Atomistic analysis of the 10(1)over-bar2 twin stability and growth in alpha-Ti

E Martinez and L Capolungo and CN Tome, PHYSICAL REVIEW MATERIALS, 2, 083603 (2018).

DOI: 10.1103/PhysRevMaterials.2.083603

10 (1) over bar2 (1) over bar 011' twin is a prominent deformation mode in hexagonal close-packed materials. It is experimentally observed that twin interfaces are not flat entities, but characterized by kink pairs (KPs) of diverse heights. It has been shown that these kinks or facets delimit basal and prismatic planes. The nature of the defects constituting the facets prescribes their properties, in terms of stability and mobility, which relates to twin growth. In this work, we examine the basic features of such kinks in alpha-Ti from an atomistic modeling viewpoint. We analyze the response of the system with KPs varying in width and height upon normal and shear stresses and under pure bending conditions. We show that bending indeed modifies the interaction energy between kinks, which raises further questions about the nature of the defects. We calculate the nucleation and migration energy barrier for the twin depending on the applied shear stress, resulting in small values, which implies that small thermal energy suffices to activate twin growth. We observe a crossover in the stable height of the KP depending on the applied stress and its width: the wider the KP the higher the most stable. We have developed a twin thickening model that accounts for the thermal KP nucleation and the propagation of the kinks. We show how the model compares satisfactorily with molecular dynamics (MD) simulations. Finally, we have developed a kinetic Monte Carlo methodology to study twin growth, with much less computational burden than MD, that is able to explore the growth rate under a broader set of external conditions.

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