Refractory Alloy Single Crystals for High Temperature Applications

Abstract : Refractory metals and intermetallic alloys are important in high temperature aerospace systems where deformation must be maintained at a low level. This DEPSCoR project was devoted to the processing such single crystals, joining of these crystals and fracture analysis of the interface. Advances have been made in these three areas, especially in the processing of single crystals with enhanced mechanical properties. An electron beam float zone melting method was used successfully to fabricate single crystals based on three alloy systems: Ni3Al, molybdenum alloys and tungsten alloys. Due to the complex Ni3Al phase diagram, slight variations in the compositions resulted in significant difference in the growth characteristics. In the case of molybdenum alloys, the ease of single crystal formation depends on the selection of the solutes and their concentration. Little difficulty was encountered when growing the Mo-Nb alloys. The ease of crystal growth in the Mo-Nb binary system was attributed to the small two-phase region and the complete solubility of Mo-Nb, The growth characteristics are in accord with the interface stability criterion of a planar interface.