Direct observation of the compositional disordering of Ni/sub 3/Al in the vicinity of grain boundaries using high resolution electron microscopy techniques

Journal Article · Tue Nov 01 04:00:00 EST 1988 · Scr. Metall.; (United States)

DOI:https://doi.org/10.1016/S0036-9748(88)80289-8· OSTI ID:6110069

Mackenzie, R A.D.; Sass, S L

The ordered compound Ni/sub 3/Al is potentially useful as a high temperature structural material, since its yield stress increases with increasing temperature up to --650/sup 0/. The major obstacle to the structural use of polycrystalline Ni/sub 3/Al is its tendency to fail intergranularly. The ductility of Ni/sub 3/Al can be improved by the addition of small amounts of boron to a slightly Ni-rich compound. The boron is found to segregate to the grain boundaries, and changes the fracture mode from intergranular to transgranular by a mechanism which is not yet understood. Possible explanations for the presence of a/2<110>-type dislocations are: (i) the dislocations are imperfect, with the associated antiphase boundary contrast not visible, or (ii) the Ni/sub 3/Al is disordered in the vicinity of the interface, resulting in a thin layer of f.c.c. material at the boundary, and the dislocations then have the expected f.c.c. Burgers vector. In support of the possibility of disordering are atom-probe field ion microscopy observations which showed that the boundary region is Ni-rich, with deviations from the average alloy composition of up to 5 at % Ni. It is reasonable to predict that the thickness of the disordered layer will be a function of temperature, and so the contribution of the disordered layer to the mechanical properties may also be temperature dependent. It can be speculated that the solubility of boron, and any other impurities that are present, will be different in disordered and ordered Ni/sub 3/Al.

• Research Organization: Dept. of Materials Science and Engineering, Cornell Univ., Ithaca, NY (US)
• OSTI ID: 6110069
• Journal Information: Scr. Metall.; (United States), Journal Name: Scr. Metall.; (United States) Vol. 22:11; ISSN SCRMB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals &amp; Alloys-- Structure &amp; Phase Studies
360104 -- Metals &amp; Alloys-- Physical Properties
ALLOY SYSTEMS
ALLOYS
ALUMINIUM ALLOYS
BINARY ALLOY SYSTEMS
BORON ADDITIONS
BORON ALLOYS
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
CORROSION
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
CRYSTALS
DISLOCATIONS
DUCTILITY
GOLD ALLOYS
GRAIN BOUNDARIES
HIGH TEMPERATURE
INTERGRANULAR CORROSION
IRON ALLOYS
LINE DEFECTS
MECHANICAL PROPERTIES
MICROSTRUCTURE
NICKEL ALLOYS
ORDER-DISORDER TRANSFORMATIONS
PHASE TRANSFORMATIONS
POLYCRYSTALS
TENSILE PROPERTIES