Ramazan Samur

Tribological Behaviour of Combined Coatings Deposited on Aluminium

In this paper the tribological performance of oxide (Cr2O3, ZrO2CaO and Al203) and combined coatings applied on a commercially pure aluminum sheet were presented. Combined coatings were produced by applying Polytetrafluoroethylene (PTFE) film on the oxide coatings. Among the oxide coatings Cr2O3 exhibited the highest and Al2O3 exhibited the lowest wear resistance, in accordance with their hardness. Combined coatings exhibited superior wear resistance than oxide coatings even at heavy wear testing conditions.

Nano-Bioceramic Production via Mechano-Chemical Conversion (Ultrasonication)

The production of nano-calcium phosphate powders, such as HA (hydroxyapatite), from synthetic chemicals can be expensive and time consuming. The skeleton or shells of sea creatures (e.g. sea urchins, shells, corals) could be an alternative source of materials to produce very fine and even nano-structured calcium phosphate biomaterial powders. Ηydrothermal conversion under very high pressures or methods such as hot-plating (chemical) or ultrasonication (mechano-chemical), have been proposed to transform naturally derived CaCO3, e.g. aragonite, into apatite based materials. The aim of the present work was to prepare inexpensive nano-sized HA and TCP bioceramics powders from a local sea snail shells as a possible raw material for HA/TCP bioceramics. Empty shells of a local sea snail (Nassarius hinia reticulatus) from Marmara Sea, Turkey were collected from a beach near Istanbul. The collected shells were ground to a particle size <75µm. Thermal analyses (DTA/TGA) were performed to determine the exact CaCO3 content and thermal behavior. The raw powder was suspended in an aqueous media which was placed in an ultrasonic bath. The temperature was set at 80°C for 15min. Then, an equivalent (to CaO content) amount of H3PO4 was added drop by drop very gently into the solution. The reaction continued for 8h, following which the liquid component was evaporated off in an incubator at 100°C for 24h. The dried sediment was collected and heat treated at two different temperatures, 400 and 800°C. The morphology of the powders produced was examined using SEM. The crystalline phases were indentified using X-ray analysis. X-ray diffractograms indicated the presence of two calcium phosphate phases, namely HA and whitlockite. SEM observations showed that the powder produced comprised nano-sized particles. FTIR results also indicated the presence of HA and whitlockite structures. The experimental results suggest that Nassariushinia reticulatus shells could be an alternative source for the production of various mono or biphasic calcium phosphates. In this study, local sea snail shells were successfully converted to HA and whitlockite with a simple mechano-chemical (ultrasonic) conversion method without the use of complex hydrothermal methods.

Tribological Performance of Ceramic Coatings Deposited on Polymer Substrates

In this study, tribological performance of ceramic coatings (Cr2O3, Al2O3TiO2 and ZrO2CaO) deposited on commercial poly ethyleneterephthalate have been examined by rubbing Al2O3 balls thereon. The Cr2O3 coating exhibited the greatest hardness and wear resitance in comparison to Al2O3TiO2 and ZrO2CaO coatings. The wear resistance of the coatings increased with increasing hardness. Introduction Polymers potentially feature great advantages in several industrial applications due to their low specific weight, low cost and ease of design. However, high temperatures and harsh tribological conditions limit their use in certain engineering applications. The service performance of polymeric machine elements and components such as prostheses, plastic molds, composites, can be improved by overlaying hard ceramic coatings [1]. Many studies have been performed to elucidate the tribological properties of vacuum arc [2,3], physical vapour deposited metal/nitride coatings [4,5] and thermal spray deposited ceramic coatings [6] on polymer substrates. In contrast, publications related to the tribological properties of flame spray deposited hard ceramic coatings on polymer substrate are scarce. In this study we aimed to examine the tribological performance of ceramic coatings deposited on polymer substrate. Experimental Commercial polyethyleneterephthalate (PET) was used as the substrate material. The Al2O3TiO2, ZrO2CaO and Al2O3 powders used were provided by Sulzermetco. In the present investigation, Cr2O3, Al2O3TiO2 and ZrO2CaO coatings were deposited on the substrate by the flame spray technique. Some physico-chemical specifications of these coating powders are listed in Table 1. Table 1. Properties of coating powders used. Code Chemistry Particle size (μm) Morphology Metco 136CP Cr2O3-5 SiO2-3 TiO2 -90+16 Clad Metco 130 Al2O3-13 TiO2 -30+5 Clad Metco 201NS ZrO2-5 CaO-0.5 Al2O30.4 SiO2-1.1 other oxides -53+11 Angular / Blocky, Fused and Crushed The coatings were characterized using thickness, roughness and hardness measurements. The thickness of the coatings was measured from the cross sections of the samples by a light optical microscope. Surface roughness of the coatings was determined by an optical profilometer, Perthometer S8P. Hardness measurements were conducted on the coatings under an indentation load of 300 g in a Vickers indenter. Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 581-584 doi:10.4028/www.scientific.net/KEM.264-268.581

Yüksek Hızlı Oksijen Yakıtlı Alev Toz Püskürtme Yöntemiyle Nikel Kaplanmış AA5754 Alüminyum Alaşımı ve DP600 Galvanizli Çeliğin Sürtünme Karıştırma Nokta Kaynağı ile Birleştirilmesinde Mikroyapı ve Mekanik Özelliklerin İncelenmesi

Bu calismada, surtunme karistirma nokta kaynaginin yuksek hizli oksijen yakitli alev toz puskurtme yontemiyle nikel kaplanmis malzemelerdeki mikroyapi ve mekanik ozelliklerinin incelenmesi amaclanmistir. AA5754 aluminyum alasimi kaynak yuzeyleri HVOF metodu kullanilarak 200 μm kalinliginda nikel ile kaplanmistir. Surtunme karistirma nokta kaynagi takimi sicak islem celiginden tasarlanmis ve imal edilmistir. Metalografik numuneler abrasif su jeti ile kaynakli parcalardan kesilmistir. Numuneler Metalografik olarak hazirlanmis ve temel metal, kaynak bolgesi ve isidan etkilenen bolge Vickers sertliginde olculmustur. Numunelerin mikro yapisi taramali elektron mikroskobu, EDS analizi ve optik mikroskop goruntuleme ile incelenmistir. Deneysel calisma sonuclari, mikroyapi ve kaynakli birlestirmenin mekanik ozellikleri analizi icin yorumlanmistir.