Primary Fabrication Processes for Nickel and Iron Aluminides

Alloys based on the intermetallic compounds Ni₃Al and Fe₃Al have been developed. Intermetallic compounds are characteristically brittle at room temperature, and some are also brittle at elevated temperatures. Nickel-aluminide alloys have been made ductile by alloying with a small amount of boron (200 ppm by weight) and adjusting the aluminum content to 24 at. % or less. Iron-aluminide alloys are ductile when chromium is added (>wt 2%) and the aluminum is adjusted to 28 at. %. These alloys begin ordering upon solidification; therefore, a greater shrinkage must be accommodated during casting. The hot-working temperature “window” for the nickel-aluminide alloy is very narrow; however, the alloy can be cold-worked large amounts. Iron-aluminide alloys have a very broad hot-working temperature range but have limited ductility (<20%) at room temperature. The strength and oxidation resistance of these alloys are such that many potential applications exist. Commercialization is in progress.