| Intermetallics are candidate materials to replace Ni-based superalloys for high-temperature structural applications. With proper alloying additions to improve their creep strength and ductility, NiAl-based intermetallic alloys have the potential to extend the operating temperatures of structural materials by hundreds of degrees. Here, we discuss the effects of Ti alloying additions on the high-temperature deformation behavior of NiAl(Ti) single crystals.;We examine creep in the solid-solution strengthened alloys: Ni-47.5Al-2.5Ti and Ni-47Al-3Ti. Single crystals were deformed in compression in the "hard" ;We attempt to understand this solid-solution strengthening effect by studying the stress and temperature dependence of the creep rate for these alloys as well as deformation transients associated with stress changes. These results suggest that solute drag effects dominate the creep resistance at the highest temperatures and lowest stresses. The solute drag hypothesis is supported by observations of solute size effects of Ti and by the form of dislocation substructures found in creep-deformed crystals.;We also examine the high-temperature deformation behavior of two-phased Ni-42.5Al-7.5Ti single crystals. Having characterized the microstructure of this alloy, we present the results of high-temperature mechanical testing, showing that this has creep strengths that compare favorably with commercial nickel-based superalloys. An examination of deformed microstructures, however, reveals that deformation in these alloys does not occur by creep. Instead, the propagation of cracks, which ultimately leads to catastrophic failure, occurs even at 1200;Finally, we present several models to describe the deformation behavior of NiAl(Ti) solid-solution single crystals at high temperatures that are based on the solute-drag-controlled deformation. We conclude that strengthening in solid-solution NiAl(Ti) occurs by solute drag as well as by ordinary dislocation hardening. |
