Libor Kovarik

Ph.D. The Ohio State University (2006)
M.S. Southern Illinois University (2000)
B.S. Technical University of Ostrava, Czech Republic (1997)
 

Tel:(614)-688-3409, kovarik.8@osu.edu

Ph.D.Thesis

    
  Research

My work is about characterization of artificially aged Al-Mg-Cu-(Si) alloys. The main interest is to study metastable phases that develop at the early and intermediate stages of aging. Alcan International Ltd. is the company that makes it happen. 

  
We are also interested in the age hardening response of this alloy. The figure on the right shows an example of an age hardening response. Perhaps the most interesting feature is the rapid increase in hardness that is achieved in less than 5 minutes of aging. This kind of rapid hardening is also found, for example, in 2xxx series Al-Cu-Mg alloys.
The conventional TEM enables us to characterize the microstructure of the alloy. We detect a presence of small lath-like particles in the matrix after several hours of aging. The edges of the lath-like particles are aligned along the [100]Al and are about 1x4x8 nm in size.
The figure below shows an High resolution transmission electron microscopy (HRTEM) image of the lath-like particle when viewed alond the long side. The particle, which we termed GPB-II zone, is visible in the matrix only due to the slight changes and variations of the periodicity with respect to the surrounding matrix. The Fourier spectrum shows the type of reflections which are associated with the GPB-II zones.
An EDX analysis reveals that the GPB-II zones are not only rich in Mg and Cu but also contain increased amount of Si.
In the later stages of aging we see the S-phase present in the microstructure. We find it both homegeneously and heterogoneuly nucleated in the matrix. Our currently undergoing work looks at the closer characterization of the S-phase, in order to better understand the origin of the modified orientation relationship OR.
For instance, this image of the S-phase was taken using a HAADF STEM. (It shows the lattice fringes of (020)S)

Publications:

  1. Kovarik, L., P.I. Gouma, C. Kisielowski, S.A. Court, and M.J. Mills, High Resolution Transmission Electron Microscopy Study of the Early Stages of Aging in Al-Mg-Cu Alloys. Materials Science Forum, 2002. 396-402: p. 1043-1048.
  2. Kovarik, L., P.I. Gouma, C. Kisielowski, S.A. Court, and M.J. Mills, A HRTEM Study of Metastable Phase Formation in Al-Mg-Cu Alloys During Artificial Aging. Acta Materialia, 2004. 52: p. 2509-2520.
  3. Kovarik, L., P.I. Gouma, C. Kisielowski, S.A. Court, and M.J. Mills, Solid Solution Decomposition of Al-Mg-Cu alloy – A High Resolution Transmission Electron Microscopy Investigation. Materials Science and Engineering, (in press 2004).
  4. Kovarik, L., S.A. Court, and M.J. Mills, HRTEM Observations and Simulations of the S’’-Phase in Al-Mg-Cu Alloys and Implications for Al-Cu-Mg Alloys. Materials Science Forum, (in press 2004).