Ll{sub 2} Al{sub 3} Ti-based alloys with Al{sub 2}Ti precipitates; I: Structure and stability of the precipitates

Journal Article · Tue Feb 01 04:00:00 EST 1994 · Acta Metallurgica et Materialia

DOI:https://doi.org/10.1016/0956-7151(94)90505-3· OSTI ID:143151

Wu, Z L; Pope, D P ^[1]

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1. Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Materials Science and Engineering

The Al{sub 2}Ti-based phase commonly seen in Ll{sub 2}Al{sub 3}Ti alloys has been studied in detail, using Fe- and Cr-modified single crystalline specimens. The formation of the phase was found to be temperature-dependent; in and in situ TEM heat treatment it was observed that the phase started to dissolve at about 750 C, is mostly dissolved by 1,000 C. The volume fraction of the phase increases with Ti content, but the composition of the phase is largely controlled by the overall Al/Fe ratio. Based on two-surface trace analysis it was determined that Al{sub 2}Ti forms as platelets on the cube planes of the Ll{sub 2} matrix. X-ray powder diffraction and computer simulation of the X-ray spectra revealed that it has a tetragonal structure of the Ga{sub 2}Hf type, the same as that of binary Al{sub 2}Ti. Due to the presence of ternary elements the lattice parameters of the phase are changed such that it can form coherently on the cube planes of the Ll{sub 2} matrix. Special crystallographic orientation relations exist between the two phases: (100){sub p}//(100){sub m} and (010){sub p}//(010){sub m}, where m and p mean ``matrix`` and ``precipitate``, respectively. It was observed using TEM and the precipitates act as strong barriers for dislocation motion on octahedral slip planes in the matrix.

• OSTI ID: 143151
• Journal Information: Acta Metallurgica et Materialia, Journal Name: Acta Metallurgica et Materialia Journal Issue: 2 Vol. 42; ISSN 0956-7151; ISSN AMATEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM BASE ALLOYS
CRYSTAL STRUCTURE
IRON ALLOYS
PHASE TRANSFORMATIONS
TEMPERATURE DEPENDENCE
TITANIUM ALLOYS