Browsing by Author "Heidarzadeh, A."

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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.
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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On the friction stir processing of additive-manufactured 316L stainless steel
(Wiley, 2022-10) Sajadifar, S. V.; Ghobadlou, Ali Hosseınzadeh; Richter, J.; Krochmal, M.; Wegener, T.; Bolender, A.; Heidarzadeh, A.; Niendorf, T.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Ghobadlou, Ali Hosseınzadeh
The novel combination of friction stir processing (FSP) and additive manufacturing (AM) is studied herein. Laser-based powder bed fusion of metals (PBF-LB/M) is used to establish 316 L stainless steel with a bimodal microstructure. Upon FSP, the as-built bimodal microstructure with an average grain size of 179 μm is transformed into the unimodal microstructure containing ultrafine grains with an average grain size of 1.2 μm. Results obtained by mechanical testing reveal that after FSP; the hardness, the yield point, and the ultimate strength of additively manufactured 316 L are enhanced by 45%, 77%, and 62%, respectively. Microstructure assessment reveals that such a unique improvement in the mechanical properties is due to considerable structural refinement leading to grain boundary strengthening. Energy-dispersive X-Ray diffraction analysis reveals that phase transformation does not occur upon FSP. Fracture analysis further indicates that severe plastic deformation (SPD) during FSP can promote the transformation of coarse voids to fine voids and, hence, densification of as-built parts.
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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.