Bulent Sencer - Academia.edu (original) (raw)

Papers by Bulent Sencer

Journal of Nuclear Materials, 2005

Specimens of 316 L stainless steel were irradiated to 0.5-10.3 dpa at 30-80°C with a mixture of 5... more Specimens of 316 L stainless steel were irradiated to 0.5-10.3 dpa at 30-80°C with a mixture of 500-800 MeV protons and spallation neutrons at the Los Alamos Neutron Science Center (LANSCE). Tensile test results of irradiated 316 L reported earlier had showed hardening and embrittlement with increasing irradiation dose, with significant irradiation hardening occurring at a dose of as low as 0.5 dpa. Transmission electron microscope (TEM) examination of the irradiated microstructure of 316 L showed black-spot damage (small loops) and somewhat larger faulted Frank loops to produce the hardening. There was an initial decrease in uniform elongation at low dose levels from 49% (unirradiated) to 30% at 1.1 dpa, followed by a second, rather abrupt contribution to ductility loss at higher doses ($2.5 dpa) from 21% at 2.5 dpa to 0.5% at 3 dpa. This second drop in ductility was not accompanied by any visible new or enhanced microstructural development. In the current study additional transmission electron microscope investigation was conducted on both as-irradiated and irradiated plus subsequently deformed 316 L in the vicinity of the second abrupt ductility loss ($2.5 dpa). The steel was observed to deform mainly by twinning and no brittle phases were found in the deformation microstructure. It is proposed that gas accumulation with increasing dpa, especially of hydrogen, may be a contributor to this second abrupt decrease in uniform elongation. Although the retained gas (helium and hydrogen) levels approached $0.6 at.% total at the highest exposure level, no discernible cavities were observed.

Controlled shock recovery experiments have been conducted to assess the role of shock pressure an... more Controlled shock recovery experiments have been conducted to assess the role of shock pressure and orientation dependence on the substructure evolution of a [100]/[01{ovr 1}] copper bicrystal. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were utilized to characterize orientation variation and substructure evolution of the post-shock specimens. Well defined dislocation cell structures were displayed in both grains and the average cell size was observed to decrease with increasing shock pressure. Twinning was occasionally observed in the 5 GPa shocked [100] grain and became the dominant substructure at higher shock pressure. The stress and directional dependence of twinning in the bicrystal was analyzed with consideration of the energetically favorable dissociation of dislocations into Shockley partials and the stress-orientation effect on the partial width. Moreover, a critical 'tear apart' stress is proposed and a good agreement is obtai...

DOE Scientific and Technical Information. DOE Scientific and Technical Information. ...

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006

ABSTRACT

Journal of Nuclear Materials, 2005

Neutron irradiation-induced relaxation was emulated using proton irradiation in order to determin... more Neutron irradiation-induced relaxation was emulated using proton irradiation in order to determine the expected amount of stress relaxation in the peened surface layer of a BWR core shroud during its 40 year lifetime. Samples of 304 SS were shot peened to induce a compressive residual stress, and then irradiated with 3.2 MeV protons at 288°C to four dose levels spanning 0.1-2.0 dpa. One set of specimens was as-peened and a second was pre-injected with 25 appm He. Depth-dependent measurements of internal stress were conducted using successive steps of X-ray line broadening measurement and electropolishing. Results showed that the compressive stress state was progressively relaxed, but was maintained at some level for the majority of the 2 dpa target dose. Helium pre-injection did not significantly affect the relaxation, but the magnitude of thermally-induced relaxation was somewhat greater, although it was observed to be largely a transient, saturable process. A new cross-section technique was developed that allows multiple observations to be made in one specimen at all depths, both in and beyond the peen-damaged range. The as-peened microstructure varies strongly with depth, consisting of deformation twins and dense dislocation networks. The radiation-induced relaxation on the microstructural level was expressed primarily in modification and reduction of the dislocation structure. A comparison was made between the proton-induced relaxation of internal stresses and predictions 0022-3115/$ -see front matter Ó

Journal of Nuclear Materials, 2004

The effect of the oversized hafnium or platinum (0.3 at.%) solutes on the evolution of irradiated... more The effect of the oversized hafnium or platinum (0.3 at.%) solutes on the evolution of irradiated microstructure in 316SS was investigated. Irradiations were conducted with 5 MeV Ni-ions at 500 °C to doses up to 50 dpa or with 3.2 MeV protons at 400 °C to a dose of 2.5 dpa, and previous studies demonstrated that these irradiations are capable of producing similar irradiated microstructure and microchemistry relevant to LWR cores. Microstructures of 316SS, 316SS+0.3 at.% Pt and 316SS+0.3 at.% Hf were characterized using transmission electron microscopy. The addition of Hf showed a strong effect in suppressing radiation-induced microstructure evolution; no voids were observed at doses up to 50 dpa for Ni-ion irradiation and 2.5 dpa for proton irradiation. The mean diameter of the Frank loops in the Hf-doped samples is about 40% smaller than loops in 316SS. The microstructural examinations from both types of particle irradiation revealed that for 0.3 at.% Pt addition there is no beneficial effect on irradiated microstructure. The mechanisms for the role of oversize solute additions on the microstructure evolution are discussed.

Journal of Nuclear Materials, 2003

ABSTRACT Solution annealed (SA) 304 and cold-worked (CW) 316 austenitic stainless steels were pre... more ABSTRACT Solution annealed (SA) 304 and cold-worked (CW) 316 austenitic stainless steels were pre-implanted with helium and were irradiated with protons in order to study the potential effects of helium, irradiation dose, and irradiation temperature on microstructural evolution, especially void swelling, with relevance to the behavior of austenitic core internals in pressurized water reactors (PWRs). These steels were irradiated with 1 MeV protons to doses between 1 and 10 dpa at 300 °C both with or without 15 appm helium pre-implanted at ∼100 °C. They were also irradiated at 340 °C, but only after 15 appm helium pre-implantation. Small heterogeneously distributed voids were observed in both alloys irradiated at 300 °C, but only after helium pre-implantation. The pre-implanted steels irradiated at 340 °C exhibited homogenous void formation, suggesting effects of both helium and irradiation temperature on void nucleation. Voids developed sooner in the SA304 alloy than CW316 alloy at 300 and 340 °C, consistent with the behavior observed at higher temperatures (>370 °C) for similar steels irradiated in the EBR-II fast reactor. The development of the Frank loop microstructure was similar in both alloys, and was only marginally affected by pre-implanted helium. Loop densities were insensitive to dose and irradiation temperature, and were decreased by helium; loop sizes increased with dose up to about 5.5 dpa and were not affected by the pre-implanted helium. Comparison with microstructures produced by neutron irradiation suggests that this method of helium pre-implantation and proton irradiation emulates neutron irradiation under PWR conditions.

Journal of Nondestructive Evaluation, 2011

The surface of an annealed 316L stainless steel coupon was laser shock peened and Vickers hardnes... more The surface of an annealed 316L stainless steel coupon was laser shock peened and Vickers hardness measurements were subsequently taken of its surface. This Vickers hardness data was compared with measurements taken using the technique of positron annihilation Doppler broadening spectroscopy. When compared, a correlation was found between the Vickers hardness data measurements and those made using Doppler broadening spectroscopy. Although materials with a high defect density can cause the S-parameter measurements to saturate, variations in the S-parameter measurements suggest that through further research the Doppler broadening technique could be used as a viable alternative to measuring a material’s hardness. In turn, this technique, could be useful in industrial settings where surface hardness and surface defects are used to predict lifetime of components.

AIP Conference …, 2006

... Copper: Experiments and Simulation. [AIP Conference Proceedings 845, 725 (2006)]. GT Gray III... more ... Copper: Experiments and Simulation. [AIP Conference Proceedings 845, 725 (2006)]. GT Gray III, E. Cerreta, CA Yablinsky, LB Addessio, BL Henrie, BH Sencer, M. Burkett, PJ Maudlin, SA Maloy, CP Trujillo, MF Lopez. Abstract. ...

Acta Materialia, 2005

ABSTRACT The mechanical response of copper (Cu) and 316 L austenitic stainless steel (SS) shock l... more ABSTRACT The mechanical response of copper (Cu) and 316 L austenitic stainless steel (SS) shock loaded to 6.6GPa in both square-topped and triangular pulse wave configurations has been investigated in compression at room temperature. The microstructure and substructure evolution due to shock pre-straining has been characterized using optical metallography and transmission electron microscopy (TEM). Both Cu and 316 L SS following shock pre-straining exhibit an increase in yield stress. There is, however, a difference in the yield stress measured in Cu samples shocked with a triangular-shaped “Taylor wave-like” pulse versus with a square-top wave; Cu samples shocked with the “Taylor wave-like” pulse shape exhibit a 10% higher yield stress than Cu samples shocked with square-topped wave. Yield stresses for both 316 L shocked with the “Taylor wave-like” and square-topped waves are essentially the same. Cu samples shocked with a triangular-shaped “Taylor wave-like” pulse show subtle microstructural differences to those shocked with a square-top shaped shock pulse loading. In addition, low temperature resistivity measurements also showed differences. Triangular wave shocked samples exhibited the highest resistivity at 4K indicating the highest defect (point and dislocation) formation in copper samples. TEM examinations of copper samples revealed a change in the microstructure after quasi-statically straining (10−3s−1) to 5% plastic strain as compared to that observed in shocked samples (shocked with square-topped and triangular shaped waves) even though the microstructure consists of only dislocation cells. TEM examinations of 316 L SS revealed similar microstructural evolution in all 316 L SS samples: 5% quasi-statically strained, square-top wave and triangular-shaped “Taylor wave-like” shock pre-strained samples, consisting of dislocations, planar slip and twins; however, the amount of twinning appeared higher in the shocked samples.

Acta Materialia, 2003

The objective of this work was to test the Thaveeprungsriporn model for the dependence of creep r... more The objective of this work was to test the Thaveeprungsriporn model for the dependence of creep rate on the coincident site lattice (CSL) fraction. The model attributed the large reduction in creep rate in alloys with a high population of CSL boundaries to the greater difficulty of extrinsic ...

Acta Materialia, 2010

Shock recovery experiments have been conducted to assess the role of shock stress and orientation... more Shock recovery experiments have been conducted to assess the role of shock stress and orientation dependence on substructure evolution and deformation twinning of a [100]/[011¯] copper bicrystal. Transmission electron microscopy of the post-shock specimens revealed that well-defined dislocation cell structures developed in both grains and the average cell size decreased with increasing shock pressure from 5 to 10GPa. Twinning occurred

Journal of Nuclear Materials, 2014

The mechanical properties of AISI 304 stainless steel irradiated for over a decade in the Experim... more The mechanical properties of AISI 304 stainless steel irradiated for over a decade in the Experimental Breeder Reactor (EBR-II) were measured using miniature mechanical testing methods. The shear punch method was used to evaluate the shear strengths of the neutron-irradiated steel and a correlation factor was empirically determined to predict its tensile strength. The strength of the stainless steel slightly decreased with increasing irradiation temperature, and significantly increased with increasing dose until it saturated above approximately 5 dpa. An effective tensile strain hardening exponent was also obtained from the data which shows a relative decrease in ductility of steel with increased irradiation damage. Ferromagnetic measurements were used to observe and deduce the effects of the stress-induced austenite to martensite transformation as a result of shear punch testing.

Journal of Nuclear Materials, 2005

Specimens of 316 L stainless steel were irradiated to 0.5-10.3 dpa at 30-80°C with a mixture of 5... more Specimens of 316 L stainless steel were irradiated to 0.5-10.3 dpa at 30-80°C with a mixture of 500-800 MeV protons and spallation neutrons at the Los Alamos Neutron Science Center (LANSCE). Tensile test results of irradiated 316 L reported earlier had showed hardening and embrittlement with increasing irradiation dose, with significant irradiation hardening occurring at a dose of as low as 0.5 dpa. Transmission electron microscope (TEM) examination of the irradiated microstructure of 316 L showed black-spot damage (small loops) and somewhat larger faulted Frank loops to produce the hardening. There was an initial decrease in uniform elongation at low dose levels from 49% (unirradiated) to 30% at 1.1 dpa, followed by a second, rather abrupt contribution to ductility loss at higher doses ($2.5 dpa) from 21% at 2.5 dpa to 0.5% at 3 dpa. This second drop in ductility was not accompanied by any visible new or enhanced microstructural development. In the current study additional transmission electron microscope investigation was conducted on both as-irradiated and irradiated plus subsequently deformed 316 L in the vicinity of the second abrupt ductility loss ($2.5 dpa). The steel was observed to deform mainly by twinning and no brittle phases were found in the deformation microstructure. It is proposed that gas accumulation with increasing dpa, especially of hydrogen, may be a contributor to this second abrupt decrease in uniform elongation. Although the retained gas (helium and hydrogen) levels approached $0.6 at.% total at the highest exposure level, no discernible cavities were observed.

Controlled shock recovery experiments have been conducted to assess the role of shock pressure an... more Controlled shock recovery experiments have been conducted to assess the role of shock pressure and orientation dependence on the substructure evolution of a [100]/[01{ovr 1}] copper bicrystal. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were utilized to characterize orientation variation and substructure evolution of the post-shock specimens. Well defined dislocation cell structures were displayed in both grains and the average cell size was observed to decrease with increasing shock pressure. Twinning was occasionally observed in the 5 GPa shocked [100] grain and became the dominant substructure at higher shock pressure. The stress and directional dependence of twinning in the bicrystal was analyzed with consideration of the energetically favorable dissociation of dislocations into Shockley partials and the stress-orientation effect on the partial width. Moreover, a critical 'tear apart' stress is proposed and a good agreement is obtai...

DOE Scientific and Technical Information. DOE Scientific and Technical Information. ...

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006

ABSTRACT

Journal of Nuclear Materials, 2005

Neutron irradiation-induced relaxation was emulated using proton irradiation in order to determin... more Neutron irradiation-induced relaxation was emulated using proton irradiation in order to determine the expected amount of stress relaxation in the peened surface layer of a BWR core shroud during its 40 year lifetime. Samples of 304 SS were shot peened to induce a compressive residual stress, and then irradiated with 3.2 MeV protons at 288°C to four dose levels spanning 0.1-2.0 dpa. One set of specimens was as-peened and a second was pre-injected with 25 appm He. Depth-dependent measurements of internal stress were conducted using successive steps of X-ray line broadening measurement and electropolishing. Results showed that the compressive stress state was progressively relaxed, but was maintained at some level for the majority of the 2 dpa target dose. Helium pre-injection did not significantly affect the relaxation, but the magnitude of thermally-induced relaxation was somewhat greater, although it was observed to be largely a transient, saturable process. A new cross-section technique was developed that allows multiple observations to be made in one specimen at all depths, both in and beyond the peen-damaged range. The as-peened microstructure varies strongly with depth, consisting of deformation twins and dense dislocation networks. The radiation-induced relaxation on the microstructural level was expressed primarily in modification and reduction of the dislocation structure. A comparison was made between the proton-induced relaxation of internal stresses and predictions 0022-3115/$ -see front matter Ó

Journal of Nuclear Materials, 2004

The effect of the oversized hafnium or platinum (0.3 at.%) solutes on the evolution of irradiated... more The effect of the oversized hafnium or platinum (0.3 at.%) solutes on the evolution of irradiated microstructure in 316SS was investigated. Irradiations were conducted with 5 MeV Ni-ions at 500 °C to doses up to 50 dpa or with 3.2 MeV protons at 400 °C to a dose of 2.5 dpa, and previous studies demonstrated that these irradiations are capable of producing similar irradiated microstructure and microchemistry relevant to LWR cores. Microstructures of 316SS, 316SS+0.3 at.% Pt and 316SS+0.3 at.% Hf were characterized using transmission electron microscopy. The addition of Hf showed a strong effect in suppressing radiation-induced microstructure evolution; no voids were observed at doses up to 50 dpa for Ni-ion irradiation and 2.5 dpa for proton irradiation. The mean diameter of the Frank loops in the Hf-doped samples is about 40% smaller than loops in 316SS. The microstructural examinations from both types of particle irradiation revealed that for 0.3 at.% Pt addition there is no beneficial effect on irradiated microstructure. The mechanisms for the role of oversize solute additions on the microstructure evolution are discussed.

Journal of Nuclear Materials, 2003

ABSTRACT Solution annealed (SA) 304 and cold-worked (CW) 316 austenitic stainless steels were pre... more ABSTRACT Solution annealed (SA) 304 and cold-worked (CW) 316 austenitic stainless steels were pre-implanted with helium and were irradiated with protons in order to study the potential effects of helium, irradiation dose, and irradiation temperature on microstructural evolution, especially void swelling, with relevance to the behavior of austenitic core internals in pressurized water reactors (PWRs). These steels were irradiated with 1 MeV protons to doses between 1 and 10 dpa at 300 °C both with or without 15 appm helium pre-implanted at ∼100 °C. They were also irradiated at 340 °C, but only after 15 appm helium pre-implantation. Small heterogeneously distributed voids were observed in both alloys irradiated at 300 °C, but only after helium pre-implantation. The pre-implanted steels irradiated at 340 °C exhibited homogenous void formation, suggesting effects of both helium and irradiation temperature on void nucleation. Voids developed sooner in the SA304 alloy than CW316 alloy at 300 and 340 °C, consistent with the behavior observed at higher temperatures (>370 °C) for similar steels irradiated in the EBR-II fast reactor. The development of the Frank loop microstructure was similar in both alloys, and was only marginally affected by pre-implanted helium. Loop densities were insensitive to dose and irradiation temperature, and were decreased by helium; loop sizes increased with dose up to about 5.5 dpa and were not affected by the pre-implanted helium. Comparison with microstructures produced by neutron irradiation suggests that this method of helium pre-implantation and proton irradiation emulates neutron irradiation under PWR conditions.

Journal of Nondestructive Evaluation, 2011

The surface of an annealed 316L stainless steel coupon was laser shock peened and Vickers hardnes... more The surface of an annealed 316L stainless steel coupon was laser shock peened and Vickers hardness measurements were subsequently taken of its surface. This Vickers hardness data was compared with measurements taken using the technique of positron annihilation Doppler broadening spectroscopy. When compared, a correlation was found between the Vickers hardness data measurements and those made using Doppler broadening spectroscopy. Although materials with a high defect density can cause the S-parameter measurements to saturate, variations in the S-parameter measurements suggest that through further research the Doppler broadening technique could be used as a viable alternative to measuring a material’s hardness. In turn, this technique, could be useful in industrial settings where surface hardness and surface defects are used to predict lifetime of components.

AIP Conference …, 2006

... Copper: Experiments and Simulation. [AIP Conference Proceedings 845, 725 (2006)]. GT Gray III... more ... Copper: Experiments and Simulation. [AIP Conference Proceedings 845, 725 (2006)]. GT Gray III, E. Cerreta, CA Yablinsky, LB Addessio, BL Henrie, BH Sencer, M. Burkett, PJ Maudlin, SA Maloy, CP Trujillo, MF Lopez. Abstract. ...

Acta Materialia, 2005

ABSTRACT The mechanical response of copper (Cu) and 316 L austenitic stainless steel (SS) shock l... more ABSTRACT The mechanical response of copper (Cu) and 316 L austenitic stainless steel (SS) shock loaded to 6.6GPa in both square-topped and triangular pulse wave configurations has been investigated in compression at room temperature. The microstructure and substructure evolution due to shock pre-straining has been characterized using optical metallography and transmission electron microscopy (TEM). Both Cu and 316 L SS following shock pre-straining exhibit an increase in yield stress. There is, however, a difference in the yield stress measured in Cu samples shocked with a triangular-shaped “Taylor wave-like” pulse versus with a square-top wave; Cu samples shocked with the “Taylor wave-like” pulse shape exhibit a 10% higher yield stress than Cu samples shocked with square-topped wave. Yield stresses for both 316 L shocked with the “Taylor wave-like” and square-topped waves are essentially the same. Cu samples shocked with a triangular-shaped “Taylor wave-like” pulse show subtle microstructural differences to those shocked with a square-top shaped shock pulse loading. In addition, low temperature resistivity measurements also showed differences. Triangular wave shocked samples exhibited the highest resistivity at 4K indicating the highest defect (point and dislocation) formation in copper samples. TEM examinations of copper samples revealed a change in the microstructure after quasi-statically straining (10−3s−1) to 5% plastic strain as compared to that observed in shocked samples (shocked with square-topped and triangular shaped waves) even though the microstructure consists of only dislocation cells. TEM examinations of 316 L SS revealed similar microstructural evolution in all 316 L SS samples: 5% quasi-statically strained, square-top wave and triangular-shaped “Taylor wave-like” shock pre-strained samples, consisting of dislocations, planar slip and twins; however, the amount of twinning appeared higher in the shocked samples.

Acta Materialia, 2003

The objective of this work was to test the Thaveeprungsriporn model for the dependence of creep r... more The objective of this work was to test the Thaveeprungsriporn model for the dependence of creep rate on the coincident site lattice (CSL) fraction. The model attributed the large reduction in creep rate in alloys with a high population of CSL boundaries to the greater difficulty of extrinsic ...

Acta Materialia, 2010

Shock recovery experiments have been conducted to assess the role of shock stress and orientation... more Shock recovery experiments have been conducted to assess the role of shock stress and orientation dependence on substructure evolution and deformation twinning of a [100]/[011¯] copper bicrystal. Transmission electron microscopy of the post-shock specimens revealed that well-defined dislocation cell structures developed in both grains and the average cell size decreased with increasing shock pressure from 5 to 10GPa. Twinning occurred

Journal of Nuclear Materials, 2014

The mechanical properties of AISI 304 stainless steel irradiated for over a decade in the Experim... more The mechanical properties of AISI 304 stainless steel irradiated for over a decade in the Experimental Breeder Reactor (EBR-II) were measured using miniature mechanical testing methods. The shear punch method was used to evaluate the shear strengths of the neutron-irradiated steel and a correlation factor was empirically determined to predict its tensile strength. The strength of the stainless steel slightly decreased with increasing irradiation temperature, and significantly increased with increasing dose until it saturated above approximately 5 dpa. An effective tensile strain hardening exponent was also obtained from the data which shows a relative decrease in ductility of steel with increased irradiation damage. Ferromagnetic measurements were used to observe and deduce the effects of the stress-induced austenite to martensite transformation as a result of shear punch testing.