Internal friction in polycrystals of technical purity was studied at temperatures ranging from 300 to 1500K by using an inverted torsion pendulum. Extruded single-phase γ-phase samples with an Al content of 54.1at% exhibited a large frequency-dependent relaxation maximum near to 1300K, during cooling from temperatures above 1400K. This was not observed during heating from ambient temperatures, or in 2-phase a2/γ-phase alloys with a lower Al content. This relaxation maximum was tentatively attributed to the motion of grain boundaries or dislocations which were pinned by precipitates in the γ-phase. The precipitates dissolved at temperatures above 1350K, and formed again below 1200K. No relaxation was observed in polycrystalline material, containing 0.009 to 0.22at%C, at temperatures below 900K. This behavior was assumed to reflect hardening by finely-dispersed precipitates.

Internal Friction in γ-TiAl at High Temperatures. U.Brossmann, M.Hirscher, H.Kronmüller: Acta Materialia, 1999, 47[8], 2401-8