1300 K compressive properties of several dispersion strengthened NiAl materials

Abstract

Recently an attempt [8] to produce dispersion hardened NiAl by rapid solidification technology (RST) was discussed; however these microstructural studies and tensile testing procedures did not yield conclusive evidence of strengthening. To examine the potential of RST as a means to fabricate dispersion strengthened aluminides, cylindrical compression samples were machined from the gauge section of their tensile specimens and tested in air at 1300 K: in addition, considerable materialography, including light optical, scanning electron and transmission electron microscopy techniques, of the as-fabricated and compression tested materials was conducted. While microscopy indicates that RST can produce fine dispersions of TiB₂, TiC and HfC in a NiAl matrix, the mechanical property data reveal that only HfC successfully strengthens the intermetallic matrix. The high stress exponents (> 10) and/or independence of strain rate on stress for NiAl-HfC materials suggest elevated temperature mechanical behaviour similar to that found in oxide dispersion strengthened alloys. Furthermore an apparent example of “departure side” pinning has been observed, and as such, it is indicative of a threshold stress for creep.