Keith Knipling

Keith Knipling at the TEM.
Research:	Aluminum Alloys
Education:	Ph.D., Materials Science Northwestern University B.S., Materials Science and Engineering Virginia Tech
Publications:	Publications by Knipling in our database
Contact
Dr. Keith Knipling Naval Research Lab Phone: Email: Fax:

Things are made of stuff. We design the stuff. That's my typical response to the oft-asked question, What is Materials Engineering. I have long held an enduring fascination in the nature and structure of materials, and I suppose it is my interest in sports like cycling, skiing, and whitewater paddling are what first got me interested in this area.

I am originally from Virginia, and grew up on Mason Neck of the Potomac River, about 20 miles south of Washington, D.C. I went to the Thomas Jefferson High School for Science and Technology, which is the Governor's Regional School serving the Northern Virginia area. During my senior year I designed and fabricated a Kevlar and carbon fiber composite whitewater kayak in the Prototyping and Engineering Materials Lab. (And yes, it floats).

I earned both my B.S. and M.S. degrees from Virginia Tech, and thru-hiked the 2,160-mile long Appalachian Trail from Maine to Georgia after my undergraduate degree. This journey, which took me 5 1/2 months, profoundly changed my life. You can go here to see some of my pictures from the AT on my personal website.

I have graduateed with a PhD under Professors David Dunand and David Seidman at Northwestern University just north of Chicago, IL. My research involved engineering a new nanoscale precipitation-strengthened aluminum alloy for high temperature applications. This work was funded by the DOE Office of Basic Energy Sciences.

Based on the behavior of nickel-base superalloys, which resist degradation of mechanical properties to approximately 75% of their absolute melting temperature, it is conceivable that aluminum-based alloys could be similarly developed which would be useful to 400 °C. As is true for γ’ in the nickel-base systems, a high-temperature aluminum alloy must contain a large volume fraction of a suitable dispersed phase, which must be thermodynamically stable at the intended service temperature. Trialuminide intermetallic compounds (Al₃X) have many attractive characteristics, such as low density, high specific strength, good heat resistance and excellent oxidation resistance. Therefore, they are excellent candidates for use as dispersoids or precipitates in the design of high strength Al alloys for high temperature applications.

My contributions to this endeavor was primarily experimental in nature, and my role was to identify the relationships between the structure of the two-phase (nanoscale precipitates imbedded in Al solid solution) alloys and the observed mechanical properties at ambient and elevated temperatures. These objectives were met by exploiting numerous materials characterization techniques. Both conventional- (CTEM) and high-resolution transmission electron microscopy (HREM) were used to identify the morphological and temporal evolution of the structure of the aged alloys on the nanometer scale. Ultimately, 3-dimensional atom probe (3DAP) microscopy was utilized to examine the chemical composition of the precipitates and their interfaces within the ternary alloys in the presence of segregating solute atoms. From these analyses we uncovered a wealth of information including: (i) the existence of cubic L1₂ precipitates in the aged alloy; (ii) the partitioning of solute atoms between the matrix and the precipitates; (iii) the relative Gibbsian interfacial excess of solute atoms at the matrix/precipitate interfaces; (iv) the mechanism of precipitate formation; and (v) the temporal evolution of the precipitates. Finally, the alloys were evaluated by examining their ambient temperature mechanical properties (utilizing microhardness measurements), their elevated temperature mechanical properties (in the form of creep properties), and ultimately correlating these results to their microstructure (precipitate size, morphology, and volume fraction)