TiAl-BASED ALLOY, PROCESS FOR PRODUCING SAME, AND ROTOR BLADE USING SAME

Abstract

A hot-forged TiAl-based alloy having excellent oxidation resistance and high strength at high temperatures, and a process for producing such an alloy. A TiAl-based alloy comprising Al: (40+a) atomic % and Nb: b atomic %, with the remainder being Ti and unavoidable impurities, wherein a and b satisfy formulas (1) and (2) below. 0≦a≦2  (1) 3+ a≦b≦ 7+ a   (2) Also, a TiAl-based alloy comprising Al: (40+a) atomic % and Nb: b atomic %, and further comprising one or more elements selected from the group consisting of V: c atomic %, Cr: d atomic % and Mo: e atomic %, with the remainder being Ti and unavoidable impurities, wherein a to e satisfy formulas (3) to (9) shown below. 0≦a≦2  (3) 3+ a≦b +1.0 c +1.8 d +3.8 e ≦7+ a   (4) b≧2  (5) c≧0  (6) d≧0  (7) e≧0  (8) c+d+e >0  (9)

1 . A TiAl-based alloy comprising
 Al: (40+a) atomic % and   Nb: b atomic %,   with a remainder being Ti and unavoidable impurities, wherein a and b satisfy formulas (1) and (2) below:
   0≦a≦2  (1), and 
   3+ a≦b≦ 7+ a   (2). 
   
     
     
         2 . A TiAl-based alloy comprising
 Al: (40+a) atomic % and   Nb: b atomic %, and further comprising   one or more elements selected from the group consisting of   V: c atomic %,   Cr: d atomic % and   Mo: e atomic %,   with a remainder being Ti and unavoidable impurities, wherein a to e satisfy formulas (3) to (9) shown below:
   0≦a≦2  (3), 
   3+ a≦b+ 1.0 c+ 1.8 d+ 3.8 e≦ 7+ a   (4), 
   b≧2  (5), 
   c≧0  (6), 
   d≧0  (7), 
   e≧0  (8) and 
     c+d+e> 0  (9). 
   
     
     
         3 . The TiAl-based alloy according to  claim 1 , having a metal structure comprising aligned lamellar grains in which an α 2 -phase and a γ-phase are stacked in an alternating manner. 
     
     
         4 . A process for producing a TiAl-based alloy, the process comprising:
 holding a TiAl-based alloy material, comprising
 Al: (40+a) atomic % and 
 Nb: b atomic %, 
 with a remainder being Ti and unavoidable impurities, wherein a and b satisfy formulas (1) and (2) below:
   0≦a≦2  (1) and 
   3+ a≦b≦ 7+ a   (2) 
 
   at a holding temperature within an equilibrium temperature range for an (α+β) phase, and   subjecting the TiAl-based alloy material held at the holding temperature to high-speed plastic working while cooling to a predetermined final working temperature.   
     
     
         5 . A process for producing a TiAl-based alloy, the process comprising:
 holding a TiAl-based alloy material, comprising
 Al: (40+a) atomic % and 
 Nb: b atomic %, and further comprising 
 one or more elements selected from the group consisting of 
 V: c atomic %, 
 Cr: d atomic % and 
 Mo: e atomic %, 
 with a remainder being Ti and unavoidable impurities, wherein a to e satisfy formulas (3) to (9) shown below:
   0≦a≦2  (3) 
   3+ a≦b+ 1.0 c+ 1.8 d+ 3.8 e≦ 7+ a   (4), 
   b≧2  (5), 
   c≧0  (6), 
   d≧0  (7), 
   e≧0  (8) and 
     c+d+e> 0  (9) 
 
   at a holding temperature within an equilibrium temperature range for an (α+β) phase, and   subjecting the TiAl-based alloy material held at the holding temperature to high-speed plastic working while cooling to a predetermined final working temperature.   
     
     
         6 . The process for producing a TiAl-based alloy according to  claim 4 , wherein
 the holding temperature is not less than 1150° C. and not more than 1350° C.   
     
     
         7 . A process for producing a TiAl-based alloy according to  claim 4 , wherein
 the final working temperature is not less than 1150° C.   
     
     
         8 . A process for producing a TiAl-based alloy according to  claim 4 , wherein
 a forging process is used for the high-speed plastic working.   
     
     
         9 . A rotor blade that uses the TiAl-based alloy according to  claim 1 .