Refining of coarse lamellar microstructure of TiAl alloys by rapid heat treatment

摘要

It is now well known that the room temperaturetensile yield strength (#sigma#_y), fracture strength (#sigma#_f),and ductility (#delta#) of TiAl alloys increase with decreasingthe colony size (d) of the fully lamellar (FL) structure. Thereforesearching a cost-effective approach to refine the coarse FLstructure becomes critical to the engineering application of thismaterial. In this study, we report our recent observation that,merely by rapid heat treatment, a FL structure with d=500#mu#m in a TiAl alloy of Ti-48Al-2Cr (at percent) could berefined to a FL structure with d being as fine as 10 #mu#m. Nothermomechanical processing such as canned forging and hotextrusion, as done in previous studies, was required. Mechanicaltesting in tension shows that with the refinement from 500 to 10#mu#m, the room temperature yield strength increased from 330to 610 MPa, fracture strength from 415 to 825 MPa and ductilityfrom 0.7 to 3.3 percent, although the fracture toughnessdecreased only slightly from 24 to 19 MPa m~(1/2).