Published online by Cambridge University Press: 01 January 1992
A number of techniques are available for making metals, non-metals, and intermetallic materials into high-purity single crystals. The most common of these for producing large crystals involve solidification from the melt. The high melting temperatures of most intermetallics of interest for structural applications result in the expected problems of achieving the required high temperatures and temperature gradients while containing the molten material in a chemically, thermally and mechanically stable environment. Processes which have produced intermetallic single crystals, and the materials which have been crystallized, are reviewed. The largest known single crystals of a high temperature intermetallic have been produced in alloys based on NiAl using a modified Bridgman-type directional solidification process, an evolution of the process commonly used to create large jet engine turbine airfoils in Ni-base superalloys. Issues related to processing are described, and the resultant solidification structures are compared with those typical of superalloys. Finally, the prospects for the various processes, and the advances required to push them toward more practical applications, are addressed.