The Mechanical Behaviour of the Intermediate Phase NiAl

The Physical and Mechanical Metallurgy of NiAl

“…During experiments with singlephase binary compounds at temperatures above approximately 1050 K, some investigators have observed significantly higher creep strengths for hard-orientation crystals (Strutt, Dodd, and Rowe 1970;). However, other investigators have not observed significant anisotropy (Pascoe and Newey 1968b;Whittenberger, Noebe, Cullers, Kumar, and Mannan 1991).…”

“…Not only is the yield strength for NiAI anisotropic, but the strain rate sensitivity is anisotropic also, with cube-oriented crystals displaying a greater sensitivity to strain rate than soft orientations at intermediate temperatures (500 to 1000 K) (Pascoe and Newey 1968b;Lahrman, Field, and Darolia 1991). The greater sensitivity of [00 1 ] crystals to strain rate is due to the decomposed core structure of <I I0> dislocations, which cannot glide conservatively in hard-orientation crystals, and the zero critical resolved shear stress on <001> dislocations, making it necessary for both types of dislocations to rely on thermal activation to assist their motion .…”

Basal slip localization in zinc single crystals. The Considère analyses

“…According to our knowledge, the term 'specimen kinking' was introduced into the literature by Orowan [17] who observed it in compressed cadmium single crystals. Earlier kinking was observed in a variety of mineral crystals [18,19] and later confirmed for metals with hcp or B2 structure (i.e., Zn and NiAl) [19][20][21]. On the other hand, the localized sliding (also referred to as the catastrophic flow) was observed in crystals with fcc [23] and bcc [24][25][26][27][28] structures.…”

“…About 90% of deformation was 21 localized in the neck region where the maximum reduction in the cross section area occurred. However, after some further reduction in area the basal slip plane was slightly inclined to the tensile axis and the neck deepening stopped.…”

Status and Prognosis for Alternative Engine Materials

“…NiAl has excellent cyclic oxidation resistance to at least 1300 °C, especially when alloyed with small additions of rare earth elements (4). Although some early work (5) reported room temperature ductility in polycrystall ine NiAl , the results have not been reproduced, and a more commonly observed behavior is a ductile to brittle transition temperature near 300 to 600 °C, depending on composition, grain size, and processing (5)(6)(7)(8). Single crystals have exhibited ductility, especially in certain orientations (7), but even single crystals suffer from a lov/ cleavage strength.…”