J. Phys. IV France 05 (1995) C8-475-C8-480
On the Effect of Volume Change and γ'-Precipitation Hardening on the Reversibility of Martensitic Transformation in Fe-Ni-Co-Ti-AlloyG. Kubla and E. Hornbogen
Ruhr-Universität Bochum, Institut für Werkstoffe, 44780 Bochum, Germany
Martensitic transformation in Fe-Ni-based alloys is accompanied with an increase of volume (ΔVγ-α≈3%). Lattice invariant shear leads to additional dilatometric changes for non-random transformations. As the result of predominantly ΔVγ-α a large thermal hysteresis (ΔTH) originates. This leads to a diffusion-controlled α→γ-transformation, i.e. the reverse reaction becomes crystallographically irreversible (α≠γ).
In the case of an aged Fe-Ni-Co-Ti alloy, ΔVγ-α depends on the magnetic state of the austenite and on the volume fraction of the precipitated γ'-particles. With increasing the volume fraction of γ, ΔVγ-α is reduced. Dislocations at the former martensite/austenite interfaces indicate incomplete reversibility of the transformation cycles, even in the ausaged condition. However, drastic reduction of ΔTH is observed during an ausaging sequence for conditions close to maximum volume fraction and minimum size of γ'.
© EDP Sciences 1995