Microstructures and properties for titanium aluminide superalloy prototypes fabricated by electron beam melting and thermally processed
Gamma TiAl has been considered to be an ideal replacement for Ni-base superalloy aerospace applications, particularly in weight-critical applications. While bulk, fully dense gamma-TiAl is 50% less dense than Ni-base superalloys, it also has excellent mechanical properties at high temperature (up to ~800°C). Pre alloyed (Ti-48Al-2Cr-2Nb) powder was used to fabricate solid, fully dense (3.85 g/cm3) components and foam components with densities ranging from 0.33 g/cm3 to 0.46 g/cm3 by electron beam melting (EBM). A 10:1 blend of 2-phase TiAl (Ti-48Al-2Cr-2Nb in a/oo) : Inconel 625 (Ni- 22Cr-6Mo-2Nb in a/ o) pre-alloyed powders produced a complex alloy having the composition 44Ti- 39Al-7Ni-4Nb-4Cr-2Mo (in a/o). Solid, reticulated mesh samples and stochastic foam samples were fabricated by electron beam melting (EBM) using this blended alloy. The microstructures of the solid and open-cellular components were observed by optical metallography (OM) and transmission electron microscopy (TEM), and confirmed by XRD analysis. The microstructure and residual hardness for solid components of 2-phase TiAl and Inconel 625 fabricated by EBM were compared to that of the blended alloy. The 2-phase TiAl alloy exhibited a duplex, equiaxed γ (TiAl) grain structure (15 μm) with lamellar colonies characterized by thin α2 (Ti3Al) plates ~20 nm thick having an orientation relationship: (111)γ::(0001)α2. The hardness (HV) of the blended alloy reached 7.5 GPa compared to 1.4 GPa for the Alloy 625 and 4.0 for the 2-phase TiAl alloy. Relative stiffness versus relative density values were plotted on a log-log basis for the reticulated mesh and stochastic foam samples for the blended alloy and were consistent with other alloys fitted to a straight line with a slope n=2 for ideal open cellular materials.
Hernandez, Jennifer, "Microstructures and properties for titanium aluminide superalloy prototypes fabricated by electron beam melting and thermally processed" (2013). ETD Collection for University of Texas, El Paso. AAI3565911.