Browsing by Author "Zhou, Xuyang"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Grain Boundary Specific Segregation in Nanocrystalline Fe(Cr)
    (2016-10-06) Zhou, Xuyang; Yu, Xiao-xiang; Kaub, Tyler; Martens, Richard L.; Thompson, Gregory B.; University of Alabama Tuscaloosa
    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.
  • Thumbnail Image
    Item
    Influence of solute segregation on stress and structure evolution in nanocrystalline thin films
    (University of Alabama Libraries, 2018) Zhou, Xuyang; Thompson, Gregory B.; University of Alabama Tuscaloosa
    Alloy thin films offer several tantalizing opportunities to engineer the growth and subsequent stress conditions in thin films. This can be achieved by the mixed interaction of two or more species. For example, grain size is a known quantity in regulating the stress and is most often controlled through processing via pressure, temperature, deposition rate, or a combination of each of these variables. In an alloy, where one species is highly segregating, the solute can also control the grain size and therefore the stress. Based on this hypothesis, this work has elucidated how alloying effects in the residual growth stresses for a series of W-Cr, W-Fe, and Fe-Cr thin films. In addition, a molecular dynamics (MD) model for the growth of elemental W and Fe films was constructed to understand how different microstructures and processing variables control stress.
  • Thumbnail Image
    Item
    Interrelationship of in Situ Growth Stress Evolution and Phase Transformations in Ti/W Multilayered Thin Films
    (2016-06-24) Thompson, Gregory B.; Wan, Li; Yu, Xiao-Xiang; Zhou, Xuyang; University of Alabama Tuscaloosa
    This paper addresses the in situ growth stress evolution and phase transformation of bcc to hcp Ti in Ti/W multilayered thin films. A series of equal layer thicknesses from 20 nm to 1 nm were deposited. As the bilayer thickness reduced, the overall film stress became less compressive until the Ti transformed from hcp (at the larger layer thicknesses) to bcc in the 1 nm/1 nm multilayer. The pseudomorphic bcc stabilization resulted in a recovery of the compressive stress to values near that for the bulk phase stabilized for the 5 nm/5 nm multilayer. A discernable change in stress slope was noted for the bcc to hcp Ti transition as a function of Ti layer thickness. The stress states for each film, during film growth, are rationalized by the lattice matching of the phase with the growth surface. These results are coupled to a molecular dynamics deposition simulation which revealed good agreement with the experimentally observed transformation thickness.