Metallurgy

I understand that this might seem like a rather peculiar post, and perhaps anybody who is not me it might think that it is, but I find that a basic understanding of the physical world around me is not only fascinating, but also helps in understanding so many aspects of the finished product.    My favorite class at University of Missouri, Rolla was metallurgy.

Early scientists accurately measured the strength of the chemical bond between copper atoms.  They then estimated how strong a bar of copper should be by adding up the strengths of all the chemical bonds of all the atoms.  They were perplexed as to why copper is only one thousandths as strong as it should be.  They started the hunt into why most materials are so incredibly much weaker than they theoretically should be.

It turns out that when you bend a metal bar, you do not have to break all the bonds between the atoms at once.  There are always imperfections in the crystal structure of a block of metal.  To bend it, you only have to move these imperfections along, which creates new ones as you do.  A great analogy is a large, heavy rug on the floor.  The imperfections in the metal are like wrinkles in this giant carpet.  Instead of having to drag the whole carpet at once, you can move it slowly along by rolling the wrinkles along and through the carpet, making new wrinkles as you do.

This simple, basic knowledge now explains so much!  This explains why alloys are almost always stronger than the pure metal.  This is because when you add a small amount of a different metal with different sized atoms, it is like placing chairs on this giant carpet.  Now, when you roll the wrinkles along, they hit the chairs and have a difficult time getting past them, thus making the metal much stronger.

This basic analogy also explains why metal gets stronger as you bend it and hammer it.  This technique is what makes Japanese Samurai swords so strong.  As you bend and deform metals, you introduce more and more wrinkles into this giant proverbial carpet.  Another thing to know is that these wrinkles are all going in different directions.  Now imagine trying to roll a wrinkle along when there are many many wrinkles going in all directions.  The wrinkles lock each other up, thus impeding their movement.

A third strengthening method is heat tempering, or quenching.  This is done when you rapidly cool a metal from its molten state such as dropping it into a bucket of water.  By cooling the metal quickly, you don’t give larger crystals time to grow.  Instead, the finished product ends up being made up of many very tiny crystals, all being oriented in different directions.  In this method, the wrinkles in the carpet can’t cross the crystal boundaries and are thus stopped be them.

All of these methods, while making the metal much stronger, also makes them more brittle.  It’s a trade off.

See how fascinating that was?   Do ya?  Do ya?   Now that you know, you can start making samurai swords and tempering you bike frames  : -)