Malzeme Bilimi ve Mühendisliği Bölümü Yayın Koleksiyonu

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Citation Count: Esen, Z., Bor, Ş. (2011). Characterization of Ti-6Al-4V alloy foams synthesized by space holder technique. Materials science and engineering a-structural materials properties microstructure and processing, 528(7-8), 3200-3209. http://dx.doi.org/10.1016/j.msea.2011.01.008
Characterization of Ti-6Al-4V alloy foams synthesized by space holder technique
(Elsevier Science S A, 2011) Esen, Ziya; Bor, Şakir; 52373
Ti-6Al-4V foams, biomedical candidate materials, were synthesized by powder metallurgical space holder technique as a result of evaporation of magnesium to achieve desired porosity content. Final products contained porosities in the range similar to 43-64% with an average macropore size between 485 and 572 mu m and a lamellar type Widmanstatten microstructure composed of alpha-platelets and beta-laths. Unlike the case of bulk Ti-6Al-4V alloy tested under compression loading, compression stress-strain curves of manufactured Ti-6Al-4V foams were similar to those of elastic-plastic foams, which contain a linear elastic region; a plateau stage: and a densification stage. In the plateau region deformation bands perpendicular to the compression axis were developed and cell collapsing took place together with the buckling and fracture of some of the cell walls and edges in a ductile manner. Calculated elastic modulus and yield strength were in the range 1.42-14.7 GPa and 28.2-150 MPa, respectively, and the foam mechanical properties were found to be dependent on micro porous cell wall properties, which in turn depends on neck size between powder particles. Around 330 MPa yield strength value was calculated for porous cell walls by the use of Ti-6Al-4V alloy powder samples sintered in loose and compacted conditions, which were utilized to simulate the cell wall structure of foams. In addition, overall mechanical properties of foam s were investigated considering macro porosity fraction, p(macro), and the yield strength of foams exhibited a power law dependence, similar to commonly used minimum solid area models, in the form of A*(1 - p(marco))(n), where the proportionality constant "A" was found to be the yield strength of micro porous cell walls
Citation Count: Butev, Ezgi; Esen, Ziya; Bor, Sakir, "Characterization of Ti6Al7Nb alloy foams surface treated in aqueous NaOH and CaCl2 solutions", Journal of the Mechanical Behavior of Biomedical Materials, Vol. 60, pp. 127-138, (2016).
Characterization of Ti6Al7Nb alloy foams surface treated in aqueous NaOH and CaCl2 solutions
(Elsevier Science BV, 2016) Bütev, Ezgi; Esen, Ziya; Bor, Şakir; 47423; 52373
Ti6Al7Nb alloy foams having 53-73% porosity were manufactured via evaporation of magnesium space holders. A bioactive 1 mu m thick sodium hydrogel titanate layer, NaxH2-xTiyO2y+1., formed after 5 M NaOH treatment, was converted to crystalline sodium titanate, Na2TiyO2y+1, as a result of post-heat treatment. On the other hand, subsequent CaCl2 treatment of NaOH treated specimens induced calcium titanate formation. However, heat treatment of NaOH-CaCl2 treated specimens led to the loss of calcium and disappearance of the titanate phase. All of the aforementioned surface treatments reduced yield strengths due to the oxidation of the cell walls of the foams, while elastic moduli remained mostly unchanged. Accordingly, equiaxed dimples seen on the fracture surfaces of as-manufactured foams turned into relatively flat and featureless fracture surfaces after surface treatments. On the other hand, Ca- and Na-rich coating preserved their mechanical stabilities and did not spall during fracture. The relation between mechanical properties of foams and macro-porosity fraction were found to obey a power law. The foams with 63 and 73% porosity met the desired biocompatibility requirements with fully open pore structures and elastic moduli similar to that of bone. In vitro tests conducted in simulated body fluid (SBF) showed that NaOH-heat treated surfaces exhibit the highest bioactivity and allow the formation of Ca-P rich phases having Ca/P ratio of 1.3 to form within 5 days. Although Ca-P rich phases formed only after 15 days on NaOH-CaCl2 treated specimens, the Ca/P ratio was closer to that of apatite found in bone. (C) 2016 Elsevier Ltd. All rights reserved.
Citation Count: Bütev Öcal, Ezgi...et al."Comparison of the Short and Long-Term Degradation Behaviors of As-Cast Pure Mg, Az91 and We43 Alloys",Materials Chemistry and Physics, Vol. 241, (2020).
Comparison of the Short and Long-Term Degradation Behaviors of As-Cast Pure Mg, Az91 and We43 Alloys
(Elsevier LTD., 2020) Bütev Öcal, Ezgi; Esen, Ziya; Aydınol, Kadri; Dericioğlu, Arcan F.; 52373
The corrosion behaviors of pure magnesium, AZ91, and WE43 alloys have been evaluated by weight loss, hydrogen evolution rate, pH change measurements and potentiodynamic polarization as well as electrochemical impedance spectroscopy (EIS) methods. Main corrosion product formed on the surface of Mg/Mg-alloys after immersion of 24 h was Mg(OH)2 on the other hand, at the end of the 20 days additional CaCO3 which was found to display a critical role in degradation characteristics of the samples, was found. Examination in the cross section of the polished surfaces revealed that protective layers became thicker and corrosion rate of the samples decreased possibly due to increased protective abilities of the surfaces. Intermetallics in AZ91 and WE43 alloys acted as cathodic centers and induced micro galvanic corrosion. Undermining of intermetallics in WE43 alloy intensified the corrosion rate. AZ91 alloy exhibited the lowest corrosion rate among the samples when tested in simulated body fluid (SBF).
Citation Count: Esen, Z...et al. "Corrosion Behaviours of Ti6Al4V-Mg/Mg-Alloy Composites", Corrosion Science, Vol. 166, (2020).
Corrosion Behaviours of Ti6Al4V-Mg/Mg-Alloy Composites
(Elsevier LTD., 2020) Esen, Ziya; Öcal, Ezgi Bütev; Akkaya, Aslı; Gürçay, Bensu; Özcan, Ceren; Özgümüş, Burcu Aslı; Duygulu, Özgür; Dericioğlu, Arcan F.; 52373
The effect of coupling of unalloyed Mg and Mg-alloys (AZ91 and WE43) with Ti6Al4V alloy on corrosion and degradation behaviours of produced composites has been investigated in simulated body fluid (SBF) by hydrogen evolution, and surface and electrochemical characterization techniques. Combining of unalloyed Mg with Ti6Al4V intensified galvanic corrosion and catastrophic failure occurred by initiation of microcracks formed by sudden hydrogen gas evolution. In contrast to other composites, Ti6Al4V-AZ91 composites, containing new TiAl3 interface layer formed during composite production, preserved their mechanical integrities due to lowest corrosion and degradation rate of AZ91 alloy.
Corrosion of Metallic Biomaterials
(Springer Verlag, 2015) Dikici, Burak; Esen, Ziya; Duygulu, Özgür; Güngör, Serap; 52373
Metallic materials have been used as biomedical implants for various parts of the human body for many decades. The physiological environment (body fluid) is considered to be extremely corrosive to metallic surfaces; and corrosion is one of the major problems to the widespread use of the metals in the human body since the corrosion products can cause infections, local pain, swelling, and loosening of the implants. Recently, the most common corrosion-resistant metallic biomaterials are made of stainless steels and titanium and its alloys along with cobalt chromium molybdenum alloys. It is well known that protective surface films of the alloys play a key role in corrosion of the metallic implants. Key documents on the corrosion behavior of the metallic biomaterials in human body have been compiled under this chapter as a review.
Citation Count: Esen, Ziya...et al. "Designing thermochemical processes for ti-alloys produced by additive manufacturing techniques", 4th INTERNATIONAL CONGRESS ON 3D PRINTING (ADDITIVE MANUFACTURING) TECHNOLOGIES AND DIGITAL INDUSTRY, pp. 1383-1387, 2019.
Designing thermochemical processes for ti-alloys produced by additive manufacturing techniques
(2019) Esen, Ziya; Doğu, Merve Nur; Bilgin, Güney Mert; Tan, Evren; Berkay Gümüş, Berkay; Dericioğlu, Arcan F.; 52373
Ti-6Al-4V alloys are extensively used in biomedical, aerospace and petro-chemical applications mainly due to their high specific strength, excellent corrosion resistance and high fatigue strength. In contrast to conventional techniques, additive manufacturing techniques make possible production of parts with complex geometries in one step by minimizing the usage of raw materials. However, post heat treatment processes need to be applied to reduce residual stresses created and to get uniform controllable microstructure so as to obtain desired mechanical properties. Conventional annealing heat treatments are effective in eliminating the residual stress and increasing the ductility. But, they usually degrade the strength and result in coarsening the microstructure. In this study, thermochemical process, called thermo-hydrogen process (THP), was applied to Ti-6Al-4V alloy parts produced by selective laser melting (SLM) and electron beam melting (EBM) with the aim of increasing ductility without degrading the alloy strength. Additively manufactured parts initially hydrogenated at 650oC for 1 h under H2+Ar gas mixture and then, dehyrogenated at 700oC for 18 h under high vacuum. As a result of alloying with hydrogen and dealloying turned martensitic microstructure in SLM parts into fine + lamellar phase mixture. On the other hand, microstructural refinement in EBM parts were limited since as-manufactured parts were already composed of fine lamellar microstructure. THP prevented grain growth and grain boundary α-phase formation in SLM parts. Ductility of the alloys increased by 110 %, while the strength decreased slightly only by 10 %. However, the effect of the THP on mechanical properties of EBM samples couldn’t be observed due to their high surface roughness which induced notch effect.
Citation Count: Tülbez, Simge; Esen, Ziya; Dericioğlu, Arcan F. (2020). "Effect of CNT impregnation on the mechanical and thermal properties of C/C-SiC composites", Advanced Composites and Hybrid Materials, Vol. 3, No. 2, pp. 177-186.
Effect of CNT impregnation on the mechanical and thermal properties of C/C-SiC composites
(2020) Tülbez, Simge; Esen, Ziya; Dericioğlu, Arcan F.; 52373
The present study investigates the effect of additional carbon source, in the form of carbon nanotubes (CNTs), on mechanical and thermal properties of carbon fiber reinforced silicon carbide (C/C-SiC) ceramic matrix composites (CMC) produced by liquid silicon infiltration (LSI) technique. The CNTs used in this study were impregnated into the C/C preforms before the liquid silicon infiltration stage. The results showed that the addition of excess carbon to the C/C preforms in the form of CNTs enhanced Si infiltration efficiency significantly resulting in C/C-SiC composites with higher density and microstructural uniformity. Accordingly, the addition of CNTs improved the flexural strength of the composites by 40% with respect to no-CNT-containing composites due to a lower amount of residual porosity and additional reinforcement effect of the unreacted CNTs. The thermal conductivity of the resulting C/C-SiC composites has been also increased by 31% and 18% parallel and perpendicular to the carbon fiber-woven fabric surface, respectively, by CNT addition.Graphical abstract
Citation Count: Rona, Nergiz...et.al. (2017). "Effect of electrical discharge machining on dental Y-TZP ceramic-resin bonding", Journal Of Prosthodontic Research, Vol.61, No.2, pp.158-167.
Effect of electrical discharge machining on dental Y-TZP ceramic-resin bonding
(Elsevier Ireland LTD, 2017) Rona, Nergiz; Yenisey, Murat; Küçüktürk, Gökhan; Gürün, Hakan; Çoğun, Can; Esen, Ziya; 3837; 52373
Purpose: The study determined (i) the effects of electrical discharge machining (EDM) on the shear-bond strength (SBS) of the bond between luting resin and zirconia ceramic and (ii) zirconia ceramic's flexural strength with the three-point bending (TPB) test. Methods: Sixty 4.8 mm x 4.8 mm x 3.2 mm zirconia specimens were fabricated and divided into four groups (n = 15): SBG: sandblasted + silane, TSCG: tribochemical silica coated + silane, LTG: Er:YAG laser treated + silane, EDMG: EDM + silane. The specimens were then bonded to a composite block with a dual-cure resin cement and thermal cycled (6000 times) prior to SBS testing. The SBS tests were performed in a universal testing machine. The SBS values were statistically analyzed using ANOVA and Tukey's test. To determine flexural strength, sixty zirconia specimens were prepared and assigned to the same groups (n = 15) mentioned earlier. After surface treatment TPB tests were performed in a universal testing machine (ISO 6872). The flexural strength values were statistically analyzed using ANOVA and Tukey's test (a = 0.05). Results: The bond strengths for the four test groups (mean SD; MPa) were as follows: SBG (Control), 12.73 +/- 3.41, TSCG, 14.99 +/- 3.14, LTG, 7.93 +/- 2.07, EDMG, 17.05 +/- 2.71. The bond strength of the EDMG was significantly higher than those of the SBG and LTG (p < 0.01). The average flexural strength values for the groups SBG (Control), TSCG, LTG and EDMG were 809.47, 800.47, 679.19 and 695.71 MPa, respectively (p > 0.05). Conclusions: The EDM process improved the SBS. In addition, there was no significant adverse effect of EDM on the flexural strength of zirconia.
Citation Count: Ozer, Seren;...et.al. (2022). "Effect of post fabrication aging treatment on the microstructure, crystallographic texture and elevated temperature mechanical properties of IN718 alloy fabricated by selective laser melting", Journal of Materials Processing Technology, Vol.306.
Effect of post fabrication aging treatment on the microstructure, crystallographic texture and elevated temperature mechanical properties of IN718 alloy fabricated by selective laser melting
(2022) Ozer, Seren; Bilgin, Güney Mert; Davut, Kemal; Esen, Ziya; Dericioglu, Arcan F.; 52373
The effect of building direction and post fabrication aging treatment on the microstructure, crystallographic texture and high temperature mechanical properties of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) method was investigated. After aging, arc-shaped structures seen in as-fabricated samples disappeared and converted into a mixture of columnar and equiaxed grains. Nano-sized γ″ and/or γ′ precipitates were formed upon aging; however, MC type carbides and Laves phase encountered in as-fabricated samples were not dissolved completely after aging. Moreover, aging did not alter the texture ((001)//building direction (BD)) of as-fabricated samples. Mechanical properties of the alloys under tension were influenced by the build direction, aging time and test temperature. As-fabricated samples produced in vertical direction exhibited higher room temperature strengths with lower ductility due to orientation of overlapped prior melt pools. Room temperature tensile test results revealed that peak aging caused a significant improvement in ultimate tensile strength (UTS), from 1066.5 MPa and 998.4 MPa to 1408.5 MPa and 1330.4 MPa whereas elongation values decreased from 27.5% and 32.2% to 19.6% and 23.7% in vertically and horizontally built samples, respectively. Peak-aged samples (aged at 700 °C for 8 h) tested at 600 °C displayed serrated regions in their stress-strain curves due to dynamic strain aging (DSA). Although strength values of the samples displayed an expected decrease by temperature, ductility of the samples reduced to minimum at temperatures around 700–800 °C, which was attributed to intermediate temperature embrittlement.
Citation Count: Atabay, Sila Ece; Esen, Ziya; Dericioğlu, Arcan F., "Effect of sn alloying on the diffusion bonding behavior of al-mg-si alloys", Metallurgical And Materials Transactions A-Physical Metallurgy And Materials Science, Vol.48A, No.7, pp.3181-3187, (2017).
Effect of sn alloying on the diffusion bonding behavior of al-mg-si alloys
(Springer, 2017) Atabay, Sıla Ece; Esen, Ziya; Dericioğlu, Arcan F.; 52373
Effect of Sn as an alloying element on the diffusion-bonding behavior of Al-Mg-Si alloy has been studied by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical testing of the diffusion-bonded joint. XRD results revealed the formation of Mg2Sn and (Sn) phases during solidification following induction casting. DSC results showed local liquid (Sn) formation during the bonding process for Sn-containing alloys, where its amount was found to be increasing with the increasing Sn content. Results revealed that Sn addition leads to an increase in the bond shear strength of the diffusion-bonded joints and elimination of the irregularities formed on the bonded interface. Fractured surfaces showed that formation of (Sn) layer at the bonded interface causes the fracture to transform from the ductile to the mixed fracture mode.
Citation Count: Ürtekin, Levent...et al. (2021). "Experimental Investigation on Wire Electric Discharge Machining of Biodegradable AZ91 Mg Alloy", Journal of Materials Engineering and Performance, Vol. 30, No. 10, pp. 7752-7761.
Experimental Investigation on Wire Electric Discharge Machining of Biodegradable AZ91 Mg Alloy
(2021) Ürtekin, Levent; Özerkan, Hacı Bekir; Çoğun, Can; Genç, Asım; Esen, Ziya; Bozkurt, Fatih; 3837; 52373
The AZ91 magnesium alloy, used commonly as a biodegradable material in biomedical applications, is generally formed by conventional casting method (CCM) and high-pressure die casting method (HPDCM). The AZ91 alloys exhibit poor machinability with conventional chip removal methods since they degrade at elevated temperatures. In this study, the wire electric discharge machining (WEDM) was presented as a candidate process to machine the AZ91 alloy since no cutting stresses and plastic deformations were applied by the cutting tool to the part causing elevated temperatures. In this context, the WEDM machinability of the AZ91 alloy samples produced by cold chamber HPDCM and CCM at different process parameters, was experimentally investigated. The machining performance outputs (the machining current (I), the machining rate (MR), the average surface roughness (Ra), and surface topography) were found for the varying process parameters [pulse time (ts), pulse-off time (toff), dielectric flushing pressure (Pd), and wire speed (Vw)]. The present study revealed that the I and the MR were significantly dependent on the density, the porosity, and the micro structure of the samples, and the HPDCM samples gave the higher MR and the smoother surface than that of the CCM. © 2021, ASM International.
Citation Count: Cetinel, Oktay; Esen, Ziya; Yildirim, Bora, "Fabrication, Morphology Analysis, and Mechanical Properties of Ti Foams Manufactured Using the Space Holder Method for Bone Substitute Materials", Metals, Vol. 9, No. 3, (March 2019)
Fabrication, Morphology Analysis, and Mechanical Properties of Ti Foams Manufactured Using the Space Holder Method for Bone Substitute Materials
(MDPI, 2019) Çetinel, Oktay; Esen, Ziya; Yıldırım, Bora; 52373
Porous titanium (Ti) offers several key attributes as a biomedical material. Among the known characteristics of Ti relevant to biomedical applications, the mechanical performance and effects of a pore structure on the deformation characteristics under compressive loading were examined. The space holder method was employed to generate Ti foams with target porosities of 60%, 70%, and 80%. A micro-computed to mography analysis and light and scanning electron microscopy were performed to examine the pore morphology and microstructure. The mechanical properties along with the elastic modulus and compressive strength were evaluated via uniaxial compression testing. Ti foam samples with three porosity levels displayed average elastic moduli and compressive strengths comparable with those of human cancellous and cortical bone. All the Ti foam samples had elastic moduli similar to those of cancellous bone with their open porous structures. Although the foam samples with similar to 60% porosity had compressive strength comparable to that of cortical bone, the samples with similar to 80% porosity displayed compressive strength similar to that of cancellous bone. The results indicate that Ti foam scaffolds produced using the space holder method have great potential for applications in hard tissue engineering, as their mechanical properties and pore structures are similar to those of bone.
Citation Count: Doğu, Merve Nur...et al. (2020). "Microstructural and texture evolution during thermo-hydrogen processing of Ti6Al4V alloys produced by electron beam melting", Materials Characterization, Vol. 168.
Microstructural and texture evolution during thermo-hydrogen processing of Ti6Al4V alloys produced by electron beam melting
(2020) Doğu, Merve Nur; Esen, Ziya; Davut, Kemal; Tan, Evren; Gümüş, Berkay; Dericioğlu, Arcan F.; 52373
The present study was conducted to reveal the effects of building angles and post heat-treatments (2-step Thermo-Hydrogen Processing (THP) and conventional annealing treatment) on the density, microstructure and texture of Ti6Al4V alloy parts produced by Electron Beam Melting (EBM). The results showed that regardless of the building angle; the density, microstructure and crystallographic texture (defined with respect to building angle) of the as-produced samples were identical; having Widmanstätten α structure and columnar β-grains which are parallel to building direction. The main texture component for the α phase was (101¯0)//building direction, and for β phase (001)//building or heat flow direction. The first step of THP, namely, the hydrogenation step, produced a needle-like microstructure and increased the local misorientations due to lattice distortion. On the other hand, after application of the second step of THP, dehydrogenation step, microstructure was refined, particularly α-grains that were larger than 10 μm and located at grain boundaries. Moreover, THP randomized the crystallographic texture since it involves β to α phase transformation, at which one β-grain can produce 12 distinct α-variants. The grain boundary misorientation distributions also changed in accordance with the microstructural changes during the 2-step THP. On the other hand, annealing coarsened the grain boundary and Widmanstätten α phases; moreover, it changed the texture so that the basal planes (0001) rotated 30° around the building direction. © 2020 Elsevier Inc.
Citation Count: Bilgin, Güney Mert...et al. "Microstructural Refinement of Ti-6Al-4V Alloy Fabricated by Additive Manufacturing Using Thermochemical Processes", 18th International Metallurgy & Materials Congress, İstanbul, Türkiye, (29 Eylül - 01 Ekim 2016).
Microstructural Refinement of Ti-6Al-4V Alloy Fabricated by Additive Manufacturing Using Thermochemical Processes
(2016) Bilgin, Güney Mert; Esen, Ziya; Kuşhan Akın, Şeniz Reyhan; Dericioğlu, Arcan Fehmi; 52373; 224219
Citation Count: Bilgin, Güney Mert...et al. (2017). "Optimization of the mechanical properties of Ti-6Al-4V alloy fabricated by selective laser melting using thermohydrogen processes", Materials Science And Engineering A-Structural Materials Properties Microstructure And Processing, Vol.700, pp. 574-582,
Optimization of the mechanical properties of Ti-6Al-4V alloy fabricated by selective laser melting using thermohydrogen processes
(Elsevier Science SA, 2017) Bilgin, Güney Mert; Esen, Ziya; Kuşhan Akın, Seniz Reyhan; Dericioğlu, Arcan F.; 52373
2-step Thermo Hydrogen Process (THP) including hydrogenation and dehydrogenation steps was applied to Ti-6Al-4V alloy fabricated by selective laser melting (SLM) process to refine the microstructure and to increase the ductility of the alloy. It was observed that as-fabricated alloy's surface was composed of oxides of titanium and aluminum, which may alter the hydrogenation kinetics. The hydrogen treatment for 1 hat 650 degrees C, the maximum hydrogen solubility temperature of the alloy, transformed starting non-equilibrium alpha'-martensitic phase to 13 and 8 (TiH2) phases. On the other hand, very fine discontinuous beta-phase was formed along with alpha-phase as a result of dehydrogenation at 700 degrees C for 18 h, which decreased the hydrogen level well below the starting value and caused transformation of delta-phase to fine alpha-phase. In contrast to commonly used THP treatments consisting of betatizing at high temperature, 2-step treatment prevented grain boundary alpha-phase formation as well as excessive grain growth. About 110% and 240% increments were detected in % Elongation (EL) and % Reduction in Area (RA) values, respectively, as a result of 2-step THP, while the strength decrease was limited to 10%. The change in ductility of the alloy was also verified by transformation of flat and shiny fracture surfaces seen in SLM fabricated alloy to a fracture surface containing equiaxed dimples after THP treatment. The hardness drop in the alloy after hydrogenation and dehydrogenation treatments was attributed to relief of residual stress and formation of equilibrium alpha and beta-phases.
Citation Count: Esen, Ziya; Öcal, Ezgi Bütev, "Surface characteristics and in-vitro behavior of chemically treated bulk Ti6Al7Nb alloys", Surface & Coatings Technology, Vol.309, pp.829-839, (2017).
Surface characteristics and in-vitro behavior of chemically treated bulk Ti6Al7Nb alloys
(Elsevier Science SA, 2017) Esen, Ziya; Öcal, Ezgi Bütev; 52373
The effect of various treatments on surface chemical composition and structure, and bioactivity of Ti6Al7Nb bulk alloys has been investigated. The alloys were treated employing aqueous solutions of NaOH and CaCl2 separately, and also by subsequent CaCl2 treatment after NaOH treatment (NaOH-CaCl2 treatment) which were followed by heat treatment. NaOH treatment was observed to be effective in enrichment of surface layer with Na. On the other hand, Na+ ions were mostly replaced by Ca2+ ions as a result of NaOH-CaCl2 treatment, while single step CaCl2 treatment was less effective in Ca incorporation. Additionally, porous network surface structure seen in NaOH and NaOH-CaCl2 treated samples was completely different than globular morphology detected in CaCl2-treated samples in single step. Subsequent heat treatments caused coarsening of surface structure and loss of some Na+ and Ca2+ ions. NaOH and NaOH-heat treated samples did not exhibit apatite formation within 15 days immersion in simulated body fluid (SBF). On the other hand, NaOH-CaCl2 samples had the highest apatite formation; however, NaOH-CaCl2-heat treated samples did not display any mineralization. Conversely, CaCl2 treated samples allowed apatite formation after heat treatment.
Citation Count: Esen, Ziya, "The effect of processing routes on the structure and properties of magnesium-TiNi composites", Vol. 558, pp. 632-640, (2012)
The Effect of Processing Routes On the Structure and Properties of Magnesium-Tini Composites
(Elsevier Science SA, 2012) Esen, Ziya; 52373
TiNi particulate-reinforced magnesium matrix composites were fabricated by rotary hot swaging and post-annealing heat treatment. The magnesium matrix of the processed composites was observed to contain elongated grains comprised of equiaxed recrystallised grains. Each elongated grain was surrounded by thin, non-continuous magnesium oxide layers composed of nanometric magnesium oxide particles. The TiNi reinforcement particles preserved their starting spherical shape during processing and testing. However, the hot deformation and annealing heat treatment changed the underlying room temperature microstructures and transformation behaviours of the reinforcements. In contrast to the majority of the ceramic reinforcements, the ductility of the composites was not significantly degraded by the addition of TiNi reinforcements; conversely, an approximately 25% enhancement was recorded in the elongation values for the Mg-5 vol% TiNi alloy. While the yield strengths of the composites changed linearly with increasing reinforcement content, the highest compression peak strength value was obtained with the addition of 5 vol% TiNi, beyond which the strength was slightly decreased. During mechanical testing, the TiNi particles debonded due to insufficient bonding between the matrix and reinforcement, and fracture resulted largely within the oxide layers present in the interfacial region and the magnesium oxide film in the magnesium grain boundaries. (C) 2012 Elsevier B.V. All rights reserved.
Citation Count: Esen, Ziya, "TiNi Reinforced Magnesium Composites by Powder Metallurgy", Magnesium Technology 2011, pp. 457-462, (2011)
Tini Reinforced Magnesium Composites By Powder Metallurgy
(John Wiley and Sons LTD., 2011) Esen, Ziya; 52373
Rod shaped Mg-TiNi composite samples were manufactured bypowder metallurgical route in which the samples were heated and deformed simultaneously using rotary hot swaging technique. Firstly, encapsulated argon filled copper tubes which contained compacts of pure magnesium and pre-alloyed TiNi alloy powder mixtures were deformed about 45% in two steps at 450 degrees C. Pre/post annealing heat treatments were applied at 450 degrees C for 20 mins between the stages of coaxial deformation to enhance the sintering degree and to homogenize the heavily deformed composite structures. Next, copper peeled and machined samples were compression tested under quasi-static conditions to investigate the mechanical properties, i.e. yield and peak strength, and ductility. Transmission and Scanning Electron Microscopy studies were carried out to examine the Mg-TiNi interface and fracture surfaces of the compression tested composites, respectively.
Citation Count: 8Esen, Z.; Dikici, Burak; Duygulu, Ozgur;..et.al., "Titanium-magnesium based composites: mechanical propertiesand in-vitro corrosion response in ringer's solution" Materials Science And Engineering A-Structural Materials Properties Microstructure And Processing, Vol.573, pp.119-126, (2013).
Titanium-magnesium based composites: mechanical propertiesand in-vitro corrosion response in ringer's solution
(Elsevier Science BV, 2013) Esen, Z; Dikici, Burak; Duygulu, Özgür; Dericioğlu, Arcan F.; 52373
Ti-Mg composite rods exhibiting both bioinert and biodegradable characteristics have been manufactured by hot rotary swaging from elemental powders of titanium and magnesium. As a result of processing, spherical magnesium powders elongated in the direction of deformation and the dendritic structure in starting magnesium powders transformed into highly equiaxed grains. Magnesium particles in the outer layer of the composites were decorated by thin layer of MgO while the interior parts were free from oxides. As expected, Young's moduli, yield and peak strengths of the composites were observed to decrease with an increase in the magnesium content, while ductility of composites was enhanced by decreasing the amount of titanium. Composites fractured at an angle 45 to the loading axis along the titanium particle boundaries and through the magnesium particles via transgranular type of fracture with the accumulation of twins near the fracture surface of magnesium. Mechanical properties of the composites were observed to be comparable to that of bone and the composites exhibited biodegradable and bioinert character upon testing in Ringer's solution such that magnesium was selectively corroded and pores were formed at prior magnesium powder sites while titanium preserved its starting skeleton structure. In addition, it was found that volume ratio of titanium and magnesium, and continuous MgO layer are the most important parameters which should be considered in designing biodegradable magnesium alloys with an appropriate corrosion rate. (C) 2013 Elsevier B.V. All rights reserved.
Citation Count: Saltik, Simge; Esen, Ziya; Dericioglu, Arcan F. (2022). "Wetting behavior and reaction layer formation in C/SiC composite-titanium alloy joints", Advances in Materials and Processing Technologies, Vol. 8, No. 4, pp. 3685-3705.
Wetting behavior and reaction layer formation in C/SiC composite-titanium alloy joints
(2022) Saltik, Simge; Esen, Ziya; Dericioglu, Arcan F.; 52373
The present study investigates the effect of brazing parameters on reaction layer formation, and mechanical properties of C/SiC composite-Ti6Al4V alloy joints produced by brazing technique. The wetting mechanism of the C/SiC composite surface by the Ag-Cu-Ti-based active brazing filler alloy has also been studied and correlated with the reaction layer formation. The strength of C/SiC composite/Ti6Al4V alloy joints increased at first and then decreased with increasing reaction layer thickness. The joints with ⁓1-µm-thick reaction layer, which were obtained by brazing at 915°C for 15 min, had the highest shear strength of ⁓33 MPa. Brazing filler alloy presented a minimum contact angle of 15° on the C/SiC composite surface at 915°C during the wetting experiments. 915°C and 15 min were determined to be the optimised brazing parameters to ensure almost complete wetting and a uniform reaction layer for effective adhesion of the C/SiC composite surface.

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