YUSUF ÖZÇATALBAŞ | Gazi University (original) (raw)

Papers by YUSUF ÖZÇATALBAŞ

Because of punch wear increases finished hole errors, Hole quality and punch wear are closely rel... more Because of punch wear increases finished hole errors, Hole quality and punch wear are closely related. This phsical errors can be found on the surface of the part and characterise its quality and accuracy. Punch errors are substantialy related with punch wear and process parameters. The purpose of this work was to investigate the effect of cryogenically treated punches on AISI 304 austenite stainless steel sheet piercing hole errors. In accordance with this purpose, the punching was carried out in a punch machine using 5, 6 and 7 mm diameters of AISI D3 cold work tool steel punches and 1.5 mm thick stainless steel sheets. One punch group in 36 hours was subjected to the deep cryogenic process at -145°C in addition to the conventional heat treatment. The deep cryogenic process was carried out to improve the wear resistance and hole quality. For this work, punch weight losses were measured and punch wear was evaluated through analysis of SEM and OM images. The hole diameter and circul...

The aim of this study is to investigate formability of Al based closed cell metallic foams at hig... more The aim of this study is to investigate formability of Al based closed cell metallic foams at high temperature. The foam specimens with rectangular section were produced from AlMg1Si0.6TiH20.8 alloy preform material. Bending and free bending tests based on gravity effect were applied to foam specimens at high temperatures. During the tests, the time-angular deformation relationships with various temperatures were determined. Deformation types formed in cell walls were investigated by means of Scanning Electron Microscopy (SEM) and optical microscopy. Bending deformation about 90° was achieved without any defect at high temperatures. The importance of a critical temperature and deformation rate was emphasized in maintaining the deformation. Significant slip lines on surface of cell walls at tensile zones of bending specimen were observed. At high strain rates, the microcrack formation in boundaries of elongated grains was determined.

Gazi Üniversitesi Mühendislik Mimarlık Fakültesi Dergisi, 1997

Gazi Üniversitesi Fen Bilimleri Enstitüsü Dergisi, 1999

Bu calismada, delik delme metoduyla H-Drill kalinti gerilme analiz programi kullanilarak kalinti/... more Bu calismada, delik delme metoduyla H-Drill kalinti gerilme analiz programi kullanilarak kalinti/kalicigerilmelerin olculmesi ve rozet tip gerinim olcerlerin kalibrasyonu amaclanmistir. Bu amacla, farkli en kesitalanlarina sahip celik cekme levhasina ASTM’ye gore standart ve standart disi D0/D oranlarina sahip farkli ikitip rozet gerinim olcerler (RGO) uygulanmistir. Yatay cekme presi ile celik cekme levhasina 30, 45 ve 60 kN’lukeksenel kuvvetler uygulanmis ve bu kuvvetlerin olusturdugu gerilmeler olculmustur. Ayrica, 60 kN’luk cekmekuvvetinin celik levhanin farkli kesitlerinde olusturdugu kalici gerilmeler belirlenmistir. Eksenel cekmegerilmelerinin belirlenmesinde, farkli RGO’lerden yaklasik ayni gerinimler elde edilmis ve teorik gerilmedegerlerine yakin sonuclar belirlenmistir. Kalici gerilme olcum sonuclarinda ise, standarda uygun RGO’lerteorik degere yakin gerilme degerleri vermistir. Ancak, standart disi RGO’lerden dusuk olcum hassasiyeti veyaklasik 36MPa daha dusuk gerilme de...

Afyon Kocatepe University Journal of Sciences and Engineering, 2021

Bu çalışmada, katı hal sinterleme ile üretilen AA6061 matrisli ve farklı B4C parçacık takviye ora... more Bu çalışmada, katı hal sinterleme ile üretilen AA6061 matrisli ve farklı B4C parçacık takviye oranlarındaki metal matrisli kompozit (MMKp) malzemelerin özelliklerine süper katı üzeri sıvı faz sinterleme (SKSFS) işlemlerinin etkisi araştırılmıştır. Ön alaşımlı AA6061 tozu ile ağırlıkça %0, %5, %10 ve %15 oranlarda B4C seramik parçacık takviye elamanı, Turbula da 45 dakika karıştırılmıştır. Karışım tozlar, 350 MPa basınçta soğuk preslenip devamında 400 o C sıcaklıkta 1 saat argon atmosferi ortamında yağlayıcı giderme işlemine tabi tutulmuştur. Ardından 560 o C sıcaklıkta 1 saat argon atmosferi altında katı hal sinterleme (KHS) işlemi uygulanarak MMKp malzemeler üretilmiştir. Devamında bu malzemelere, 610C ve 620C olmak üzere iki farklı sıcaklıkta 1 saat süre ile SKSFS işlemleri uygulanmıştır. SKSFS ile ikincil bir sinterleme işlemi uygulanan MMKp malzemelerin mikroyapıları ve fiziksel özellikleri; mevcut fazlar, sertlik ve yoğunluk ölçümleri çapraz kırılma dayanımları (ÇKD) ve tarama elektron mikroskop (SEM) incelemeleri ile karakterize edilmiştir. Artan SKSFS sıcaklığı ile birlikte, sinterleşme oranı da artmıştır. Bu durum, MMKp malzemelerin ÇKD ve süneklik değerlerini belirgin oranda arttırmıştır. Bununla birlikte; B4C takviye oranındaki artışla ÇKD değerlerinde ve sünekliklerde azalma, sertlikte ise artış gözlenmiştir. En yüksek çapraz kırılma dayanımı ve süneklik değeri, SKSFS uygulanan %5 B4C içeren MMKp malzemede belirlenmiştir. SKSFS işlemleri oluşan sıvı fazın B4C-matris arayüzey bağını artırıcı olumlu etkileri görülmüştür.

Journal of Polytechnic, 2019

Machinability is a feature of the material being processed and can only be changed by changing th... more Machinability is a feature of the material being processed and can only be changed by changing the properties of the material. This is achieved by changes in the chemical and physical properties of the material. The aim of this compilation study is to explain the machinability concept extensively and to discuss the works done to improve the machinability of the steels. When evaluating the machinability of steels, their mechanical properties and especially their hardness are taken into consideration. The machinability depending on the microstructures formed by heat treatments and the amount of carbon which is the main element that increases the hardness are evaluated. However, the addition of S, Pb, Bi and Te etc. elements increase the machinability without significant changes in the mechanical properties of steel. The machinability is graded by taking into consideration of the cutting force, tool life, surface quality and chip shape generated during the machining process. The effect of chemical composition and microstructure on machinability of steels is one of the most investigated subjects in the field of materials and metallurgical science. In addition to the variables in the production process of steel, microstructure-based machinability assessments generated by heat treatments are also important. The heterogeneous distribution of the phases in the microstructure provided by the mentioned processes should not be ignored in the machinability assessments.

$Research paper thumbnail of Mechanical and fracture behavior of B4C reinforced Al composites produced by hot pressing$

Materials Testing, 2016

In this study, the effects of particle addition on the microstructure, mechanical properties and ... more In this study, the effects of particle addition on the microstructure, mechanical properties and fracture behaviors of Al/B4C particle reinforced composite produced by hot pressing method were investigated. After the production of 5, 10 and 15 wt.-% of B4C reinforced composites, T6 heat treatment was applied. It was specified that a strong interface bond occurred between the matrix and particles, and during the fracturing of composites, this effect increased the particle fracture. It was observed that particles were fractured parallel to the fracture surface and to each other fracture surface of MMCp. In general, cavity of particle separated from the matrix was not seen. In the production of MMCp, it was also observed that hot pressing provided a density higher than 99 %. After the heat treatment the maximum hardness value of 173 HB was reached with 15 wt.-% B4C reinforced sample. The transverse rupture strength (TRS) decreased with the increase of reinforcement ratio. The highest T...

Practical Metallography, 2016

The microstructural changes, mechanical properties and residual stress distribution of 7075-T651 ... more The microstructural changes, mechanical properties and residual stress distribution of 7075-T651 Al alloy joined using friction stir welding were investigated in this study. Welding was performed at 900, 1 250, and 1 600 rev/min and 20, 40, and 60 mm/min welding speeds. Mechanical tests were carried out on the welded joints in addition to microstructural examinations performed using a scanning electron microscope. Furthermore, residual stress distribution of the joints was determined by the hole drilling method. Generally, higher tensile strength was obtained at medium rotational and welding speeds. Tunnel defects were formed in the root of the weld seam. At high welding speeds, insufficient filling in the joints led to microvoids and large grain bands on the retreating side of the weld seam. The tensile strength of the welded specimens decreased at the rate of 26 – 45 % compared to the reference material. Lower residual stresses were determined in the specimens joined at a high rot...

Materials Testing, 2015

Although the number of experimental studies investigating the effect of friction stir welding (FS... more Although the number of experimental studies investigating the effect of friction stir welding (FSW) parameters on joining properties have increased recently, there are not sufficient numbers of studies on the effect of the stirring tool material in friction stir welding. This study investigated the effect of stirring tool materials on microstructure, mechanical properties and residual stress of joints. Samples of 7075-T651 Al alloys were joined by FSW using uncoated and TiN-coated X210Cr12 alloy steel stirring tools. The welding processes were performed at rotational speeds of 900, 1250 and 1600 rpm and at a welding speed of 60 mm × min−1. Mechanical and metallographic tests were applied to the welded joints and residual stress analysis was performed using the hole drilling method. The best mechanical properties were determined in the welded samples joined by the uncoated tool at a rotational speed of 900 rpm. It was also determined that the TiN-coated tool negatively affected the m...

Journal of the Faculty of Engineering and Architecture of Gazi University

Bonfring International Journal of Industrial Engineering and Management Science, 2014

Fusion welding of copper and its alloys tends to degrade the mechanical strength at the weld join... more Fusion welding of copper and its alloys tends to degrade the mechanical strength at the weld joint area due to high thermal diffusivity and high melting point. Friction Stir Welding (FSW) is an excellent alternative for joining of these materials against fusion joining. FSW is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a nonconsumable tool to generate frictional heat in the abutting surfaces. The main objective of this investigation is to use FSW for joining of 3 mm thick copper sheet using taper cylindrical tool pin profile. The defect free welds were obtained at a tool rotational speed of 900 rpm and traverse speed of 25, 31.5 and 40 mm/min respectively. Mechanical and microstructure analysis has been performed to evaluate the characteristics of friction stir welded copper. From the investigation it is found that the joints fabricated at a traverse speed of 40mm/min resulted in better mechanical properties compared to other traverse speeds. The tensile properties of all weld joints showed a relative correspondence to the variation of the hardness in the weld zone. The observed results were correlated with the microstructure and fracture features.

Materials Testing, 2014

The effect of the weld joint configuration on components has been studied, which are under servic... more The effect of the weld joint configuration on components has been studied, which are under service loads, under repair or construction and the residual stresses as well as the mechanical properties of the joint have been determined. For this purpose, a horizontal positioned tensile testing device and a semi-automatic MIG welding machine have been used and then the weld joints of the plates were subjected to different elastic stresses. When the temperature of the joined elements decreased to room temperature, applied elastic stresses were released. By this means, the effects of the existing tensile stresses in the joined parts and the tensile stresses created by the welding processes were investigated. The tensile stresses occurring in the joined elements were determined by using the photo-elasticity analysis method and the hole-drilling method. Also, tensile-shear tests were applied in order to determine the effect of permanent tensile loads on the mechanical properties of the joint...

Journal of Materials Processing Technology, 2003

In this study, the effects of microstructure and mechanical properties on the machinability of ho... more In this study, the effects of microstructure and mechanical properties on the machinability of hot rolled SAE 1050 steel that was annealed and normalised before machining, have been investigated. The machinability has been characterised by measuring the tool life, chip root morphology, cutting forces, surface finish, and tool/chip interface temperature. Here, the optimum machinability, especially from the stand point of tool life, has been determined for hot rolled steel which had minimum impact energy and minimum ductility.By annealing this material, a coarse pearlitic microstructure and a microstructure having 10% spherical cementite was obtained with an increasing ferrite+pearlite banding. This led to an increase in ductility and impact energy, but the decrease in hardness shortened the tool life and worsened the machinability. With normalising heat treatment, on the other hand, the banding disappeared, hardness, ductility and impact energy increased; but the tool life shortened more and more. The maximum built-up edge (BUE) thickness occurred at lower cutting speeds in machining annealed specimens. The minimum surface roughness was observed on the hot rolled specimen at final cutting speeds. The heat treatment operations applied did not bring about a considerable difference in cutting forces. A significant correlation between the machinability and the hardness of specimens could not be determined.

Çukurova Üniversitesi Mühendislik-Mimarlık Fakültesi Dergisi, 2016

Bu çalışmada, kompleks kaynaklı birleştirmeli konstrüksiyonların imalat sürecinde ve sonrasında o... more Bu çalışmada, kompleks kaynaklı birleştirmeli konstrüksiyonların imalat sürecinde ve sonrasında oluşabilecek çarpılmaların belirlenmesi için yeni bir metot geliştirilmiş ve uygulanmıştır. Kaynaklı birleştirme sürecinde çarpılma kuvvetlerinin ölçülmesi esasına dayanan bu yöntemin uygulanması ile karmaşık kaynaklı yapıların kaynak sıralarının (KS) optimizasyonu yapılabilmektedir. Yöntemin esası, rijit bir kafes hücre içerisine yerleştirilmiş konstrüksiyon modeline uygulanan kaynak sıralarının meydana getirdiği çarpılma kuvvetlerinin ölçülmesine dayanır. Üç boyutlu ölçülen kuvvetlerin yönleri ve şiddetlerine bağlı olarak çarpılma eğilimleri belirlenebilir. Çeşitli KS uygulamalarından elde edilen kuvvetlerin sayısal değerleri kullanılarak yapılan analizlerle çarpılma formları oluşturulabilir. Kaynaklı konstrüksiyonlarda en uygun kaynak sıralarının belirlenmesi ve minimum çarpılma/kalıntı gerilme oluşturulması açısından uygun bir metot olarak değerlendirilmiştir.

Gazi Üniversitesi Fen Bilimleri Dergisi, 2018

In this study, 4.5 wt. %Cu powder was added to Al powder and mixed for 45 minutes to produce prem... more In this study, 4.5 wt. %Cu powder was added to Al powder and mixed for 45 minutes to produce premixed metal powders. Premixed powders were compacted by cold pressing at 20 MPa. After that these samples were pressed at 500℃ under 200 MPa for 30 minutes by hot pressed method. Hot pressed block samples were subjected to diffusion annealing at 540 ℃ for 2, 4, 8, 16, 32 hours. These samples, produced by powder metallurgy, are used at metallographic and microscopic researches to investigate the diffusion process. During the diffusion annealing, it was determined that significant amount of copper powder particles was dissolved in the Al matrix by diffusion. Diffusion annealing was followed by aging heat treatment, characterized by metallographic and mechanical tests. According to the increasing the annealing time, the homogeneity of the chemical composition is not provided, however the increasing of the heat treatment (T6) capability of the produced parts, and partial porosity which is bel...

Journal of Polytechnic

❖ Ön sıkıştırma basıncı ve çinko stearatın giderilmesi/ Pre-compression pressure and removel of z... more ❖ Ön sıkıştırma basıncı ve çinko stearatın giderilmesi/ Pre-compression pressure and removel of zinc stearate. ❖ T/M malzemenin sinterlenmesinde yağlayıcı etkisi/ The effect of lubricant on sintering of P/M material. ❖ Çinko stearat ve T/M malzeme mikroyapısı/ Zinc stearate and P/M material microstructure. ❖ Ön karışımlı Alumix 123 tozu ve Al-Cu alaşımlanması/ Pre-mixed Alumix 123 powder and Al-Cu alloying. ❖ Çinko stearat ve T/M malzeme özellikleri/ Zinc stearate and P/M material properties.

Talas kaldirma islemlerinde, harcanan enerjinin hemen hemen tamamina yakin kismi isiya donusur. B... more Talas kaldirma islemlerinde, harcanan enerjinin hemen hemen tamamina yakin kismi isiya donusur. Bu sebeple kesme bolgesinde olusan isi, talas kaldirma isleminde onemli bir faktor olup, takim omru ve is parcasinin yuzey kalitesi uzerinde bir etkisinin oldugu bilinmekte ve bu sicakligin olculebilmesi icin kullanilacak yontemler surekli olarak arastirilmaktadir. Bu calismada, takim/is parcasi isil cift yontemi ile takim-talas ara yuzey sicakligi uzerinde kaplama malzemesinin etkisi arastirilmistir. Ozellikleri iyi bilinen AISI 1040 celigi uzerinde yapilan talas kaldirma deneylerinde, takim kaplama malzemelerinin, kesme hizi ve ilerleme parametrelerine bagli olarak takim-talas ara yuzey sicakliginin degisimi uzerindeki etkileri incelenmistir. Elde edilen grafiklerden, kesme hizinin sicaklik uzerinde daha etkili bir parametre oldugu gorulurken, ilerlemenin etkisinin daha az oldugu gorulmustur. Al2O3 kaplanmis ve en ustte TiN kaplama ihtiva eden uc katli kaplamali takimlarla yapilan deney...

Gazi Üniversitesi Fen Bilimleri Dergisi Part C: Tasarım ve Teknoloji

Bu deneysel calismada, sicak presleme aktif sinterleme yontemi ile uretilen Al6061 matrisli B4C p... more Bu deneysel calismada, sicak presleme aktif sinterleme yontemi ile uretilen Al6061 matrisli B4C parcacik takviyeli Metal Matrisli Kompozit (MMKp) malzemelerin ozelliklerine takviye orani ve sivi faz sinterlemenin etkisi arastirilmistir. Agirlikca %0, %5, %10 ve %15 oranlarinda B4C seramik parcacik takviye elemanlari ile on alasimli Al6061 metal tozu turbula cihazinda 45 dakika sure ile karistirilmistir. Karisim tozlar, 40x60mm2 boyutlarindaki kalip icerisinde oda sicakliginda 200 MPa on presleme basincinda sikistirilmistir. Devaminda ayni kalip blogu icerisinde argon atmosferi altinda 400oC sicaklikta 45 dakika boyunca yaglayici giderme islemi uygulanmistir. Ardindan, 550oC sicaklikta 100 MPa basinc altinda 1 saat boyunca argon atmosferi altinda sicak presleme (SP) aktif sinterleme islemi uygulanarak MMKP malzemeler uretilmistir. Bu numunelere 610oC sicaklikta 1 saat sureyle super kati uzeri sivi faz sinterleme (SKSS) isleminin uygulanmasiyla ikincil sinterleme islemi gerceklestirilmistir. Uretilen kompozit malzemelerin mikroyapilari ve fiziksel ozellikleri; metalografik muayene, sertlik ve yogunluk olcumleri, capraz kirilma dayanimlari (CKD) ve kirik yuzey analizi taramali elektron mikroskobu (SEM) ile karakterize edilmistir. SKSS islemi sonunda numuneler suda hizli (S) ve firinda yavas (F) sogutularak, soguma hizinin etkisi de incelenmeye calisilmistir. SKSS islemi, SP ile uretilen MMKp malzemelerin yogunlugunu kismen dusurmustur. Bu etki ozellikle firin ortaminda yavas sogutmaya birakilan numunelerde daha fazladir. Bununla birlikte suda hizli sogutulan numunelerin sertlik ve CKD degerlerinde onemli miktarda artis meydana gelmistir.