The deformation properties and electron microscopy studies of the intermetallic compound NiAl

The Physical and Mechanical Metallurgy of NiAl

“…Smallman (1966a and1966b) were the first researchers to make a complete slip system determination for NiAI by identifying a <001> slip vector and (110} slip plane in all soft orientations and at all temperatures investigated (300 to 1273 K). They also observed cross slip or pencil glide on orthogonal ( 110) planes.…”

“…Regardless of whether the material is Ni-rich or Al-rich, the effects of nonstoichiometry on strength become negligible around 1000 K ( fig. 3(b)), and a reversal in strength occurs at higher temperatures such that stoichiometric alloys become stronger than nonstoichiometric compositions (Ball and Smallman 1966a;Whittenberger, Noebe, Cullers, Kumar, and Mannan 1991).…”

“…Furthermore, intergranular fracture in both tensile and compression specimens at low temperatures appear to confirm that the limited ductility of binary, near-stoichiometric NiAI is the result of incompatible shape changes of neighboring grains. These incompatible shape changes are due, in turn, to an insufficient number of slip systems (Ball and Smallman 1966a;.…”

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.…”

GRAIN BOUNDARY CHEMISTRY OF NiAl

“…['~l Therefore only a limited general plasticity is possible. [11] In contrast to Ni,AI, interstitial element additions such as boron have been shown to have little effect on ductility. ['2] Substitutional additions such as titanium, iron, molybdenum, and niobium also have been shown to have little effect upon ductility and fracture b e h a~i o r .…”