Rate Theory Modeling of Irradiation-induced Phosphorus Segregation in FCC nickel Using First Principles Calculations
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1125-R07-35
Rate Theory Modeling of Irradiation-induced Phosphorus Segregation in FCC nickel Using First Principles Calculations Ken-ichi Ebihara*1, Masatake Yamaguchi1, Hideo Kaburaki1, and Yutaka Nishiyama2 1 Center for Computational Science & e-Systems, Japan Atomic Energy Agency (JAEA), Tokai-mura, Naka-gun, Ibaraki 319-1195 JAPAN 2 Nuclear Safety Research Center, Japan Atomic Energy Agency (JAEA), Tokai-mura, Naka-gun, Ibaraki 319-1195 JAPAN *corresponding author: [email protected]
ABSTRACT We have evaluated phosphorus (P) segregation in ion-irradiated nickel (Ni) by the rate theory model incorporating the results of first principles calculations. We find from our first principles calculation that the transport of P via the rotation mode of a mixed-dumbbell is unlikely to occur, and the transport coefficient of phosphorus by the vacancy mechanism is much larger than that reported previously. On the basis of our first principles results, we have also proposed to include the effect of free migration of P via the octahedral interstitial site of FCC Ni crystal in the rate theory model. With all these renewed parameters, we have successfully obtained the P distribution in irradiated Ni, which is very close to experiment, by adjusting the effect of P transport by the vacancy mechanism. INTRODUCTION Irradiation of high energy particles causes damage to materials, and sometimes significantly changes their mechanical properties. Hardening and embrittlement are two of the typical irradiation-induced phenomena that need to be assessed by experiment and simulation. In particular, intergranular embrittlement under the irradiation condition has been focused on from the standpoint of integrity of structural materials in nuclear reactors, because it may lead to degradation of toughness of materials [1]. Intergranular embrittlement is mostly induced by segregation of impurity or solute atoms in the bulk to grain boundaries. Segregation of large atoms is particularly enhanced by the presence of interstitials and vacancies created by irradiation. The mechanism of intergranular embrittlement incurred by sulfur (S) and P has been recently explained from the atomistic level using the first principles method [2]. Segregation of P to grain boundaries is of the utmost importance in reference to irradiation-induced embrittlement [3,4], and a numerical method should be devised to correctly describe this process based on the first principles calculations. In the recent papers [5,6], the detailed atomistic process of segregation in the BCC iron is clarified by the first principles method, and the results are incorporated into the rate theory model to simulate segregation of P to grain boundaries. The validity of the model should finally be checked by experiment, however, this is often hindered by the unavailability of experimental data for irradiated BCC pure iron. On the other hand, the detailed distribution of P due to the irradiation is obtained experimentally for the FCC pure Ni [7], and the transport process of P is simulate
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