load increase played a detrimental role in removing a nano crystallization surface layer and diminishing the positive influence of SSP and UNSM.
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    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, Sara
    This 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.
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    Effects of conventional shot peening, severe shot peening, re-shot peening and precised grinding operations on fatigue performance of AISI 1050 railway axle steel
    (Elsevier Sci Ltd, 2022) Unal, Okan; Maleki, Erfan; Karademir, Ibrahim; Husem, Fazil; Efe, Yusuf; Das, Turan
    In this study, effects of conventional shot peening, severe shot peening, re-shot peening and precised grinding were performed to AISI 1050. By two-stage operations (SSP + RSP), residual stress depth and the magnitude on the surface were quite high. While deepest compressive stress was measured in A24 + G, maximum stress was observed in A24 + N14. Grinding and re-shot peening powerfully reduced the roughness. The increase in SP intensity improved the hardness considerably, besides the most effective hardness depth was observed after A36. N7 and N14 contributed effective results in the low cycle fatigue, whereas A24, A18, A18 + N14 and A36 in high cycle fatigue.
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    Effects of conventional, severe, over, and re-shot peening processes on the fatigue behavior of mild carbon steel
    (Elsevier Science Sa, 2018) Maleki, Erfan; Unal, Okan; Kashyzadeh, Kazem Reza
    The present study investigates experimentally the effects of different shot peening treatments, including conventional, severe, over, and re-shot peening on microstructure, mechanical properties, and fatigue behavior of AIM 1050 mild carbon steel. Different shot peening treatments were performed using various effective parameters by considering the influences of increasing Almen intensity and coverage. Optical microscopy and field emission scanning electron microscopy observations and X-Ray diffraction measurements were carried out to analyze grains refinement in each shot peening treatment. Microhardness and residual stress measurements were taken from shot peened surfaces to the core material to investigate the mechanical properties. The fatigue behaviors of the specimens were examined by using the axial fatigue test. The results indicated that post-grinding, re-shot peening, and severe shot peening processes have significant effects on fatigue life improvement.
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    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.
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    Effects of Laser Shock Peening on Corrosion Resistance of Additive Manufactured AlSi10Mg
    (Mdpi, 2023) Maleki, Erfan; Unal, Okan; Shao, Shuai; Shamsaei, Nima
    Mechanical properties of Al alloys make them an ideal candidate for different sections of marine, aerospace, automotive, etc. industries. Recently taking the advantages of additive manufacturing (AM), many complex infrastructures/components can be fabricated with very high design freedom via Al alloys. Although Al alloys have good natural corrosion resistance, however improving this property attracts lots of attention in the past few years. Post-processing methods can play a key role for addressing the issues related to internal and surface anomalies associated with as-built AM parts. Generally, these anomalies have detrimental effects on mechanical properties. In the present study, the effect of laser shock peening (LSP) treatment with different laser pulse overlaps and energies was investigated comprehensively on microstructure, surface texture, porosity, hardness, residual stresses as well as corrosion resistance of laser powder bed fused (L-PBF) AlSi10Mg samples. LSP provides strain deformation on the surface, and the deformation enhances by laser beam energy. LSP1 (laser energy of 1.5 J and 50% overlap) and LSP3 (laser energy of 4.5 J and 50% overlap) introduce maximum local strain of 7.5 and 10.7, respectively. The surface roughness of as-built state mu m in terms of Rv was effectively diminished to 16.33 after LSP6 (laser energy of 4.5 J and 75% overlap). The results indicated that due to the modified surface texture, improved hardness and induced high compressive residual stresses in the surface layer. (surface hardness improvement and inducing high surface compressive residual stresses were obtained after LSP6 up to 26% and 289 MPa, respectively); the LSP treated samples exhibited higher corrosion resistance with the corrosion rate decreasing down to 50% as compared to the as-built state.
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    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.
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    Effects of severe plastic deformation on pre-osteoblast cell behavior and proliferation on AISI 304 and Ti-6Al-4V metallic substrates
    (Elsevier Science Sa, 2019) Tevlek, Atakan; Aydin, Halil Murat; Maleki, Erfan; Varol, Remzi; Unal, Okan
    In this study, titanium alloy (Ti-6Al-4V) and austenitic stainless steel (AISI 304) biomedical alloys were subjected to surface severe plastic deformation (SSPD) via severe shot peening (SSP) with the conditions of A28-30 Almen intensity. SSP is widely accepted as much more effective than the conventional surface modification techniques since it forms a nano-grain layer with large number of dislocations and grain boundaries. The SSP treatment in this study was led to a very thin rough layer in Ti-6Al-4V titanium alloy compared to that of AISI 304. The thicker layer of AISI 304 was created by twin-twin intersections and a martensite structure transformations. SSP treatment was resulted in a severe plastically deformed material surface and led to an increase in full width half maximum (FWHM) that expresses grain size reduction below nanometer regime. Also, SSP treatment increased the surface roughness of materials by forming pits and bumps and led to deterioration on surface topography. Besides physical and microstructural innovations, SSP treatment was improved the surface mechanical properties of the metals. On the other hand, it was noted that the effects of the alteration of surface topography and structural innovations (nano-grain crystal-deformation induced layer) were led to improved cellular behavior and increased cell proliferation regardless of material type.
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    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, Sara
    As 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.
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    Effects of static load on microstructural and mechanical performance of AISI 1050 medium carbon steel subjected to ultrasonic nanocrystal surface modification
    (Elsevier Science Sa, 2022) Unal, Okan; Husem, Fazil; Maleki, Erfan; Karademir, Ibrahim; Efe, Yusuf; Das, Turan
    In this study, the effects of mild (M1, M2, M3), moderate (O1,O2), and severe (S1, S2, S3) static loads of ultrasonic nanocrystal surface modification (UNSM) on AISI 1050 steel were investigated. The layer affected by severe plastic deformation at moderate and severe static loadings became much thicker and the nanocrystalline layer became dominant around the surface region. The layer thickness influenced by the UNSM reached approximately 350 mu m. UNSM had a positive effect on the surface roughness and morphology via reducing the Ra between 0,3 mu m and 0,8 mu m excluding the highest static loads. Oxidation formation was observed on the surface at severe static load conditions. The microhardness showed a significant improvement independently of static loads, and the hardness depth reached up to approximately 250 mu m after the UNSM. Remarkable alteration in surface hardness was observed by increasing static load. Higher static loads ensured both deposition the compressive residual stress to the surface and propagation towards interior. The compressive stress of-700 MPa and a stress depth of over 1 mm were obtained by severe static loading. The processes implemented by moderate and severe static loads showed better performance over both low and high-cycle fatigue behavior.
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    Efficiency Analysis of Shot Peening Parameters on Variations of Hardness, Grain Size and Residual Stress via Taguchi Approach
    (Korean Inst Metals Materials, 2019) Maleki, Erfan; Unal, Okan; Reza Kashyzadeh, Kazem
    In the present study, the main purpose is to detect the most key factors of shot peening (SP) process on the microhardness, grain size, and residual stress of AISI 1060 high carbon steel. The specimens were treated using various types of SP process namely conventional shot peening and severe shot peening. Several experiments were performed to study metallurgical and mechanical properties of AISI 1060 steel. Almen intensity and surface coverage from one side and microhardness, grain size, and residual stress from the other side were considered as input and output parameters for the design of experiment methodology, respectively. The L18(21and31) mixed level of Taguchi orthogonal array design was used to study all cases. The test results were investigated by signal-to-noise ratio formula. It was identified that the surface coverage is the most key factors for shot peening process considering the affected depth. Also, the effect of this parameter on the microhardness, grain size and residual stress was obtained approximately 68, 89 and 57%, respectively. Eventually, the results obtained from all Taguchi sensitivity analysis indicated that it would be better to adjust the surface coverage factor in comparison with Almen intensity factor in order to create the surface compressive residual stress on the material and consequently to increase the fatigue lifetime of component using shot peeningy
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    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.