Effect of multi-stage heat treatment on mechanical properties and microstructure transformation of Ti–48Al–2Cr–2Nb alloy

Refining the grain size of γ-TiAl alloys to improve their strength and ductility is of academic interest. Thus, we report a multi-stage heat treatment method consisting of solution treatment, cyclic heat treatment, annealing, short heat treatment, and aging to refine the microstructure of the Ti–48Al–2Cr–2Nb alloy. The solution-treated microstructure was refined from 1100 to 191 μm by cyclic heat treatment, promoting feathery γ packets. Fine duplex grains below 23 μm were obtained through discontinuous coarsening, which was accelerated in the cyclic-heat-treated alloys owing to the high driving force resulting from the presence of feathery γ packets and fine interlamellar spacing. Through the short heat treatment and aging at single α and α2 + γ fields, a tailored duplex structure with a grain size of 24 μm and interlamellar spacing of 42 nm was achieved. Through microstructure refinement, tensile strength and elongation were improved to 697 MPa and 2.1%, respectively, compared to those of the conventional forged specimen (622 MPa and 1.3%, respectively). We believe that our study provides a simple pathway to refine the grain size and interlamellar spacing of γ-TiAl alloys.