An Alloy of Iron and Aluminum Is as Good as Titanium, Tenth the Cost
February 5th, 2015Via: The Economist:
The obvious way out of this is to alloy steel with a lighter metal. And the obvious one to choose is aluminium, which is, like iron (steel’s principal component), cheap and abundant. An alloy of iron, aluminium and carbon (steel’s other essential ingredient) is too brittle to be useful. Adding manganese helps a bit, but not enough for aluminium-steel to be used in vehicles.
Dr Kim and his colleagues have, however, found that a fifth ingredient, nickel, overcomes this problem. To a chemist, an alloy is a mixture of materials rather than a true chemical compound. But metals do sometimes react to form real compounds, and one class of these, known as B2 intermetallic compounds (which have equal numbers of atoms of two different metals within them), lies at the heart of Dr Kim’s invention. The nickel reacts with some of the aluminium to create B2 crystals a few nanometres across. These crystals form both between and within the steel’s grains when it is annealed (a form of heat treatment).
B2 crystals are resistant to shearing, so when a force is applied to the new material they do not break. This stops tiny cracks propagating through the stuff, which gives it strength. That strength, allied with the lightness brought by the aluminium, is what Dr Kim was after.
