Metastable phases in the Al sub 3 X (X = Ti, Zr, and Hf) intermetallic system

Journal Article · Fri Nov 01 00:00:00 EST 1991 · Scripta Metallurgica; (United States)

OSTI ID:5879598

Srinivasan, S; Desch, P B; Schwarz, R B ^[1]

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1. Los Alamos National Lab., NM (United States). Materials Science and Technology Div.

There is considerable interest in ordered intermetallics based on aluminum, such as Al{sub 3}Ti, Al{sub 3}Zr, and Al{sub 3}Hf, which have high melting points and low densities. These are being investigated to be used as single- phase high-temperature structural materials and as precipitation strengtheners in two-phase aluminum alloys. The latter alloys have the potential for developing low-density alloys useful to 75% of the absolute melting point of aluminum. In precipitation-strengthened Al-Cu alloys, coarsening of the CuAl{sub 2} precipitates due to prolonged exposure to high temperatures can lead to a drastic drop in strength. Thermodynamic and kinetic factors suggest that Al{sub 3}X (X = Ti, Zr, Hf) precipitates should have a lesser tendency to coarsen than CuAl{sub 2} for two reasons. First, Al{sub 3}X precipitates closely match aluminum in structure and lattice parameters (to a few percent), and the expected decrease in the matrix/precipitate interfacial energy should reduce the driving force for precipitate coarsening. Second, in contrast to copper, transition metals (TM) such as Ti and Zr have much lower chemical diffusivities in Al; thus these precipitates should be more stable. We have also used mechanical alloying (MA), a high-energy ball-milling technique, to prepare powders of Al{sub 3}Ti, Al{sub 3}Zr, and Al{sub 3}Hf. The MA synthesis route has various advantages over conventional casting. The as-mechanically- alloyed powders are highly homogeneous in composition and are in a state of high chemical and structural internal energy, which may result in the formation of extended solid solutions or metastable phases (crystalline or amorphous). Crystalline mechanically alloyed powders usually have extremely small grain sizes. In this paper, the authors report the synthesis of Al{sub 3}X alloys by MA, formation of metastable phases, the thermal stability of these phases, and their lattice parameters.

• OSTI ID: 5879598
• Journal Information: Scripta Metallurgica; (United States), Vol. 25:11; ISSN 0036-9748
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
SYNTHESIS
HAFNIUM ALLOYS
TITANIUM ALLOYS
ZIRCONIUM ALLOYS
AMORPHOUS STATE
CRYSTALS
GRAIN SIZE
INTERMETALLIC COMPOUNDS
LATTICE PARAMETERS
MECHANICS
MILLING
PHASE STUDIES
POWDERS
SOLID SOLUTIONS
STABILITY
TEMPERATURE DEPENDENCE
ALLOYS
CRYSTAL STRUCTURE
DISPERSIONS
MACHINING
MICROSTRUCTURE
MIXTURES
SIZE
SOLUTIONS
360101* - Metals & Alloys- Preparation & Fabrication
360102 - Metals & Alloys- Structure & Phase Studies
360104 - Metals & Alloys- Physical Properties