Browsing by Author "Bal, B."

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Assessment of biocompatibility of novel TiTaHf-based high entropy alloys for utility in orthopedic implants
(ELSEVIER SCIENCE SAPO BOX 564, 1001 LAUSANNE, SWITZERLAND, 2021) Gurel, S.; Nazarahari, A.; Canadinc, D.; Cabuk, H.; Bal, B.; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, B.
This paper presents the findings of experimentally observed corrosion response of novel TiTaHf-based high entropy alloys (HEAs) in fetal bovine serum (FBS) to evaluate their biocompatibility in presence of proteins and potential to be used as implant materials. Particularly, TiTaHfNb, TiTaHfNbZr and TiTaHfMoZr HEAs were subjected to static immersion experiments in FBS media, and both the HEA samples and the immersion fluids underwent thorough characterization. The findings presented herein show that Zr and Mo addition to the TiTaHf solid solution increased the total ion release from the resulting HEAs in FBS, while the TiTaHfNb HEA became prominent in terms of biocompatibility owing to the reduced ion release in FBS. Moreover, hydroxy apatite (HA) formation was evident on the surfaces of all three HEAs upon immersion in FBS, indicating the potential of the three TiTaHf-based HEAs to form desired binding with the human bone. Considering the fact that passive oxide layer formation facilitating lower susceptibility to corrosion in long-term applications was also observed in the studied HEAs, further elaboration on their mechanical and biological responses is warranted for the sake of a comprehensive assessment regarding their utility as orthopedic implant materials.
Experimental investigation on chloroprene and acrylonitrile butadiene rubber types reinforced with nano-materials
(IOP PUBLISHING LTD, TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND, 2019) Dogan, O.; Esat, V.; Bal, B.; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
In this research, the effects of three different nano-materials (Nano-Carbon Black, Nano-ZnO, and Multi-Walled Carbon Nanotubes (MWNTs)) on two different rubber types (Chloroprene Rubber (CR), and Acrylonitrile Butadiene Rubber (NBR)) were experimentally investigated. In order to achieve this purpose, mechanical tests and detailed aging tests (in air, oil and fuel) were conducted conforming to international standards. Three different nano-materials were added to rubber with different combinations. A good dispersion of MWNTs within the polymer matrix was monitored by using field-emission Scanning Electron Microscopy (FE-SEM). It was observed that nano-materials both have positive and detrimental effects on hardness, tensile strength, ductility and aging tests performance. It was observed that nano-material reinforced rubber composites are thermally more stable than current products. Most significantly, it was seen that compression set value, which is a critical property for rubber grade, decreased with the addition of MWNTs. Therefore, rubber products with higher sealing capacity and longer service life can be obtained by adding MWNTs.
Fracture behavior of novel biomedical Ti-based high entropy alloys under impact loading
(ELSEVIER SCIENCE SAPO BOX 564, 1001 LAUSANNE, SWITZERLAND, 2021) Gurel, S.; Yagci, M. B.; Canadinc, D.; Gerstein, G.; Bal, B.; Maier, H. J.; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, B.
This paper focuses on the mechanical properties and fracture behavior of newly developed body-centered-cubic structured TiTaHfNb, TiTaHfNbZr and TiTaHfMoZr high entropy alloys (HEAs) under impact loading as part of an effort to evaluate their potential utility as implant materials. The experimental findings showed all three Ti based HEAs have lower Young's modulus as compared to the conventionally used implant materials. Fractography analysis revealed that the TiTaHfNb HEA demonstrated significant ductility with the highest energy absorption capacity, while the TiTaHfNbZr and the TiTaHfMoZr alloys exhibited mixed mode fracture with relatively low ductility. Specifically, the reduction of ductility and energy absorption capacity under impact loading was attributed to the addition of Zr and Mo into Ti-based HEA system, which facilitates formation of additional dislocations in the microstructure due to increased lattice distortion. The current findings demonstrate that, from a mechanical point of view, the TiTaHfNb HEA could be considered as an alternative implant material for applications demanding high wear and corrosion resistance, such as hip or knee implants, and thus, warrant further investigation of the biomedical performance of this alloy.Y
Microstructure and tribological properties of TiTaHfNbZr high entropy alloy coatings deposited on Ti-6Al-4V substrates
(ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2019) Tuten, N.; Canadinc, D.; Motallebzadeh, A.; Bal, B.; 0000-0002-7389-9155; 0000-0001-6753-9316; 0000-0001-9961-7702; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
We report on the microstructure and tribological behavior of equimolar TiTaHfNbZr high entropy alloy (HEA) thin films deposited on the biomedical Ti-6Al-4V substrates by RF magnetron sputtering. Results of nanoindentation and sliding wear experiments were evaluated along with the microstructure and topographical information obtained from scanning electron microscopy and atomic force microscopy. The findings clearly demonstrate that the TiTaHfNbZr HEA not only forms a homogenous and dense coating mechanically compatible with the Ti-6Al-4V substrates, but also provides a significantly enhanced surface protection against wear and cracking, which could prove valuable especially in long-term orthopedic implants that bear dynamic contact loading, such as in the cases of hip or knee joints.
On the Utility of Crystal Plasticity Modeling to Uncover the Individual Roles of Microdeformation Mechanisms on the Work Hardening Response of Fe-23Mn-0.5C TWIP Steel in the Presence of Hydrogen
(ASME, TWO PARK AVE, NEW YORK, NY 10016-5990 USA, 2018) Bal, B.; Koyama, M.; Canadinc, D.; Gerstein, G.; Maier, H. J.; Tsuzaki, K.; 0000-0002-7389-9155; 0000-0002-5006-9976; 0000-0003-2119-824X; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
This paper presents a combined experimental and theoretical analysis focusing on the individual roles of microdeformation mechanisms that are simultaneously active during the deformation of twinning-induced plasticity (TWIP) steels in the presence of hydrogen. Deformation responses of hydrogen-free and hydrogen-charged TWIP steels were examined with the aid of thorough electron microscopy. Specifically, hydrogen charging promoted twinning over slip-twin interactions and reduced ductility. Based on the experimental findings, a mechanism-based microscale fracture model was proposed, and incorporated into a visco-plastic self-consistent (VPSC) model to account for the stress-strain response in the presence of hydrogen. In addition, slip-twin and slip-grain boundary interactions in TWIP steels were also incorporated into VPSC, in order to capture the deformation response of the material in the presence of hydrogen. The simulation results not only verify the success of the proposed hydrogen embrittlement (HE) mechanism for TWIP steels, but also open a venue for the utility of these superior materials in the presence of hydrogen.
The Precise Determination of the Johnson-Cook Material and Damage Model Parameters and Mechanical Properties of an Aluminum 7068-T651 Alloy
(ASME, TWO PARK AVE, NEW YORK, NY 10016-5990 USA, 2019) Bal, B.; Karaveli, K. K.; Cetin, B.; Gumus, B.; 0000-0002-5990-8203; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
Al 7068-T651 alloy is one of the recently developed materials used mostly in the defense industry due to its high strength, toughness, and low weight compared to steels. The aim of this study is to identify the Johnson-Cook (J-C) material model parameters, the accurate Johnson-Cook (J-C) damage parameters, D-1, D-2, and D-3 of the Al 7068-T651 alloy for finite element analysis-based simulation techniques, together with other damage parameters, D-4 and D-5. In order to determine D-1, D-2, and D-3, tensile tests were conducted on notched and smooth specimens at medium strain rate, 10(0) s(-1), and tests were repeated seven times to ensure the consistency of the results both in the rolling direction and perpendicular to the rolling direction. To determine D-4 and D-5 further, tensile tests were conducted on specimens at high strain rate (10(2) s(-1)) and temperature (300 degrees C) by means of the Gleeble thermal-mechanical physical simulation system. The final areas of fractured specimens were calculated through optical microscopy. The effects of stress triaxiality factor, rolling direction, strain rate, and temperature on the mechanical properties of the Al 7068-T651 alloy were also investigated. Damage parameters were calculated via the Levenberg-Marquardt optimization method. From all the aforementioned experimental work, J-C material model parameters were determined. In this article, J-C damage model constants, based on maximum and minimum equivalent strain values, were also reported which can be utilized for the simulation of different applications.