Publications

The stress evolution during electrodeposition of NiMn from a sulfamate-based bath was investigated as a function of Mn concentration and current density. The NiMn stress evolution with film thickness exhibited an initial high transitional stress region followed by a region of steady-state stress with a magnitude that depended on deposition rate, similar to the previously reported stress evolution in electrodeposited Ni [S. J. Hearne and J. A. Floro, J. Appl. Phys. 97, 014901-1 (2005)]. The incorporation of increasing amounts of Mn resulted in a linear increase in the steady-state stress at constant current density. However, no significant changes in the texture or grain size were observed, which indicates that an atomistic process is driving the changes in steady-state stress. Additionally, microstrain measured by ex situ x-ray diffraction increased with increasing Mn content, which was likely the result of localized lattice distortions associated with substitutional incorporation of Mn and/or increased twin density.

As current experimental and simulation methods cannot determine the mobility of flat boundaries across the large misorientation phase space, we have developed a computational method for imposing an artificial driving force on boundaries. In a molecular dynamics simulation, this allows us to go beyond the inherent timescale restrictions of the technique and induce non-negligible motion in flat boundaries of arbitrary misorientation. For different series of symmetric boundaries, we find both expected and unexpected results. In general, mobility increases as the grain boundary plane deviates from (111), but high-coincidence and low-angle boundaries represent special cases. These results agree with and enrich experimental observations.

Abstract not provided.

The dynamic compression of molten metals including Sn is of current interest. In particular, experiments on the compression of molten Sn by Davis and Hayes will be described at this conference. Supporting calculations of the equation of state and structure of molten Sn as a function of temperature and pressure are in progress. The calculations presented are ab initio molecular dynamics simulations based on electronic density functional theory within the local density approximation. The equation of state and liquid structure factors for zero pressure are compared with existing experimental results. The good agreement in this case provides validation of the calculations.

Atomistic simulations of the growth of helium bubbles in metals are performed. The metal is represented by embedded atom method potentials for palladium. The helium bubbles are treated via an expanding repulsive spherical potential within the metal lattice. The simulations predict bubble pressures that decrease monotonically with increasing helium to metal ratios. The swelling of the material associated with the bubble growth is also computed. It is found that the rate of swelling increases with increasing helium to metal ratio consistent with experimental observations on the swelling of metal tritides. Finally, the detailed defect structure due to the bubble growth was investigated. Dislocation networks are observed to form that connect the bubbles. Unlike early model assumptions, prismatic loops between the bubbles are not retained. These predictions are compared to available experimental evidence.