CARBIDE-DISPERSION-STRENGTHENED B2 NIAL

The microstructure and high temperature deformation behavior of a rapidly solidified and hot-extruded NiAl-4%HfC alloy are described. Rapid solidification processing led to the incorporation of 20-50 nm sized HfC precipitates in a B2-ordered NiAl matrix. The carbide precipitates were found to be stable and resistant to coarsening at temperatures as high as 1500 K. The as-extruded microstructure consisted of a recrystallized grain structure, with grain size in the range 5-8 μm. Transmission electron microscopy on the as-extruded alloy revealed the presence of subgrains, and a dislocation substructure stabilized by the carbide precipitates. Departure side pinning of matrix dislocations at the carbide precipitates was observed in the as-extruded material. The flow characteristics of NiAl-4%HfC alloy were investigated by constant-velocity compression testing at 1200 and 1300 K, with strain rates ranging from 10-4 to 10-7 s-1. It was observed that carbide-containing NiAl continuously work hardened at all temperatures and strain rates investigated. The flow stress-strain rate data indicated the presence of a threshold stress for the creep deformation of carbide-dispersion-strengthened NiAl intermetallic, and departure side pinning of dislocations by the carbide precipitates was also observed in the deformed sample.