MULTIPHASE INTERMETALLICS

Ordered intermetallic compounds, notably the aluminides of nickel, tit anium, iron and niobium, have been under intensive investigation for t he past two decades as prospective load-bearing materials for high tem peratures, with special emphasis on aerospace applications. The strong er of these phases are all catastrophically brittle at and near ambien t temperature and this difficulty has proved obdurate. A promising sol ution appears to be to alloy such phases in such a way that the result is a two-phase or multiphase material. The extra phases may be disord ered and intrinsically ductile: the presence of such phases lowers the high-temperature strength but is apt to enhance the plastic deformabi lity of the material even at ambient temperature. There are also insta nces of multiphase alloys in which all the phases are ordered intermet allics, some stronger and more brittle, others weaker and more ductile , and the end-result can be a promising combination of strength and du ctility, as well as good creep resistance.