1200 to 1400 K Slow Strain Rate Compressive Properties of NiAl/Ni2AlTi-Base Materials

ABSTRACTOwing to their superior strength in comparison to other single phase intermetallics, NiAl-Ni2AlTi alloys have potential for the matrix material in high temperature composites. An investigation of two compositions, Ni-40Al-10Ti and Ni-45Al-5Ti with and without 20 vol. pct. TiB2 in the form of −1μm diameter particles, was initiated with materials produced by the Martin Marietta XDTM process and compacted by hot pressing. The as fabricated materials were fully dense and polycrystalline where the grain sizes measured −8μm for Ti-poor and about 15μm for the Ti-rich unreinforced materials but could not be determined for ei her TiB2-containing composite. Elevated temperature compression testing was conducted to approximately 8 percent deformation between 1200 and 1400 K with strain rates varying from −10−4 to −10−7 s−1. While the majority of the tests exhibited diffuse yielding over approximately one percent strain followed by negative strain hardening, a few experiments resulted in steady state behavior where deformation continued under a constant stress. The flow strengths on yielding of both forms of Ni-40Al-1OTi were higher than those for the Ni-45Al-5Ti versions. Although for each matrix composition the addition of 20 vol. pct. TiB2 decreased the strength at the higher strain rates in comparison to the TiB2-free forms, the particles do provide reinforcement during slow deformation conditions. Optical microscopy of tested specimens revealed that these materials are generally quite brittle as numerous longitudinal and transverse cracks were found irrespective of the type of stress-strain behavior.