https://doi.org/10.1051/epjap:2001163
First stage of the structural evolution of austenite in Cu-Al-Ni shape memory alloys
Laboratoire de Mécanique et de Physique des Matériaux ENSMA, BP 40109,
86961 Futuroscope-Chasseneuil, France
Corresponding author: pelosin@lmpm.ensma.fr
Received:
27
November
2000
Revised:
27
March
2001
Accepted:
30
March
2001
Published online: 15 July 2001
Two shape memory Cu-Al-Ni alloys, a polycrystal and a single crystal, exhibiting a martensitic
transformation close to 130 °C (in the as-quenched state) have been studied. Specimens have been quenched
after heat treatment at 850 °C. The structural evolutions of the high temperature phase (austenite) have been
studied for thermal treatments performed below 200 °C. Investigations have been carried out using electrical
resistivity measurements, TEM (Transmission Electron Microscopy) observations and X-ray diffraction
analysis. The main structural modifications are observed in the polycrystalline alloy and concern first, the
reordering process of the austenite structure (B2
L21), and second, the precipitation
of the (Cu9Al4) γ2 phase. In the single crystal alloy, the evolutions are very
slight and localized on the structural defects. Particular attention is paid to the role of
the quenched-in vacancy elimination on the observed mechanisms. In addition, the incidence
of the structural evolution on the transformation temperatures is also discussed.
PACS: 81.30.Hd – Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder / 81.30.Kf – Martensitic transformations / 61.72.Ff – Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, X-ray topography, etc.)
© EDP Sciences, 2001
