ABSTRACT
The effects of the secondary processes of Hot Isostatic Pressing (HIP) at 920 °C and Heat Treatment (HT) at 1000 °C of Electron Beam-Melted (EBM) Ti-6Al-4V alloy on the microstructure and hydrogen embrittlement (HE) after electrochemical hydrogen charging (EC) were investigated. Comprehensive characterization, including microstructural analysis, X-ray diffraction (XRD), thermal desorption analysis, and mechanical testing, was conducted. After HIP, the ß-phase morphology changed from discontinuous Widmanstätten to a more continuous structure, 10 times and ~1.5 times larger in length and width, respectively. Following HT, the ß-phase morphology changed to a continuous "web-like" structure, ~4.5 times larger in width. Despite similar mechanical behavior in their non-hydrogenated state, the post-treated alloys exhibit increased susceptibility to HE due to enhanced hydrogen penetration into the bulk. It is shown that hydrogen content in the samples' bulk is inversely dependent on surface hydride content. It is therefore concluded that the formed hydride surface layer is crucial for inhibiting further hydrogen penetration and adsorption into the bulk and thus for reducing HE susceptibility. The lack of a hydride surface layer in the samples subject to HIP and HT highlights the importance of choosing secondary treatment process parameters that will not increase the continuous ß-phase morphology of EBM Ti-6Al-4V alloys in applications that involve electrochemical hydrogen environments.
ABSTRACT
Short range ordered (SRO) plasmonic nanohole arrays have a distinct surface plasmon polariton resonance in the visible region and exhibit an excellent sensing capability toward changes in the surrounding refractive index. While SRO and perfectly ordered plasmonic hole arrays have similar sensing properties, SRO arrays have clear advantages in fabrication, simplicity, and scalability. In this study, we use SRO gold nanoholes, which are subjected to pressure and temperature cycles, for vacuum and temperature sensing. The response of the transmission spectra to pressure changes in the range 10-3-105 Pa and temperature scans in the range 20-400 °C was recorded. Upon pressure cycling, a reversible response was observed. Upon initial temperature annealing, an irreversible blue shift in the resonance dip position was observed. Upon further temperature cycling, the resonance dip position shifts reversibly, with a notable red shift upon temperature increase. The results are discussed and interpreted based on possible molecular adsorption/desorption upon pressure cycling and in terms of the gold film's recrystallization, thermal expansion, and free electron density variations.
