Microstructural control in Ti-Al for enhanced mechanical properties

A study was initiated to understand the effect of grain refinement on mechanical properties of TiAl-based alloys at room and elevated temperatures. The following was found in that study. Utilizing a processing approach that includes homogenizing annealing or deformation in the α-phase field, followed by multi-step isothermal forging in the γ+ α₂ phase range at relatively low strain rates and a continuously decreasing temperature, homogeneous submicro-crystalline structures were produced in titanium aluminides, facilitating further processing such as superplastic forming at temperatures below 1,000°C. Also described in this paper is a fully lamellar structure with a colony size as small as 15 μm, produced in gamma TiAl-based alloys containing borides by the fast-heating of an initially submicro-crystalline structure in the alpha-phase range followed by air cooling. For more information, contact F.H. Froes, Institute for Materials and Advanced Processes, University of Idaho, Mines Building, Room 321, Moscow, Idaho 83844-3026; (208) 885-7989; fax (208) 885-4009; e-mail imap@uidaho.edu.