A turbine engine works by forcing hot combustion gases from the
burning of fuel to flow through a series of fans, causing them
to spin like a windmill in the wind. Except in this case the
wind is a supersonic blast of burning hot gas and the windmill
is spinning at 20,000+ RPM. To operate efficiently (and they are
very efficient) turbine engines must run at high speeds and high
temperatures, which means the stresses on the turbine blades are
incredible. They have to be very strong,and more importantly
they have to be very strong at very high temperatures. Nickel-
based superalloys make this possible. These particular turbine
blades are old ones taken out of service. They were used in the
famous "Huey" helicopters you've seen countless times in the
movies. Analysis by x-ray fluorescence spectroscopy at the
Center for Microanalysis of Materials, University of Illinois
(partially supported by the U.S. Department of Energy under
grant DEFG02-91-ER45439) indicates that they are mostly iron,
20% chromium, 4% nickel.