Electron beam powder bed fusion of Y2O3/γ-TiAl nanocomposite with balanced strength and toughness

This paper reports the use of multi-spot melt strategy coupled with smaller layer thickness to additively manufacture Y2O3/γ-TiAl nanocomposite. In contrast to the hatch melt, the multi-spot melt strategy results in a lower fraction of γ and B2-phase, a smaller lamellar spacing of 208 ± 72 nm with straight interface between α2/γ, and a uniformly distributed nanoparticles with a finer size of 90 ± 38 nm. Twins can form in the equiaxed γ grains and within γ lamellae; this applies to both the multi-spot and hatch melt samples. Twins within the γ lamellae can propagate across the twin interface but terminate at the γ/α2 interface. A good combination of 556 ± 11 MPa (tensile strength) and 17.0 ± 3.1 % (ductility) at 800 ℃ with 16.5 ± 0.3 MPa√m (room-temperature fracture toughness) is achieved in the as-built condition. Quantitative microscopy confirms a homogeneous microstructure within the x-y plane for the multi-spot sample, whilst the use of smaller layer thickness helps to reduce the microstructure degradation due to thermal cycling. In terms of the Y2O3 nanoparticles, both the rod-like Y2O3 with monoclinic and the near spherical Y2O3 with cubic crystal system are identified using transmission electron microscopy (TEM). High-resolution TEM reveals that the Y2O3/TiAl interface is clean, free of interfacial reactions, and with a semi-coherent or coherent type, suggesting a strong bonding.