J. Phys. IV France 05 (1995) C2-299-C2-304
Nucleation and Growth of the Ni5Al3 Phase in Ni-Al Austenite and MartensiteD. Schryvers1, L. Toth2, Y. Ma1 and L. Tanner3
1 EMAT, RUCA, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
2 MFKI, Department of Thin Films, P.O. Box 76, H-1325 Budapest, Hungary
3 Chemistry & Materials Science, LLNL, Livermore CA 94550, U.S.A.
The nucleation and growth mechanisms of Ni5Al3 precipitates and microtwinned plates in B2 austenite and 2M (3R) martensite phases are described on the basis of conventional and high resolution electron microscopy. In the Ni62.5Al37.5 B2 austenite matrix short annealings at 550°C introduce three-pointed star shaped precipitates consisting of twin related parts of different variants of the Ni5Al3 structure. Longer annealings result in plates growing separately from these wings and developing microtwinning in order to accommodate stress built-up at the interfaces with the surrounding matrix. Annealing of Ni65Al35 2M martensite plates induces simple reordering into the Ni5Al3 phase, increasing the fct c/a ratio by about 1%. As a result stracking faults are introduced in the smallest twin variants.
© EDP Sciences 1995