Havva Zeytin - Academia.edu (original) (raw)

Papers by Havva Zeytin

Materials Characterization, Aug 1, 2006

In this study the composition of a Ni–Cr–Co based superalloy was modified with silicon additions ... more In this study the composition of a Ni–Cr–Co based superalloy was modified with silicon additions in order to observe its effects on the microstructure. The evolution of the microstructure was investigated by electron microscopy of as-cast samples containing various amounts of Si ranging from 0.48 to 5.43 wt.%. The precipitated phases were identified through electron diffraction to be σ (sigma),

Materiali in Tehnologije, Aug 12, 2016

This study was undertaken to investigate the microstructure and mechanical properties of hot roll... more This study was undertaken to investigate the microstructure and mechanical properties of hot rolled Fe-13Mn-0.2C-1Al-1Si TWIP steel. Tensile tests were carried out at different strain rates to determine the Portevin-Le Chatelier (PLC) effect during deformation. Subsequently, the samples were investigated by light microscopy and SEM. The sample microstructures revealed inhomogeneous dislocation zones, deformation twinning and twin-dislocation interactions. Consequently, the PLC effect during deformation was determined to be responsible for the excellent mechanical properties of the TWIP steel.

Fen Bilimleri Enstitüsü, 1998

Journal of Dynamic Behavior of Materials, 2017

High Temperature Materials and Processes, 2000

The secondary phases occurring in a Cr-Ni-Co superalloy, modified by silicon additions, have been... more The secondary phases occurring in a Cr-Ni-Co superalloy, modified by silicon additions, have been identified. The microstructures of the alloy in the as cast and heat treated conditions have been examined and the effect of the silicon content on the resulting microstructure studied. The influence of the microstructure on the hardness and wear resistance of the alloy has also been investigated.

High Temperature Materials and Processes, 2000

Chromium (Cr)-nickel (Ni)-cobalt (Co)-based superalloys are used in structural parts of steel ann... more Chromium (Cr)-nickel (Ni)-cobalt (Co)-based superalloys are used in structural parts of steel annealing furnaces. This application requires the alloy to be modified by silicon (Si) to enhance the service life. This investigation firstly attempts to identify the microstructural changes that occur following silicon modification of the Cr-Ni-Co superalloy in as cast and heat treated conditions and then goes on to study the structure-high temperature properties correlations.

Mechanical properties have an important role in the thermal characteristics of DP 600 steel struc... more Mechanical properties have an important role in the thermal characteristics of DP 600 steel structures due to the rapid reduction in mechanical properties such as yield strength and elastic modulus under elevated temperature conditions and associated reduction to the load carrying capacities. Hence there is a need to fully understand the thermal characteristics of yield strength and elastic modulus of DP 600 steels at elevated temperatures. Therefore, an experimental study was undertaken to investigate the elevated temperature mechanical properties of DP 600 steels. Tensile tests were undertaken using a steady state test method for temperatures in the range 20–800 o C. Test results were compared with the currently available reduction factors for strength and elastic modulus, and stress–strain curves.

Corrosion Reviews, 2005

The reasons for the damage to a radiator in a heating system made of AA 6063 aluminum alloy with ... more The reasons for the damage to a radiator in a heating system made of AA 6063 aluminum alloy with T6 temper that led to perforation under service conditions were investigated. To analyze the failure, circulating water in the radiator system was analyzed; corrosion products were examined using optical and scanning electron microscopy and x-ray diffractometry. The combined effects of galvanic effects due to the precipitation of the heavy metals copper and iron, intergranular corrosion and environmental effects caused the radiator's failure.

High manganese TWIP (twinning-induced plasticity) steels are particularly attractive for automoti... more High manganese TWIP (twinning-induced plasticity) steels are particularly attractive for automotive applications because of their exceptional properties of strength combined with an excellent ductility. However, the microstructure and properties of TWIP steels are affected by excessive thermal cycles, such as welding and heat treatment. This paper deals with characterization and understanding the effect of welding current and time on the mechanical properties and microstructure of the resistance spot welded TWIP steel. For this purpose, weld nugget diameter was evaluated and the hardness, tensile shear strength of the weldment, and failure mode of samples were also determined. It has been found that the tensile shear strength of the samples increased with increasing welding current and welding time without expulsion, which reduces the strength of the weldment. Tensile shear samples failed by a partial interfacial fracture mode for low-heat input welds. The pullout fractures were obs...

This study was undertaken to investigate the microstructure and mechanical properties of hot roll... more This study was undertaken to investigate the microstructure and mechanical properties of hot rolled Fe-13Mn-0.2C-1Al-1Si TWIP steel. Tensile tests were carried out at different strain rates to determine the Portevin-Le Chatelier (PLC) effect during deformation. Subsequently, the samples were investigated by light microscopy and SEM. The sample microstructures revealed inhomogeneous dislocation zones, deformation twinning and twin-dislocation interactions. Consequently, the PLC effect during deformation was determined to be responsible for the excellent mechanical properties of the TWIP steel.

Journal of Materials Engineering and Performance

In this study, a nickel aluminide coating was obtained on CMSX-4 via a chemical vapor aluminizing... more In this study, a nickel aluminide coating was obtained on CMSX-4 via a chemical vapor aluminizing (CVA) technique. The CVA coating process was carried out for 4 and 6 hours at 1070°C to examine the effects of CVA process time on the properties of the nickel aluminide coating. Heat treatment processes were subsequently applied to nickel aluminide-coated samples for 2 hours at 1050 and 1100°C to examine the effects of heat treatment temperature on the coating. The characterization of coated samples was carried out via SEM, EDS, XRD, GDOES and Vickers hardness analyses. The results showed that the increment in CVA process time induced an increase in inter-diffusion zone thickness due to the increased Ni outward diffusion from the CMSX-4 substrate. The additive layer of the four-hour CVA coating is composed of the δ-Ni2Al3 phase due to the dominance of Al inward diffusion. The phase transformation from δ-Ni2Al3 to the desired β-NiAl was observed in four-hour CVA coating structure subsequent to the heat treatment processes. However, the additive layer of six-hour CVA coating consists of the β-NiAl phase both before and after the heat treatment processes. Heat treatment processes increase the thickness of the coatings because they provide increased Al inward and Ni outward diffusion. The results of the Vickers hardness tests demonstrated that the heat treatment processes cause a decrease in the hardness of the additive layer of the four-hour CVA coating from 754 to 578 HV for heat treatment at 1050°C, and to 522 HV for heat treatment at 1100°C due to phase transformation phenomena.

TWIP (Twinning-induced Plasticity) steels have exceptionally good combinations of strength, ducti... more TWIP (Twinning-induced Plasticity) steels have exceptionally good combinations of strength, ductility and damage tolerance which satisfy the recent requirements of automotive industries. Firstly, TWIP has the most beneficial effect on the work-hardening. It is believed that deformation twins increase the work-hardening rate by acting as obstacles against gliding dislocations. Moreover, TWIP steels have low to intermediate stacking fault energy and hence undergo extensive mechanical twinning during deformation, which in turn leads a good combination of both strength and ductility. To explain the mechanical characteristics and the mechanical behavior of the TWIP steels, we have been made some investigations and experiments that show the effects of microalloying elements and deformation mechanisms. In this study, three different compositions of TWIP steels have been produced. The microstructure and mechanical properties are characterized by using optical, electron microscopy and mechan...

Praktische Metallographie

In dual phase steels, the microstructure consists of a ferrite matrix and martensite islands alon... more In dual phase steels, the microstructure consists of a ferrite matrix and martensite islands along the grain boundaries of the ferrite. In this study, the microstructures of dual phase steels with different chemical compositions are characterized by applying different etchants and by using optical and electron microscopy. The most successful result was obtained with LePera and Na-metabisulfite etchants, which were applied using a special method.

Journal of Iron and Steel Research, International, 2011

Heat treatment methods were applied to white cast iron for improving the impact and wear resistan... more Heat treatment methods were applied to white cast iron for improving the impact and wear resistance. Additionally, chemical composition optimization was made. Furthermore, the effect of boron addition on such applications was investigated. Samples were investigated by using optical and electron microscope methods. Hardness, wear and impact tests were conducted. The results showed that the secondary carbides in the standard alloy were iron-enriched, needlelike carbides M3C when the boron-added alloy contained FeZ3 (C , B)d type, globular secondary carbides. It was concluded that heat treatment B provided higher wear and hardness properties, compared to the standard heat treatment. Optimum mechanical properties were obtained by lower destabilisation temperatures and increasing temperature reduced the wear resistance and hardness.

Journal of Iron and Steel Research International, 2010

The effects of some intercritical annealing parameters including heating rate, soaking temperatur... more The effects of some intercritical annealing parameters including heating rate, soaking temperature, soaking time, and quench media on the microstructure and mechanical properties of cold-rolled dual phase steel were studied. The microstructure of specimens quenched after each annealing stage was analyzed using optical microscope. The tensile properties, determined for specimens submitted to complete annealing cycles, were influenced by the volume fractions of multiphases (originated from martensite, bainite, and retained austenite), which depend on the annealing process parameters. The results obtained showed that the yield strength and the ultimate tensile strength increase with increasing the intercritical temperature and cooling rate. This can be explained by higher martensite volume ratio with the increased volume fraction of austenite formed at the higher temperatures and cooling rates.

Materials Characterization, 2008

The copper–zinc alloy pipes used in the condensed water system of a power plant failed within a p... more The copper–zinc alloy pipes used in the condensed water system of a power plant failed within a period of 5 to 6 years. Because the service life of such a system was expected to be on the order of 20 years, an investigation was carried out to determine the possible causes for early failure of the pipes. Visual inspection revealed that the damage was generally in the form of holes. Further examination revealed that the pipes damaged over this relatively short period of time were constructed of copper–zinc alloys that are not resistant to dezincification corrosion.

Materials Characterization, 2006

In this study the composition of a Ni–Cr–Co based superalloy was modified with silicon additions ... more In this study the composition of a Ni–Cr–Co based superalloy was modified with silicon additions in order to observe its effects on the microstructure. The evolution of the microstructure was investigated by electron microscopy of as-cast samples containing various amounts of Si ranging from 0.48 to 5.43 wt.%. The precipitated phases were identified through electron diffraction to be σ (sigma), χ (chi), and M23C6. The σ precipitates of blocky morphology appeared to enclose the precipitates of χ phase. Lamellar regions consisting of σ and M23C6 were observed to form along the boundaries between the σ particles and the neighboring phases. These lamellar cells were observed to have grown into the intermetallic phases σ and χ. A crystallographic relationship was also found to exist between the σ and M23C6.

Materials Letters, 2008

Dual phase steels are a class of steels characterized by a microstructure consisting of a soft fe... more Dual phase steels are a class of steels characterized by a microstructure consisting of a soft ferrite matrix with hard martensite islands at the grain boundaries. The temperature in the dual phase (α + γ) region and the holding time are two important parameters in the intercritically annealing process. In this study, different grades of commercial low alloy steels have been heat treated to a constant annealing temperature by changing the holding time. It is observed that the effect of holding time is dependent on the steel composition. In this context, a microstructural examination has been carried out using optical, scanning electron microscope and electron probe micro-analysis and hardness values have been determined.

Journal of Iron and Steel Research International, 2009

Ductile cast irons are used as high temperature materials in internal combustion engines, because... more Ductile cast irons are used as high temperature materials in internal combustion engines, because they are microstructurally stable at high operating temperatures. SiMo granular graphite cast irons contain Fe2 MoC and M6C carbide precipitates due to their higher concentration of both silicon and molybdenum. The microstructure of these cast irons consists of carbides dispersed within the ferrite matrix. The microstructural change and the crack formation mechanism in manifolds produced from SiMo ductile iron are studied. Chemical analysis, optical and scanning electron microscope studies have been completed and evaluated.

Materials Characterization, Aug 1, 2006

In this study the composition of a Ni–Cr–Co based superalloy was modified with silicon additions ... more In this study the composition of a Ni–Cr–Co based superalloy was modified with silicon additions in order to observe its effects on the microstructure. The evolution of the microstructure was investigated by electron microscopy of as-cast samples containing various amounts of Si ranging from 0.48 to 5.43 wt.%. The precipitated phases were identified through electron diffraction to be σ (sigma),

Materiali in Tehnologije, Aug 12, 2016

This study was undertaken to investigate the microstructure and mechanical properties of hot roll... more This study was undertaken to investigate the microstructure and mechanical properties of hot rolled Fe-13Mn-0.2C-1Al-1Si TWIP steel. Tensile tests were carried out at different strain rates to determine the Portevin-Le Chatelier (PLC) effect during deformation. Subsequently, the samples were investigated by light microscopy and SEM. The sample microstructures revealed inhomogeneous dislocation zones, deformation twinning and twin-dislocation interactions. Consequently, the PLC effect during deformation was determined to be responsible for the excellent mechanical properties of the TWIP steel.

Fen Bilimleri Enstitüsü, 1998

Journal of Dynamic Behavior of Materials, 2017

High Temperature Materials and Processes, 2000

The secondary phases occurring in a Cr-Ni-Co superalloy, modified by silicon additions, have been... more The secondary phases occurring in a Cr-Ni-Co superalloy, modified by silicon additions, have been identified. The microstructures of the alloy in the as cast and heat treated conditions have been examined and the effect of the silicon content on the resulting microstructure studied. The influence of the microstructure on the hardness and wear resistance of the alloy has also been investigated.

High Temperature Materials and Processes, 2000

Chromium (Cr)-nickel (Ni)-cobalt (Co)-based superalloys are used in structural parts of steel ann... more Chromium (Cr)-nickel (Ni)-cobalt (Co)-based superalloys are used in structural parts of steel annealing furnaces. This application requires the alloy to be modified by silicon (Si) to enhance the service life. This investigation firstly attempts to identify the microstructural changes that occur following silicon modification of the Cr-Ni-Co superalloy in as cast and heat treated conditions and then goes on to study the structure-high temperature properties correlations.

Mechanical properties have an important role in the thermal characteristics of DP 600 steel struc... more Mechanical properties have an important role in the thermal characteristics of DP 600 steel structures due to the rapid reduction in mechanical properties such as yield strength and elastic modulus under elevated temperature conditions and associated reduction to the load carrying capacities. Hence there is a need to fully understand the thermal characteristics of yield strength and elastic modulus of DP 600 steels at elevated temperatures. Therefore, an experimental study was undertaken to investigate the elevated temperature mechanical properties of DP 600 steels. Tensile tests were undertaken using a steady state test method for temperatures in the range 20–800 o C. Test results were compared with the currently available reduction factors for strength and elastic modulus, and stress–strain curves.

Corrosion Reviews, 2005

The reasons for the damage to a radiator in a heating system made of AA 6063 aluminum alloy with ... more The reasons for the damage to a radiator in a heating system made of AA 6063 aluminum alloy with T6 temper that led to perforation under service conditions were investigated. To analyze the failure, circulating water in the radiator system was analyzed; corrosion products were examined using optical and scanning electron microscopy and x-ray diffractometry. The combined effects of galvanic effects due to the precipitation of the heavy metals copper and iron, intergranular corrosion and environmental effects caused the radiator's failure.

High manganese TWIP (twinning-induced plasticity) steels are particularly attractive for automoti... more High manganese TWIP (twinning-induced plasticity) steels are particularly attractive for automotive applications because of their exceptional properties of strength combined with an excellent ductility. However, the microstructure and properties of TWIP steels are affected by excessive thermal cycles, such as welding and heat treatment. This paper deals with characterization and understanding the effect of welding current and time on the mechanical properties and microstructure of the resistance spot welded TWIP steel. For this purpose, weld nugget diameter was evaluated and the hardness, tensile shear strength of the weldment, and failure mode of samples were also determined. It has been found that the tensile shear strength of the samples increased with increasing welding current and welding time without expulsion, which reduces the strength of the weldment. Tensile shear samples failed by a partial interfacial fracture mode for low-heat input welds. The pullout fractures were obs...

This study was undertaken to investigate the microstructure and mechanical properties of hot roll... more This study was undertaken to investigate the microstructure and mechanical properties of hot rolled Fe-13Mn-0.2C-1Al-1Si TWIP steel. Tensile tests were carried out at different strain rates to determine the Portevin-Le Chatelier (PLC) effect during deformation. Subsequently, the samples were investigated by light microscopy and SEM. The sample microstructures revealed inhomogeneous dislocation zones, deformation twinning and twin-dislocation interactions. Consequently, the PLC effect during deformation was determined to be responsible for the excellent mechanical properties of the TWIP steel.

Journal of Materials Engineering and Performance

In this study, a nickel aluminide coating was obtained on CMSX-4 via a chemical vapor aluminizing... more In this study, a nickel aluminide coating was obtained on CMSX-4 via a chemical vapor aluminizing (CVA) technique. The CVA coating process was carried out for 4 and 6 hours at 1070°C to examine the effects of CVA process time on the properties of the nickel aluminide coating. Heat treatment processes were subsequently applied to nickel aluminide-coated samples for 2 hours at 1050 and 1100°C to examine the effects of heat treatment temperature on the coating. The characterization of coated samples was carried out via SEM, EDS, XRD, GDOES and Vickers hardness analyses. The results showed that the increment in CVA process time induced an increase in inter-diffusion zone thickness due to the increased Ni outward diffusion from the CMSX-4 substrate. The additive layer of the four-hour CVA coating is composed of the δ-Ni2Al3 phase due to the dominance of Al inward diffusion. The phase transformation from δ-Ni2Al3 to the desired β-NiAl was observed in four-hour CVA coating structure subsequent to the heat treatment processes. However, the additive layer of six-hour CVA coating consists of the β-NiAl phase both before and after the heat treatment processes. Heat treatment processes increase the thickness of the coatings because they provide increased Al inward and Ni outward diffusion. The results of the Vickers hardness tests demonstrated that the heat treatment processes cause a decrease in the hardness of the additive layer of the four-hour CVA coating from 754 to 578 HV for heat treatment at 1050°C, and to 522 HV for heat treatment at 1100°C due to phase transformation phenomena.

TWIP (Twinning-induced Plasticity) steels have exceptionally good combinations of strength, ducti... more TWIP (Twinning-induced Plasticity) steels have exceptionally good combinations of strength, ductility and damage tolerance which satisfy the recent requirements of automotive industries. Firstly, TWIP has the most beneficial effect on the work-hardening. It is believed that deformation twins increase the work-hardening rate by acting as obstacles against gliding dislocations. Moreover, TWIP steels have low to intermediate stacking fault energy and hence undergo extensive mechanical twinning during deformation, which in turn leads a good combination of both strength and ductility. To explain the mechanical characteristics and the mechanical behavior of the TWIP steels, we have been made some investigations and experiments that show the effects of microalloying elements and deformation mechanisms. In this study, three different compositions of TWIP steels have been produced. The microstructure and mechanical properties are characterized by using optical, electron microscopy and mechan...

Praktische Metallographie

In dual phase steels, the microstructure consists of a ferrite matrix and martensite islands alon... more In dual phase steels, the microstructure consists of a ferrite matrix and martensite islands along the grain boundaries of the ferrite. In this study, the microstructures of dual phase steels with different chemical compositions are characterized by applying different etchants and by using optical and electron microscopy. The most successful result was obtained with LePera and Na-metabisulfite etchants, which were applied using a special method.

Journal of Iron and Steel Research, International, 2011

Heat treatment methods were applied to white cast iron for improving the impact and wear resistan... more Heat treatment methods were applied to white cast iron for improving the impact and wear resistance. Additionally, chemical composition optimization was made. Furthermore, the effect of boron addition on such applications was investigated. Samples were investigated by using optical and electron microscope methods. Hardness, wear and impact tests were conducted. The results showed that the secondary carbides in the standard alloy were iron-enriched, needlelike carbides M3C when the boron-added alloy contained FeZ3 (C , B)d type, globular secondary carbides. It was concluded that heat treatment B provided higher wear and hardness properties, compared to the standard heat treatment. Optimum mechanical properties were obtained by lower destabilisation temperatures and increasing temperature reduced the wear resistance and hardness.

Journal of Iron and Steel Research International, 2010

The effects of some intercritical annealing parameters including heating rate, soaking temperatur... more The effects of some intercritical annealing parameters including heating rate, soaking temperature, soaking time, and quench media on the microstructure and mechanical properties of cold-rolled dual phase steel were studied. The microstructure of specimens quenched after each annealing stage was analyzed using optical microscope. The tensile properties, determined for specimens submitted to complete annealing cycles, were influenced by the volume fractions of multiphases (originated from martensite, bainite, and retained austenite), which depend on the annealing process parameters. The results obtained showed that the yield strength and the ultimate tensile strength increase with increasing the intercritical temperature and cooling rate. This can be explained by higher martensite volume ratio with the increased volume fraction of austenite formed at the higher temperatures and cooling rates.

Materials Characterization, 2008

The copper–zinc alloy pipes used in the condensed water system of a power plant failed within a p... more The copper–zinc alloy pipes used in the condensed water system of a power plant failed within a period of 5 to 6 years. Because the service life of such a system was expected to be on the order of 20 years, an investigation was carried out to determine the possible causes for early failure of the pipes. Visual inspection revealed that the damage was generally in the form of holes. Further examination revealed that the pipes damaged over this relatively short period of time were constructed of copper–zinc alloys that are not resistant to dezincification corrosion.

Materials Characterization, 2006

In this study the composition of a Ni–Cr–Co based superalloy was modified with silicon additions ... more In this study the composition of a Ni–Cr–Co based superalloy was modified with silicon additions in order to observe its effects on the microstructure. The evolution of the microstructure was investigated by electron microscopy of as-cast samples containing various amounts of Si ranging from 0.48 to 5.43 wt.%. The precipitated phases were identified through electron diffraction to be σ (sigma), χ (chi), and M23C6. The σ precipitates of blocky morphology appeared to enclose the precipitates of χ phase. Lamellar regions consisting of σ and M23C6 were observed to form along the boundaries between the σ particles and the neighboring phases. These lamellar cells were observed to have grown into the intermetallic phases σ and χ. A crystallographic relationship was also found to exist between the σ and M23C6.

Materials Letters, 2008

Dual phase steels are a class of steels characterized by a microstructure consisting of a soft fe... more Dual phase steels are a class of steels characterized by a microstructure consisting of a soft ferrite matrix with hard martensite islands at the grain boundaries. The temperature in the dual phase (α + γ) region and the holding time are two important parameters in the intercritically annealing process. In this study, different grades of commercial low alloy steels have been heat treated to a constant annealing temperature by changing the holding time. It is observed that the effect of holding time is dependent on the steel composition. In this context, a microstructural examination has been carried out using optical, scanning electron microscope and electron probe micro-analysis and hardness values have been determined.

Journal of Iron and Steel Research International, 2009

Ductile cast irons are used as high temperature materials in internal combustion engines, because... more Ductile cast irons are used as high temperature materials in internal combustion engines, because they are microstructurally stable at high operating temperatures. SiMo granular graphite cast irons contain Fe2 MoC and M6C carbide precipitates due to their higher concentration of both silicon and molybdenum. The microstructure of these cast irons consists of carbides dispersed within the ferrite matrix. The microstructural change and the crack formation mechanism in manifolds produced from SiMo ductile iron are studied. Chemical analysis, optical and scanning electron microscope studies have been completed and evaluated.