Atomistic modeling of radiation-induced disordering and dissolution at a Ni/Ni 3 Al interface
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Alfredo Caro Materials Science and Technology Division, Los Alamos National Laboratory, New Mexico 87545, USA
Michael J. Demkowicz Department of Materials Science and Engineering, Massachusetts Institute of Technology, Massachusetts 02139, USA (Received 22 September 2014; accepted 25 November 2014)
L12-ordered c9 precipitates embedded in a fcc c matrix impart excellent mechanical properties to nickel-base superalloys. However, these enhanced mechanical properties are lost under irradiation, which causes the c9 precipitates to disorder and dissolve. We conduct an atomic-level study of radiation-induced disordering and dissolution at a coherent (100) facet of an initially ordered c9 Ni3Al precipitate neighboring a pure Ni c matrix. Using molecular dynamics, we simulate collision-induced events by sequentially introducing 10 keV primary knock-on atoms with random positions and directions. In the absence of thermally assisted recovery processes, the ordered Ni3Al layer disorders rapidly within 0.1–0.2 dpa and then gradually dissolves into the adjacent Ni layer at higher doses. Both the disordering efficiency and mixing parameter calculated from the simulations lie within the range of values found by experiments carried out at room temperature, where thermally activated diffusion is insignificant.
I. INTRODUCTION
L12-ordered intermetallic c9 precipitates embedded in a disordered fcc c matrix impart excellent mechanical properties to nickel-base superalloys.1 However, c9 precipitates undergo disordering and dissolution under irradiation, thereby degrading the mechanical properties of these alloys. A great deal of experimental2–11 and theoretical12–18 effort has been devoted to study the stability of the c/c9 microstructure in these superalloys under irradiation. Moreover, several atomic-scale modeling studies have been carried out to elucidate the mechanisms of disordering in Ni3Al,19–30 which is a common c9 precipitate composition in Ni-base alloys. These mechanisms operate over picosecond-scale times, making them difficult to investigate experimentally. Nevertheless, atomic-level simulations of the disordering and dissolution processes of a c9 precipitate in a c matrix under high-dose irradiation have not been conducted before. Such simulations are a means to connect the well-known microscopiclevel mechanisms governing c9 behavior under irradiation to macroscale disordering and dissolution rates. The aim of this study is to present an atomistic model that provides an accurate prediction of radiation-induced disordering and dissolution of c9 precipitates in a c
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.377 J. Mater. Res., 2014
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matrix. Following Zhang and Demkowicz,31 we use classical potential molecular dynamics (MD) to model high-dose irradiation by sequentially simulating multiple collision cascades at a coherent interface of a c9 precipitate in a c matrix. This approach models collision cascadeinduced effect
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