M. Öveçoğlu - Academia.edu (original) (raw)

Papers by M. Öveçoğlu

Ceramics International, 2018

This study reports on the preparation of diiron boride (Fe 2 B) powders via mechanochemical synth... more This study reports on the preparation of diiron boride (Fe 2 B) powders via mechanochemical synthesis (MCS) followed by a purification step and on the embedment of pure Fe 2 B nanoparticles into silica (SiO 2) nanospheres. Fe 2 O 3 , B 2 O 3 and Mg powders used as starting materials were blended in stoichiometric amounts and mechanochemically synthesized up to 7 h in a high-energy ball mill. As-synthesized powders were purified from the undesired Mg-based by-products by HCl leaching. After that, pure Fe 2 B nanoparticles with sizes of smaller than 40 nm were embedded in SiO 2 nanospheres using a tetraethyl orthosilicate (TEOS) and ammonia (NH 3) containing solution. Characterization investigations of the as-synthesized, leached and SiO 2-embedded powders were carried out using X-ray diffractometer (XRD), scanning electron microscope/energy dispersive spectrometer (SEM/EDS), particle size analyzer (PSA), transmission electron microscope (TEM), Fourier transform infrared spectrometer (FTIR) and vibrating sample magnetometer (VSM). The average particle size of the Fe 2 B incorporated SiO 2 nanospheres was measured as about 330 nm. Magnetic measurements revealed that pure Fe 2 B powders and their SiO 2-embedded samples had soft ferromagnetic behaviour with coercivity of 125 and 168 Oe, respectively.

Ceramics International, 2016

Samarium borate (SmBO 3) powders were fabricated from oxide raw materials by a two-step solid-sta... more Samarium borate (SmBO 3) powders were fabricated from oxide raw materials by a two-step solid-state synthesis method including mechanical activation and annealing. Blends containing stoichiometric amounts of samarium oxide (Sm 2 O 3) and boron oxide (B 2 O 3) were mechanically activated in a highenergy ball mill and subsequently annealed in air. Afterwards, mechanically activated and annealed powders were washed with distilled water in order to remove probable unreacted B 2 O 3 phase. The effects of mechanical activation duration (15 min, 1 h, 3 h and 9 h) and annealing temperature (700-1250°C) on the resultant powders were investigated. Compositional, microstructural, physical, thermal and optical properties of the powders obtained throughout the different process steps were characterized by using an X-ray diffractometry (XRD), particle size analysis (PSA), stereomicroscopy (SM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), gas pycnometry, differential scanning calorimetry (DSC), heating stage microscopy (HSM), atomic absorption spectrometry (AAS), Fourier transform infrared (FTIR) spectrometry and ultraviolet-visible spectrophotometry (UV-vis) techniques. Fine-grained and pure SmBO 3 powders were successfully synthesized via a simple, feasible and scalable route, yielding both triclinic and hexagonal crystal structures. Triclinic SmBO 3 powders were synthesized after mechanical activation for 1 h and annealing at 700°C for 2 h. The polymorphic transformation temperature of SmBO 3 powders from triclinic to hexagonal is about 1080°C. Due to the effect of mechanical activation, the synthesis of triclinic SmBO 3 phase and its transformation to hexagonal form were found to take place at ∼50-100°C lower temperatures than those reported in other methods. Mainly hexagonal SmBO 3 powders were obtained after annealing at 1150°C in the presence of a very small amount of triclinic SmBO 3. The resultant powders showed intense UV absorptions in the range between 1025 and 1150 nm with minimum reflectivity of 0.57% (triclinic SmBO 3 phase) and 0.68% (hexagonal SmBO 3 phase) depending on their crystal structures.

Key Engineering Materials, 2004

... The porcelain discs were then embedded in chemical-cured acrylic resin cylinders (MeliodentTM... more ... The porcelain discs were then embedded in chemical-cured acrylic resin cylinders (MeliodentTM,Bayer) with the dimensions of 35 mm in diameter x 23 mm in height. ... We also thank Ms. NurtenDinçer for her help during SEM characterizations of this investigation. References ...

Key Engineering Materials, 2004

Although porcelain is the most esthetic restorative material available, it is subject to fracture... more Although porcelain is the most esthetic restorative material available, it is subject to fracture during function. Glazing reduces the size of flaws in the surface of the porcelain and increases its resistance to crack propagation. The purpose of this study is to compare several polishing systems and the effects on the flexural strength of the ceramic material. 28 specimens were prepared from a feldsphatic body porcelain (Finesse-Dentsply Inc.) fabricated by sintering. These specimens were randomly divided into four groups. Whereas the specimens in the first group were glazed, those in the second were autoglazed and those in third and fourth groups were mechanically polished using different diamond polishing pastes. Surface roughness and 4-point bending tests were conducted on these specimens to determine the effects of using different polishing systems on dental ceramic surfaces. The glazed group displayed the highest flexural strength values and there were no statistically significant differences in the strength and the surface roughness values of the other three groups.

Materials Science and Engineering: A, 2010

A metal-matrix composite composed of Al-4 wt.% Cu and 10 wt.% of particulates of ZrC with average... more A metal-matrix composite composed of Al-4 wt.% Cu and 10 wt.% of particulates of ZrC with average initial particle sizes of 8 and 157 m were mechanically alloyed (MA'ed) for 90, 120, 150, 180 and 210 min. Steady-state conditions were obtained after 180 min of MA'ed time. These powders were consolidated by vacuum hot pressing under 70 MPa at 550 • C for 1 h. A rod-shaped Al 7 Cu 2 Fe intermetallic phase was observed in the sintered samples due to the reaction of Al-Cu matrix with Fe from balls and/or vials during MA process. The particle size of the ZrC particles in the consolidated samples were 0.3-1.5 m and 1.5-6 m for the MMC with initial 8 and 157 m ZrC powders, respectively. Composite samples comprising the smaller ZrC particles exhibited higher hardness and lower wear resistance compared to those reinforced with coarser ZrC particles. The larger reinforcement particles (1.5-6 m) remained intact on the worn surface and continuously protected the composite against the steel ball counterface.

Proceedings of the 2nd World Congress on Mechanical, Chemical, and Material Engineering, 2016

Vanadium boride (VB)particulate reinforced Al-7 wt.% Si based metal matrix composites (MMC) were ... more Vanadium boride (VB)particulate reinforced Al-7 wt.% Si based metal matrix composites (MMC) were synthesized using mechanical alloying (MA) and pressureless sintering. (Al-7 wt. % Si)-2 wt.% VB blends were mechanically alloyed for 4h in a high energy ball mill. Particle size measurement, Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM) investigation and thermal analysis were conducted to characterize the mechanically alloyed powders. As-blended and mechanically alloyed powders were compacted in anuniaxial hydraulicpress with a pressure of 450 MPa and green compacts were sintered at 570⁰C under Ar gas flowing conditions. Microstructural and phase characterizations of the sintered samples were carried out using optical microscope (OM), SEM and X-ray diffractometer (XRD). Physical and mechanical properties of the sintered composites were investigated in terms of density measurements, microhardness measurements and wear rate. MA enhances the physical and mechanical properties of the composites. (Al-7 wt.% Si)-2wt.% VB MA'd for 4 h had relative density value of 95.55%, microhardness value of 1.04±0.11 GPa and wear rate of 1.42x10-5 mm 3 /mm.

Ceramics International, 2017

Abstract This study reports the effect of milling type on the microstructural, physical and mecha... more Abstract This study reports the effect of milling type on the microstructural, physical and mechanical properties of the W-Ni-ZrC-Y 2 O 3 composites. Powder blends having the composition of W-1 wt% Ni-2 wt% ZrC-1 wt% Y 2 O 3 were milled at room temperature for 12 h using a Spex™ 8000D Mixer/Mill or cryomilled in the presence of externally circulated liquid nitrogen for 10 min using a Spex™ 6870 Freezer/Mill or sequentially milled at room temperature and cryogenic condition. Then, powders were compacted in a hydraulic press under a uniaxial pressure of 400 MPa and green bodies were sintered at 1400 °C for 1 h under Ar/H 2 atmosphere. Phase and microstructural characterization of the milled powders and sintered samples were performed using X-ray diffractometer (XRD), TOPAS software, scanning electron microscope/energy dispersive spectrometer (SEM/EDS), X-ray fluorescence (XRF) spectrometer and particle size analyzer (PSA). Archimedes density and Vickers microhardness measurements, and sliding wear tests were also conducted on the sintered samples. The results showed that sequential milling enables the lowest average particle size (214.90 nm) and it is effective in inhibiting W grain coarsening during sintering. The cryomilled and sintered composite yielded a lower hardness value (5.80±0.23 GPa) and higher wear volume loss value (149.42 µm 3 ) than that of the sintered sample after room temperature milling (6.66±0.39 GPa; 102.50 µm 3 ). However, the sequentially milled and sintered sample had the highest relative density and microhardness values of 95.09% and 7.16±0.59 GPa and the lowest wear volume loss value of 66.0 µm 3 .

Proceedings of the 2nd World Congress on Mechanical, Chemical, and Material Engineering, 2016

This study reports the effect of NbB2 particles on the Al-12.6 wt.% Si matrix powders and composi... more This study reports the effect of NbB2 particles on the Al-12.6 wt.% Si matrix powders and composites in regard of physical, microstructural and mechanical properties. In order to obtain hybrid powders, Al-12.6 wt.% Si-2 wt.% NbB2 blends were mechanically alloyed (MA'd) for various durations (1, 4 and 8 h) in a Spex™ Mixer/Mill using hardened steel vial/balls with a 7/1 ball-to-powder weight ratio. A hydraulic press with a uniaxial pressure of 450 MPa was used for the compaction of the as-blended/MA'd powders. Green compacts were sintered at 570°C for 2 h under Ar gas atmosphere. X-ray diffractometry (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) techniques were utilized for the microstructural characterization of the as-blended/MA'd powders and the sintered composites. Differential scanning calorimetry (DSC) analyses were also conducted on the powder products. Sintered samples were characterized by density and Vickers microhardness measurements and sliding wear tests. With increasing MA time, mechanical improvement in composite properties was observed. Reinforcing particles had positive effect on the mechanical properties of the matrix: Al-12.6 wt.% Si-2 wt.% NbB2 MA'd for 4 h showed higher microhardness value (158.50±10.02 MPa) and lower wear volume loss (0.161 mm 3) than those of Al-12.6 wt.% Si matrix MA'd for 4 h. Al-12.6 wt.% Si matrix MA'd for 4 h showed microhardness value (146.70±8.81 MPa) and wear volume loss (0.194 mm 3).

Ceramics International, 2016

Transactions of Nonferrous Metals Society of China, 2016

Niobium boride powders having NbB, NbB2 and Nb3B4 phases in various amounts and single phase NbB ... more Niobium boride powders having NbB, NbB2 and Nb3B4 phases in various amounts and single phase NbB powders were successfully synthesized by using powder metallurgy methods from related metal oxide raw materials in the presence of a strong reducing agent. Nb2O5, B2O3 and Mg powder blends were milled at room temperature by a high-energy ball mill for different time. Subsequently, undesired MgO phase was removed from the milled powders by HCl leaching to constitute NbB–NbB2–Nb3B4 as final products and they were subjected to an annealing process at 1500 °C for 4 h to observe probable boride transformation. Characterization was carried out by XRD, DSC, PSA, SEM/EDX, TEM and VSM. The effects of milling time (up to 9 h) on the formation, microstructure and thermal behavior of the final products were investigated. Reduction reaction took place after milling stoichiometric powder blends for 2 h. Nano-sized NbB–NbB2–Nb3B4 powders in high purity were obtained in the absence of any secondary phase and any impurity via mechanochemistry by milling for 5 h and leaching with 4 mol/L HCl. After annealing, pure and nano-sized NbB–NbB2–Nb3B4 powders transformed to a single NbB phase without leaving behind NbB2 and Nb3B4 phases.

Key Engineering Materials, 2004

Abstract. Microstructures of cordierite ceramics produced from natural raw materials and syntheti... more Abstract. Microstructures of cordierite ceramics produced from natural raw materials and synthetic powders were examined. Two batches to constitute the cordierite composition (2Al2O3. 2MgO. 5SiO2) were prepared from raw materials (kaolinite, sinter magnesite, talc ...

Key Engineering Materials, 2004

The retail scenario is one of the fastest growing industries in India over the last couple of yea... more The retail scenario is one of the fastest growing industries in India over the last couple of years. India retail sector comprises of organized retail and unorganized retail sector. Traditionally the retail market in India was largely unorganized; however with changing consumer preferences, organized retail is gradually becoming popular. Unorganized retailing consists of small and medium grocery store, medicine stores, subzi mandi etc. More than 90% of retailing in India fall into the unorganized sector, the organized sector is largely concentrated in big cities. Organized retail in India is expected to grow 25-30 per cent yearly and is expected to increase from Rs35, 000 crore in 2004-05 to Rs109, 000 crore ($24 billion) by 2010.

Key Engineering Materials, 2004

Crystallization behaviors of 0.7TeO 2-0.3GeO 2 and 0.9TeO 2-0.1GeO 2 glasses were studied using D... more Crystallization behaviors of 0.7TeO 2-0.3GeO 2 and 0.9TeO 2-0.1GeO 2 glasses were studied using DTA, XRD and SEM. Thermal measurements showed that the effect of different GeO 2-contents in these glass system resulted in different crystallizing phases. On the basis of DTA, crystallization experiments of two glass samples were carried out at different temperatures for 10 min. The crystallized phases were identified by X-ray diffraction analysis. In both glasses, crystalline phases formed as a result of bulk crystallization.

Key Engineering Materials, 2004

ABSTRACT Zinc-tellurite glasses, comprising 80 mol% TeO2 - 20 mol% ZnO (hereafter referred to as ... more ABSTRACT Zinc-tellurite glasses, comprising 80 mol% TeO2 - 20 mol% ZnO (hereafter referred to as 0.8TeO2 - 0.2ZnO) and 60 mol% TeO 2 - 40 mol% ZnO (hereafter referred to as 0.6TeO2 - 0.4ZnO), were crystallized at different temperatures on the basis of DTA analyses. Using XRD, SEM and EDS analyses, the crystallizing phases, with their shapes and sizes, were determined in these glass compositions. Thus, different effects of ZnO content on crystallization of binary zinc-tellurite glasses were studied. It was found that crystallizing phases were different for two different samples. In the 80TeO2 - 20ZnO glasses, αx-TeO2 (paratellurite) crystallizes first at around 428°C, and Zn 2Te3O8 phase crystallizes at around 458°C. On the other hand, in the 60TeO2 - 40ZnO glass, only the Zn 2Te3O8 phase crystallizes. Since this crystallization takes place at around 432°C, it can be concluded that increasing the ZnO content in zinc-tellurite glasses slightly increases the crystallization temperature.

Key Engineering Materials, 2004

ABSTRACT

Key Engineering Materials, 2004

ABSTRACT

physica status solidi (c), 2011

... germanate glasses Mithat Cem Elbizim*, Demet Tatar, Deniz Yılmaz, and M. Lütfi Öveçoğlu Parti... more ... germanate glasses Mithat Cem Elbizim*, Demet Tatar, Deniz Yılmaz, and M. Lütfi Öveçoğlu Particulate Materials Laboratories, Department of Metallurgical and Materials Engineering, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey ...

Journal of Materials Research, 1996

Blended elemental W–7 wt.%Ni–3 wt. %Fe powders were mechanically alloyed in a planetary ball mill... more Blended elemental W–7 wt.%Ni–3 wt. %Fe powders were mechanically alloyed in a planetary ball mill and a heavy duty attritor. The structural and morphological characteristics of the as-milled powders were characterized by x-ray diffraction and electron microscopy techniques. A ternary solid solution of Fe and Ni in W formed in both the cases; the amount of Ni and Fe dissolved is higher in the attritor-milled powder than in the ball-milled powder. Morphologically, the W-rich particles in the attritor-milled powders were spheroidal, smaller in size, and showed a narrower size distribution than in the ball-milled condition. These differences led to increased density in the attritor-milled powder compact and significant differences in chemical composition of the matrix region and W-rich grains. Transmission electron microscopy investigations of the matrix region in the compacts revealed the presence of Fe2W precipitates uniformly distributed in an Ni(Fe, W) matrix.

IOP Conference Series: Materials Science and Engineering, 2010

... Tech. 184 219 [9] Abbas M, Qazi IA, Samina A, Masaood M, Majeed A, Haq A 1995 J. Vac. Sci. Te... more ... Tech. 184 219 [9] Abbas M, Qazi IA, Samina A, Masaood M, Majeed A, Haq A 1995 J. Vac. Sci. Technol. A 13 151 [10] Tahar RBH, Ban T, Ohya Y, Takahashi Y 1997 J. Appl. Phys. 82 865 [11] Adurodija FO, Izumi H, Ishihara T, Yoshioka H, Matsui H, Motoyama M 1999 Appl. ...

International Journal of Refractory Metals and Hard Materials, 2011

In this study, the effect of Y 2 O 3 additions on the microstructural and the physical properties... more In this study, the effect of Y 2 O 3 additions on the microstructural and the physical properties of W-SiC composites was investigated. Powder blends of W-4 wt.% SiC, W-4 wt.% SiC-1 wt.% Y 2 O 3 and W-4 wt.% SiC-5 wt.% Y 2 O 3 were mechanically alloyed (MA'd) using a Spex mill for 24 h. MA'd composite powders were sintered under inert Ar and reducing H 2 gas conditions at 1680°C for 1 h. Microstructural and morphological characterizations of composite powders and sintered samples were carried out via SEM and XRD analyses. Furthermore, density measurements and hardness measurements of sintered samples were carried out. A highest Vickers microhardness value of 11.4 GPa was measured for the sintered W-4 wt.% SiC-5 wt.% Y 2 O 3 while W-4 wt.% SiC sample possessed the highest relative density value of 97.7%.

Ceramics International, 2018

This study reports on the preparation of diiron boride (Fe 2 B) powders via mechanochemical synth... more This study reports on the preparation of diiron boride (Fe 2 B) powders via mechanochemical synthesis (MCS) followed by a purification step and on the embedment of pure Fe 2 B nanoparticles into silica (SiO 2) nanospheres. Fe 2 O 3 , B 2 O 3 and Mg powders used as starting materials were blended in stoichiometric amounts and mechanochemically synthesized up to 7 h in a high-energy ball mill. As-synthesized powders were purified from the undesired Mg-based by-products by HCl leaching. After that, pure Fe 2 B nanoparticles with sizes of smaller than 40 nm were embedded in SiO 2 nanospheres using a tetraethyl orthosilicate (TEOS) and ammonia (NH 3) containing solution. Characterization investigations of the as-synthesized, leached and SiO 2-embedded powders were carried out using X-ray diffractometer (XRD), scanning electron microscope/energy dispersive spectrometer (SEM/EDS), particle size analyzer (PSA), transmission electron microscope (TEM), Fourier transform infrared spectrometer (FTIR) and vibrating sample magnetometer (VSM). The average particle size of the Fe 2 B incorporated SiO 2 nanospheres was measured as about 330 nm. Magnetic measurements revealed that pure Fe 2 B powders and their SiO 2-embedded samples had soft ferromagnetic behaviour with coercivity of 125 and 168 Oe, respectively.

Ceramics International, 2016

Samarium borate (SmBO 3) powders were fabricated from oxide raw materials by a two-step solid-sta... more Samarium borate (SmBO 3) powders were fabricated from oxide raw materials by a two-step solid-state synthesis method including mechanical activation and annealing. Blends containing stoichiometric amounts of samarium oxide (Sm 2 O 3) and boron oxide (B 2 O 3) were mechanically activated in a highenergy ball mill and subsequently annealed in air. Afterwards, mechanically activated and annealed powders were washed with distilled water in order to remove probable unreacted B 2 O 3 phase. The effects of mechanical activation duration (15 min, 1 h, 3 h and 9 h) and annealing temperature (700-1250°C) on the resultant powders were investigated. Compositional, microstructural, physical, thermal and optical properties of the powders obtained throughout the different process steps were characterized by using an X-ray diffractometry (XRD), particle size analysis (PSA), stereomicroscopy (SM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), gas pycnometry, differential scanning calorimetry (DSC), heating stage microscopy (HSM), atomic absorption spectrometry (AAS), Fourier transform infrared (FTIR) spectrometry and ultraviolet-visible spectrophotometry (UV-vis) techniques. Fine-grained and pure SmBO 3 powders were successfully synthesized via a simple, feasible and scalable route, yielding both triclinic and hexagonal crystal structures. Triclinic SmBO 3 powders were synthesized after mechanical activation for 1 h and annealing at 700°C for 2 h. The polymorphic transformation temperature of SmBO 3 powders from triclinic to hexagonal is about 1080°C. Due to the effect of mechanical activation, the synthesis of triclinic SmBO 3 phase and its transformation to hexagonal form were found to take place at ∼50-100°C lower temperatures than those reported in other methods. Mainly hexagonal SmBO 3 powders were obtained after annealing at 1150°C in the presence of a very small amount of triclinic SmBO 3. The resultant powders showed intense UV absorptions in the range between 1025 and 1150 nm with minimum reflectivity of 0.57% (triclinic SmBO 3 phase) and 0.68% (hexagonal SmBO 3 phase) depending on their crystal structures.

Key Engineering Materials, 2004

... The porcelain discs were then embedded in chemical-cured acrylic resin cylinders (MeliodentTM... more ... The porcelain discs were then embedded in chemical-cured acrylic resin cylinders (MeliodentTM,Bayer) with the dimensions of 35 mm in diameter x 23 mm in height. ... We also thank Ms. NurtenDinçer for her help during SEM characterizations of this investigation. References ...

Key Engineering Materials, 2004

Although porcelain is the most esthetic restorative material available, it is subject to fracture... more Although porcelain is the most esthetic restorative material available, it is subject to fracture during function. Glazing reduces the size of flaws in the surface of the porcelain and increases its resistance to crack propagation. The purpose of this study is to compare several polishing systems and the effects on the flexural strength of the ceramic material. 28 specimens were prepared from a feldsphatic body porcelain (Finesse-Dentsply Inc.) fabricated by sintering. These specimens were randomly divided into four groups. Whereas the specimens in the first group were glazed, those in the second were autoglazed and those in third and fourth groups were mechanically polished using different diamond polishing pastes. Surface roughness and 4-point bending tests were conducted on these specimens to determine the effects of using different polishing systems on dental ceramic surfaces. The glazed group displayed the highest flexural strength values and there were no statistically significant differences in the strength and the surface roughness values of the other three groups.

Materials Science and Engineering: A, 2010

A metal-matrix composite composed of Al-4 wt.% Cu and 10 wt.% of particulates of ZrC with average... more A metal-matrix composite composed of Al-4 wt.% Cu and 10 wt.% of particulates of ZrC with average initial particle sizes of 8 and 157 m were mechanically alloyed (MA'ed) for 90, 120, 150, 180 and 210 min. Steady-state conditions were obtained after 180 min of MA'ed time. These powders were consolidated by vacuum hot pressing under 70 MPa at 550 • C for 1 h. A rod-shaped Al 7 Cu 2 Fe intermetallic phase was observed in the sintered samples due to the reaction of Al-Cu matrix with Fe from balls and/or vials during MA process. The particle size of the ZrC particles in the consolidated samples were 0.3-1.5 m and 1.5-6 m for the MMC with initial 8 and 157 m ZrC powders, respectively. Composite samples comprising the smaller ZrC particles exhibited higher hardness and lower wear resistance compared to those reinforced with coarser ZrC particles. The larger reinforcement particles (1.5-6 m) remained intact on the worn surface and continuously protected the composite against the steel ball counterface.

Proceedings of the 2nd World Congress on Mechanical, Chemical, and Material Engineering, 2016

Vanadium boride (VB)particulate reinforced Al-7 wt.% Si based metal matrix composites (MMC) were ... more Vanadium boride (VB)particulate reinforced Al-7 wt.% Si based metal matrix composites (MMC) were synthesized using mechanical alloying (MA) and pressureless sintering. (Al-7 wt. % Si)-2 wt.% VB blends were mechanically alloyed for 4h in a high energy ball mill. Particle size measurement, Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM) investigation and thermal analysis were conducted to characterize the mechanically alloyed powders. As-blended and mechanically alloyed powders were compacted in anuniaxial hydraulicpress with a pressure of 450 MPa and green compacts were sintered at 570⁰C under Ar gas flowing conditions. Microstructural and phase characterizations of the sintered samples were carried out using optical microscope (OM), SEM and X-ray diffractometer (XRD). Physical and mechanical properties of the sintered composites were investigated in terms of density measurements, microhardness measurements and wear rate. MA enhances the physical and mechanical properties of the composites. (Al-7 wt.% Si)-2wt.% VB MA'd for 4 h had relative density value of 95.55%, microhardness value of 1.04±0.11 GPa and wear rate of 1.42x10-5 mm 3 /mm.

Ceramics International, 2017

Abstract This study reports the effect of milling type on the microstructural, physical and mecha... more Abstract This study reports the effect of milling type on the microstructural, physical and mechanical properties of the W-Ni-ZrC-Y 2 O 3 composites. Powder blends having the composition of W-1 wt% Ni-2 wt% ZrC-1 wt% Y 2 O 3 were milled at room temperature for 12 h using a Spex™ 8000D Mixer/Mill or cryomilled in the presence of externally circulated liquid nitrogen for 10 min using a Spex™ 6870 Freezer/Mill or sequentially milled at room temperature and cryogenic condition. Then, powders were compacted in a hydraulic press under a uniaxial pressure of 400 MPa and green bodies were sintered at 1400 °C for 1 h under Ar/H 2 atmosphere. Phase and microstructural characterization of the milled powders and sintered samples were performed using X-ray diffractometer (XRD), TOPAS software, scanning electron microscope/energy dispersive spectrometer (SEM/EDS), X-ray fluorescence (XRF) spectrometer and particle size analyzer (PSA). Archimedes density and Vickers microhardness measurements, and sliding wear tests were also conducted on the sintered samples. The results showed that sequential milling enables the lowest average particle size (214.90 nm) and it is effective in inhibiting W grain coarsening during sintering. The cryomilled and sintered composite yielded a lower hardness value (5.80±0.23 GPa) and higher wear volume loss value (149.42 µm 3 ) than that of the sintered sample after room temperature milling (6.66±0.39 GPa; 102.50 µm 3 ). However, the sequentially milled and sintered sample had the highest relative density and microhardness values of 95.09% and 7.16±0.59 GPa and the lowest wear volume loss value of 66.0 µm 3 .

Proceedings of the 2nd World Congress on Mechanical, Chemical, and Material Engineering, 2016

This study reports the effect of NbB2 particles on the Al-12.6 wt.% Si matrix powders and composi... more This study reports the effect of NbB2 particles on the Al-12.6 wt.% Si matrix powders and composites in regard of physical, microstructural and mechanical properties. In order to obtain hybrid powders, Al-12.6 wt.% Si-2 wt.% NbB2 blends were mechanically alloyed (MA'd) for various durations (1, 4 and 8 h) in a Spex™ Mixer/Mill using hardened steel vial/balls with a 7/1 ball-to-powder weight ratio. A hydraulic press with a uniaxial pressure of 450 MPa was used for the compaction of the as-blended/MA'd powders. Green compacts were sintered at 570°C for 2 h under Ar gas atmosphere. X-ray diffractometry (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) techniques were utilized for the microstructural characterization of the as-blended/MA'd powders and the sintered composites. Differential scanning calorimetry (DSC) analyses were also conducted on the powder products. Sintered samples were characterized by density and Vickers microhardness measurements and sliding wear tests. With increasing MA time, mechanical improvement in composite properties was observed. Reinforcing particles had positive effect on the mechanical properties of the matrix: Al-12.6 wt.% Si-2 wt.% NbB2 MA'd for 4 h showed higher microhardness value (158.50±10.02 MPa) and lower wear volume loss (0.161 mm 3) than those of Al-12.6 wt.% Si matrix MA'd for 4 h. Al-12.6 wt.% Si matrix MA'd for 4 h showed microhardness value (146.70±8.81 MPa) and wear volume loss (0.194 mm 3).

Ceramics International, 2016

Transactions of Nonferrous Metals Society of China, 2016

Niobium boride powders having NbB, NbB2 and Nb3B4 phases in various amounts and single phase NbB ... more Niobium boride powders having NbB, NbB2 and Nb3B4 phases in various amounts and single phase NbB powders were successfully synthesized by using powder metallurgy methods from related metal oxide raw materials in the presence of a strong reducing agent. Nb2O5, B2O3 and Mg powder blends were milled at room temperature by a high-energy ball mill for different time. Subsequently, undesired MgO phase was removed from the milled powders by HCl leaching to constitute NbB–NbB2–Nb3B4 as final products and they were subjected to an annealing process at 1500 °C for 4 h to observe probable boride transformation. Characterization was carried out by XRD, DSC, PSA, SEM/EDX, TEM and VSM. The effects of milling time (up to 9 h) on the formation, microstructure and thermal behavior of the final products were investigated. Reduction reaction took place after milling stoichiometric powder blends for 2 h. Nano-sized NbB–NbB2–Nb3B4 powders in high purity were obtained in the absence of any secondary phase and any impurity via mechanochemistry by milling for 5 h and leaching with 4 mol/L HCl. After annealing, pure and nano-sized NbB–NbB2–Nb3B4 powders transformed to a single NbB phase without leaving behind NbB2 and Nb3B4 phases.

Key Engineering Materials, 2004

Abstract. Microstructures of cordierite ceramics produced from natural raw materials and syntheti... more Abstract. Microstructures of cordierite ceramics produced from natural raw materials and synthetic powders were examined. Two batches to constitute the cordierite composition (2Al2O3. 2MgO. 5SiO2) were prepared from raw materials (kaolinite, sinter magnesite, talc ...

Key Engineering Materials, 2004

The retail scenario is one of the fastest growing industries in India over the last couple of yea... more The retail scenario is one of the fastest growing industries in India over the last couple of years. India retail sector comprises of organized retail and unorganized retail sector. Traditionally the retail market in India was largely unorganized; however with changing consumer preferences, organized retail is gradually becoming popular. Unorganized retailing consists of small and medium grocery store, medicine stores, subzi mandi etc. More than 90% of retailing in India fall into the unorganized sector, the organized sector is largely concentrated in big cities. Organized retail in India is expected to grow 25-30 per cent yearly and is expected to increase from Rs35, 000 crore in 2004-05 to Rs109, 000 crore ($24 billion) by 2010.

Key Engineering Materials, 2004

Crystallization behaviors of 0.7TeO 2-0.3GeO 2 and 0.9TeO 2-0.1GeO 2 glasses were studied using D... more Crystallization behaviors of 0.7TeO 2-0.3GeO 2 and 0.9TeO 2-0.1GeO 2 glasses were studied using DTA, XRD and SEM. Thermal measurements showed that the effect of different GeO 2-contents in these glass system resulted in different crystallizing phases. On the basis of DTA, crystallization experiments of two glass samples were carried out at different temperatures for 10 min. The crystallized phases were identified by X-ray diffraction analysis. In both glasses, crystalline phases formed as a result of bulk crystallization.

Key Engineering Materials, 2004

ABSTRACT Zinc-tellurite glasses, comprising 80 mol% TeO2 - 20 mol% ZnO (hereafter referred to as ... more ABSTRACT Zinc-tellurite glasses, comprising 80 mol% TeO2 - 20 mol% ZnO (hereafter referred to as 0.8TeO2 - 0.2ZnO) and 60 mol% TeO 2 - 40 mol% ZnO (hereafter referred to as 0.6TeO2 - 0.4ZnO), were crystallized at different temperatures on the basis of DTA analyses. Using XRD, SEM and EDS analyses, the crystallizing phases, with their shapes and sizes, were determined in these glass compositions. Thus, different effects of ZnO content on crystallization of binary zinc-tellurite glasses were studied. It was found that crystallizing phases were different for two different samples. In the 80TeO2 - 20ZnO glasses, αx-TeO2 (paratellurite) crystallizes first at around 428°C, and Zn 2Te3O8 phase crystallizes at around 458°C. On the other hand, in the 60TeO2 - 40ZnO glass, only the Zn 2Te3O8 phase crystallizes. Since this crystallization takes place at around 432°C, it can be concluded that increasing the ZnO content in zinc-tellurite glasses slightly increases the crystallization temperature.

Key Engineering Materials, 2004

ABSTRACT

Key Engineering Materials, 2004

ABSTRACT

physica status solidi (c), 2011

... germanate glasses Mithat Cem Elbizim*, Demet Tatar, Deniz Yılmaz, and M. Lütfi Öveçoğlu Parti... more ... germanate glasses Mithat Cem Elbizim*, Demet Tatar, Deniz Yılmaz, and M. Lütfi Öveçoğlu Particulate Materials Laboratories, Department of Metallurgical and Materials Engineering, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey ...

Journal of Materials Research, 1996

Blended elemental W–7 wt.%Ni–3 wt. %Fe powders were mechanically alloyed in a planetary ball mill... more Blended elemental W–7 wt.%Ni–3 wt. %Fe powders were mechanically alloyed in a planetary ball mill and a heavy duty attritor. The structural and morphological characteristics of the as-milled powders were characterized by x-ray diffraction and electron microscopy techniques. A ternary solid solution of Fe and Ni in W formed in both the cases; the amount of Ni and Fe dissolved is higher in the attritor-milled powder than in the ball-milled powder. Morphologically, the W-rich particles in the attritor-milled powders were spheroidal, smaller in size, and showed a narrower size distribution than in the ball-milled condition. These differences led to increased density in the attritor-milled powder compact and significant differences in chemical composition of the matrix region and W-rich grains. Transmission electron microscopy investigations of the matrix region in the compacts revealed the presence of Fe2W precipitates uniformly distributed in an Ni(Fe, W) matrix.

IOP Conference Series: Materials Science and Engineering, 2010

... Tech. 184 219 [9] Abbas M, Qazi IA, Samina A, Masaood M, Majeed A, Haq A 1995 J. Vac. Sci. Te... more ... Tech. 184 219 [9] Abbas M, Qazi IA, Samina A, Masaood M, Majeed A, Haq A 1995 J. Vac. Sci. Technol. A 13 151 [10] Tahar RBH, Ban T, Ohya Y, Takahashi Y 1997 J. Appl. Phys. 82 865 [11] Adurodija FO, Izumi H, Ishihara T, Yoshioka H, Matsui H, Motoyama M 1999 Appl. ...

International Journal of Refractory Metals and Hard Materials, 2011

In this study, the effect of Y 2 O 3 additions on the microstructural and the physical properties... more In this study, the effect of Y 2 O 3 additions on the microstructural and the physical properties of W-SiC composites was investigated. Powder blends of W-4 wt.% SiC, W-4 wt.% SiC-1 wt.% Y 2 O 3 and W-4 wt.% SiC-5 wt.% Y 2 O 3 were mechanically alloyed (MA'd) using a Spex mill for 24 h. MA'd composite powders were sintered under inert Ar and reducing H 2 gas conditions at 1680°C for 1 h. Microstructural and morphological characterizations of composite powders and sintered samples were carried out via SEM and XRD analyses. Furthermore, density measurements and hardness measurements of sintered samples were carried out. A highest Vickers microhardness value of 11.4 GPa was measured for the sintered W-4 wt.% SiC-5 wt.% Y 2 O 3 while W-4 wt.% SiC sample possessed the highest relative density value of 97.7%.