Molecular Statics Simulations of the Motion of a Single Kink in NiAl
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MOLECULAR STATICS SIMULATIONS OF THE MOTION OF A SINGLE KINK IN NiA! T.A.PARTHASARATHY*, D.M.DIMIDUK# AND G.SAADA@
* UES, Dayton, OH-45432 # Wright Laboratory, WL/MLLM, WPAFB, OH-45433 @LEM-CNRS, ONERA, France ABSTRACT
Atomistic simulations of dislocation motion in intermetallics have so far been limited to straight dislocations. In this work, this limitation is relaxed by developing a technique to construct and study dislocation kinks. Using the EAM method, the intermetallic compound, NiAl, is studied using OK simulations of single kinks on a mixed dislocation in the { 110) slip system. The threshold stress for the motion of the kink is calculated as 0.00125-0.00185g(-160-230 MPa), which is fairly close to the CRSS measured at 77 K. These results, suggest that kink motion may be a contributory factor to the slip response of NiAl at low temperatures. INTRODUCTION
The intermetallic NiAl is now recognized as a potential structural material for aerospace applications in the intermediate temperature regime, between 600 & 1000)C [1], although very little is understood about its mechanical behavior. The slip response of NiAl is of particular interest due to its unusual sensitivity to dilute ternary solutes [1,2], heat treatment, and prior thermo-mechanical history [1]. Attempts to develop an understanding of the slip response based on continuum elasticity theories have failed (for a review see[3]). Recent work by Parthasarathy etal. [4] suggests that atomistic simulations of dislocation motion may prove to be a useful technique in understanding the slip response of NiAl. Although, as observed in ref.[4], the atomistic simulations are not without limitations, it is expected that these limitations will be relaxed, moving gradually towards more realistic simulations. The present work addresses one of these limitations and how it may be overcome to yield new details about dislocation motion in this compound. With only a few exceptions, all atomistic simulations of dislocations made to date have been on straight dislocations. However, in reality the motion of dislocations is known to be dominated by the motion of kinks [5]. Further, there are reasons to believe that the high sensitivity of ductility in NiAl single crystals to small amounts of solutes may be related to the interaction of the solutes with dislocation kinks. Thus simulation of the motion of straight dislocations may be an important first step but it cannot be considered complete in capturing all the relevant details. The only work on the simulation of kinks has been that of Duesbery [6,7]. Motivated by the fact that the calculated threshold stress for the motion of the screw dislocation was much larger than the observed flow stress of bcc metals, he studied the behavior of an isolated kink on the screw dislocations of bcc potassium and iron using pairpotentials [6]. He found that the stress to initiate motion of kinks can be much smaller than that required to move straight screw segments. However, this threshold stress for kink motion was too low to explain t
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