Ph.D. Student (alumnus)

Dispersion Strengthened Cast aluminum-scandium alloys.

Email: john.defouw(@gmail.com)

B.S., Engineering and Applied Science, California Institute of Technology

I am originally from Richland, WA. It was there that I first developed an interest in materials science--through blacksmithing. I earned my Bachelor of Science degree from the California Institute of Technology in 2002 in Engineering and Applied Science. I studied materials science there. I worked at the Laser Interferometer Gravitational Wave Observatory at Hanford for one summer. I then did research with Assistant Professor Ersan Üstündag's group, including work for the Spectrometer for Materials Research at Temperature and Stress at Los Alamos National Lab.

At Northwestern University, I studied Al-Sc alloys with additional rare earth elements, which are heat resistant. The rare earth additions are expected to change the aging behavior and properties of the precipitates. In addition to performing creep experiments and simulations, I employed Transmission Electron Microscopy and 3-Dimensional Atom Probe Microscopy to study the microstructure of the material.

I also concluded a study of aluminum-scandium (Al-Sc) and aluminum-scandium-zirconium (Al-Sc-Zr) alloys that are reinforced with alumina (Al2O3) particles. The several nanometer Al3ScZr precipitates and the sub-micron Al2O3 both strengthen the alloy. These high temperature aluminum alloys can be used effectively up to at least 350 C.

The precipitates are formed after aging the alloy which was conventionally cast with master alloys. Particle reinforcements are added by Dispersion Strengthened Casting (DSC) by Chesapeake Composites. I then studied the mechanical properties of the material--most notably its creep resistance. DSC-Al-Sc and DSC-Al-Sc-Zr exhibit very high threshold stresses. If the loading does not exceed these threshold stresses, the creep rate isn't experimentally measurable. I also employed dislocation climb and detachment models in order to explain this behavior.

Publications

1. R. A. Karnesky, et al., "Best-Fit Ellipsoids of Atom-Probe Tomographic Data to Study Coalescence of ?' (L12) Precipitates in Ni-Al-Cr," Scripta Materialia, 57 , 353-356 (2007).
2. R. A. Karnesky, et al., "Direct Measurement of 2-Dimensional and 3-Dimensional Interprecipitate Distance Distributions from Atom-Probe Tomographic Reconstructions," Applied Physics Letters , 91 , 013111:1-3 (2007).
3. Alan Brothers, Richard Scheunemann, John DeFouw, David Dunand. “Processing and Structure of Open-Celled Amorphous Metal Foams.” Scripta Materialia 52 335 2005.
4. R. A. Karnesky, et al., "Strengthening Mechanisms in Aluminum Containing Coherent Al3Sc Precipitates and Incoherent Al2O3 Dispersoids," Acta Materialia, 55 , 1299-1308 (2007).
5. R. A. Karnesky, et al., "Creep of Al-Sc Microalloys with Rare-Earth Element Additions," Materials Science Forum , 519-521, 1035-1040 (2006).