Room temperature tensile ductility in polycrystalline B2 NiAl

Journal Article · Sun Jan 01 04:00:00 EST 1989 · Scr. Metall.; (United States)

DOI:https://doi.org/10.1016/0036-9748(89)90083-5· OSTI ID:5855681

Hahn, K H; Vedula, K

The lack of tensile ductility in polycrystalline B2 NiAl has been attributed to the lack of five independent slip systems to satisfy von Mises' criterion for compatibility in polycrystalline deformation. Single crystal studies (4-10) show that the deformation of this alloy is highly anisotropic. The non-<100> oriented crystals (soft orientations) are much more ductile than the <100> oriented crystals (hard orientations) at low temperature. This is because the critical resolved shear stress required to activate primary slip of the <100> type is much less than that required to activate other slip systems as the <111> type. All orientations possess considerable ductility even when tested in tension at intermediate temperatures (>-- 673K). There is general agreement that for non-<100> oriented crystals, deformation involves (100) <001> and /l brace/110/r brace/ <100> slip systems at low as well as intermediate temperatures. The behavior of <100> oriented crystals is less clear and conflicting data exist: <111> slip direction with /l brace/123/right brace/ and /l brace/112/r brace/ slip planes have been observed at low temperatures; while <111>, <110> and <100> directions have been reported for high temperature deformation. The number of slip systems which operate if only the /l brace/110/r brace/<100> slip occurs is insufficient for von Mises's criterion for polycrystalline deformation. In compression, ductility is observed since there is no driving force to open cracks that must form at grain boundaries due to the lack of sufficient slip systems. In tension, however, the applied stress acts directly to open the crack and failure may occur before further deformation can take place. On the other hand, if <111> slip is possible (as in the case of disordered BCC alloys as well as some other compounds), there are enough slip systems of the type /l brace/110/r brace/ <111>, to satisfy von Mise's criterion and lead to polycrystalline tensile ductility.

• Research Organization: Dept. of Materials Science and Engineering, Case Western Reserve Univ., Cleveland, OH (US)
• OSTI ID: 5855681
• Journal Information: Scr. Metall.; (United States), Journal Name: Scr. Metall.; (United States) Vol. 23:1; ISSN SCRMB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102 -- Metals &amp; Alloys-- Structure &amp; Phase Studies
360103* -- Metals &amp; Alloys-- Mechanical Properties
360104 -- Metals &amp; Alloys-- Physical Properties
ALLOYS
ALUMINIUM ALLOYS
ANISOTROPY
CRYSTAL STRUCTURE
CRYSTALS
DEFORMATION
DUCTILITY
FRACTURE PROPERTIES
HIGH TEMPERATURE
LOW TEMPERATURE
MECHANICAL PROPERTIES
NICKEL ALLOYS
POLYCRYSTALS
STOICHIOMETRY
TENSILE PROPERTIES