MICROMECHANISMS OF PLASTIC-DEFORMATION OF 2-PHASE TIAL-BASE ALLOY AT ROOM-TEMPERATURE

The room-temperature deformation modes and the activities of various d eformation systems in two-phase TiAl-base alloys have been studied by means of TEM diffraction-contrast examination on compressively deforme d structures and in-situ tensile observations. The results show that o rdinary dislocation slipping and deformation twinning are very active in gamma-matrix, while the critical resolved shear stress for superdis location slip systems is at least 3.8-4.2 times as large as that of or dinary dislocation ones. The [011] shear strain in gamma-lamella can b e realized by the combination of deformation twinning and ordinary dis location slipping. Besides, a detailed analysis on deformation compati bility shows that the necessary condition for compatible deformation a mong polycrystalline grains cannot he satisfied only by ordinary dislo cation slipping and deformation twinning. Based on the above considera tion, the relationship between room-temperature ductility and grain si ze has been established: epsilon(f) = a/d+b.