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Additive manufacturing is being increasingly used in the fabrication of Ti-6Al-4V parts to combine excellent mechanical properties and biocompatibility with high precision. Unfortunately, due to the build-up of thermal residual stresses and the formation of martensitic structure across a wide range of typical processing conditions, it is generally necessary to use a post-thermal treatment to achieve superior mechanical performance. This investigation aims to obtain a deeper understanding of the micro/nanostructural evolution (a 0 martensite phase decomposition), accounting for the kinetics of phase transformation during the heat treatment of 3D-printed Ti-6Al-4V alloy. As the mechanism of phase transformation and stress relaxation is still ambiguous, in this study the changes in crystal lattice, phase, composition and lattice strain were investigated up to 1000°C using both in situ high temperature X-ray diffraction (XRD) and transmission electron microscopy (TEM). Based on the result a mechanism of phase transformation is proposed, via the accommodation/substitution of Al, V and Ti atoms in the crystal lattice. The proposed mechanism is supported based on elemental concentration changes during heat treatment, in combination with changes in crystal structure observed using the high temperature XRD and TEM measurements. This study provides a deeper understanding on the mechanism of phase transformation through martensitic decomposition, as well as a deeper understanding of the influence of post-thermal treatment conditions on the alloy's crystal structure.

. (2016). Fabrication and characterisation of GaAs nanopillars using nanosphere lithography and metal assisted chemical etching. RSC Advances: an international journal to further the chemical sciences, 6 30468-30473.Fabrication and characterisation of GaAs nanopillars using nanosphere lithography and metal assisted chemical etching AbstractWe present a low-cost fabrication procedure for the production of nanoscale periodic GaAs nanopillar arrays, using the nanosphere lithography technique as a templating mechanism and the electrochemical metal assisted etch process (MacEtch). The room-temperature photoluminescence (PL) and Raman spectroscopic properties of the fabricated pillars are detailed, as are the structural properties (scanning electron microscopy) and fabrication process. From our PL measurements, we observe a singular GaAs emission at 1.43 eV with no indications of any blue or green emissions, but with a slight redshift due to porosity induced by the MacEtch process and characteristic of porous GaAs (p-GaAs). This is further confirmed via Raman spectroscopy, where additionally we observe the formation of an external cladding of elemental As around our nanopillar features. The optical emission is enhanced by an order magnitude (~300%) for our nanopillar sample relative to the planar unprocessed GaAs reference. We present a low-cost fabrication procedure for the production of nanoscale periodic GaAs nanopillar arrays, using the nanosphere lithography technique as a templating mechanism and the electrochemical metal assisted etch process (MacEtch). The room-temperature photoluminescence (PL) and Raman spectroscopic properties of the fabricated pillars are detailed, as are the structural properties (scanning electron microscopy) and fabrication process. From our PL measurements, we observe a singular GaAs emission at 1.43 eV with no indications of any blue or green emissions, but with a slight redshift due to porosity induced by the MacEtch process and characteristic of porous GaAs (p-GaAs). This is further confirmed via Raman spectroscopy, where additionally we observe the formation of an external cladding of elemental As around our nanopillar features. The optical emission is enhanced by an order magnitude ($300%) for our nanopillar sample relative to the planar unprocessed GaAs reference.

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