• Nuclear Engineering and Technology
• /
• 제56권6호
• /
• pp.2071-2078
• /
• 2024

The precipitation of solutes is a major cause of irradiation hardening and embrittlement limiting the service life of reactor pressure vessel (RPV) steels. Impurities play a significant role in the formation of precipitation in RPV materials. In this study, the effects of carbon on cluster formation and irradiation hardening were investigated in an RPV alloy Fe-1.35Mn-0.75Ni using C and Fe ions irradiation at 290 ℃. Nanoindentation results showed that C ion irradiation led to less hardening below 1.0 dpa, with hardening continuing to increase gradually at higher doses, while it was saturated under Fe ion irradiation. Atom probe tomography revealed a broad size distribution of Ni-Mn clusters under Fe ion irradiation, contrasting a narrower size distribution of small Ni-Mn clusters under C ion irradiation. Further analysis indicated the influence of carbon on the cluster formation, with solute-precipitated defects dominating under C ion irradiation but interstitial clusters dominating under Fe ion irradiation. Simulations suggested that carbon significantly affected solute nucleation, with defect clusters displaying smaller size and higher density as carbon concentration increased. The higher hardening at doses above 1.0 dpa was attributed to a substantial increase in the number density of defect clusters when carbon was present in the matrix.

• 한국분말재료학회지
• /
• 제30권5호
• /
• pp.431-435
• /
• 2023

An irradiation hardening of Inconel 718 produced by selective laser melting (SLM) was studied based on the microstructural observation and mechanical behavior. Ion irradiation for emulating neutron irradiation has been proposed owing to advantages such as low radiation emission and short experimental periods. To prevent softening caused by the dissolution of γ' and γ" precipitates due to irradiation, only solution annealing (SA) was performed. SLM SA Inconel 718 specimen was ion irradiated to demonstrate the difference in microstructure and mechanical properties between the irradiated and non-irradiated specimens. After exposing specimens to Fe³⁺ ions irradiation up to 100 dpa (displacement per atom) at an ambient temperature, the hardness of irradiated specimens was measured by nano-indentation as a function of depth. The depth distribution profile of Fe³⁺ and dpa were calculated by the Monte Carlo SRIM (Stopping and Range of Ions in Matter)-2013 code under the assumption of the displacement threshold energy of 40 eV. A transmission electron microscope was utilized to observe the formation of irradiation defects such as dislocation loops. This study reveals that the Frank partial dislocation loops induce irradiation hardening of SLM SA Inconel 718 specimens.

• Nuclear Engineering and Technology
• /
• 제53권9호
• /
• pp.2960-2967
• /
• 2021

In this work, a new hardening model is proposed for the depth-dependent hardness of ion-irradiated polycrystals with obvious grain size effect. Dominant hardening mechanisms are addressed in the model, including the contribution of dislocations, irradiation-induced defects and grain boundaries. Two versions of the hardening model are compared, including the linear and square superposition models. A succinct parameter calibration method is modified to parametrize the models based on experimentally obtained hardness vs. indentation depth curves. It is noticed that both models can well characterize the experimental data of unirradiated polycrystals; whereas, the square superposition model performs better for ion-irradiated materials, therefore, the square superposition model is recommended. In addition, the new model separates the grain size effect from the dislocation hardening contribution, which makes the physical meaning of fitted parameters more rational when compared with existing hardness analysis models.

• Nuclear Engineering and Technology
• /
• 제48권3호
• /
• pp.758-764
• /
• 2016

Specimens of stainless steel reactor internals were irradiated with 240 keV protons and 6 MeV Xe ions at room temperature. Nanoindentation constant stiffness measurement tests were carried out to study the hardness variations. An irradiation hardening effect was observed in proton- and Xe-irradiated specimens and more irradiation damage causes a larger hardness increment. The Nix-Gao model was used to extract the bulk-equivalent hardness of irradiation-damaged region and critical indentation depth. A different hardening level under H and Xe irradiation was obtained and the discrepancies of displacement damage rate and ion species may be the probable reasons. It was observed that the hardness of Xe-irradiated specimens saturate at about 2 displacement/atom (dpa), whereas in the case of proton irradiation, the saturation hardness may be more than 7 dpa. This discrepancy may be due to the different damage distributions.

• Nuclear Engineering and Technology
• /
• 제51권8호
• /
• pp.1970-1977
• /
• 2019

Understanding the irradiation hardening effect of structural steels under various irradiation conditions plays an important role in developing advanced nuclear systems. Such being the case, a crystal plasticity model for body-centered cubic (BCC) crystal based on the density of dislocations and irradiation defects is summarized and numerically implemented in this paper. Based on this model, nano-indentation hardness of Chinese A508-3 steels with ion irradiation is calculated. Very good agreement is observed between simulation and experimental data of several different irradiation doses subjected to various operating temperatures, from which, it can be concluded that indentation hardness increases with increasing irradiation dose at both room temperature and high temperature. Consequently, the validity of this model has been proved properly, and furthermore, the model established in this paper could guide the study of irradiation hardening effect and temperature effect to some extent.

• Nuclear Engineering and Technology
• /
• 제54권7호
• /
• pp.2408-2417
• /
• 2022

The nanoindentation behavior of P92 steel with thermomechanical treatment under 3.5 MeV Fe¹³⁺ ion irradiation at room temperature, 400 and 700 ℃ was investigated. Pop-in behavior is observed for all the samples with and without irradiation at room temperature, while the temperature dependence of pop-in behavior is only observed in irradiated samples. The average load and penetration depth at the onset of pop-in increase as the irradiation temperature increases, in line with the results of the maximum shear stress. Irradiation induced hardening is exhibited for all irradiated samples, but there is a significant reduction in the hardness of sample irradiated at 700 ℃ in comparison to the samples irradiated at room temperature and 400 ℃. The ratio of hardness to elastic modulus for all samples decreases with increasing penetration depth except for samples at 700 ℃. With the increasing of irradiation temperature, the ratio of the irreversible work to the total work gradually decreases. In contrast, it increases for samples without irradiation.

• 한국세라믹학회지
• /
• 제41권6호
• /
• pp.430-434
• /
• 2004

The values of fracture energy and mechanical flexural strength of Fiber Reinforced Cement (FRC) with polypropylene (PP) fiber modified by Ion Assisted Reaction (JAR), by which functional groups were grafted on the surface of PP fiber, was improved about 2 times as those of fracture energy and flexural strength of cement reinforced by untreated PP fiber. PP fiber was irradiated in O$_2$ environment by Ar$\^$+/ ion. The contact angle of PP treated by IAR decreased largely when compared with untreated PP. From this result, we expected that surface energy and interfacial adhesion force of treated PP fiber increased. The strain hardening occurred in the strain-stress curve of FRC including PP treated by IAR when compared with that of FRC with untreated PP. These enhanced mechanical properties might be due to strong interaction between hydrophilic group on modified PP fiber and hydroxyl group in cement matrix. This hydrophilic group on surface modified PP fiber was confirmed by XPS analysis. We clearly observed hydration products that were fixed at modified PP fiber due to the strong adhesion force of interface in cement reinforced modified PP by SEM (Scanning Electron Microscopy) study.

• 한국레이저가공학회지
• /
• 제3권2호
• /
• pp.35-43
• /
• 2000

Laser direct patterning of the coated photoresit (PMER-NSG31B) layer was studied to make halftone dots on gravure printing roll. The selective laser hardening of photoresist by Ar-ion laser(wavelength : 333.6nm∼363.8nm) was controlled by the A/O modulator. The coating thickness in the range of 5㎛∼11㎛ could be obtained by using the up-down directional moving device along the vertically located roll. The width, thickness and hardness of the hardened lines formed under laser power of 200∼260㎽ and irradiation time of 4.4∼6.6$\mu$ sec/point were investigated after developing. The hardened width increased according to the increase of coating thickness. Though the hardened thickness was changed due to the effect of the developing solution, the hardened layer showed good resistance to the scratching of 2H pencil. Also, the hardened minimum line widths of 10㎛ could be obtained. The change of line width was also found after etching, and the minimum line widths of 6㎛ could be obtained. The hardened lines showed the good resistance to the etching solution. Finally, the experimental data could be applied to make gravure halftone dots using the developed imaging process, successfully.

• International Journal of Precision Engineering and Manufacturing
• /
• 제3권1호
• /
• pp.26-32
• /
• 2002

Laser direct patterning of the coated photoresist (PMER-NSG31B) layer was studied to make halftone dots on the gravure printing roll. The selective laser hardening of the photoresist by Ar-ion laser(wavelength: 333.6∼363.8 nm) was controlled by the A/O modulator. The coating thickness in the range of 5∼11㎛ could be obtained by using the up-down directional moving device along the vertically located roll. The width, thickness and hardness of the hardened lines farmed under the laser power of 200∼260mW and irradiation time of 4.4∼6.6 $\mu$ sec/point were investigated after developing. The hardened width increased as the coating thickness increased. Though the hardened thickness was changed due to the effect of the developing solution, the hardened layer showed good resistance to the scratching of 2H pencil. Also, the hardened minimum line width of 10㎛ could be obtained. The change of line width was also found after etching, and the minimum line widths of 6㎛ could be obtained. The hardened lines showed the good resistance to the etching solution. Finally, the experimental data could be applied to make gravure halftone dots using the developed imaging process, successfully.

• Radiation Oncology Journal
• /
• 제14권4호
• /
• pp.323-332
• /
• 1996

목적 : 방사선 치료에 있어서 조직내 등선량 분포곡선을 변형시킬 목적으로 쐐기 차폐물이 사용되고 있는데 최근 기존의 고정 쐐기와는 다르게 비대칭적인 콜리메이터인 Independent Jaw에 의해 등선량 분포곡선을 변형시키는 동적 쐐기 기법이 실용화 되고 있으나 아직 그 방사선 물리학적인 특성에 대해서는 잘 알려져 있지 않다. 이에 본 저자는 기존의 고정 쐐기와 비교하여 조직내 방사선량 분포의 특성을 알아보고자 본 연구를 계획하였다. 대상 및 방법 : 물 판톰, 폴리 스타이린 판톰, 평균 유방 모형 판톰을 대상으로 전리함, 필름, TLD 등을 이용하여 동적 쐐기와 고정 쐐기의 선량 분포를 측정하여 비교하였다. 방사선원은 선형 가속기의 6MV x선을 사용하였고 $15{\times}15$ 조사면에서 15, 30, 45도 쐐기를 이용하였다 조직내선량 분포는 전리함과 필름 선량계를 사용하였고, 유방 접선 치료방식에서의 반대편 유방 조사선량은 TLD를 사용하였다. 결과 : 1) 조직내 $\%$심도 선량은 고정 쐐기의 경우 심도 선량 깊이가 깊어지는 방사선의 경화 현상이 뚜렷하였으나 동적 쐐기의 경우에는 발견할 수 없었으며 그 $\%$심도선량은 개방 조사면과 유사하였다. 2) 조직내 등선량 분포 곡선을 보면 동적 쐐기의 경우 고정 쐐기와는 달리 원하는 깊이, 원하는 조사면에서 원하는 쐐기 각도를 얻을 수 있었으며 쐐기 각도를 이루는 등선량 분포 곡선이 고정 쐐기에 비해 더욱 직선적이었다. 3) 산란선량은 동적 쐐기의 경우 개방 조사면과 그 양이 거의 동일하였으며 유방보존술에서의 접선 조사방식의 방사선치료에서 고정 쐐기 대신에 동적 쐐기를 사용함으로써 반대측 유방으로의 피폭선량을 감소시킬 수 있었다. 결론적으로 동적 쫴기 기법은 단순히 고정 쐐기를 대체할 수 있을 뿐만 아니라 고정 쐐기의 단점을 보완해 줄 수 있으며 향후 방사선 치료에 있어서 더 다양한 유용성을 가질 수 있으리라 생각한다.