Scripta Materialia, Vol. 36, No. 1, pp. 21-28, 1997 Elsevia Science Ltd Copyright 0 1996 Acta Metallurgica Inc. Printed in the USA. All rights reserved 1359-6462/97 $17.00 + .OO PII S1359-6462(96)00341-7 THE DEFORMATION MECHANISMS IN THE p-METASTABLE p-CEZ TITANIUM ALLOY Thierry Grosdidier, Christophe Roubaud, Marie-Jeanne Philippe and Yves Combres* Laboratoire d’Etude des Textures Appliquees aux Materiaux, CNRS URA-2090, Universite de Metz, Ile du saulcy, 57045, METZ, FRANCE *Centre de Recherche de CEZUS, BP 33,734OO UGINE, FRANCE (Received June 281996) Introduction p metastable alloys have, potentially, better cold formability and age-hardening response than a-p titanium alloys. In the p metastable alloys, the MS temperature is below room temperature and the p phase can be retained in a metastable state. The deformation of this p phase can involve slip, (332) <113> twinning and the formation of stress or @rain mduced martensites (SIM) (l-8). Crystallographic slip occurs in alloys with large enough stability of the p phase. In many of the less stable p titanium alloys, stress or strain induced formation of martensite (SIM) has been reported to result in the formation of hexagonal closed packed cc’ or orthorombic a” phases [6]. The (332) <I 13> twinning also operates in alloys with large metastability of the p phase and is accompanied by the formation of stress induced o phase (4). It is essential to identify and control the deformation mechanisms of the p metastable alloys for two major reasons. Firstly, the deformation mechanisms strongly affect their mechanical behaviour (5,7, 8). Many of the alloys that deform solely by slip have high yield strength and small elongation (5). On the contrary, both .(332} twinning and deformation induced martensitic transformation cause lower apparent yield strength when they are activated fast during the deformation (1,2, 5, 8). From the point of view of cold formability, these alloys with lower yield strength, higher strain hardening and often higher ductility are more likely to be suitable than those which deform solely by slip. Secondly, knowledge of the de- formation mechanisms is also important because the precipitation hardening response of cold deformed microstructures is strongly influenced by the type of defects introduced during deformation (9). This gen- erates differences in the microstructure of the heat-treated material and consequently affects the me- chanical behaviour ( 10). p-Cez is an alloy initially developed for turbine compressor applications (11). Most of the research on this alloy has cloncentrated on its structural stability (12), its high temperature deformation microstructures (13) its phase transformation kinetics ( 14-16) and the structure/mechanical properties relationships ( 14, 17). Little information is however available concerning the room temperature deformation mechanisms that actually control the mechanical properties of the alloy. Production of wires or thin sheets of the p-Cez alloy that are obtained by cold deformation and subsequent heat treatments is currently under develop- ment. The optimisation of such manufacturing processes has made it necessary to examine more precisely 21