Department of Metallurgical and Materials Engineering

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Browsing Department of Metallurgical and Materials Engineering by Subject "BEHAVIOR"

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    Carbide Nanoparticle Dispersion Techniques for Metal Powder Metallurgy
    (MDPI, 2021) Rocky, Bahrum Prang; Weinberger, Christopher R.; Daniewicz, Steven R.; Thompson, Gregory B.; University of Alabama Tuscaloosa; Colorado State University
    Nanoparticles (NP) embedded into a matrix material have been shown to improve mechanical properties such as strength, hardness, and wear-resistance. However, the tendency of NPs to agglomerate in the powder mixing process is a major concern. This study investigates five different mechanochemical processing (MCP) routes to mitigate agglomeration to achieve a uniform dispersion of ZrC NPs in an Fe-based metal matrix composite. Our results suggest that MCP with only process controlling agents is ineffective in avoiding aggregation of these NPs. Instead, the uniformity of the carbide NP dispersion is achieved by pre-dispersing the NPs under ultrasonication using suitable surfactants followed by mechanically mixing of the NPs with iron powders in an alcohol solvent which is then dried. High-energy MCP is then used to embed the NPs within the powders. These collective steps resulted in a uniform dispersion of ZrC in the sintered (consolidated) Fe sample.
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    Ferromagnetic (Mn, N)-codoped ZnO nanopillars array: Experimental and computational insights
    (American Institute of Physics, 2014-01-16) Wang, D. D.; Xing, G. Z.; Yan, F.; Yan, Y. S.; Li, S.; Jiangsu University; University of New South Wales Sydney; Harvard University; University of Alabama Tuscaloosa
    To reveal the mechanism responsible for ferromagnetism in transition metal and hole codoped oxide semiconductors, we carry out a comparative study on Mn-doped and (Mn, N)-codoped ZnO nanopillars. Compared with Mn-doped ZnO samples, (Mn, N)-codoped ZnO nanopillars exhibit an enhanced room temperature ferromagnetism. The modulation of bound magnetic polarons via Mn and N codoping corroborates the correlation between the ferromagnetism and hole carriers, which is also verified by first-principles density functional theory calculations. Our study suggests that the electronic band alteration as a result of codoping engineering plays a critical role in stabilizing the long-range magnetic orderings. (C) 2014 AIP Publishing LLC.
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    Plasticity mechanisms in HfN at elevated and room temperature
    (Nature Portfolio, 2016-10-06) Vinson, Katherine; Yu, Xiao-Xiang; De Leon, Nicholas; Weinberger, Christopher R.; Thompson, Gregory B.; University of Alabama Tuscaloosa; Drexel University
    HfN specimens deformed via four-point bend tests at room temperature and at 2300 degrees C (similar to 0.7 T-m) showed increased plasticity response with temperature. Dynamic diffraction via transmission electron microscopy (TEM) revealed < 110 > {111} as the primary slip system in both temperature regimes and < 110 > {110} to be a secondary slip system activated at elevated temperature. Dislocation line lengths changed from a primarily linear to a curved morphology with increasing temperature suggestive of increased dislocation mobility being responsible for the brittle to ductile temperature transition. First principle generalized stacking fault energy calculations revealed an intrinsic stacking fault (ISF) along < 112 > {111}, which is the partial dislocation direction for slip on these close packed planes. Though B1 structures, such as NaCl and HfC predominately slip on < 110 > {110}, the ISF here is believed to facilitate slip on the {111} planes for this B1 HfN phase.