Friday, January 21, 2011

Catchy Blog Post Title of the Day

When Cleavage is a Bad Thing.

Written by Diandra Leslie-Pelecky over at Cocktail Party Physics, that post discusses a recent Nature Materials report by Demetriou, et alon a tough metallic glass made from an alloy of palladium.

In everyday English, 'strong' and 'tough' may appear to mean the same thing, but in materials engineering, they mean two distinct properties : a material is strong if it resists deformation (denting, bending, or shape change) being hit, poked or pounded; it is tough if it resists fracture (breaking or shattering). Here's Leslie-Pelecky on this difference:

Cleavage [a particularly easy form of fracture] is a good thing for materials you want to break; however, this is not a desireable property if you are trying to build airplanes or buildings. You need a material that is strong which means that it resists changing shape when it is pushed or pulled. You want to be able to put a heavy load on your material without the material denting or bending. You're also looking for toughness, which is a resistance to shattering. If a material is going to give, you'd like it to bend or dent, not shatter.

The study by Demetriou, et al has been making waves -- see here and here -- not only because their palladium-based glass sets a new record for toughness for metallic glasses, but also because it is the first metallic glass that has proven to be "tougher than steel".