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Journal Articles

Energetics of segregation and embrittling potency for non-transition elements in the Ni 5 (012) symmetrical tilt grain boundary; A First-principles study

Yamaguchi, Masatake; Shiga, Motoyuki; Kaburaki, Hideo

Journal of Physics; Condensed Matter, 16(23), p.3933 - 3956, 2004/06

https://doi.org/10.1088/0953-8984/16/23/013

Times Cited Count：97 Percentile：93.71(Physics, Condensed Matter)

A series of non-transition elements bound to the Ni 5(012) symmetrical tilt grain boundary (GB) and the (012) free surface (FS) systems has been studied by first-principles calculation using WIEN2k code. The multilayer relaxations in presence/absence of the solutes are determined by the force minimization. The binding energies at some GB/FS/bulk sites including both interstitial and substitutional sites are calculated for all the non-transition elements between H and $_{86}$ Rn. The GB/FS segregation energy is obtained by calculating the binding energy difference between the GB/FS site and the bulk site. The embrittling potency energy is obtained by calculating the difference between the GB and FS segregation energies based on Rice-Wang model. Our results show that most of the non-transition elements have negative GB/FS segregation energies. Here, this means that there exists a segregation site in the GB/FS. The embrittling potency energies are positive for most of the solutes. However, some exceptions like Be, B, C, and Si having negative and large embrittling potency can enhance the GB cohesion. Our results are found to be consistent with the experimental findings.

Journal Articles

Damage evaluation techniques for FBR and LWR structural materials based on magnetic and corrosion properties along grain boundaries

Hoshiya, Taiji*; Takaya, Shigeru*; Ueno, Fumiyoshi; Nemoto, Yoshiyuki; Nagae, Yuji*; Miwa, Yukio; Abe, Yasuhiro*; Omi, Masao; Tsukada, Takashi; Aoto, Kazumi*

Transactions of the Materials Research Society of Japan, 29(4), p.1687 - 1690, 2004/06

JAERI and JNC have begun the cooperative research of evaluation techniques of structural material degradation in FBR and LWR, which based on magnetic and corrosion properties along grain boundaries. Magnetic method has been proposed as the one of the non-destructive detection techniques on the early stage of creep-damage before crack initiation for aged structural materials of FBRs. The effects of applied stress on natural magnetization were investigated on paramagnetic stainless steels having creep-damages. On the other hand, corrosion properties and magneto-optical characteristics of ion-irradiated stainless steels in the vicinity of grain boundaries were estimated by AFM and Kerr effect microscope, respectively. These degradations were induced by changes in characteristics in the vicinity of grain boundaries. It is found that the initial level of progressing process of damage can detect changes in magnetic and corrosion properties along grain boundaries of aged and degraded nuclear plants structural materials.

Journal Articles

First-principles study on segregation energy and embrittling potency of hydrogen in Ni5(012) tilt grain boundary

Yamaguchi, Masatake; Shiga, Motoyuki; Kaburaki, Hideo

Journal of the Physical Society of Japan, 73(2), p.441 - 449, 2004/02

https://doi.org/10.1143/JPSJ.73.441

Times Cited Count：24 Percentile：71.65(Physics, Multidisciplinary)

The electronic structures of 5(012) symmetrical tilt grain boundary (GB) and (012) free surface (FS) systems for nickel including hydrogen are calculated by the full-potential linearized augmented plane wave method with the generalized gradient approximation. The difference of the binding energies between the 5(012)GB/FS site and the inner bulk site is obtained as the GB/FS segregation energy, and the difference between GB and FS segregation energies as the embrittling potency energy. The segregation position of hydrogen atom is determined by the force minimization. We find that hydrogen atom prefers 5(012)GB to inner bulk energetically by about 0.3 eV/H, while it prefers (012)FS to the GB by about 0.3-0.4 eV/H. The open space at GB may be occupied by an additional interstitial Ni atom since it increases the GB energy by only about 10%. In this case, the GB segregation energy of hydrogen reduces, which makes the segregation difficult. The calculated zero-point energies of hydrogen at inner bulk, GB, and FS sites are within 0.12-0.16eV/H.

Journal Articles

AFM evaluation of grain boundary corrosion behavior on ion irradiated stainless steel

Nemoto, Yoshiyuki; Miwa, Yukio; Tsukada, Takashi; Tsuji, Hirokazu

JAERI-Conf 2003-001, p.397 - 404, 2003/03

https://jopss.jaea.go.jp/pdfdata/JAERI-Conf-2003-001.pdf

It is essential to evaluate corrosion behavior at grain boundary of irradiated materials for mechanistic understanding of Irradiation assisted stress corrosion cracking (IASCC). However there is no suitable technique to evaluate grain boundary corrosion behavior of irradiated materials. The aim of this work is to develop the measurement method for the grain boundary corrosion behavior of irradiated materials using atomic force microscope (AFM). Ni ion was irradiated to solution annealed Fe-18Cr-12Ni alloy at about 573K. The peak damage level was estimated as 1 dpa. To study relationship of grain boundary character and corrosion behavior, orientation imaging microscope (OIM) observation was conducted. After potentiostatic corrosion procedure, the surface of the specimens were examined with AFM and OIM. Some of grain boundaries were corroded, and these were random coincidence grain boundaries. The depth of the corroded region at grain boundaries was successfully evaluated with AFM in nanometer scale.

Journal Articles

Evaluation of corrosion behavior of ion irradiated stainless steel using atomic force microscope

Nemoto, Yoshiyuki; Miwa, Yukio; Tsuji, Hirokazu; Tsukada, Takashi

Dai-12-Kai MAGDA Konfarensu (Oita) Koen Rombunshu, p.191 - 196, 2003/00

Development and research about analytical method for the study of corrosion behavior of austenitic stainless steel after irradiation was conducted from the point of view for basic study of IASCC (Irradiation Assisted Stress Corrosion Cracking). Ion irradiations were conducted with several irradiation conditions these were irradiation temperature, radiation damage, the contents of helium (He) implantation. AFM (Atomic Force Microscope) was used to evaluate surface condition of irradiated specimens after corrosion procedure. Corrosion condition was developed to obtain good surface condition of irradiated specimens to evaluate corrosion behavior by AFM. It was succeeded and corrosion behavior at inside of grains and grain boundaries of irradiated specimens was obtained. EBSP (Electron Backscatter Diffraction Pattern) was used to evaluate relation of corrosion behavior with grain boundary character. Moreover, relations of corrosion behavior with irradiation condition were discussed.

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