Effects of heat treatment and processing conditions on the microstructure and mechanical properties of a novel Ti-6.3Cu-2.2Fe-2.1Al alloy

Adding transition alloying elements to achieve a columnar to equiaxed transition (CET) in Ti-alloys is gaining attention in additive manufacturing (AM). AM which may be categorized as an advanced solidification process, is commonly a near-net-shape process. This thus does not allow traditional thermo-mechanical processing to reduce grain size, which drives research toward novel alloys able to establish a primary grain structure with equiaxed grains upon solidification. The Ti-Cu alloy system caught attention through inducing the CET, but so far, no focus was placed on its secondary, solid state, phase transformations during the heat treatment. Therefore, requiring modified heat treatment strategies to accommodate for the inability of mechanical preforming prior to heat treating and thus achieving desired mechanical properties. This work provides insights on microstructural evolution and tensile properties of a novel Ti-6.3Cu-2.2Fe-2.1Al alloy gained in an extensive heat treatment study. Results show a lamellar α+β Widmannstätten microstructure with Ti2Cu precipitation and other features including grain boundary α, precipitate-free zones, and very fine secondary α precipitates. Utilizing micrographs and fractographic imaging, the fracture mode is identified as quasi-cleavage mode with preferential crack initiation at grain boundary α layers. Tensile tests on heat treated samples show high strengths with simultaneously limited ductility.