Small is Beautiful

by ErinRose Handy


"Is it scandium?"

This is the question du jour among mountain bike enthusiasts, and they're willing to pay top dollar—upwards of $2,500—for a frame constructed with it. Welcome to the world of high-performance sporting equipment, where participants pay a premium for gear. Strength of material can save athletes from devastating injury, and a single ounce can mean a competitive edge.

An expert in designing metals for mechanical performance, Assistant Professor Chad Sinclair studies nanostructured metals. Unlike traditional engineering materials, the internal structure of nanostructured metals is composed of sheets, ribbons or spheres separated by as little as a few atoms. For instance, aluminum-scandium alloys used in high-performance mountain-bike frames contain scandium in the form of perfect spheres no more than five atoms in diameter, dispersed within the aluminum. It is these very small spheres that impart the strength to the lightweight aluminum bike frames.


Chad Sinclair
(Photo: ErinRose Handy)

 

"It's a common adage in the industry-small is beautiful," says Sinclair, referring to the creation of bulk materials from the smallest of particles. Nanostructured materials can reflect properties that do not obey simple laws deduced for bulk materials but instead may offer extraordinary strength, hardness and resistance to fracture. In many cases these mechanical properties can be obtained in combination with other important properties, such as electrical and thermal conductivity, temperature resistance, low density and/or magnetic properties that make these materials relevant today and very promising for future applications.

Sinclair is conducting pioneering research to develop materials on a microstructural scale. Microstructure refers to the lengthscales within a material that dictate its behaviour-such as how strong or hard it is. A piece of metal may appear uniform, but it is in fact constructed of constituent crystals, in turn made up of sub-crystals that are in turn made from groupings of atoms. Each of these layers in the material is associated with a smaller and smaller length. The atom is the smallest length Sinclair works with.

"By experimenting with these scales, we can force materials to behave in a way that Mother Nature never intended," says Sinclair. "We frustrate the material by inserting roadblocks in the form of
internal boundaries." Imagine, for instance, a crack in a material. For the material to break, the
crack must travel through the material. At each internal boundary, the crack is forced to change direction or to slow down, thereby frustrating the process of fracture. The more internal boundaries, the greater the force that must be applied to keep the crack moving through the material. Using a concept similar to genetic engineering, Sinclair can select a desirable quality and replicate it from the most basic level, tailoring engineering materials from the atomic scale up.

Since his position commenced in the Department of Materials Engineering in 2001, Sinclair has worked on a variety of nanostructured materials, including aluminum-scandium alloys used in sporting-equipment and in aerospace industries, novel high-strength stainless steels used in the automotive industry and copperniobium materials used in the construction of very strong magnets used in magnetic-resonance imaging (MRI) machines. The goal of his work has been to understand how and why these materials perform in the way that they do and to find new ways of fabricating advanced materials.  

In the twenty-first century, demand for new materials is being driven by the need for increasingly sophisticated combinations of properties-mechanical, electrical and optical-
unavailable in traditional engineering materials. Nanostructured metals appear well positioned
to address the desideratum. As long as there is a desire for lighter, stronger, better, there will be an
increasing impetus to make materials engineered from the atomic scale.

 

This article was first published in Ingenuity, the Faculty of Applied Science Engineering newsletter.