Search

This study aimed to improve mechanical properties, which decreased in the weld area, with deep cryogenic treatment at different holding times. In the study, firstly, the formation of heat damaging the welding area was observed. The temperatures in the welding zone were measured on the shoulder with a thermal camera, on the material surface, and inside the material with a thermocouple. The effects of these temperatures during welding on the surface topography and mechanical properties were investigated. The effect of tempering heat treatment after deep cryogenic treatment applied for 6, 12, 18, and 24 h was investigated. It has been observed that tempering after cryogenic treatment applied to 7xxx series aluminum alloys reduces the hardness of the nugget zone but increases the hardness in the heat unaffected zone. In addition, it was observed that deep cryogenic treatment applied at different holding times positively affected the hardness, tensile strength, and % elongation in the weld area.

This study investigated the effects of shallow and deep cryogenic treatment on the microstructural and mechanical properties of Sverker 21 tool steel. After conventional heat treatment, shallow cryogenic treatment at −80 °C for 2, 12, and 24 h and deep cryogenic treatment at −180 °C for 2, 18, and 36 h were applied on the steel samples. After that, the samples were tempered at 200 °C for 2 h. As a result of these treatments, the steel samples’ hardness, toughness, and wear rate changes were determined, and their microstructural properties were investigated. As a result of the study, it was observed that the cryogenic treatment had positive effects on the mechanical and microstructural properties of Sverker 21 steel. Mechanical properties also improved with increasing holding time for both cryogenic treatment types. It has been found that the deep cryogenic treatment provides better mechanical properties compared to the shallow cryogenic treatment. The maximum hardness and wear resistance were obtained in the deep cryogenically treated sample for 36 h. Compared to the CHT sample, the hardness and impact energy of the DCT(36) sample increased by approximately 11.75% and 17.36%. An improvement of approximately 64% was observed in the wear rate.

In this study, machining experiments were performed by metal cutting in different cutting parameters with CVD - Chemical Vapor Deposition (MT-TiCN + TiC +Al2O3 + TiN) and PVD - Physical Vapor Deposition (TiAIN) coated carbide tools NIMAX plastic mold steel in a universal lathe. Changes in surface roughness, cutting temperature, vibration, and noise that occurred during machining were examined. The test specimens were machined with 18 different parameters using three different cutting speeds (120, 160, 200 m/min) at three different feed rates (0.1, 0.15, and 0.2 mm/rev) and a constant depth of cut (0.5 mm). As a result of the experiments performed, surface roughness, cutting temperature, vibration, and noise values were examined, and the best performance was obtained with PVD-coated cutting tool. Taguchi optimization was also applied to the experimental results of the study. The turning parameters giving the lowest Ra value were determined. The most effective turning parameters and effect ratios on Ra were determined by ANOVA analysis.

The cryogenic treatment, known as holding materials at sub-zero temperatures, is a method used to improve the properties of metal and non-metallic materials in recent years. This method is mainly applied to tool steels used in mold making. In our country, the use of cryogenic processes continues to be widespread by many private sector organizations, primarily in mold materials. The benefits of this process have been recognized in many sectors, from the defense industry to the automotive industry. Sleipner cold work tool steel is widely used in blanking and fine blanking, shearing, forming, coining, cold forging, cold extrusion, thread rolling, drawing and deep drawing, powder pressing molds where high wear resistance, high chipping resistance and high compressive strength are required. In this study, the macro hardness, micro hardness and microstructure properties of Sleipner cold work tool steel, which was applied traditional heat treatment and deep cryogenic process for 24 hours, were examined and the changes in the mechanical properties and microstructure of the material were determined. However, by measuring the residual stress and residual austenite amounts in the materials with the X-Ray Diffraction (XRD) Method, the difference between the samples was determined. Deep cryogenic treatment increased the macro and micro hardness by 0.5 HRc and 27.57 HV, respectively. The amount of residual austenite decreased by 36% after deep cryogenic processing. Axial and circumferential residual stress values also decreased by 48.84% and 36.52%, respectively. As a result, the deep cryogenic process provided positive improvements by increasing the hardness of Sleipner cold work tool steel, homogenizing the microstructure, reducing the residual austenite and residual stress values., Sıfırın altındaki sıcaklıklarda malzemelerin bekletilmesi olarak bilinen kriyojenik işlem, son yıllarda metal ve metal olmayan malzemelerin özelliklerini iyileştirmek için uygulanan bir yöntemdir. Bu yöntem daha çok kalıp yapımında kullanılan takım çelikleri için uygulanmaktadır. Ülkemizde, birçok özel sektör kuruluşu tarafından öncelikle kalıp malzemeleri olmak üzere birçok üründe kriyojenik işlem kullanımı yaygınlaşmaya devam etmektedir. Savunma sanayiinden otomotiv sanayiine kadar birçok sektörde bu işlemin faydaları kabul görmüştür. Bu çalışmada, geleneksel ısıl işlem uygulanmış (CHT) ve 24 saat derin kriyojenik işlem uygulanmış (DCT-24) Sleipner soğuk iş takım çeliğinin makro sertlik, mikro sertlik ve mikroyapı özellikleri incelenerek, malzemenin mekanik özellikleri ve mikroyapısındaki değişimler tespit edilmiştir. Bununla birlikte, X-Işını Kırınımı (XRD) Yöntemi ile malzemelerdeki kalıntı gerilme ve kalıntı östenit miktarları ölçülerek, numuneler arasındaki fark belirlenmiştir. CHT ve DCT-24 numunelerinin makro sertliği sırasıyla 60,96 HRC ve 61,46 HRC olarak ölçülmüştür. Mikro sertlik değerleri de sırasıyla 734,26 HV ve 761,83 HV olarak ölçülmüştür. Derin kriyojenik işlem makro ve mikro sertliği sırasıyla 0,5 HRC ve 27,57 HV arttırmıştır. Kalıntı östenit miktarı derin kriyojenik işlemden sonra % 36 oranında düşmüştür. Eksenel ve çevresel kalıntı gerilme değerleri de sırasıyla % 48,84 ve % 36,52 oranında düşmüştür. Sonuç olarak derin kriyojenik işlem Sleipner soğuk iş takım çeliğinin sertliği arttırmış, mikroyapıyı homojenleştirmiş, kalıntı östenit ve kalıntı gerilme değerlerini düşürerek olumlu iyileşmeler sağlamıştır.

Good surface roughness and topography are of great importance in plastic mold materials. This study investigated the effects of cutting parameters on cutting temperature, vibration (g), surface roughness (Ra), and noise (N) in the turning of AISI P20 die steel using coated tungsten carbide cutting tools. Experiments were carried out using the Taguchi L-18 experimental design with cutting tools with two different types of coatings (CVD and PVD), three different cutting speeds (100, 150, and 200 m/min), three different feed rates (0.1, 0.15, and 0.2 mm/rev), and a constant cutting depth (1 mm). As a result of the study, the PVD-coated tools exhibited a higher performance for all outputs (cutting temperature, g, Ra, and N). It was observed that the vibration and surface roughness were proportional, vibration was mostly affected by feed rate, and increasing cutting speed and feed rate also increased the temperature and noise in the cutting zone. According to ANOVA results, the most effective parameter on surface roughness was feed rate (97.24%), the most effective parameter on vibration was cutting tool type (57.34%), and finally, the most effective parameter on noise was feed rate (50.37%). WOS:000687546800008 2-s2.0-85113340973

İçeriğindeki elementler ve uygulanan yaşlandırmalar sonrası yüksek mekanik özelliklere sahip7xxx serisi alüminyum alaşımları, düşük özgül ağırlığa ve yüksek özgül mukavemete sahiptirler. Ayrıca uygulanan ısıl işlemler ile mükemmel korozyon dirençlerine sahiptirler. Bu sebeplerden ötürü enerji sarfiyatının çok önemli olduğu otomotiv, havacılık ve uzay sanayisinde sıklıkla tercih edilmektedirler. Ancak erime noktası düşük olan bu alaşımların kaynaklanması oldukça güç olduğundan sürtünme karıştırma kaynağı önemli bir alternatif sunmaktadır. Fakat kaynaklanan noktalardaki mekanik özellikler sürtünme karıştırma kaynağında da diğer yöntemlere kıyasla az da olsa düşmektedir. Sorunun çözümü için bu çalışmada sürtünme karıştırma kaynağı ile birleştirilen parçalara -180°C’de derin ve -80°C’de sığ kriyojenik işlem uygulanmıştır. Sürtünme karıştırma kaynağı sonrası gerçekleştirilen kriyojenik işlem kaynak bölgesi sertliği ve mikroyapısında önemli değişikliklere neden olmuştur. Özellikle derin kriyojenik işlem sonrası parçaların birleşme bölgelerinde gözlemlenen sertlik artışı oldukça önemlidir.

This paper presents the effect of cutting tool, cutting speed and feed rate on the flank wear and surface roughness of austenitic stainless steel (AISI 304) during wet turning. Turning tests were designed based on the Taguchi method (L18). An orthogonal array, the signal-to-noise ratio (S/N) and the ANOVA were used to investigate the machinability of AISI 304 stainless steel with PVD and CVD coated tungsten carbide inserts. As a result of ANOVA, it was found that the feed rate was the most effective parameter on both flank wear and surface roughness.

Today, developments in technology have gained momentum more than ever, and the need for efficiency in production as well as in the ecological domain has increased significantly. Studies examining dry machining and coolant removal have been superseded by those presenting new cooling and lubrication techniques. The effects on surface roughness directly related to final product quality are being investigated in terms of tool life and employee health. This has resulted in more frequent use of the eco-friendly minimum quantity lubrication (MQL) technique, which has now become a major competitor to dry and coolant machining. In this study, AISI D2 cold work tool steel, a material widely used in the mold industry, was used as the workpiece. Tests were carried out under dry and MQL conditions and the temperature, cutting tool vibration amplitude, tool wear, surface roughness and tool life were evaluated. The experiments were carried out using two different cutting tool coating types (CVD-chemical vapor deposition and PVD-physical vapor deposition) and three different cutting speeds (60, 90 and 120 m/min) at a constant cutting depth (1 mm) and feed rate (0.09 mm/rev). Results revealed that tool wear, cutting temperature and cutting tool vibration amplitude were lower by 23, 25, and 45%, respectively, compared to dry cutting. Because of these improvements, the surface roughness of the workpiece was improved by 89% and tool life was increased by up to 267%. (C) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Duzce University Scientific Research Projects UnitDuzce University [2019.06.05.974]; Zirve Industrial Products We would like to thank the Duzce University Scientific Research Projects Unit for their contribution to the project coded 2019.06.05.974 and Zirve Industrial Products for their support. WOS:000547380500015 2-s2.0-85078737956

Caves are laboratories for many disciplines that work in natural sciences including mineralogy, biology, hydrogeology, and archaeology. In this study, bi-monthly samplings were carried out from three sampling locations within and around the Güvercinkaya Cave, a high-altitude cave located in northwestern Turkey, to evaluate the hydrochemical and microbiological properties and the aquatic macroinvertebrates of the cave stream. Some parameters of the water including pH, electrical conductivity, temperature, oxidation-reduction potential, and dissolved oxygen were measured in-situ, while elemental (70 in total) and ionic composition of water were analyzed in the laboratory. Microbiological analyses of the cave stream were examined through analyses of total bacteria, total coliforms, fecal coliforms, fecal Streptococcus, and Escherichia coli. According to the Piper diagram of hydrochemical data, the cave stream had mainly Ca-Mg-HCO3 character, on the other hand, the Schoeller diagram indicated a common water source in Güvercinkaya cave due to the similar components of the main ionic components of the water. As a result of microbiological analysis, fecal contamination was determined, indicating active wildlife in the cave. Additionally, several aquatic macroinvertebrates taxa, Rhynchelmis limosella, Dugesia sp., Gammarus uludagi which have non-troglobiont character were found in the cave stream. Rhynchelmis limosella detected in this study is the first record for the Turkish fauna., Mağaralar maden bilimi, biyoloji, hidrojeoloji ve arkeoloji dahil olmak üzere doğa bilimlerinin pek çok disiplini için bir laboratuvar niteliğindedir. Bu çalışmada, Türkiye'nin kuzeybatısında yer alan yüksek rakımlı bir mağara olan Güvercinkaya Mağarası'nın seçilen bölümlerinden, hidrokimyasal ve mikrobiyolojik özellikleri ile sucul makroomurgasızlarının değerlendirilmesi için iki aylık periyotlarda bir yıl örneklemeler yapılmıştır. Suyun pH, elektriksel iletkenlik, sıcaklık, oksidasyon-redüksiyon potansiyeli, çözünmüş oksijen gibi bazı parametreleri yerinde ölçülürken, elementler (toplam 70 adet) ve suyun bazı iyonları laboratuvarda analiz edilmiştir. Mikrobiyolojik analizlerde toplam bakteri, toplam koliform, fekal koliform, fekal Streptococcus ve Escherichia coli analizleri yapılmıştır. Hidrokimyasal verilerin Piper diyagramı değerlendirildiğinde, mağara deresinin esas olarak Ca-Mg-HCO3 karakterine sahip olduğunu, Schoeller diyagramının ise ana iyonik bileşenlerin, aynı modeli takip etmesinden dolayı ortak bir su kaynağını işaret ettiği görülmüştür. Mikrobiyolojik analizler sonucunda, mağarada aktif bir yaban hayatı olduğunu gösteren, dışkı kaynaklı bir kontaminasyon belirlenmiştir. Ayrıca mağara deresinde, troglobiont olmayan sucul omurgasızlardan Rhynchelmis limosella, Dugesia sp. ve Gammarus uludagi tespit edilmiştir. Bu çalışmada tespit edilen Rhynchelmis limosella Türkiye faunası için ilk kayıttır.

Ozbek, Orhan/0000-0002-7388-0542; OZBEK, Onur/0000-0002-8372-3487; Altan Ozbek, Nursel/0000-0003-3241-9423 WOS: 000367757000027 In this study, the effects of cryogenic treatment on tool wear of uncoated tungsten carbide inserts were investigated in the turning of AISI 316 stainless steel. It was found that notch wear appeared at low and medium cutting speeds, while flank wear and crater wear formed at all combinations of the process parameters selected for turning. In addition, treated inserts exhibited superior wear performance to untreated ones. This can be attributed to high wear resistance and low thermal conductivity of treated inserts. The results were verified by analyses of microstructure and hardness, image processing and Xray diffraction. (C) 2015 Elsevier Ltd. All rights reserved. Gazi University Scientific Research Project DivisionGazi University [07/2010-23] The authors wish to place their sincere thanks to Gazi University Scientific Research Project Division for financial support for the Project no. 07/2010-23.

Ozbek, Orhan/0000-0002-7388-0542; OZBEK, Onur/0000-0002-8372-3487; Altan Ozbek, Nursel/0000-0003-3241-9423 WOS: 000387856000065 This study investigated the effects of deep cryogenic treatment (DCT) on the wear performance of uncoated tungsten carbide inserts. AISI 304 austenitic stainless steel, widely used in industry, was selected as the workpiece material. Cutting experiments showed that the amount of wear significantly increased with increasing cutting speed. In addition, it was found that DCT contributed to the wear resistance of the turning inserts. The treated turning inserts were less worn by 48 and 38 pct in terms of crater wear and notch wear, respectively, whereas they exhibited up to 18 pct superior wear performance in terms of flank wear. This was attributed to the precipitation of new and finer eta-carbides and their homogeneous distribution in the microstructure of the tungsten carbide material after deep cryogenic treatment. Analyses via image processing, hardness measurements, and SEM observations confirmed these findings. Gazi University Scientific Research Project DivisionGazi University [07/2010-23] The authors wish to place their sincere thanks to Gazi University Scientific Research Project Division for the financial support for the Project No. 07/2010-23.

This paper is a review of recent data exploring the subsistence patterns of the prehistoric populations living between 12 ka and 6 ka BP on the long and narrow Gallipoli (Gelibolu) Peninsula, situated between the Marmara and Aegean Seas. Located in southern Thrace, the sea level fluctuations were different in the north and south of the peninsula. Previously, the earliest human occupation traces from Southern Turkish Thrace came from Neolithic sites ca. 8500 BP, including Hoca Cesme, Hamaylitarla and Kaynarca. In 2011, reconnaissance work discovered clear indications of Palaeolithic localities including Ucdutlar that may date as early as Early Upper Paleolithic. On the Gallipoli Peninsula, a site of nearly 2.5 ha yielded a prehistoric flaked stone industry, with traits earlier than Neolithic. Despite the proximity of this Palaeolithic site to the sea, the Neolithic sites on the peninsula are usually found far from the coast, some km inland. Research is in the initial steps to discover the whole history of Southern Turkish Thrace.

Özbek Onur. Hamaylıtarla Reconsidered : A Neolithic Site and its Environmental Setting in Southern Turkey. In: Anatolia Antiqua, Tome 18, 2010. pp. 1-21.

In the marble cutting process, generally, normal and tangential forces are taken into account. However, the axial forces (Fz) on the cutting disc affect the economic life of the disc and segment wear significantly. In this study, the effect of the axial forces on discs, which are used in the marble cutting process, on cutting performance was investigated. Therefore, by taking into account different cutting parameters (peripheral speed, traverse speed and depth of cut), the axial forces on circular saw were measured by means of a dynamometer. In addition to this, using a laser displacement meter, the amount of axial deviation for each cutting parameter in the course of cutting was determined. According to the experimental results obtained, the increase of traverse speed and depth of cut also significantly increases the axial deviation of the cutting disc. Moreover, it is observed that traverse speed and depth of cut have an impact on axial deviation of the saw at the initial moment when the saw starts to cut.

Özbek Onur. Kaynarca : A Neolithic Mound in Gelibolu Peninsula. In: Anatolia Antiqua, Tome 16, 2008. pp. 1-12.

Bu çalışmada AISI 304 ve AISI 316 östenitik paslanmaz çeliklerin işlenebilirliğini değerlendirmek amacıyla kaplamasız tungsten karbür kesici takımlar kullanılarak tornalama deneyleri yapılmıştır. Deneyler, kuru kesme şartlarında sabit kesme derinliği (2,4 mm), dört kesme hızı (100, 120, 140 ve 160 m/dak) ve üç ilerleme hızında (0,15, 0,3 ve 0,45 mm/dev) gerçekleştirilmiştir. AISI 304 ve AISI 316 çeliklerin işlenebilirliği takım aşınması, esas kesme kuvveti ve yüzey pürüzlülüğü açısından değerlendirilmiştir. Deney sonuçları AISI 316 çeliğinin işlenmesinde kesici takımın daha fazla aşındığını göstermiştir. Ayrıca AISI 316 çeliğinde daha yüksek kesme kuvveti ve yüzey pürüzlülüğü değerleri ölçülmüştür. Deneysel çalışma sonunda, AISI 316 çeliğinin AISI 304 çeliğine kıyasla işlenebilirliğinin zor olduğu ortaya konulmuştur., In this study, turning tests were performed to assess machinability of AISI 304 and AISI 316 austenitic stainless steels using uncoated tungsten carbide tools. The tests were conducted at four cutting speeds (100, 120, 140 and 160 m/min), three feed rates (0.15, 0.3 and 0.45 mm/rev), and a fixed depth of cut (2.4 mm) under dry cutting conditions. Machinability of AISI 304 and AISI 316 steels was evaluated in terms of tool wear, main cutting force and surface roughness. Experimental results showed that larger wear damages formed on the cutting inserts used for machining of AISI 316 steel. In addition, higher values of cutting forces and surface roughness were measured in machining of AISI 316 steel. In consequence of experimental study, it was found that AISI 316 steel had harder machinability characteristics than AISI 304 steel.

Ozbek, Orhan/0000-0002-7388-0542; OZBEK, Onur/0000-0002-8372-3487; Altan Ozbek, Nursel/0000-0003-3241-9423 WOS: 000342254300004 Cutting tool costs is one of the most important components of machining costs. For this reason, tool life should be improved using some methods such as cutting fluid, optimal cutting parameters, hard coatings and heat treatment. Recently, another one of the methods commonly used to improve tool life is cryogenic treatment. This study was designed to evaluate the effects of different holding times of deep cryogenic treatment on tool wear in turning of AISI 316 austenitic stainless steel. The cemented carbide inserts were cryogenically treated at -145 degrees C for 12, 24, 36, 48 and 60 h. Wear tests were conducted at four cutting speeds (100, 120, 140 and 160 m/min), a feed rate of 0.3 mm/rev and a 2.4 mm depth of cut under dry cutting conditions. The wear test results showed that flank wear and crater wear were present in all combinations of the cutting parameters. However, notch wear appeared only at lower cutting speeds (100 and 120 m/min). In general, the best wear resistance was obtained with cutting inserts cryogenically treated for 24 h. This case was attributed to the increased hardness and improved microstructure of cemented carbide inserts. These improvements were confirmed through hardness, image processing, and XRD analyses. (C) 2014 Elsevier Ltd. All rights reserved. Gazi University Scientific Research Project DivisionGazi University [07/2010-23] The authors wish to place their sincere thanks to Gazi University Scientific Research Project Division for financial support for the Project no. 07/2010-23.

Özbek Onur, Erol Kenan. Étude pétrographique des haches polies du Hamaylıtarla et Fenerkadutlar (Turquie). In: Anatolia Antiqua, Tome 9, 2001. pp. 1-7.