Microstructures and mechanical properties of Ti6Al4V-Ti48Al2Cr2Nb alloys fabricated by laser melting deposition of powder mixtures

Ti6Al4V (TC4)/Ti48Al2Cr2Nb (TiAl) functionally graded materials (FGM) is the premium material for aeroengine turbine blisk in which TC4 and TiAl were used as blades and disks, respectively, and has wide application prospect. In this work, TC4-xTiAl (x = 20%, 40%, 60%, 80% wt%) alloys without metallurgical defects were fabricated by laser melting deposition (LMD) from mixtures of TC4/TiAl powders. The influence of TiAl content on microstructure morphology, phase composition, and tensile properties was systematically studied in detail and a composition-microstructure-property relationship was simultaneously set up. The microstructure gradually transformed from basket weave structure to lamellar structure, accompanying with the formation of alpha(2), gamma, and B2 with increasing TiAl contents. In addition, a series of phase transformations occurred in these alloys: beta -> alpha, alpha -> alpha(2), and alpha(2) -> gamma. The addition of TiAl can reduce the tensile properties at room temperature (RT), the TC420%TiAl alloy has the highest ultimate tensile strength (UTS) (1083 MPa) and elongation (4.60%). Compared to other alloys, the TC4-60%TiAl alloy exhibited the best tensile property a 650 degrees C and 750 degrees C, the UTS of which was 572 MPa and 562 MPa, respectively. The tensile properties a RT and high-temperature are strongly dependent on phase composition. The formation of alpha(2) and gamma intermetallic compounds can improve the thermal stability, but reduce the room-temperature strength and plasticity. In particular, the gamma phase is more stable than the alpha(2) phase a high temperatures.