Effect of lamellar spacing on the mechanical properties of (Nb)/(Nb, Ti)(5)Si-3 two-phase alloys

Effects of lamellar spacing on the mechanical properties of (Nb)/(Nb, Ti)(5 )Si-3 two-phase alloys with a fine lamellar structure have been investigate d for an improvement in room-temperature toughness and high-temperature str ength. Lamellar spacing of the ahoy are controlled, without changing the vo lume fraction and composition of each phase, by varying annealing temperatu re for the decomposition of high-temperature phase (Nb, Ti)(3)Si into (Nb) and (Nb, Ti)(5)Si-3. A Time-Temperature-Transformation diagram (TTT diagram ) was determined for a Nb-25 mol%Si-10 mol%Ti ahoy. It was found that the d ecomposition of (Nb, Ti)(3)Si in the Nb-Si-Ti system is kinetically faster than that of Nb3Si in the binary Nb-Si system. Average lamellar spacing, la mbda, of the alloy is characterized by the degree of super-cooling, DeltaT, following a relationship as "lambda proportional to1/DeltaT". Coarse lamel lar structure shows better room temperature compressive plastic strain befo re fracture and higher elevated temperature strength. The alloys investigat ed in this study show superior compressive strength at over 1000 degreesC a s compared with some commercial Ni-based superalloys.