Correlation of deformation mechanisms with the tensile and compressive behavior of NiAl and NiAl(Zr) intermetallic alloys

The Physical and Mechanical Metallurgy of NiAl

“…( Bowman et al 1992). Similarly, deviations from stoichiometry reduce the sensitivity of binary NiAI to cooling rate effects (Nagpal and Baker 1990a).…”

“…At higher temperatures (>600 K, which is above the brittle-to-ductile transition temperature (BDTT) for [001] crystals), the operative slip vector changes, and deformation occurs by nonconservative motion of <001> and <011> dislocations (Kim and Gibala 1991;Field, Lahrman, and Darolia 1991b). Bowman et al 1992 Pascoe and Newey 1968b…”

“…Consequently, changes in slope on an Arrhenius plot usually indicate a change in the deformation mechanism. When the polycrystalline NiAI yield strength data of Bowman et al (1992) from figure 3(b) are replotted in an Arrhenius form, three distinct deformation regimes are observed (fig. 4).…”

Assessment of Microalloying Effects on the High Temperature Fatigue Behavior of NiAl

“…For NiAI(Zr), the test temperature was just below its BDTT, therefore, recovery was not significant, and this led to the higher and more homogeneous dislocation structure that was observed within the grains (16). Additionally, Zr atoms are very effective in pinning dislocations below the BDTT (12)(13)(14) and increasing the viscous drag force on dislocations at higher temperatures (9). Consequently, the mutual interactions between dislocations and the solid solution hardening due to the Zr atoms resulted in significantly higher cyclic stresses and a high n'.…”

“…Zr additions decrease the already limited room temperature tensile ductility of polycrystalline NiAl and significantly increase the brittle-toductile transition temperature (BDTT) (6,12). The increase in BDTT was attributed to the segregation of Zr to the grain boundaries (13) and the subsequent inhibition of localized deformation mechanisms that are necessary for meeting the Von Mises criterion, and therefore, limiting tensile ductility (14).…”