The Effect of Temperature on The Structure of Grain Boundaries in Ni 3 Al with and without Boron
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THE EFFECT OF TEMPERATURE ON THE STRUCTURE OF GRAIN BOUNDARIES IN Ni3Al WITH AND WITHOUT BORON DONGLIANG LIN (T. L. LIN), JIAN SUN, DA CHEN AND MIN LU
Department of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200030, P. R. China
ABSTRACT Monte Carlo computer simulations with embedded atom method potentials are used to study the structure and energy of symmetric tilt grain boundaries in NisA1 at high temperatures and compared with those at absolute zero, which is conducted with static relaxation method. The effect of stoichiometry and boron addition on the structure and energy of grain boundary are also investigated. The simulation results show that there exists more compositional disorder at grain boundaries than in the bulk in non-stoichiometric Ni3 AI with and without boron. At absolute zero the grain boundary consists of periodically distributed structural units which are distorted with the increasing temperature. The effect of temperature on the structure and energy of grain boundaries in NiA1 with and without boron was discussed. INTRODUCTION The main reason for studies of grain boundaries in intermetallic compound Ni3A1 is that the grain boundaries are intrinsically brittle, and the segregation of boron to grain boundaries dramatically improves the ductility in polycrystalline Ni3Al. Recently, there has been some atomic simulation studies of the structure and property of grain boundaries in intermetallic Ni3A1 [1-4]. It has been shown that the intrinsic brittleness of grain boundaries in ordered compound is related to the preference for chemical order [1], and the presence of boron at grain boundaries increases the grain boundary cohesion, in particular at Ni-rich grain boundaries [2]. These results suggest that boron doping at grain boundaries should decrease the tendency for brittle fracture in polycrystalline NiSA]. However, most of these calculations have been conducted at zero temperature. The temperature effects are particularly important because compositional disordering and spatial disordering at grain boundaries are expected for high temperatures. The Monte Carlo and Free Energy simulations have been conducted to calculate these questions [3,4]. In the present study, Monte Carlo (MC) simulation with embedded atom method (EAM) potentials are used to study the structure and energy of symmetric tilt grain boundaries (GBs) [101] 3 / (121) in NiA1 at 500K and 1200 K, and compared with those at zero temperature, which is conducted with energy gradient method. The effect of stoichiometry and boron addition on the structure and energy of GBs are also considered in this study. Finally, the effect of temperature on the structure and energy of the GBs was discussed.
COMPUTATIONAL PROCEDURES Monte Carlo simulations were performed empolying EAM potentails on bi-crystal slab, which used the N. Metropolis et al. algorithm [5] based on a stochastic process which, by moving atoms one at a time, generates a Boltzmanweighted chain of phase configurations of a given N-atom system. We ad
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