INVESTIGATION INTO CREEP BEHAVIOR IN POLYCRYSTALS OF TITANIUM ALUMINIDE INTERMETALLIC COMPOUNDS

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Creep behaviors have been investigated on single-phase polycrystalline intermetallics of Ti-50mol%Al, Ti-51.5mol%Al and Ti-53.4mol%Al under compressive stresses of 100-398MPa at 1000-1200K. Creep characteristics and their dependence upon temperatures, stresses, grain sizes and chemical compositions are summarized as follows.1. Creep curves in titanium aluminide polycrystalline intermetallics are generally composed of four stages: an instantaneous plastic strain, a primary transient of the normal type, a region representing the minimum creep rate, and a stage in which the creep rate increases gradually. General feature of the creep curve is not influenced by deformation conditions in Ti-50mol%Al. On the other hand, in Ti-51.5mol%Al and in Ti-53.4mol%Al materials the shape of creep curves are sensitive to stresses.2. Minimum creep rate is sensitive to chemical compositions, and it becomes greater as the composition is enriched in aluminum. Stress level to yield a certain value of minimum creep rate is about 20-30% higher in Ti-50mol%Al than in Ti-53.4mol%Al.3. Grain size dependence of minimum creep rates varies with chemical composition. Negative grain-size dependence is observed in Ti-50mol%Al polycrystals, and its degree becomes greater as the stress is lowered. On the other hand, grain sizes make insignificant effect on the creep rates in TI-53.4mol%Al.