Aging of the ß21S titanium alloy

Ti-b21S is an alloy developed by Timet USA in 1990. It was developed to be used as a matrix in composite materials. It is a b-metastable titanium alloy, currently used in industry such as aeronautics, because of its cold formability, good mechanical properties at elevated temperature, low density and its strong resistance to oxidation. This alloy is hardened by an a-phase precipitation in the b-matrix.

The purposes of the present research are to establish the effects of aging on microstructure and mechanical properties of Ti-b21S alloy. Different thermal aging tests have been carried out at high temperature for 500 hours in air. Two initial microstructures have been studied: the first one corresponding to as-received solution-state, and the second one being an a precipitated state. The microstructure evolution has been examined after each thermal treatment by means of Scanning Electron Microscope and chemical analysis. Mechanical properties have been studied by tensile tests performed at room and high temperature but also by microhardness testing to characterize the local evolution of properties close to the surfaces. The evolution after heat treatment of tensile properties, such as 0.2% proof stress, ultimate stress and elongation, is correlated to microstructure evolution. A significant different evolution is observed between the two initial microstructures. The role of oxidation and oxygen dissolution on both microstructure and mechanical properties will be emphasized.