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Register a new userInterface characteristics in an {alpha}+{beta} titanium alloy
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The alpha/beta interface in Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) is investigated via centre of symmetry analysis, both as-grown and after 10% cold work. Semi-coherent interface steps are observed at a spacing of 4.5 +/-1.13 atoms in the as-grown condition, in good agreement with theory prediction (4.37 atoms). Lattice accommodation is observed, with elongation along [-1 2 -1 0]alpha and contraction along [1 0 -1 0]alpha . Deformed alpha exhibited larger, less coherent steps with slip bands lying in {110}beta. This indicates dislocation pile-up at the grain boundary, a precursor to globularisation, offering insight into the effect of deformation processing on the interface, which is important for titanium alloy processing route design.
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Atom probe tomography (APT), electron probe microanalysis (EPMA) and nanoindentation were used to characterise the oxygen-rich layer on an in-service jet engine compressor disc, manufactured from the titanium alloy TIMETAL 834. Oxygen ingress was quantified and related to changes in mechanical properties through nanoindentation studies. The relationship between oxygen concentration, microstructure, crystal orientation and hardness has been explored through correlative hardness mapping, EPMA and electron backscatter diffraction (EBSD). The role of microstructure on oxygen ingress has been studied and oxygen ingress along a potential alpha/ beta interface was directly observed on the nanoscale using APT.
We provide a complete quantitative explanation for the anisotropic thermal expansion of hcp Ti at low temperature. The observed negative thermal expansion along the c-axis is reproduced theoretically by means of a parameter free theory which involves both the electron and phonon contributions to the free energy. The thermal expansion of titanium is calculated and found to be negative along the c-axis for temperatures below $sim$ 170 K, in good agreement with observations. We have identified a saddle-point Van Hove singularity near the Fermi level as the main reason for the anisotropic thermal expansion in $alpha-$titanium.
The mechanism of AgCl-induced stress corrosion cracking of Ti-6246 was examined at SI{500}{megapascal} and SI{380}{celsius} for SI{24}{hour} exposures. SEM and STEM-EDX examination of a FIB-sectioned blister and crack showed that metallic Ag was formed and migrated along the crack. TEM analysis also revealed the presence of ce{SnO2} and ce{Al2O3} corrosion products mixed into ce{TiO2}. The fracture surface has a transgranular nature with a brittle appearance in the primary $alpha$ phase. Long, straight and non-interacting dislocations were observed in a cleavage-fractured primary $alpha$ grain, with basal and pyramidal traces. This is consistent with a dislocation emission view of the the cracking mechanism.
Work function-mediated charge transfer in graphene/$alpha$-RuCl$_3$ heterostructures has been proposed as a strategy for generating highly-doped 2D interfaces. In this geometry, graphene should become sufficiently doped to host surface and edge plasmon-polaritons (SPPs and EPPs, respectively). Characterization of the SPP and EPP behavior as a function of frequency and temperature can be used to simultaneously probe the magnitude of interlayer charge transfer while extracting the optical response of the interfacial doped $alpha$-RuCl$_3$. We accomplish this using scanning near-field optical microscopy (SNOM) in conjunction with first-principles DFT calculations. This reveals massive interlayer charge transfer (2.7 $times$ 10$^{13}$ cm$^{-2}$) and enhanced optical conductivity in $alpha$-RuCl$_3$ as a result of significant electron doping. Our results provide a general strategy for generating highly-doped plasmonic interfaces in the 2D limit in a scanning probe-accessible geometry without need of an electrostatic gate.
The onset and kinetics of martensitic transformations are controlled by impurities trapped during the transformation. For the alpha to omega transformation in Ti, ab initio methods yield the changes in both the relative stability of and energy barrier between the phases. Using the recently discovered transformation pathway, we study interstitial O, N, C; substitutional Al and V; and Ti interstitials and vacancies. The resulting microscopic picture explains the observations, specifically the suppression of the transformation in A-70 and Ti-6Al-4V titanium alloys.
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