Electron beam melted TiC/high Nb–TiAl nanocomposite: Microstructure and mechanical property

To enhance the process stability and densification, semi-melt step has been introduced when fabricating the TiC/high Nb–TiAl nanocomposite via electron beam melting. The homogenous TiAl matrix microstructure with dispersed nano-scale carbides was realised. During the EBM melt, most TiC nanoparticles dissolved and Ti2AlC formed with near-spherical and rod-like shapes. The particles had an influence on solidification behaviour and the subsequent microstructural degradation. High Nb–TiAl nanocomposites with 1.2 wt% TiC addition exhibited a duplex microstructure with dispersed carbides, while a nearly lamellar microstructure (carbide-free) was found in samples with 0.6 and 0.8 wt% TiC. Furthermore, a lower scanning speed resulted in higher relative density, greater Al loss, increased α2-phase but reduced carbide fractions. The microhardness of 433 ± 10 HV0.2, ultimate tensile strength of 657 ± 155 MPa and fracture toughness of 8.1 ± 0.1 MPa√m in 1.2 wt% TiC/high Nb–TiAl nanocomposite processed by EBM are very promising. In addition, the compressive yield strength of 1085 ± 55 MPa, fracture strength of 2698 ± 34 MPa and strain to fracture of 26.1 ± 1.0%, are superior to those processed by conventional means. The strengthening and toughening mechanisms have been interpreted on the basis of crack path observation

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

Highly active and stable CuAlOx/WO3photoanode for simultaneous pollutant degradation, hydrogen and electricity generation

An unassisted solar water-energy nexus system (SWENS) based on an ultra-thin CuAlOx overlayer coated WO3 nanoplate array (CuAlOx/WO3) photoanode, a rear silicon solar cell and a Pt-black/Pt cathode was proposed to efficiently degrade refractory organic pollutants and simultaneously produce hydrogen and electricity. The formed p-n junction between p-type CuAlOx and n-type WO3 effectively facilitated the charge separation in the CuAlOx/WO3 photoanode. Moreover, the CuAlOx overlayer enhanced the capture of photogenerated holes and isolated WO3 from the solution, thereby improving the charge transfer and inhibiting the photocorrosion of WO3. Therefore, the optimized CuAlOx/WO3 photoanode showed a significantly enhanced and stable photocurrent density of ∼2.82 mA cm-2 at 1.0 V vs. Ag/AgCl, which was ∼4 times higher than that of the pristine WO3. Based on this outstanding photoelectrocatalytic performance, the assembled SWENS showed a degradation efficiency of nearly 100% for tetracycline, a hydrogen generation rate of ∼26.8 μmol·h-1·cm-2 and a power density of ∼593 μW cm-2 under simulated solar light illumination. Our SWENS also exhibited outstanding universality in degrading various refractory organic pollutants for green energy production