Phase transitions and modulated structures in ordered (Cu-Mn)/sub 3/Al alloys

Journal Article · Mon Dec 01 04:00:00 EST 1975 · Acta Metall.; (United States)

DOI:https://doi.org/10.1016/0001-6160(75)90159-5· OSTI ID:7199818

Bouchard, M; Thomas, G

Quenched and aged alloys along the composition line Cu/sub 3/Al--Cu/sub 2/MnAl have been studied by electron diffraction and microscopy. Quenching produces an ordered solid solution based on the DO/sub 3/ structure of Cu/sub 3/Al and the L2/sub 1/ structure of Cu/sub 2/MnAl. Below 350/sup 0/C the alloys decompose inside a miscibility gap into a Cu/sub 2/MnAl-rich phase and a Cu/sub 3/Al-rich phase. The resulting microstructures possess all the metallographic characteristics of spinodal decomposition. In the Al-rich asymmetrical alloy, the Cu/sub 2/MnAl-rich phase heterogenously nucleates at /sup 1///sub 4/a(111)APB's. In the symmetrical alloy, the structure of the Cu/sub 3/Al-rich particles varies with the decomposition temperature. At temperatures close to the miscibility gap, the structure of the particles is DO/sub 3/. These DO/sub 3/ particles are further modulated by a dense array of small regions having the LI/sub 0/ superstructure and exhibit tweed strain contrast. At lower temperatures, the particles are composed of a regular arrangement of twelve possible variants of the LI/sub 0/ phase. At all temperatures, the structure of the CU/sub 2/MnAl-rich phase is L2/sub 1/. During overaging of the symmetrical alloy at temperatures close to the miscibility gap, the Cu/sub 3/Al-rich phase transforms to the ..gamma.. phase having a composition near Cu/sub 3/Al/sub 4/. Thus it is suggested that for the symmetrical alloy the decomposition tie line is close to Cu/sub 9/Al/sub 4/--Cu/sub 2/./sub 2/MnAl/sub 0/./sub 8/. (LK)

• Research Organization: Univ., of California, Berkeley
• OSTI ID: 7199818
• Journal Information: Acta Metall.; (United States), Journal Name: Acta Metall.; (United States) Vol. 23:12; ISSN AMETA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
AGING
ALLOY SYSTEMS
ALLOYS
ALUMINIUM ALLOYS
COHERENT SCATTERING
COPPER ALLOYS
CRYSTAL STRUCTURE
DIFFRACTION
DISPERSIONS
ELECTRON DIFFRACTION
HEAT TREATMENTS
INTERMETALLIC COMPOUNDS
MANGANESE ALLOYS
MICROSCOPY
MIXTURES
ORDER PARAMETERS
PHASE TRANSFORMATIONS
QUENCHING
SCATTERING
SOLID SOLUTIONS
SOLUTIONS
TERNARY ALLOY SYSTEMS