Alloy design of ordered intermetallics
Ordered intermetallics based on aluminides and silicides constitute a unique class of metallic materials promising high-temperature properties. However, brittle fracture and poor ductility limited their use as engineering materials in most cases. During the past ten years extensive research has been conducted on ordered intermetallics. As a result, significant progress has been made in identifying various causes of brittle fracture, and their relative importance in different ordered alloys. In some cases this understanding has helped achieve dramatic improvements in ductility. We review here three different classes of brittle fracture in ordered intermetallics and discuss the results in terms of model alloy systems chosen from each class. Ni{sub 3}Al and NiAl are discussed as prototypical ordered alloys prone to intrinsic intergranular brittleness. They are used to review our current understanding of intrinsically weak grain boundaries and the mechanisms by which boron is thought to suppress intergranular fracture. Next, FeAl and Fe{sub 3}Al are discussed as examples of ordered intermetallics that are susceptible to environmental embrittlement at ambient temperature. Recent discoveries in these two alloy systems are reviewed with special emphasis on some of the rather interesting but subtle effects of test environment. Finally, Al{sub 3}X type intermetallic (Al{sub 3}Sc,Al{sub 3}Ti-base, and Al{sub 3}Zr-base alloys) are discussed as examples of ordered alloys that have high symmetry (Ll{sub 2} structure), are relatively soft, yet cleave transgranularly with very little ductility. In all these cases, experimental results are compared with theoretical calculations. 125 refs., 8 figs., 5 tabs.
- Research Organization:
- Oak Ridge National Lab., TN (USA)
- Sponsoring Organization:
- DOE/ER
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 6716882
- Report Number(s):
- CONF-900466-80; ON: DE90016031
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360102 -- Metals & Alloys-- Structure & Phase Studies
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
ALUMINIUM ALLOYS
BORON
BRITTLENESS
CHEMICAL REACTIONS
CLEAVAGE
CORROSION
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DISLOCATIONS
DUCTILITY
ELEMENTS
EMBRITTLEMENT
GRAIN BOUNDARIES
INTERMETALLIC COMPOUNDS
IRON ALLOYS
IRON BASE ALLOYS
LINE DEFECTS
MECHANICAL PROPERTIES
METALLURGICAL EFFECTS
MICROSTRUCTURE
NICKEL ALLOYS
NICKEL BASE ALLOYS
SEMIMETALS
SILICIDES
SILICON COMPOUNDS
TEMPERATURE DEPENDENCE
TENSILE PROPERTIES
YIELD STRENGTH