Halil I. BAKAN | Kocaeli University (original) (raw)

Papers by Halil I. BAKAN

Metal matrix composite foams based on 316L stainless steel and reinforced with TiC0.7N0.3 were pr... more Metal matrix composite foams based on 316L stainless steel and reinforced with TiC0.7N0.3 were produced by the replication method using polyurethane sponge as a template. The rheological properties of the slurry appeared to be the key issue in the preparation of the composite foams. A homogeneous distribution of TiC0.7N0.3 particles throughout the 316L matrix and a good interaction between the 316L matrix and TiC0.7N0.3 reinforcement particles were obtained. Compression strength results showed that TiC0.7N0.3 particles acted as the real reinforcement medium. The values of the compressive yield strength and the elastic modulus of the metal matrix composite foams increased significantly with increasing TiC0.7N0.3 content when compared to the open cell 316L stainless steel foams.

The biocompatible metals made available for powder injection moulding (PIM) are increasing, and a... more The biocompatible metals made available for powder injection moulding (PIM) are increasing, and as a result, the PIM process is becoming attractive for manufacturers of medical implants and surgical instruments. In addition, friction and wear properties play an important role in biomaterial applications. This study aimed to systematically investigate the fretting wear properties of 316L stainless steel parts produced by PIM under dry contact conditions. The fretting experiments were performed under gross-slip regime. The influence of a number of fretting test parameters on the friction and wear behaviour was investigated, as the contact frequency, the normal load, and number of reciprocating sliding cycles. Fretting tests were performed against corundum counter bodies. After the tests, the wear scars were examined by laser surface profilometry, scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis. The results indicate that wear occurred predominantly by abrasion, plastic deformation, and cracking. K e y w o r d s : fretting, stainless steel, powder injection moulding, biomaterials

Highly porous 316L stainless steel samples with 70 vol.% porosity were manufactured using water l... more Highly porous 316L stainless steel samples with 70 vol.% porosity were manufactured using water leaching and sintering methods. Irregular carbamide powders were used as a space holder material. Complete removal of carbamide from the green compact and the desired macro-pore framework were achieved by water leaching at room temperature. The macro-pore framework remained nearly unchanged after sintering. It was shown that the pore shape, size and distribution could be controlled with this water leaching and sintering process.

Journal of The European Ceramic Society, 2010

In the present study, magnetic properties of barium ferrite foams were investigated. We especiall... more In the present study, magnetic properties of barium ferrite foams were investigated. We especially examine the effects of porosity on interparticle interactions and remanence properties of these materials. It was observed that magnets become harder with porosity. On the other hand, saturation magnetization decreases slightly. Existence of porosities increases the strength of demagnetising-like interactions of neighboring particles.

Journal of The European Ceramic Society, 2011

In the present study, we have investigated the influence of B 2 O 3 addition on structural and ma... more In the present study, we have investigated the influence of B 2 O 3 addition on structural and magnetic properties of hard magnetic BaFe 12 O 19 foams. In the presence of B 2 O 3 open-celled foams were successfully fabricated at a calcination temperature of 1300 • C. Magnetization values have been improved by 50% with B 2 O 3 -addition. Remanence magnetization (M R ), specific magnetization at 1.5 T (M S ) and coercive field (H c ) values were obtained to be 32.7 emu/g, 63.0 emu/g and 2100 Oe, respectively for the 0.5 wt% B 2 O 3 containing foams having 30 pores/in. Foams with these magnetic properties have the potential to be used in different areas of technology as permanently magnetic materials.

Materials Chemistry and Physics, 2010

In the present study, permanently magnetic barium ferrite foams synthesized using a replication t... more In the present study, permanently magnetic barium ferrite foams synthesized using a replication technique were characterized. Structural analysis have shown that the products are single phase of BaFe 12 O 19 and pore sizes reach up to 1 mm in diameter with a significantly uniform distribution. Magnetic properties were examined and compared with that of a sintered compact sample. It was observed that magnets become slightly harder with porosity. Our findings reveal that these materials may be applied to different technologies and can be used for understanding the physical interactions of hybrid structures.

A partially water soluble binder system was successfully derived and tested for injection mouldin... more A partially water soluble binder system was successfully derived and tested for injection moulding of alumina powder. The major binder of the binder system was comprised of poly(2-ethly-2oxaline) and polyethylene glycol and these constituents formed the water soluble fraction of the system. The rheological properties of the feedstock were investigated systematically over a temperature range of 120 to 160uC and a shear rate range of 100 to 1000 s 21 . Binder removal was accomplished using a two stage process. The water soluble constituents were removed by water leaching. The remaining binder constituents were removed by thermal pyrolysis. The solvent debinding kinetics of the water leaching process were studied as a function of temperature, ranging from 40 to 80uC. Solvent debinding is a two stage process consisting of dissolution and diffusion. In this study, dissolution was the rate limiting step during the first stage of water leaching over a leaching time of 90 min at 40uC. As the process proceeds, it is shown that diffusion becomes the rate limiting step.

A stainless steel (316L) powder having a median particle size of y25 mm was injection moulded usi... more A stainless steel (316L) powder having a median particle size of y25 mm was injection moulded using binders composed of polyethylene glycols (PEG) and polymethylmethacrylate (PMMA). The PEG content was leached in water and debinding kinetics studied as a function temperature. At 40uC, the removal of PEG was controlled by dissolution of the polymer in water and by diffusion of water and PEG for leaching time ,60 min and .60 min, respectively. Water soluble PEG was completely removed within 180 min and the diffusion mechanism controlled the de-binding process at 60 and 80uC. Sintered properties improved with increased sintering temperature and time. The improvement in mechanical properties was less pronounced for a longer soaking time owing to more grain coarsening.

Kovove Materialy-metallic Materials, 2010

Electrospark deposition (ESD) method is a promising process to produce hard and wear--resistant c... more Electrospark deposition (ESD) method is a promising process to produce hard and wear--resistant coatings on metallic substrates. In this study, ESD has been successfully applied to deposit TiC0.7N0.3-based cermet coatings on steel substrate. It has been possible to obtain a fully dense and strong adherent coating layer with a thickness of 20 µm. The microstructures of the deposited coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy. In addition, the friction and wear properties of the coatings and substrates were investigated systematically by conducting ball-on-disc sliding wear tests. The experimental results demonstrate that the wear resistance of the steel substrate, which contains a TiCN coating deposited via the ESD process, is noticeably enhanced under the dry sliding wear conditions. In addition, while the microhardness of substrate is 232 HV on average, the microhardness of the coating reaches 870 HV onto the surface.

Physica B-condensed Matter, 2005

The alternating current (AC) conductivity and dielectric properties of the Co-doped TiO 2 were in... more The alternating current (AC) conductivity and dielectric properties of the Co-doped TiO 2 were investigated. The temperature dependence of AC conductivity and the parameter s, is reasonably well interpreted by the correlated barrier hopping (CBH) model. The activation energy (E), and the density of states at Fermi level, N(E F ) were determined. The dielectric constant decreases with frequency at low frequencies and increases at high frequencies. r

Materials Science and Technology, 2006

ABSTRACT The space charge limited conduction (SCLC) mechanism in Co doped TiO2 has been investiga... more ABSTRACT The space charge limited conduction (SCLC) mechanism in Co doped TiO2 has been investigated at different temperatures. At lower electric fields, ohmic behaviour is observed while at higher electric fields nonohmic behaviour is observed. The results obtained confirm the presence of SCLC in Co doped TiO2. The electronic parameters such as the position of the Fermi level above the valence band edge E-F, the density of states in valence band N-V and effective mass of holes m(h) were found as 12.32 meV, 1.26 x 10(15) m(-3) and 1.33 x 10(-7) m(e), respectively. The distribution of localised states in the forbidden band gap of the Co doped TiO2 was characterised by current-voltage measurements and the density of localised states near the Fermi level N(E-F) was found to be 2.11 x 10(17) eV(-1) m(-3).

Physica B-condensed Matter, 2005

The surface morphology, phases existing in the microstructure and conductivity behavior of Co-dop... more The surface morphology, phases existing in the microstructure and conductivity behavior of Co-doped TiO 2 have been investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), electrical conductivity measurements and X-ray diffraction technique. The semiconducting phase is found to obey Mott's variable range hopping mechanism of the conduction. The conduction mechanism of the ceramic shows a crossover from the, exp½ÀðT 0 =TÞ 1=4 law to a simply activated law, expðÀDE=kTÞ: This behavior is attributed to temperature-induced transition from 3D to thermally activated behavior. The hopping conduction parameters such as the characteristic temperature (T 0 ), localization length (a), hopping distance (R), activation energy (DE) and density of states at Fermi level ðNðE F Þ have been calculated. Surface morphology shows that the ceramic has a regular surface. The SEM study indicates that there are grains which have a certain type in the microstructure. Rutile phases with different plane in microstructure were found. r

Powder Metallurgy, 2003

or under hydrogen atmosphere having dewpoint of 70°C or 60°C. Following this process, hot isostat... more or under hydrogen atmosphere having dewpoint of 70°C or 60°C. Following this process, hot isostatic pressure is The sintering behaviour of Cu-25 wt-%Cr contact applied to reach a high sintered density.1-6 materials produced by powder metallurgy is investigated

Journal of Non-crystalline Solids, 2008

Metal matrix composite foams based on 316L stainless steel and reinforced with TiC0.7N0.3 were pr... more Metal matrix composite foams based on 316L stainless steel and reinforced with TiC0.7N0.3 were produced by the replication method using polyurethane sponge as a template. The rheological properties of the slurry appeared to be the key issue in the preparation of the composite foams. A homogeneous distribution of TiC0.7N0.3 particles throughout the 316L matrix and a good interaction between the 316L matrix and TiC0.7N0.3 reinforcement particles were obtained. Compression strength results showed that TiC0.7N0.3 particles acted as the real reinforcement medium. The values of the compressive yield strength and the elastic modulus of the metal matrix composite foams increased significantly with increasing TiC0.7N0.3 content when compared to the open cell 316L stainless steel foams.

The biocompatible metals made available for powder injection moulding (PIM) are increasing, and a... more The biocompatible metals made available for powder injection moulding (PIM) are increasing, and as a result, the PIM process is becoming attractive for manufacturers of medical implants and surgical instruments. In addition, friction and wear properties play an important role in biomaterial applications. This study aimed to systematically investigate the fretting wear properties of 316L stainless steel parts produced by PIM under dry contact conditions. The fretting experiments were performed under gross-slip regime. The influence of a number of fretting test parameters on the friction and wear behaviour was investigated, as the contact frequency, the normal load, and number of reciprocating sliding cycles. Fretting tests were performed against corundum counter bodies. After the tests, the wear scars were examined by laser surface profilometry, scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis. The results indicate that wear occurred predominantly by abrasion, plastic deformation, and cracking. K e y w o r d s : fretting, stainless steel, powder injection moulding, biomaterials

Highly porous 316L stainless steel samples with 70 vol.% porosity were manufactured using water l... more Highly porous 316L stainless steel samples with 70 vol.% porosity were manufactured using water leaching and sintering methods. Irregular carbamide powders were used as a space holder material. Complete removal of carbamide from the green compact and the desired macro-pore framework were achieved by water leaching at room temperature. The macro-pore framework remained nearly unchanged after sintering. It was shown that the pore shape, size and distribution could be controlled with this water leaching and sintering process.

Journal of The European Ceramic Society, 2010

In the present study, magnetic properties of barium ferrite foams were investigated. We especiall... more In the present study, magnetic properties of barium ferrite foams were investigated. We especially examine the effects of porosity on interparticle interactions and remanence properties of these materials. It was observed that magnets become harder with porosity. On the other hand, saturation magnetization decreases slightly. Existence of porosities increases the strength of demagnetising-like interactions of neighboring particles.

Journal of The European Ceramic Society, 2011

In the present study, we have investigated the influence of B 2 O 3 addition on structural and ma... more In the present study, we have investigated the influence of B 2 O 3 addition on structural and magnetic properties of hard magnetic BaFe 12 O 19 foams. In the presence of B 2 O 3 open-celled foams were successfully fabricated at a calcination temperature of 1300 • C. Magnetization values have been improved by 50% with B 2 O 3 -addition. Remanence magnetization (M R ), specific magnetization at 1.5 T (M S ) and coercive field (H c ) values were obtained to be 32.7 emu/g, 63.0 emu/g and 2100 Oe, respectively for the 0.5 wt% B 2 O 3 containing foams having 30 pores/in. Foams with these magnetic properties have the potential to be used in different areas of technology as permanently magnetic materials.

Materials Chemistry and Physics, 2010

In the present study, permanently magnetic barium ferrite foams synthesized using a replication t... more In the present study, permanently magnetic barium ferrite foams synthesized using a replication technique were characterized. Structural analysis have shown that the products are single phase of BaFe 12 O 19 and pore sizes reach up to 1 mm in diameter with a significantly uniform distribution. Magnetic properties were examined and compared with that of a sintered compact sample. It was observed that magnets become slightly harder with porosity. Our findings reveal that these materials may be applied to different technologies and can be used for understanding the physical interactions of hybrid structures.

A partially water soluble binder system was successfully derived and tested for injection mouldin... more A partially water soluble binder system was successfully derived and tested for injection moulding of alumina powder. The major binder of the binder system was comprised of poly(2-ethly-2oxaline) and polyethylene glycol and these constituents formed the water soluble fraction of the system. The rheological properties of the feedstock were investigated systematically over a temperature range of 120 to 160uC and a shear rate range of 100 to 1000 s 21 . Binder removal was accomplished using a two stage process. The water soluble constituents were removed by water leaching. The remaining binder constituents were removed by thermal pyrolysis. The solvent debinding kinetics of the water leaching process were studied as a function of temperature, ranging from 40 to 80uC. Solvent debinding is a two stage process consisting of dissolution and diffusion. In this study, dissolution was the rate limiting step during the first stage of water leaching over a leaching time of 90 min at 40uC. As the process proceeds, it is shown that diffusion becomes the rate limiting step.

A stainless steel (316L) powder having a median particle size of y25 mm was injection moulded usi... more A stainless steel (316L) powder having a median particle size of y25 mm was injection moulded using binders composed of polyethylene glycols (PEG) and polymethylmethacrylate (PMMA). The PEG content was leached in water and debinding kinetics studied as a function temperature. At 40uC, the removal of PEG was controlled by dissolution of the polymer in water and by diffusion of water and PEG for leaching time ,60 min and .60 min, respectively. Water soluble PEG was completely removed within 180 min and the diffusion mechanism controlled the de-binding process at 60 and 80uC. Sintered properties improved with increased sintering temperature and time. The improvement in mechanical properties was less pronounced for a longer soaking time owing to more grain coarsening.

Kovove Materialy-metallic Materials, 2010

Electrospark deposition (ESD) method is a promising process to produce hard and wear--resistant c... more Electrospark deposition (ESD) method is a promising process to produce hard and wear--resistant coatings on metallic substrates. In this study, ESD has been successfully applied to deposit TiC0.7N0.3-based cermet coatings on steel substrate. It has been possible to obtain a fully dense and strong adherent coating layer with a thickness of 20 µm. The microstructures of the deposited coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy. In addition, the friction and wear properties of the coatings and substrates were investigated systematically by conducting ball-on-disc sliding wear tests. The experimental results demonstrate that the wear resistance of the steel substrate, which contains a TiCN coating deposited via the ESD process, is noticeably enhanced under the dry sliding wear conditions. In addition, while the microhardness of substrate is 232 HV on average, the microhardness of the coating reaches 870 HV onto the surface.

Physica B-condensed Matter, 2005

The alternating current (AC) conductivity and dielectric properties of the Co-doped TiO 2 were in... more The alternating current (AC) conductivity and dielectric properties of the Co-doped TiO 2 were investigated. The temperature dependence of AC conductivity and the parameter s, is reasonably well interpreted by the correlated barrier hopping (CBH) model. The activation energy (E), and the density of states at Fermi level, N(E F ) were determined. The dielectric constant decreases with frequency at low frequencies and increases at high frequencies. r

Materials Science and Technology, 2006

ABSTRACT The space charge limited conduction (SCLC) mechanism in Co doped TiO2 has been investiga... more ABSTRACT The space charge limited conduction (SCLC) mechanism in Co doped TiO2 has been investigated at different temperatures. At lower electric fields, ohmic behaviour is observed while at higher electric fields nonohmic behaviour is observed. The results obtained confirm the presence of SCLC in Co doped TiO2. The electronic parameters such as the position of the Fermi level above the valence band edge E-F, the density of states in valence band N-V and effective mass of holes m(h) were found as 12.32 meV, 1.26 x 10(15) m(-3) and 1.33 x 10(-7) m(e), respectively. The distribution of localised states in the forbidden band gap of the Co doped TiO2 was characterised by current-voltage measurements and the density of localised states near the Fermi level N(E-F) was found to be 2.11 x 10(17) eV(-1) m(-3).

Physica B-condensed Matter, 2005

The surface morphology, phases existing in the microstructure and conductivity behavior of Co-dop... more The surface morphology, phases existing in the microstructure and conductivity behavior of Co-doped TiO 2 have been investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), electrical conductivity measurements and X-ray diffraction technique. The semiconducting phase is found to obey Mott's variable range hopping mechanism of the conduction. The conduction mechanism of the ceramic shows a crossover from the, exp½ÀðT 0 =TÞ 1=4 law to a simply activated law, expðÀDE=kTÞ: This behavior is attributed to temperature-induced transition from 3D to thermally activated behavior. The hopping conduction parameters such as the characteristic temperature (T 0 ), localization length (a), hopping distance (R), activation energy (DE) and density of states at Fermi level ðNðE F Þ have been calculated. Surface morphology shows that the ceramic has a regular surface. The SEM study indicates that there are grains which have a certain type in the microstructure. Rutile phases with different plane in microstructure were found. r

Powder Metallurgy, 2003

or under hydrogen atmosphere having dewpoint of 70°C or 60°C. Following this process, hot isostat... more or under hydrogen atmosphere having dewpoint of 70°C or 60°C. Following this process, hot isostatic pressure is The sintering behaviour of Cu-25 wt-%Cr contact applied to reach a high sintered density.1-6 materials produced by powder metallurgy is investigated

Journal of Non-crystalline Solids, 2008