Browsing by Author "Radi, Amin"

Now showing 1 - 13 of 13

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Addressing the strength-ductility trade-off in a thermomechanical-processed high entropy alloy
(Elsevier, 2023-12-15) Radi, Amin; Işıl, Canay; Seyedmohammadi, Seyedveghar; Kim, H. S.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin; Işıl, Canay; Seyedmohammadi, Seyedveghar
High entropy alloys (HEAs) have garnered significant attention due to their exceptional mechanical behavior. However, the influence of secondary phases and dislocation substructures has yet to be thoroughly investigated. This study focuses on the incorporation of the decomposed η-phase within a face-centered cubic (FCC) microstructure at different recrystallization levels, aiming to achieve adequate ductility while maintaining strength at gigapascal levels. Various characterization techniques were employed to analyze the microstructure of both homogenized and annealed+aged conditions. Implementing a sub-micron grain size distribution and introducing a favorable dislocation substructure significantly enhanced the mechanical properties of yield strength, ultimate tensile strength, and ductility, reaching up to 1291 MPa, 1450 MPa, and 17.5%, respectively. The results highlight the influential role of grain size in facilitating the generation of geometrically necessary dislocations during plastic deformation.
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Advanced surface enhancement of a high strength aluminum alloy through friction stir processing
(Springer, 2022) Ghobadlou, Ali Hosseınzadeh; Radi, Amin; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Ghobadlou, Ali Hosseınzadeh; Radi, Amin
The current study investigates the effect of severe plastic deformation (SPD) on the mechanical behavior of a commercial aluminum alloy (Al7075). In-process cooled friction stir processing (FSP) was used to enhance the mechanical properties of annealed Al7075. Substantial enhancements in the microhardness, strength, and strain at failure were achieved through the application of this SPD technique without further thermal treatments.
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Design and processing of multi-phase high entropy alloys
Radi, Amin; Yapıcı, Güney Güven; Yapıcı, Güney Güven; Başol, Altuğ Melik; İpekoğlu, M.; Department of Mechanical Engineering; Radi, Amin
The multi-principal element alloys (MPEAs) known as high- and medium-entropy alloys possess promising properties due to their highly distorted atomic crystal structures. Employing multi-elements as principal elements has enabled a new platform for novel alloy designs and fabrications. Adding other phases as a heterogeneous phase in MPEAs structures can boost the mechanical behavior. Therefore, the heterogeneous MPEAs address the strength-strain trade-off in most of the conventional alloys. In this thesis, the microstructural evolution and mechanical behavior of two novel heterogeneous high-entropy alloys (HEA) are investigated through thermo-mechanical processing. Using the CALPHAD approach the compositions have been confirmed and subsequently cast. The homogenized samples for both compositions possessed a single-phase uniaxed face centered subic (FCC) structure with high ductility. Possessing high ductility levels in the homogenized condition enabled us to apply high thickness reductions via rolling at room temperature without crack propagation from edges. This study confirms that the sigma phase contribution becomes more significant in the microstructure at higher annealing temperatures. However, the body centered cubic (BCC) phase contribution as a suitable hard-domain becomes less with increasing the annealing temperature. As such, a systematic approach to investigate the effects of the sigma phase and degree of recrystallization on the microstructure and mechanical behavior of the HEAs is presented. In addition, samples subjected to annealing exhibit transformation-induced plasticity (TRIP) under plastic deformation. Results show that the sigma phase can limit the TRIP mechanism in the alloy system since the TRIP-assisted BCC phase is decreased with increased sigma phase present in the microstructure. As such, the designed TRIP-assisted multi-phase HEA enables a combination of 1 GPa yield strength and about 10% of strain at failure for the optimum condition of post-rolled annealed at 750 ℃ for 30 minutes samples. Moreover, this work introduces a novel high strength HEA with proposing a proper combination of homogenization, rolling, annealing, and aging sequences and details for this composition.
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Effect of a multi-phase structure on the damping response of a novel high entropy alloy
(Elsevier, 2022-12-01) Işıl, Canay; Radi, Amin; Seyedmohammadi, Seyedveghar; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Işıl, Canay; Radi, Amin
In this study, dynamic behavior of a novel multi-phase high entropy alloy (HEA) was investigated. Thermo-mechanical processes containing an 80 % thickness reduction at room temperature rolling followed by annealing at 750 °C and 850 °C were applied to modify the microstructure and the resulting damping properties of the HEA. Annealing at 750 °C introduced the BCC phase, while at 850 °C, the sigma phase was prevalent in the microstructure, leading to over 1 GPa strength with decent ductility in the latter condition. The storage modulus and the internal friction values of the annealed alloys are noticeably improved, indicating that application of suitable heat treatments could enhance both the mechanical response and the damping performance of this HEA.
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Effect of stress aging induced precipitates on corrosion behavior of NiTi shape memory alloys
(Springer, 2021-10) Radi, Amin; Khalil-Allafi, J.; Heidarzadeh, A.; Yapıcı, Güney Güven; Etminanfar, M. R.; Mechanical Engineering; YAPICI, Güney Güven
In this study, the influences of the stress aging process on the electrochemical behaviors toward evaluating corrosion resistance of NiTi shape memory alloys in the in-vitro condition have been investigated. For this approach, the samples have been manufactured by introducing multiple precipitation morphology in the alloy structure via applying different levels of stresses during the aging process. The samples were characterized using multiply electron microscopy, electrochemical methods, X-ray diffraction, and differential scanning calorimetry. Results show that by prolonging aging time from 1 to 5 h and increasing the stress aging level (15-60-150 MPa) the corrosion resistance improves, which is implied a better formation of a protective layer. It seems that homogeneous precipitation of Ni-rich phases under the stress aging process improves the corrosion resistance of the alloy.
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Effects of aging on the microstructure and phase transformation behavior of cu-al-mn shape memory alloy
(Trans Tech Publications Ltd, 2021) Seyedmohammadi, Seyedveghar; Radi, Amin; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Seyedmohammadi, Seyedveghar; Radi, Amin
In the present study, the effects of artificial aging heat treatment on the transformation temperatures and hardness of Cu-Al-Mn shape memory alloy have been investigated. The aging processes have been performed on the one-time re-melted and 90% rolled samples. Differential scanning calorimetry reveals that reverse transformation is present for the re-melted sample which is aged at 400°C. However, in 90% rolled condition, this transformation takes place at 200°C and 300°C. Hardness examination shows that the aged specimens possess higher values in hardness in comparison to un-aged samples at all studied temperatures. Although, the peak-aged condition was demonstrated at 300°C for the re-melted sample, the rolled sample displayed increased hardness levels up to 500o C. Based on the DSC measurements and microstructural observations, it can be asserted that the thermo-mechanical processing including rolling plus aging at 300o C provides favorable transformation characteristics for shape memory behavior.
Open Access
Formation of nano-sized compounds during friction stir welding of Cu–Zn alloys: effect of tool composition
(Elsevier, 2020-12) Heidarzadeh, A.; Radi, Amin; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin
For the first time, the origin of tool composition effect on microstructure and mechanical properties of the friction stir welded joints has been disclosed. For this aim, nanoindentation, orientation image microscopy, and transmission electron microscopy were employed to analyze the microstructure and mechanical properties in the case of copperzinc alloy joints welded by different tool compositions. The results showed that the nanosized intermetallic compounds were formed in the stir zone when using a hot-work steel tool, which increased the strength of the joint. The outcomes of this work can be used to modify the friction stir welded joints of various metals and alloys.
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Low-cycle fatigue behavior of friction stir-welded copper joints
(Springer, 2021-11) Ghobadlou, Ali Hosseinzadeh; Salahi, Salar; Radi, Amin; Sajadifar, Seyed Vahid; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Ghobadlou, Ali Hosseinzadeh; Salahi, Salar; Radi, Amin; Sajadifar, Seyed Vahid
Investigation of the fatigue response of friction stir-welded (FSWed) joints is especially important in the design and manufacturing of components with exposure to cyclic loading. In this study, cyclic response of FSWed pure copper joints is investigated in the low-cycle fatigue regime. Microstructural characterizations revealed that FSW introduced a severely deformed microstructure in the nugget zone (NZ). Fatigue response was determined at a strain ratio of 0.1 by varying the total strain amplitude from 0.1 to 0.6%. Cyclic softening was observed for the low strain amplitude of 0.1%, whereas hardening was detected at higher strain amplitudes. The hysteresis loops demonstrated symmetricity along with noticeable linear behavior after the reversals. Typical fractures occurred in the heat affected zone (HAZ) rather than the NZ or the base metal due to grain coarsening of the HAZ. Improved cyclic properties of the NZ along with stable behavior up to 1000 cycles at a total strain amplitude of 0.3% were attributed to its fine and homogeneous microstructure. Moreover, fracture surface analysis demonstrated a ductile behavior represented by dimples in the sample strained at 0.1% in contrast with a brittle fracture surface of the sample fatigued at 0.5% strain amplitude.
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On the development of a novel multi-phase high entropy alloy with transformation-induced plasticity effect
(Elsevier, 2022-06-05) Radi, Amin; Asghari-Rad, P.; Kim, H. S.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin
In the present work, microstructural evolution, and mechanical behavior of a novel high entropy alloy (HEA) are investigated through thermo-mechanical processing. The homogenized samples possess a single-phase cubic structure with high ductility. The rolled and subsequently annealed samples at various treatment conditions exhibit multi-phase microstructures. This study confirms that the sigma phase contribution becomes more significant on the mechanical response at higher annealing temperatures. Effects of phase distribution and degree of recrystallization on the microstructural evolution are examined in detail to probe the variation in the mechanical response. Samples subjected to annealing exhibit transformation-induced plasticity (TRIP) under plastic deformation. As such, the designed TRIP-assisted multi-phase HEA enables a combination of 1 GPa yield strength and about 10% of strain at failure.
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On the low-cycle fatigue behavior of a multi-phase high entropy alloy with enhanced plasticity
(Elsevier, 2023-08) Radi, Amin; Sajadifar, S.; Seyedmohammadi, Seyedveghar; Krochmal, M.; Bolender, A.; Wegener, T.; Niendorf, T.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin; Seyedmohammadi, Seyedveghar
A multi-phase non-equiatomic FeCrNiMnCo high entropy alloy (HEA) was fabricated using vacuum induction melting. Thermo-mechanical treatments consisting of cold rolling and annealing at 750 °C and 850 °C were employed to improve the mechanical properties of the HEA in focus. Tensile experiments revealed that yield strength and ultimate tensile strength levels can be enhanced significantly after thermo-mechanical processing (TMP). At the same time, ductility remains at an adequate level. Strain-controlled low-cycle fatigue (LCF) experiments were carried out in order to assess the mechanical properties of this HEA under cyclic loading conditions. At the same strain amplitude, the stress levels of the processed samples were considerably higher than that of the as-received counterpart. Similarly, fatigue lives of the former could surpass the base condition at the strain amplitudes of 0.2% and 0.4%; however, at the higher strain amplitudes, cyclic softening was observed. Electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) results revealed that phase transformation from face-centered cubic (FCC) to body-centered cubic (BCC/B2) took place at a higher occurrence with increasing strain amplitude (0.2% to 0.6%). Furthermore, transmission electron microscopy (TEM) studies confirm that upon tensile deformation additional plasticity mechanisms, i.e., deformation twinning and phase transformation, contribute to the overall mechanical behavior of the multi-phase HEA.
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On the strain rate sensitivity of a TRIP assisted high entropy alloy
(Elsevier, 2023-02-15) Radi, Amin; Duygulu, O.; Işıl, Canay; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin; Işıl, Canay
In the present work, the strain rate sensitivity is investigated in a novel high entropy alloy with transformation-induced plasticity (TRIP) effect. Herein, it is aimed to reflect the effect of phase constitution on the mechanical behavior under different strain rates. It is shown that TRIP mechanism is operational in the annealed microstructures at all examined rates. It is also demonstrated that strength and strain hardening rate levels show dependency to strain rate with varying trends based on the microstructural condition.
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Severe plastic deformation as a processing tool for strengthening of additive manufactured alloys
(Elsevier, 2021-08) Ghobadlou, Ali Hosseinzadeh; Radi, Amin; Richter, J.; Wegener, T.; Sajadifar, S. V.; Niendorf, T.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Ghobadlou, Ali Hosseinzadeh; Radi, Amin
For the first time, the novel combination of multi-pass equal channel angular extrusion/pressing (ECAE/P) and selective laser melting (SLM) was investigated. Herein, four passes of ECAP via route Bc at 150 °C were applied as a severe plastic deformation (SPD) technique on the SLM as-built AlSi12 to promote superior mechanical properties. The microstructure and mechanical behavior of AlSi12 fabricated by SLM were studied before and after ECAP, applying several mechanical and microstructural characterization techniques. Results of the tensile experiments revealed that the yield point, the ultimate strength, and the ductility of the as-built sample were improved by 56%, 11%, and 55% after 4 passes of ECAP, respectively. This enhancement is attributed to the effective grain refinement and the persisting silicon phase network after SPD as evidenced by electron backscatter diffraction and elemental mapping results. Moreover, micro-computed tomography analysis disclosed that ECAP considerably reduces the remnant porosity of the post-treated SLM AlSi12 samples eventually further affecting the strength of the ultra-fine grained AlSi12 in a positive way. Findings presented herein indicate that it is viable to utilize ECAP as a post-AM processing tool for mechanical property improvement of laser powder bed fused microstructures with the virtue of enhanced densification. Even if geometrical restrictions exist in ECAP, results obtained herein are transferrable to other SPD techniques with suitable processing windows, which would pave the way to advanced properties of adequately post-treated conditions.
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Solid state routes for composite materials production
(Elsevier, 2021) Heidarzadeh, A.; Radi, Amin; Ghobadlou, Ali Hosseinzadeh; Yapıcı, Güney Güven; Brabazon, D.; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin; Ghobadlou, Ali Hosseinzadeh
Solid-state methods are frequently used to fabricate metal matrix composites, which usually lead to superior mechanical properties compared to liquid state routes. In this article, different solid-state routes including powder metallurgy, diffusion bonding, forging, accumulative roll bonding, extrusion, explosive bonding, and friction stir processing are elucidated for the production of metal matrix composites. For this aim, the different stages and capabilities of each of these processes are presented. This is an area in which both research and commercial activity is expected to grow significantly in the coming years.