Grains
We spend a lot of time talking about grains in material science. Grains this, grains that.
Most people don’t know about grains. Who can blame ‘em, they’re usually really tiny, invisible to the human eye, waiting to be have their secrets uncovered by a curious metallographer.
Trees
Most people understand trees - those big things in the yard that look pretty in the autumn. Trees provide us precious oxygen and shade. They are strong, permanent structures that grow imperceptibly slow over our lifetimes. Silent watchers, alive, but unmoving.
I recently visited Savannah, Georgia and stumbled upon the Candler Oak tree. All the trees in savannah are impressive, but the Candler Oak stood out. This tree is the logo for Savannah College of Art and Design and parked outside one of their campus buildings. It’s a very nice tree. Savannah has lots of very nice trees. I didn’t take a picture, but I should have. My phone camera sucks. Here’s someone else’s pic:
The Candler Oak is on Drayton street adjacent to the park in Savannah, you should check it out if you’re in the area. It has some pretty cool history that you should read up on if you are so inclined. It had a role to play in the civil war and is older than the dirt it’s rooted in.
What does that have to do with grains?
Wood
Trees grow from the roots up. Their growth is directional.
Most people can understand that wood has a grain – you can see it in the lines and patterns on a polished piece of wood, running in a certain direction. This grain in wood is a result of the way the tree's cells are arranged and grow.
Wood’s grain structure has drastic implications on the properties of wood. Wood’s grain affects it’s strength, workability, aesthetics, and acoustic properties. In materials science we refer to wood as an anisotropic material, meaning it’s properties are directionally dependent. It doesn’t look the same from all sides and it isn’t as strong from all sides either. An isotropic material has the same properties in all directions. Being anisotropic is neither good nor bad, it simply depends on the application. Wood is an excellent material, scientists can’t do what trees do.
Here’s some nice scanning electron microscopy images and a link to a VERY in-depth write up about reliability in timber structures. You’ll have to click the links to download the full-texts on researchgate. Hopefully I’ll post some of my own wood micrographs someday.
Steak
Steak has a grain, just like wood. Muscles are composed of fibers, cells called myofibrils. They are responsible for contracting and relaxing to enable movement. The fibers grow and align based on the function of a particular muscle. After slaughter, rigor mortis takes hold and the muscles become stiff.
The carnivorous among us recommend cutting your steak against the grain to break up the long muscle fibers. This gives a more tender bite.
Wood is like tree meat. Or is steak like cow wood? Hmm.
Metals
In metal, grains are somewhat similar, but on a microscopic scale. Instead of cells, metals have grains, which are tiny crystals formed during the solidification process. When molten metal cools and solidifies, atoms arrange themselves into a crystalline structure. These crystals grow in various directions and meet, forming boundaries. Each individual crystal is called a grain, and the boundaries where they meet are known as grain boundaries.
The size, shape, and orientation of these grains can significantly affect the properties of the metal, such as its strength, toughness, and ductility. This is why we’re very interested in grain boundaries as metallographers and metallurgists.
Here’s an 11 minute video on solidification/freezing/crystallization, whatever you want to call it. The visuals in that video really help you see how the process of a metal going from molten to solid - freezing. It’s the same mechanism that turns water to ice. I think it’s easy to get hung up on freezing being for “cold” things. When I start thinking about metal solidification like ice, it’s easier for me to wrap my head around.
Whether it’s steak, wood, or metal- grains are there, hiding their secrets beneath the surface. Just like you can count the rings on a tree to determine age, there are many intricacies to be learned by looking at the grain structure of metals.
