Phase transformations in the Fe-Al system studied by ``in situ`` TEM heating

Book · Tue Aug 01 04:00:00 EDT 1995

OSTI ID:78324

Korner, A ^[1]

---

1. Univ. Wien, Vienna (Austria). Inst. fuer Festkoerperphysik

The domain structure and the evolution of antiphase boundaries (APBS) have been investigated in Fe-Al by means of ``in-situ`` transmission electron microscopy (TEM) heating experiments. Single crystals with composition Fe22.lat%Al and Fe25.6at%Al have been used. The grown-in structure of the Fe22.lat%al single crystal is composed of DO{sub 3} ordered particles embedded in the disordered a-matrix. A bimodal distribution of the particles was found. Small ordered particles are in between the large precipitates which are surrounded by particle-free zones. Numerous of this large ordered precipitates contain APBS. Crossing the transition temperature to the disordered phase, the small particles dissolve into the {alpha}-matrix and the large particles start to shrink by dissolving. The single crystal with composition Fe25.6at%Al was found to be completely DO{sub 3} ordered. The grown-in domains are separated by APBs of type a{alpha}{prime}{sub 0}/2{l_angle}100{r_angle}. At temperatures far below the transition temperature to the B2 phase no significant change in the APB and domain structure has been detected. In contrast, a remarkable evolution in the APB structure has been observed approaching the transition temperature. Coarsening of the domains has been found. Furthermore, APBs of B2-type (a{prime}{sub 0}/4{l_angle}111{r_angle} shear) are dragged out by dislocation motion. B2 and DO{sub 3}-type APBs react and junctions are formed. With increasing annealing time, the density of B2-type boundaries increases. The TEM image is dominated by B2-type boundaries linked by the DO{sub 3}-type boundaries. The DO{sub 3} superlattice spots are clearly excited approaching the transition temperature to B2. Above the transition temperature, the DO{sub 3} spots disappear completely and the diffraction pattern reveals B2 long range order.

• OSTI ID: 78324
• Report Number(s): CONF-941144--; ISBN 1-55899-265-0
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
EXPERIMENTAL DATA
HEAT RESISTING ALLOYS
IRON BASE ALLOYS
LATTICE PARAMETERS
MICROSTRUCTURE
PHASE DIAGRAMS