Transformations structurales dans l'alliage de titane , β-CEZ études des mécanismes de précipitation après traitement de mise en solution

Abstract

The β-CEZ, a high strength titanium alloy developed for aerospace engine applications, is a α/β near β alloy. A wide variety of phase transformations and attendant nodular, lamellar and mixed microstructures are possible according to thermomechanical treatment conditions. The aim of this present paper is to illustrate the influence of solution treatment temperature on equilibrium microstructwes and continuous cooling transformations. Solution treatment temperature controls the volume fraction of primary a particles and composition of the β-matrix. Therefore the transformation during continuous cooling from α/β or β field depends on β-matrix stability and potential sites amount of a precipitation. After a β solution treatment, the α particles are disappeared and the β phase contains all alloying elements; the continuous cooling transformation produces a Widmanstatten structure. If the cooling rate or/and the solution treatment temperature in the α/β field are sufficiently low, the microstructure consists only of nodular morphology. During a particles growth the a volume fraction increases as equilibrium and the decreasing of growth kinetic leads to supersatured β matrix and Widmanstatten a precipitation. The final microstructures are mixed. The influence of solution treatment temperature and cooling rate on nucleation and growth mechanisms is specially developed