TiAl ALLOY AND METHOD OF MANUFACTURING THE SAME

Abstract

A TiAl alloy contains 48 at % or more and 50 at % or less of Al, 3 at % or more and 5 at % or less of Nb, 0.1 at % or more and 0.3 at % or less of B, and the balance being Ti and inevitable impurities.

What is claimed is: 
     
         1 . A TiAl alloy, consisting of:
 48 at % or more and 50 at % or less of Al;   3 at % or more and 5 at % or less of Nb;   0.1 at % or more and 0.3 at % or less of B; and   the balance being Ti and inevitable impurities.   
     
     
         2 . The TiAl alloy according to  claim 1 , wherein
 a content of Al is 49 at %.   
     
     
         3 . The TiAl alloy according to  claim 1 , wherein
 a metal structure is formed of a lamellar grain and a γ grains, and is free of a segregation of Nb.   
     
     
         4 . The TiAl alloy according to  claim 3 , wherein
 a volume fraction of the lamellar grain is 80 volume % or more, relative to a total of the volume fraction of the lamellar grain and the volume fraction of the γ grain being 100 volume %.   
     
     
         5 . The TiAl alloy according to  claim 1 , wherein
 Vickers hardness at a room temperature is 200 HV or more.   
     
     
         6 . The TiAl alloy according to  claim 1 , wherein
 room temperature ultimate tensile strength is 400 MPa or more and room temperature tensile fracture strain is 1.0% or more.   
     
     
         7 . The TiAl alloy according to  claim 1 , wherein
 creep strain after an elapse of 200 hours is 2% or less, when a temperature is 800° C. and applied stress is 150 MPa.   
     
     
         8 . A method of manufacturing a TiAl alloy, comprising:
 a casting step of casting a TiAl alloy raw material which consists of 48 at % or more and 50 at % or less of Al, 3 at % or more and 5 at % or less of Nb, 0.1 at % or more and 0.3 at % or less of B, and the balance being Ti and inevitable impurities.   
     
     
         9 . The method of manufacturing the TiAl alloy according to  claim 8 , wherein
 in the casting step, a solidification process passes through an α single phase region.   
     
     
         10 . The method of manufacturing the TiAl alloy according to  claim 8 , comprising:
 a hot isostatic pressing process step for performing a hot isostatic pressing process of applying hot isostatic pressing to the cast TiAl alloy at a temperature range from 1250° C. or higher to 1350° C. or lower, for a hour range from 1 hour or more to 5 hours or less, at an applied stress range from 158 MPa or higher to 186 MPa or lower, and then furnace cooling the cast TiAl alloy subjected to the hot isostatic pressing to 900° C., followed by rapid cooling of the cast TiAl alloy subjected to the hot isostatic pressing from 900° C.   
     
     
         11 . The method of manufacturing the TiAl alloy according to  claim 10 , comprising:
 a stress relieving step of relieving stress by holding the TiAl alloy subjected to the hot isostatic pressing process at a temperature range from 800° C. or higher to 950° C. or lower for a hour range from 1 hour or more to 5 hours or less.