Ian McCue
Ian McCue, a graduate student in Dr. Jonah Erlebacher‘s research group, was recently awarded the MRS Graduate Student Award for a presentation on bridging scales in heterogeneous materials at the MRS 2014 Fall Meeting in Boston.
The MRS Graduate Student Awards are intended to honor and encourage graduate students whose academic achievements and current materials research display a high order of excellence and distinction. MRS seeks to recognize students of exceptional ability who show promise for future substantial achievement in materials research. Emphasis is placed on the quality of the student and his/her research ability.
Ian’s presentation was titled “Hierarchical, Bicontinuous Refractory-Based Nanocomposites.” It focused on using liquid metal dealloying to create bulk (cubic centimeters) nanostructures in minutes.
Traditional strengthening mechanisms in metals affect and alter the internal microstructure of the material (dubbed an intrinsic effect), but the overall shape of the material remains unaltered. In contrast, biological materials such as mollusk shells and bone add strength and ductility by controlling the shape of the material (an extrinsic parameter). Over the past decade researchers have been studying a particular extrinsic effect in metal micropillars where the strength of the material increases as you decrease the pillar diameter. You can get up to a factor of 10 increase in strength by just altering the diameter of the material.
The difficulty is scaling up this concept and fabricating a bulk nanostructure, and most attempts are no larger than 100x100x100 um.
Bulk nanostructure developed through liquid metal dealloying. The feature sizes are approximately 2 um.
Using liquid metal dealloying, it is possible to fabricate Ti-X alloys, where X is a refractory element (e.g. Ta, Nb, Mo, Re, W) and immerse them into baths of molten Cu. During this process the Ti atoms dissolve out of the alloy while allowing the refractory component to reorganize into a single crystalline network. Copper remains in the pores and takes the place of the titanium and once the sample is cooled there is a bicontinuous composite with two distinct phases. The mechanical properties are quite amazing, boasting very high strengths as well as high ductility (somewhat unusual because strength and ductility tend to be inversely related).