Tyler Kaub

Grain Boundary Specific Segregation in Nanocrystalline Fe(Cr)

A cross-correlative precession electron diffraction – atom probe tomography investigation of Cr segregation in a Fe(Cr) nanocrystalline alloy was undertaken. Solute segregation was found to be dependent on grain boundary type. The results of which were compared to a hybrid Molecular Dynamics and Monte Carlo simulation that predicted the segregation for special character, low angle, and high angle grain boundaries, as well as the angle of inclination of the grain boundary. It was found that the highest segregation concentration was for the high angle grain boundaries and is explained in terms of clustering driven by the onset of phase separation. For special character boundaries, the highest Gibbsain interfacial excess was predicted at the incoherent ∑3 followed by ∑9 and ∑11 boundaries with negligible segregation to the twin and ∑5 boundaries. In addition, the low angle grain boundaries predicted negligible segregation. All of these trends matched well with the experiment. This solute-boundary segregation dependency for the special character grain boundaries is explained in terms of excess volume and the energetic distribution of the solute in the boundary.

Intrinsic stress response of low and high mobility solute additions to Cu thin films

Thin film stress is frequently controlled through adjustments applied to the processing parameters used during film deposition. In this work, we explore how the use of solutes with different intrinsic growth properties influences the residual growth stress development for a common solvent Cu film. The findings demonstrated that the addition of a high atomic mobility solute, Ag, or a low atomic mobility solute, V, results in both alloy films undergoing grain refinement that scaled with increases in the solute content. This grain refinement was associated with solute segregation and was more pronounced in the Cu(Ag) system. The grain size reduction was also associated with an increase in the tensile stresses observed in both alloy sets. These findings indicate that solutes can be used to control the grain size under the same deposition conditions, as well as alter the stress evolution of a growing thin film.Thin film stress is frequently controlled through adjustments applied to the processing parameters used during film deposition. In this work, we explore how the use of solutes with different intrinsic growth properties influences the residual growth stress development for a common solvent Cu film. The findings demonstrated that the addition of a high atomic mobility solute, Ag, or a low atomic mobility solute, V, results in both alloy films undergoing grain refinement that scaled with increases in the solute content. This grain refinement was associated with solute segregation and was more pronounced in the Cu(Ag) system. The grain size reduction was also associated with an increase in the tensile stresses observed in both alloy sets. These findings indicate that solutes can be used to control the grain size under the same deposition conditions, as well as alter the stress evolution of a growing thin film.

Ti segregation in regulating the stress and microstructure evolution in W-Ti nanocrystalline films

This paper explores the effect of Tis segregation and corresponding effect on the intrinsic thin film growth stress and microstructural evolution in a series of W1-x(Ti)x alloys where x is varied from 0 to 20 at. %. We report that the addition of the Ti solute reduces the compressive W growth stress, with further reductions achieved through in-situ annealing during growth. Upon examination of the microstructure, Ti did not appear to have a dramatic effect in altering the films grain size and distribution, but it did increase the fraction of low angle grain boundaries. We confirmed that the A15 to bcc W phase transformation, which occurs in the early stages of W growth, diminished with increasing Ti content. This has been explained with respect to Tis preference for gettering residual oxygen, a known stabilizer for the A15 phase. Collectively, this work demonstrates the impact of solute segregation in the control of residual stresses, specific grain boundary formations, and phase transformation control ...

Investigation into Solute Stabilizing Effects in Nanocrystalline Materials: An Atom Probe Characterization Study

Over the past few years, there has been a concerted interest in understanding how solute segregation to grain boundaries stabilizes nanocrystalline materials against grain growth and stress effects [1-3]. To elucidate this behavior, the ability to quantitatively probe the chemistry of the grain boundary is essential. Atom probe tomography is ideally suited to achieve this level of atomic scale chemical analysis. This talk will address how atom probe is providing insights into solute segregation that leads to a variety of different nanocrystalline stabilization conditions.