Ahmet TURK - Academia.edu (original) (raw)

Papers by Ahmet TURK

Linköping Electronic Press Workshop and Conference Collection

Thermal barrier coatings have significant interest for protecting of the effect of high temperatu... more Thermal barrier coatings have significant interest for protecting of the effect of high temperature the materials used under high temperature. To coat the materials used under high temperature such as gas turbine liners, is considerably important. Yttria stabilized zirconia (YSZ) is the most common material used for that purposes in commercial applications. Thermal barrier coatings damage due to the thermal expansion and internal stress, formed by the temperature variation. The micro and macro cracks, which are formed under service life of the coating, causes the coating failures such as spallation by developing crack network. In this research SiC and B4C powders added into commercial YSZ powder to improve thermal shock resistance. Two different powder ratio were prepared as %25(%12,5 SiC +B4C) %75 YSZ and %50(%25 SiC +B4C) %50 YSZ. After preparing powders coatings were manufactured using F4 plasma gun. Coated samples were subjected to thermal shock test in burner rig testing equipm...

MAS Journal Of Applied Sciences, 2022

Graphene consists of sp2 hybridized carbon (C) atoms arranged in a honeycomb shape as single laye... more Graphene consists of sp2 hybridized carbon (C) atoms arranged in a honeycomb shape as single layer. Graphene oxide (GO) structures have importance over graphene, because of hydrophobic nature of graphene, non-adjustable band gap, complex production processes and its production costs. GO structures are generally synthesized using graphite or carbon sources which are similar compounds compare to graphene. GO consists of both sp2 and sp3 hybridized C atoms to which functional groups are attached at the top and bottom of the layer. The mechanical, electronical and thermal properties of GO structures can be controlled during the production phase thanks to these oxygen-containing functional groups in their structure. These functional groups consist of oxygen (O) and hydrogen (H) elements in the form of carbonyl, hydroxyl, carboxyl or epoxide and they are highly dependent on the production method. Among the various methods for producing GO structures, the Hummers method stands out with its...

International Conference on Plasma Surface Engineering, 2012

This work focuses on the micro-abrasion wear and microstructural properties of CoNiCrAlY coatings... more This work focuses on the micro-abrasion wear and microstructural properties of CoNiCrAlY coatings fabricated on nickel based super alloy substrates by using the atmospheric plasma spraying (APS), high-velocity oxygen fuel (HVOF), cold gas dynamic spraying (CGDS) methods. Tribological tests were performed on the samples in order to understand the wear mechanism of thermally sprayed coatings and influence of the coating microstructure on wear mechanism. The microstructures of as sprayed and weared coatings were investigated by scanning electron microscopy. Initial surface topography was examined by surface profilometer. Coating hardness measurements were performed with a micro-hardness tester. The micro-abrasion tests were carried out with some different durations. The lateral fracture was observed as wear mechanism on the specimens. The wear surface resistance have changed with coating process and surface features of specimens depending on the coating process.

Hydroxyapatite (HA) is one of the most popular biomaterial which has a wide variety of applicatio... more Hydroxyapatite (HA) is one of the most popular biomaterial which has a wide variety of applications. Although HA biomaterials superior properties, dissolution behavior and implant stability properties of HA needs to be improved. One of the promising solution for these problems is incorporating Flourine (F) and Zinc (Zn) ions into HA structure. Sol-gel technique which has an effortless process control procedure, emerged as an ideal candidate for producing ion doped HA powders. Pure, F and Zn substituted HA powders obtained through sol-gel technique and SEM, EDX, XRD and FTIR analysis were performed. Results showed that F and Zn substitution into HA lattice was successful.

Polyetheretherketone (PEEK) is a semi-crystalline synthetic thermoplastic polymer that has excell... more Polyetheretherketone (PEEK) is a semi-crystalline synthetic thermoplastic polymer that has excellent mechanical properties, elastic modulus similar to bone, chemical stability and good biocompatibility. However, PEEK has a bio-inert surface and because of that it does not interact enough with host environment. One of the best methods to solve this problem and improve the surface properties of PEEK is surface coating with bioactive materials. The aim of this study is coating PEEK substrates with Titanium (Ti) and Hydroxyapatite (HA) using Atmospheric Plasma Spraying (APS) and characterization coated PEEK biomaterials. Structural characterization performed by Scanning Electron Microscope (SEM) and X-ray Diffractometer (XRD). Roughness measurements and micro hardness tests were performed in order to mechanical characterization. The results showed that biocompatibility of PEEK biomaterials can be improved with the Ti/HA multilayer coatings.

Metallic biomaterials are attractive materials for application orthopaedic implants because of th... more Metallic biomaterials are attractive materials for application orthopaedic implants because of their significant mechanical properties. However, metallic biomaterials are generally biocompatible and are required to coat with osteoconductive coatings such as hydroxyapatite (HA) that is natural mineral found in bone tissue. Hydroxyapatite (HA), formulated as Ca10(PO4)6(OH)2, which has a great osteoconductivity properties with human organism and formed an inorganic part of the bone is used as a biomaterial to repair hard tissues and their configurations. Different methods such as plasma spraying, High velocity oxy-fuel (HVOF), laser, electrophoresis, dip coating, sol-gel methods are widely used to coat the metallic implant materials. On one hand plasma spraying is the most common and economical method for industrial applications, on the other hand, high process temperature of plasma spraying causes defects on HA structure and occurrence of secondary phases. The main effect on the decom...

Journal of Materials Science: Materials in Electronics, 2021

The present research demonstrates the synthesis and characterization of LaMnO 3 perovskite powder... more The present research demonstrates the synthesis and characterization of LaMnO 3 perovskite powders using the sol-gel technique for dye-sensitive solar cell applications. With this respect, transparent solutions were prepared from La and Mn based precursors, distilled water and citric acid monohydrate. Ammonium hydroxide was incorporated into the La-Mn solution in order to neutralize/precipitate at 24 o C for 1 hour in the air. The solution was allowed to evaporate on a hot plate device at 90 °C in the air. The obtained solutions were dried at 90 o C for 24 hours to form a xerogel structure, dried at 200 o C for 2 hours and consequently annealed at 500 and 850 o C for 2 hours in the air. Thermal, structural, microstructural, optical and magnetic properties of the powders were characterized through differential thermal analysisthermogravimetry (DTA-TG), Fourier transform infrared (FTIR), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM), Malvern zeta sizer (PSD), UV-vis spectrometer and vibrating sample magnetometer (VSM). The obtained results indicate promise, especially the low band range, that LaMnO 3 powders can be used in dye-sensitized solar cells and can positively affect performance and e ciency.

Gazi Üniversitesi Mühendislik-Mimarlık Fakültesi Dergisi, 2018

Bu PDF belgesi, kabul edilmiş olan makalenin dizgi işlemi yapılmamış halidir. Kabul edilmiş makal... more Bu PDF belgesi, kabul edilmiş olan makalenin dizgi işlemi yapılmamış halidir. Kabul edilmiş makalelerin kullanılabilir olması amacıyla makalenin dizgisiz hali internet üzerinden yayımlanmıştır. Makale, nihai formunda yayımlanmadan önce yazım ve dilbilgisi olarak kontrol edilecek, daha sonra dizgilenecek ve yeniden gözden geçirilmesi işlemine tabi tutulacaktır. Bu dizgileme işlemleri esnasında içeriği etkileyebilecek hataların bulunabileceğini ve Gazi Üniversitesi Mühendislik ve Mimarlık Dergisi için geçerli olan yasal sorumluluk reddi beyanlarının bulunduğunu lütfen unutmayın.

Progress in Gas Turbine Performance, 2013

Materials and Manufacturing Processes, 2014

ABSTRACT

Tribology Transactions, 2013

ABSTRACT The current study focuses on the microabrasion wear and microstructural properties of Co... more ABSTRACT The current study focuses on the microabrasion wear and microstructural properties of CoNiCrAlY coatings fabricated on nickel-based superalloy substrates using atmospheric plasma spraying (APS), high-velocity oxygen fuel (HVOF), and cold gas dynamic spraying (CGDS) methods. The microabrasion tests were performed on the samples for different durations in order to understand the wear mechanism of thermally sprayed coatings and influence of the coating microstructure on the wear mechanism. The microstructures of as-sprayed coatings and wear mechanisms on the worn coatings were investigated. Initial surface topography was examined using a surface profilometer. Coating hardness measurements were performed with a microhardness tester. The lateral fracture was observed as the wear mechanism on the samples. The wear resistance of the coatings has changed with the surface features of the samples depending on the coating production process.

Academic Platform Journal of Engineering and Science, 2013

Termal sprey kaplamalar, hedef bir altlık malzeme üzerine yüksek ısıl ve/veya kinetik enerjiye sa... more Termal sprey kaplamalar, hedef bir altlık malzeme üzerine yüksek ısıl ve/veya kinetik enerjiye sahip, erimiş ya da yarı erimiş formdaki toz parçacıkların gönderilmesi yoluyla elde edilmektedir. Günümüzde termal sprey kaplamalar güncel olarak; havacılık ve savunma sektörleri başta olmak üzere otomotiv, enerji, elektronik ve biyomedikal uygulamalar gibi birçok alanda kullanım olanı bulmaktadır. Uygulandıkları yüzeyler üzerinde aşınma, oksidasyon, korozyon ve yüksek mekaniksel dayanım gibi üstün özelliklerin eldesine imkan veren bu kaplamalar istenilen yüzey özelliklerine göre farklı sprey kaplama yöntemleri kullanılarak uygulanabilmektedir. Yaygın olarak kullanılan hızlı, ekonomik ve verimli bir kaplama üretimine olanak veren plazma sprey kaplamaların yanında yüksek kaliteye sahip kaplama üretimine olanak veren Yüksek Hızlı Oksi-Yakıt Püskürtme (HVOF) kaplamalarda endüstride geniş bir yelpazede kullanım alanı bulmakta ancak kullanılan ekipman ve proses özellikleri yönüyle daha maliyetli bir teknolojiye sahiptir. Son yıllarda, plazma sprey ve HVOF kaplamalara alternatif olarak üstün özelliklerde, oksitsiz ve yoğun kaplama yapısının elde edildiği Soğuk Gaz Dinamik Sprey (CGDS) kaplamalar ön plana çıkmaktadır. Bu sistemin 'Soğuk Gaz Dinamik Sprey' olarak isimlendirilmesinin sebebi, göreceli olarak nozuldaki mevcut olan gaz çıkış sıcaklığının diğer yöntemlere göre düşük olmasıdır. Bu çalışmada, araştırmacı ve endüstriyel kullanıcılar için ilgi odağı oluşturan CGDS kaplama teknolojisi ele alınarak açıklanmaya çalışılmıştır.

Journal of Materials Processing Technology, 2008

... O. Culha a , E. Celik a , NF Ak Azem a , I. Birlik a , M. Toparli a , Corresponding Author Co... more ... O. Culha a , E. Celik a , NF Ak Azem a , I. Birlik a , M. Toparli a , Corresponding Author Contact Information , E-mail The ... In addition, HVOF is a versatile method which can be used to deposit powders of intermetallic compounds as dense, adherent and homogeneous coatings ...

International Journal of Surface Science and Engineering, 2011

A significant improvement in efficiency has been achieved by using thermal barrier coatings (TBCs... more A significant improvement in efficiency has been achieved by using thermal barrier coatings (TBCs) in gas turbines and diesel engines. A typical TBC is a multilayered coating system that comprises an oxidation-resistant metallic bond coating (BC) and a thermally insulating ceramic top coating (TC). Under service conditions an Al2O3 inter-layer, the thermally grown oxide (TGO), forms in the interface between the bond and the top coating, by a chemical reaction between the metallic aluminum from the BC material and the oxygen that comes from the environment through the pore channels of the TC. The aim of the present study is to describe the TGO formation on metallic bond coats deposited using the high-velocity oxygen fuel (HVOF) spraying technique. Therefore, TBCs that consist of a YSZ top (ZrO2 + 8 % Y2O3) and YSZ-Al2O3 double-layer systems with CoNiCrAlY bond coats were deposited on Inconel 718 super-alloy substrates. The bond coats were applied via HVOF, with the ceramic top coats being applied by atmospheric plasma spraying (APS) as well. The oxidation behaviors of the TBC systems were investigated. The oxidation tests were performed at 1000°C in an air atmosphere for (8, 24, 50) h. The formation and growth of the TGO layers and the microstructural changes during the oxidation tests were scrutinized systematically. The results indicate that the TBC coating with the YSZ-Al2O3 double layer had a higher oxidation resistance and a lower TGO layer growth than that of the traditional TBC system. Likewise, the initial state of the porosity plays a critical role in enhancing or limiting the growth of the TGO scale in the TBC. Keywords: thermal barrier coatings (TBCs), oxidation behavior, thermally grown oxide (TGO), high-velocity oxygen fuel (HVOF), atmospheric plasma spraying (APS) Dose`eno je bilo ob~utno izbolj{anje u~inkovitosti plinskih turbin in dieselskih motorjev z uporabo toplotnih za{~itnih prevlek (TBC). Zna~ilni TBC je ve~slojni varovalni sistem, ki vklju~uje prevleko, odporno proti oksidaciji, s kovinsko vezjo (BC) in toplotno izolativno kerami~no vrhnjo plastjo (TC). Pri obratovalnih razmerah vmesni sloj Al2O3 omogo~a nastanek oksidov (TGO) na stiku med vezivnim in vrhnjim slojem, s kemijsko reakcijo kovinskega aluminija iz BC-materiala in kisika, ki iz okolice prodira skozi pore TC. Namen te {tudije je opisati nastanek TGO na kovinskem vezivu, nanesenem z nabrizgavanjem s kisikovim plamenom z veliko hitrostjo (HVOF). TBC, ki sestoji na vrhu iz YSZ (ZrO2 + 8 % Y2O3) ter z dvoslojnim sistemom YSZ-Al2O3 z vezivno plastjo CoNiCrAlY so bili naneseni na podlago iz superzlitine Inconel 718. Vezivna plast je bila nanesena z HVOF, kerami~ni vrhnji sloj pa z atmosfersko plazmo (APS). Preiskovane so bile zna~ilnosti oksidacije TBS-sistema. Preizkusi oksidacije so bili izvr{eni na zraku pri 1000°C, za (8, 24 in 50) h. Med preizkusi oksidacije so bili sistemati~no preiskovani nastanek in rast TGO-plasti ter spremembe v mikrostrukturi. Rezultati ka`ejo, da ima TBC-prevleka YSZ-Al2O3 z dvojnim slojem bolj{o odpornost proti oksidaciji in manj{o rast TGO-plasti v primerjavi z navadnim TBC-sistemom. Videti je, da ima za~etna poroznost klju~no vlogo pri pospe{evanju ali zaviranju rasti TGO-plasti na TBC. Klju~ne besede: termi~ni varovalni sloj (TBC), vedenje pri oksidaciji, termi~na rast oksida (TGO), kisikov plamen z veliko hitrostjo (HVOF), atmosfersko plazemsko nabrizgavanje (APS)

Materiali in tehnologije, 2011

Zn, Al and Zn/15Al coatings can be produced in optimum conditions by the twin wire arc (TWEA) spr... more Zn, Al and Zn/15Al coatings can be produced in optimum conditions by the twin wire arc (TWEA) spraying technique. The coatings are used for corrosion protection in a variety of industrial applications. In this study, the accelerated corrosion behavior of Zn, Al and Zn/15Al coatings on a steel surface during the salt-spray testing period was investigated. The surfaces of steel coupons were coated with Zn, Al and Zn/15Al using the TWEA spray-deposition system. The corrosion test was performed in a chloride atmosphere in a salt-spray test for over 2000 h. The corrosion of samples is assessed as the ratio of the corroded area of the specimens. The salt-spray test results showed that Al and Zn/15Al coatings have a better corrosion resistance than Zn coatings.

Various recycling processes for WC-Co cermets from cutting tools, such as chemical modification, ... more Various recycling processes for WC-Co cermets from cutting tools, such as chemical modification, thermal modification, the cold-stream method and the electrochemical method have been investigated and some of them are actually employed in industry. However, these conventional methods have many problems to be solved and they are not always established technologies. Therefore, a more economical and high-efficiency recycling procedure needs to be developed. In this study we investigated the applicability of the zinc-melt method (ZMM) for recycling WC-Co as a powder from cutting-tool scraps. It was proven that ZMM is an available technique for recovering the WC powder from the cutting tools. WC-Co powders are recovered and then spray dried, sintered and obtained as a feedstock material for thermal-spray coating processes.

Advanced Engineering Materials, 2013

ABSTRACT Thermal barrier coatings (TBCs) are effective in protecting gas turbine blades by insula... more ABSTRACT Thermal barrier coatings (TBCs) are effective in protecting gas turbine blades by insulating them from hot gas passing through. In addition, they provide prevention of thermal shock, oxidation resistance and improved engine efficiency. A major life-limiting weakness of TBCs is their susceptibility to get damaged by thermally-induced stresses. The thermal shock behaviour of TBC systems subjected to thermal shock loading and the influence of the cracks on the coating durability was investigated experimentally. In this study, TBCs (NiCrAlY + YSZ), which have different sample geometry were subjected to both of gas burner and furnace thermal cycle tests. Sample geometry and cycle test type effect on the correlation of thermal shock behaviour of TBC coatings were characterized by macroscopic and microstructural investigations.