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Öğe Effect of Boronizing and Shot Peening on the Fatigue Properties of an Iron Based FeCu-Graphite P/M Material(Carl Hanser Verlag, 2014) Yilmaz, Selim Sarper; Unlu, Bekir Sadik; Kurgan, Naci; Varol, RemziIron based materials manufactured by powder metallurgy (P/M) method are widely used in industry. These materials are very important in applications where no machining is required, they can also be used as journal bearing material due to their self-lubricated property, and can be used for applications in the medical industry. In this study, powder metal parts were manufactured from composites based on FeCu-graphite by P/M method. Fatigue test was carried out on manufactured samples, which were only treated by boronizing or boronizing and shot peeing. The fatigue properties of these parts were investigated by a rotating bending fatigue test rig.Öğe Effect of material thickness and reduction ratio on roughness transfer in skin-pass rolling to DC04 grade sheet materials(Emerald Group Publishing Ltd, 2021) Ozakin, Batuhan; Colak, Bilal; Kurgan, NaciPurpose The last stage of the cold rolling process is skin-pass rolling and one of its most significant goals is to obtain appropriate topography on the surface of the sheet steel used extensively such as in automotive industry. The purpose of this paper is to investigate the effect of thickness change and various reduction ratios on roughness transfer of DC04 grade sheet material. Design/methodology/approach DC04 grade sheet materials with different reduction ratios and several thicknesses were subjected to skin-pass rolling process in the rolling equipment with a two-high roll. Some roughness parameters were determined as a result of roughness measurements from the surfaces of roughened sheet materials. Findings While the roughness transfer is higher in 1-mm thick material in reduction ratios up to 430 micrometers; in reduction ratios above 430 micrometers, it is higher for 1.5-mm thick materials. As the reduction ratio increases in DC04 grade sheet materials, the homogeneity of the roughness distribution in 1-mm thickness sheet material deteriorates, while the roughness distribution in 1.5-mm thickness sheet material is more homogeneous. Originality/value This paper demonstrates how material thickness and reduction ratio affect the roughness transfer in skin-pass rolling. The results obtained can be used by optimizing in manufacturing processes.Öğe Effect of porosity and density on the mechanical and microstructural properties of sintered 316L stainless steel implant materials(Elsevier Sci Ltd, 2014) Kurgan, NaciIn this study, the microstructure and mechanical properties of sintered AISI 316L stainless steel implant materials produced by powder metallurgy (P/M) method were investigated as a function of porosity amount. AISI 316L stainless steel powders were cold-pressed with 800 MPa pressure and sintered at 1200 degrees C, 1250 degrees C and 1300 degrees C for 30 min in a nitrogen atmosphere. The mechanical properties of the 316L implant samples were determined by tensile, fatigue and microhardness tests. Metallographic studies such as pore formation, and fractured surface analyses were performed by Scanning Electron Microscopy (SEM) and Light Optical Microscopy (LOM). The results of this study indicate that, irregular pore formation tendencies increase with an increase in porosity (%). Furthermore, an increase in porosity was shown to decrease the mechanical properties of sintered AISI 316L stainless steel. Sintering temperature is important parameter in decreasing the porosity of P/M materials. (C) 2013 Elsevier Ltd. All rights reserved.Öğe Effects of sintering atmosphere on microstructure and mechanical property of sintered powder metallurgy 316L stainless steel(Elsevier Sci Ltd, 2013) Kurgan, NaciIn this study, nitrogen and argon were used as the sintering atmosphere for AISI 316L stainless steel compacts. The effects of sintering atmosphere on sintered density, grain morphology and mechanical properties were investigated. The mechanical and microstructural characteristics of the sintered compacts were evaluated using optical microscopy, and scanning electron microscope. Tensile strength and hardness of the compacts sintered in nitrogen atmosphere are 290 MPa and 355.2 HV0.1, respectively. When argon was used as the sintering atmosphere, the tensile strength and hardness of the 316L stainless steel sintered compacts have become 226 MPa and 181.8 HV0.1 respectively. The results of this study indicate that the compacts sintered in nitrogen atmosphere exhibits higher strength and hardness than that of the steels sintered in argon atmosphere. (C) 2013 Elsevier Ltd. All rights reserved.Öğe An experimental investigation into roughness transfer in asymmetrical rolling of steel strips(2023) Çolak, Bilal; Ahmed, Zahoor; Özakın, Batuhan; Kurgan, NaciThis study investigated the effect of rolling parameters such as speed, thickness reduction, roll surface roughness, material thickness, surface condition (dry or lubricated), and rolling force on the roughening characterization in asymmetrical rolling. The surface roughness of the samples subjected to rolling tests was measured. The roughness values' average and standard deviation were found, and 3-D scanning images were acquired. Lubricated texturing experiments revealed that lubrication reduced roughness transfer. It was found that the introduction of roughness on the material surface decreased as the rolling speed increased. On the other hand, a higher speed increases the rolling force, which increases the surface roughness. The effect of speed on the standard deviation varies in direct proportion. Furthermore, lubricated rolling produced a more homogenous roughness distribution at higher speeds, while dry rolling produced homogeneous roughness at lower speeds. It was revealed that the rolling force is higher with thicker materials. While the roll roughness did not affect the rolling force using thicker material much, this effect was more pronounced in the very rough roll using thinner material. The standard deviation was lower in smaller reduction ratios using rough and very rough rolls. According to the results, although asymmetrical rolling has some advantages compared to conventional rolling, it was concluded that it is not a suitable method for roughening steel strips.Öğe An experimental investigation into roughness transfer in skin-pass rolling of steel strips(Springer London Ltd, 2018) Colak, Bilal; Kurgan, NaciThe surface of sheet metals should have a certain level of roughness in terms of forming and dyeing quality. Surface roughness is mainly introduced to the material by rolling with rough rolls, which is called temper rolling. The roughness of a roll is transferred to the material, depending on the rolling parameters. A 2-high rolling setup equipped with a load-cell measuring the rolling force, which can roll at different speeds and reduction ratios, was used to observe the change in the amount of roughness transfer. Surface roughness values of specimens were measured after tests, their average and standard deviation values were calculated, and 3-D field scanning images were investigated. The results obtained were evaluated in terms of rolling parameters and roughness transfer. It was concluded that each parameter that increased the rolling force also increased the roughness transfer. It was seen that rolling force, and thus roughness transfer, was higher in the tests conducted at high speeds and high reduction ratios with thinner materials. Lubricated roughening tests indicated that the introduction of roughness on material surface decreased due to lubrication. Moreover, a more homogeneous roughness distribution was obtained in lubricated rolling compared to dry rolling. It was observed that the roughness at small reduction ratios was obtained within a narrower range.Öğe An Experimental Investigation of the Lubrication Effects on Formability In Warm Deep Drawing(Gazi Univ, 2016) Sen, Nuri; Kurgan, Naci; Karaagac, Ibrahim; Uluer, OnuralpThe lubrication reduces to effects of friction forces that it is between die and blank holder in deep drawing process. The affecting factors to friction forces are material, surface quality of die and blank holder, temperature, blank holder force and lubrication properties. In this study, the effects of lubricant type on drawing ratio (DR) and forming force have been investigated experimentally. Graphite spray and composition of graphite spray-Teflon (PTFE) materials were used as lubricant materials. Compared with the use of spray, in case of using graphite and Teflon spray composition as lubrication type, it was observed that friction force was decreased. As a result of this decrease, the forming force decreased. The depending on lubrication type, the DR increased maximum 11.26 % for HC300LA sheet material. Also, The DR increased maximum 11.51 % for HC420LA sheet material.Öğe Ilık derin çekme prosesinde yağlayıcı etkisinin şekillendirilebilirlik açısından deneysel araştırılması(2016) Şen, Nuri; Kurgan, Naci; Karaagaç, İbrahim; Uluer, OnuralpDerin çekme prosesinde yağlayıcı kullanılması şekillenme esnasında kalıp elemanları ve sac malzeme temas yüzeylerinde oluşansürtünme kuvvetlerinin etkisini azaltmaktadır. Malzeme, kalıp ve baskı plakası yüzey kalitesi, sıcaklık, baskı plakası kuvveti vekullanılan yağlayıcının özellikleri sürtünme kuvvetlerine etki eden faktörlerdir. Bu çalışmada; yüksek mukavemetli HC300LA(Erdemir 7128) ve HC420LA (Erdemir 7140) sac malzemelerinin ılık derin çekme yöntemiyle şekillendirilmesi sırasında kullanılan yağlayıcı türünün çekme oranına (DR) ve şekillendirme kuvvetine etkileri, deneysel olarak incelenmiştir. Çalışmada, grafitsprey ve grafit sprey ile teflon (PTFE) bileşiminin birlikte kullanıldığı iki tür yağlayıcı kullanılmıştır. Yağlayıcı türü olarak grafitsprey ve teflon bileşimi kullanıldığında sürtünme kuvvetinin grafit sprey kullanımına oranla azaldığı ve bunun sonucu olarak daşekillendirme kuvvetinin de azaldığı gözlenmiştir. Yağlayıcı türüne bağlı olarak DR’nin HC300LA sac malzeme için en büyük %11,26, HC420LA sac malzeme için de en büyük % 11,51 oranlarında arttığı tespit edilmiştir.Öğe Improving deep drawability of HC300LA sheet metal by warm forming(Springer London Ltd, 2016) Sen, Nuri; Kurgan, NaciThe formability of high-strength sheet materials is limited at room temperatures. In this study, the first of its kind to be conducted, experimental research was performed on the formability of HC300LA-grade sheet material using the warm deep drawing (WDD) method. Temperature control is among the most important parameters in the WDD method. To increase the limiting drawing ratio (LDR) of HC300LA-grade sheet material, a new warm deep drawing method featuring sensitive temperature control was designed and manufactured. With this new method, the formability of HC300L-grade sheet material was considerably increased by heating the flange zone of the blanks under blank-holder force (BHF). Before the experimental study, unidirectional tensile tests were applied at room temperature (RT), 150 degrees C, and 300 degrees C. At the completion of the test conducted at 300 degrees C, dynamic strain aging (DSA) was seen in the test specimen. As a result of DSA, the HC300LA-grade sheet material became brittle and its formability decreased. Experimental studies were therefore conducted in the temperature range of 170 and 295 degrees C. LDR for a 1.2-mm sheet thickness of HC300LA-grade sheet material, which is 2.14 at RT, increased to 2.61 after applying this method. In experimental studies on LDR involving 1.5-mm sheet thickness, which is 2.15 at RT, the ratio increased to 2.59. The drawing ratio (DR) increased by 21.96 and 20.45 % for 1.2 mm sheet thickness and 1.5 mm sheet thickness, respectively. Moreover, the microstructures of the warm cup's punch corner region, and wall and bottom regions were investigated under an optical microscope. The results showed whether any changes occurred in the microstructures.Öğe Investigation of fatigue properties of shot peened and plasma nitrocarburized P/M FC0205 steel(Korean Soc Mechanical Engineers, 2013) Basaran, Ali; Kurgan, Naci; Varol, RemziOne of the widely used powder metal materials in automotive industry, which is copper steel FC 0205 (Fe + 2% Cu + 0.5% C), was used in this study. The pressed samples has been prepared at the compression pressure of 680 MPa and sintered in conventional furnace at 1120 degrees C for 30 minutes. The samples with 7 Mg/m(3) densities were used as fatigue and shot peening processes. Shot peening were applied with 20A and 32A and the others were not peened. Plasma nitrocarburizing process was performed at 555 degrees C for 2 hours under 600-900 Pa pressure. Fatigue tests were conducted at room temperature on a rotating bending type fatigue test device. It was determined that shot peening should be used where increased fatigue strength is needed, and plasma nitrocarburizing should be preferred where surface hardness is required, and plasma nitrocarburizing after shot peening process is much more useful.Öğe Investigation of the effect of diffusion bonding parameters on microstructure and mechanical properties of 7075 aluminium alloy(Springer London Ltd, 2014) Kurgan, NaciIn the present study, diffusion bonding of aluminium alloy (AA7075) sheet materials which are used especially in the automobile and aerospace industry has been investigated at temperatures of 425 and 450 A degrees C and pressures of 2 and 3 MPa for 180 min in argon atmosphere. The microstructural and mechanical properties of bonding have been characterized with different welding parameters such as bonding temperature and pressure. The microstructure was characterized by light optical microscope, scanning electron microscope and energy dispersive spectroscopy, while the mechanical properties were determined by tensile-shear tests and microhardness tests. The results obtained are discussed from both the microstructural and mechanical points of view. It was observed in the microstructural investigations that the interfacial oxide layer decreased with increasing of the bonding temperature and pressure. The maximum shear strength was found to be 131 MPa for the Al 7075 sample bonded at 450 A degrees C and 3 MPa for 180 min. It is shown that in certain extent, the bonding temperature and bonding pressure have great effect on the joint shear strength. With the increasing of bonding temperature and pressure, the shear strength of the joints increases due to diffusion of atoms in the interface. The strength achieved after bonding were dependent on interface grain boundary migration and on grain growth during the bonding process. The maximum hardness value of the Al 7075 sample bonded at 450 A degrees C, 3 MPa for 180 min is 92.5 HV0.2. Increasing hardness with increasing temperature can be attributed to the formation of metallic bond at high temperatures and pressures.Öğe Production of 316L stainless steel implant materials by powder metallurgy and investigation of their wear properties(Science Press, 2012) Kurgan, Naci; Sun, Yavuz; Cicek, Bunyamin; Ahlatci, HayrettinIn this study, the mechanical and wear properties of AISI 316L stainless steel implant materials, produced by powder metallurgy (P/M), were investigated. AISI 316L stainless steel powder was cold-pressed with 800 MPa of pressure and then sintered at 1200, 1250 and 1300A degrees C for 30 min as three sample groups. The microstructure, and mechanical and wear properties of the resulting steels were investigated. Light optical and scanning electron microscopiese were used to characterize the microstructure of the steels. Room temperature mechanical properties of the steels were determined by hardness measurements and impact tests. Wear was determined using the pin-on-disc wear test, and the results were evaluated according to weight loss. The results indicate that the sintering temperature, time and atmosphere are important parameters that affect the porous ratio of materials produced by P/M. Sintering at high temperature can eliminate small pores and make the residual pores spherical. The wear tests showed that the wear of the AISI 316L stainless steel implants changed depending on the sintering temperature and load. Spherical pores in the samples increase the wear resistance. Moreover, decreasing the porosity ratio of these materials improves all of their mechanical properties.Öğe Tribological properties of boronized ferrous based PM journal bearings(Carl Hanser Verlag, 2015) Unlu, Bekir Sadik; Yilmaz, Selim Sarper; Kurgan, Naci; Varol, RemziFerrous based PM (powder metallurgical) materials are widely used in journal bearings since they provide a good tribological performance. These bearings are self-lubricating and can be used in places where lubricating is not possible. This also applies to the shaft material which shows adhesive wear. Tribological properties can be improved and adhesive wear can be decreased by boronizing. In this study, tribological properties of ferrous based boronized and non-boronized Fe-graphite, FeCu-graphite and CuSnFe-graphite bearings manufactured by PM method have been determined and compared. Boronizing treatment was carried out at 950 degrees C for 4 hours. The SAE 1050 steel shaft was used as counter abrader. Experiments were carried out at 20 N loads and 1500 rpm every 30 minutes for 2.5 hours.
