EFFECTS OF ALLOYING ELEMENTS AND HEAT-TRE ATMENT ON THE STRENGTH AND DUCTILITY OF CAST-HIPPED TIAL

The effects of alloying elements and post annealing on the strength an d ductility in cast-Hipped TiAl were investigated. The aluminum conten t was varied from 46 to 49 at% in Ti-Al system, and various alloying e lements were added by around 2 at% in TiAl with Al/(Ti + Al) of 0.48 a tomic ratio. Tensile properties of all alloys showed a linear relation ship between 0.2% offset yield strength and elongation. Cr and Mn addi tion results in ductility improvement accompanied with a reduction of strength, and the other alloying elements reduced ductility with an in crease of strength. The Al content or alloying elements in TiAl varied widely the volume fraction of grains in lamellar form and the spacing in the lamellar structure, which markedly affected the overall streng th of alloys and the hardness of lamellar grains, respectively. The yi eld strengths of various alloys with a two phase structure consisting of equiaxed gamma and lamellar grains were analyzed based on the rule of mixture. Addition of Mo or Cr tended to form the beta phase. The po st annealing at 1603 K resulted in a significant improvement of streng th-ductility balance although the strength was markedly decreased. The microstructural factors controlling the strength and ductility of TiA l were discussed in detail.