Brittle fracture and ductility improvement in nickel and iron aluminides

Conference · Mon Jan 01 00:00:00 EST 1990

OSTI ID:6884155

George, E P; Liu, C T

Nickel and iron aluminides are two potentially useful ordered intermetallic alloy systems that share a problem common to many ordered intermetallics, namely brittle fracture and poor ductility at room temperature. However, recent developments have shown that it is possible to overcome this problem and get significantly improved room-temperature ductilities in both these alloy systems by employing a combination of micro-and macro-alloying techniques. Concurrently, our understanding of the underlying causes of brittle fracture in ordered intermetallics has improved dramatically. We review here recent results related to the ductility and fracture behavior of two nickel aluminides (Ni{sub 3}Al and NiAl), and two iron aluminides (FeAl, and Fe{sub 3}Al). We will show that the major difference between Ni{sub 3}Al and the two iron aluminides is the following: in the former, brittle fracture is a result of intrinsically weak grain boundaries, whereas in the latter, brittle fracture is a result of an extrinsic factor, namely moisture-induced environmental embrittlement. The brittleness of Ni{sub 3}Al can be overcome by microalloying with boron and carefully controlling the alloy stoichiometry, whereas the ductilization of iron aluminides requires modification of their surface composition (or environment) to minimize the chemical reaction with moisture in air. NiAl also has weak grain boundaries (like Ni{sub 3}Al), which can be strengthened by the addition of small amounts of boron. However, because of its other problems, like poor cleavage strength and insufficient number of deformation modes, the ductility of NiAl is not significantly improved even after intergranular fracture is totally suppressed. 71 refs., 5 figs., 2 tabs.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: DOE/ER
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6884155
• Report Number(s): CONF-900632-1; ON: DE90017319
• Resource Relation: Conference: Meeting of the International Materials Research Society, Beijing (China), 18-22 Jun 1990
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
DUCTILITY
IRON BASE ALLOYS
NICKEL BASE ALLOYS
BORON
BRITTLENESS
FRACTURE PROPERTIES
GRAIN BOUNDARIES
HYDROGEN EMBRITTLEMENT
INTERMETALLIC COMPOUNDS
TENSILE PROPERTIES
YIELD STRENGTH
ALLOYS
CRYSTAL STRUCTURE
ELEMENTS
EMBRITTLEMENT
IRON ALLOYS
MECHANICAL PROPERTIES
MICROSTRUCTURE
NICKEL ALLOYS
SEMIMETALS
360103* - Metals & Alloys- Mechanical Properties
360102 - Metals & Alloys- Structure & Phase Studies