BETTER THAN METALS

Metals are hard, elastic, strong (in tension), and stiff (in bend-ing, compression, torsion, and shear); they can withstand com-paratively high temperatures; and they are, or can be made, malleable and ductile.

But they are also heavy, and they corrode. And in some situa-tions, their fracture can shoot out lethal shards.

However, dream materials are on the way, and some of them are already here. They are stronger and stiffer than metals and can withstand much higher temperatures without disintegrating, but they are light, do not corrode, and when they do break, they go with a whimper, not a bang. Moreover, these materials can be tailored to specific applications to have a specified strength in a certain direction and other properties as needed.

These materials, which have been developed over the last 25 years, are now beginning to come into their own. They are called composites, for they are not homogeneous (made of the same stuff everywhere), but generally consist of two parts: the matrix or car-rier, which is made of a certain bulk material and has the geometric shape of whatever the part is needed for; and the rein-forcement, made of a different material, which is incorporated in the matrix in certain geometric ways, for example: long fibers stretching all one way, whiskers (short fibers) oriented in random directions; particulates filling the matrix with a certain uniform density; or fabrics with the fibers interwoven like the threads of a cloth and the matrix acting as a filler.

The matrix (carrier, filler, bulk material) can be made of one of three materials, which gives the resulting composite its name:

ceramics (ceramic matrix composite, CMC)

polymers (PMC), and

metals (MMC).

A polymer is an organic chemical (in this case a plastic) whose molecule is made up of a chain of identically structured links. Each link consists of a number of chemical elements bonded in the same way to each other and to the next link.

The basic idea of composites is to get the best of both worlds. For example, ceramics can withstand high temperature, but they are brittle, because the tiniest flaw will propagate into a large crack under stress. Filling a ceramic matrix with fibers will stop the propagation of the crack, increasing the strength of the machine part many times, especially when the fibers are oriented in a direc-tion where they best counteract the direction of the stress.

Materials that are many times stronger than metals, can withstand higher temperatures and are lighter, open up pos-sibilities that defy description. Imagine that someone in 1840 had asked "What can you do with all that steel?" What follows is the equivalent of saying "~Well, you can make bridge girders and sewing needles from it."

In the energy field alone, they will revolutionize turbine technol-ogy in its many applications (including power generation) and fuel efficiency of transportation.