OPTIMIZING THE PROPERTIES OF TIAL SHEET MATERIAL FOR APPLICATION IN HEAT PROTECTION SHIELDS OR PROPULSION SYSTEMS

The present work represents a survey on the production of TiAl sheet material on an industrial scale and on the properties of these sheets. Using different final heat treatments, near-gamma and duplex microstructures have been produced. The mechanical properties as a function of the microstructure have been examined at room temperature (RT) and 700 degrees C. Additionally, the parameter field of temperature and strain rate for which superplastic forming of the sheet material is possible has been established. Mechanical testing at RT revealed that the strength of Ti-48Al-2Cr sheet material is mainly governed by grain size if the microstructure is homogeneous. The volume fraction and distribution of the second phase (alpha(2)-Ti3Al) appears to be of minor influence. Room temperature ductilities between 0.25 and 0.051 have been measured. At 700 degrees C the duplex microstructures show slightly improved strength compared to near-gamma microstructures. Depending on the deformation rate, fracture strains between O.11 and 0.80 have been detected. Superplastic behaviour of Ti-48Al-2Cr (at.%) is governed by dynamic recrystallization or dynamic grain growth, depending on the initial grain size and the deformation parameters temperature and strain rate.