Atomistic Study of Grain Boundary Sliding



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Creep is the time-dependent mechanical plastic deformation at high temperatures (usually higher than half of the melting temperature) and stresses far below the yield stress. In both the creep deformation and damage, grain boundary sliding (GBS) plays a critical role. For example, in ceramics, GBS is the predominant mechanism since dislocation activity is quite suppressed. Although decades of work have gone in understanding GBS, there are several open questions like an appropriate GBS constitutive law and determination of the threshold stress for sliding. Molecular Dynamics (MD) simulation performed by Qi and Krajewski establish a linear fit to the constitutive response which gives a sliding velocity of the order of km/sec. Their predicted threshold stress is 20 times the yield stress of the material. Since this is due to the time scale limitations of the MD method, we adopt a novel algorithm, Autonomous Basin Climbing (ABC) in conjunction with Nudged Elastic Band (NEB) and Transition State Theory (TST) to do atomistic calculation.

The observations in atomistic calculations, that the sliding rate is lower than the previous atomistic calculations by several orders of magnitude, has given a way to bridge the gap between experiments and simulations on GBS. Finally, we propose a constitutive law for GBS which shows a trend towards lower values of threshold stress.



Creep, Grain boundaries, Sliding, Materials, Aluminum, Autonomous Basin Climb