INVESTIGATION INTO CREEP BEHAVIOR IN POLYCRYSTALS OF TITANIUM ALUMINIDE INTERMETALLIC COMPOUNDS

研究了Ti-50mol%Al、Ti-51.5mol%Al和Ti-53.4mol%Al单相多晶金属间化合物在100-398MPa、1000-1200K压应力作用下的蠕变行为。蠕变特性及其对温度、应力、晶粒尺寸和化学成分的依赖性总结如下：钛铝多晶金属间化合物的蠕变曲线一般由四个阶段组成：瞬时塑性应变阶段、正常型初级瞬态阶段、代表最小蠕变速率的区域和蠕变速率逐渐增大的阶段。在Ti-50mol%Al中，变形条件不影响蠕变曲线的一般特征。另一方面，在Ti-51.5mol%Al和Ti-53.4mol%Al材料中，蠕变曲线的形状对应力敏感。最小蠕变速率对化学成分敏感，随着成分中铝含量的增加，最小蠕变速率增大。在Ti-50mol%Al中产生最小蠕变速率的应力水平比在Ti-53.4mol%Al中高20-30%。最小蠕变速率的晶粒大小随化学成分的不同而变化。Ti-50mol%Al多晶晶粒尺寸呈负相关，且随应力的降低晶粒尺寸负相关程度增大。另一方面，晶粒尺寸对TI-53.4mol%Al中蠕变速率的影响不大。

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.