Structure and Growth of Core–shell Nanoprecipitates in Al–Er–Sc–Zr–V–Si High-temperature Alloys

Lightweight Sc-containing aluminum alloys exhibit superior mechanical performance at high temperatures due to core–shell, L12-ordered trialuminide nanoprecipitates. In this study, the structure of these nanoprecipitates was studied, using different transmission electron microscopy (TEM) techniques, for an Al–Er– Sc–Zr–V–Si alloy that was subjected to a two-stage overaging heat treatment. Energy-dispersive X-ray spectroscopy of the spherical Al3(Sc, Zr, Er ,V) nanoprecipitates revealed a core–shell structure with an Sc- and Er-enriched core and a Zr-enriched shell, without a clear V outer shell. This structure is stable up to 72% of the absolute melting temperature of Al for extended periods of time. High-angle annular dark-field scanning TEM was used to image the {100} planes of the nanoprecipitates, demonstrating a homogeneous L12-ordered superlattice structure for the entire nanoprecipitates, despite the variations in the concentrations of solute atoms within the unit cells. A possible growth path and compositional trajectory for these nanoprecipitates was proposed using high-resolution TEM observations, where different rod-like structural defects were detected, which are considered to be precursors to the spherical L12-ordered nanoprecipitates. It is also hypothesized that the structural defects could consist of segregated Si; however, this was not possible to verify with HAADF-STEM because of the small differences in Al and Si atomic numbers. The results herein allow a better understanding of how the Al–Sc alloys’ core–shell nanoprecipitates form and evolve temporally, thereby providing a better physical picture for future atomistic structural mappings and simulations

Secrets in the sky: on privacy and infrastructure security in DVB-S satellite broadband

Demands for ubiquitous global connectivity have sparked a satellite broadband renaissance. Secure satellite broadband is vital to ensuring that this growth does not beget unanticipated harm. Motivated by this need, this paper presents an experimental security analysis of satellite broadband signals using the Digital Video Broadcasting for Satellite (DVB-S) protocol. This analysis comprises 14 geostationary platforms encompassing over 100 million square kilometers of combined coverage area. Using less than €300 of widely available equipment, we demonstrate the ability to identify individual satellite customers, often down to full name and address, and their web browsing activities. Moreover, we find that these vulnerabilities may enable damaging attacks against critical infrastructure, including power plants and SCADA systems. The paper concludes with a discussion of possible confidentiality protections in satellite broadband environments and notes a need for further cryptographic research on link-layer encryption for DVB-S broadband

Secrets in the sky: on privacy and infrastructure security in DVB-S satellite broadband

Demands for ubiquitous global connectivity have sparked a satellite broadband renaissance. Secure satellite broadband is vital to ensuring that this growth does not beget unanticipated harm. Motivated by this need, this paper presents an experimental security analysis of satellite broadband signals using the Digital Video Broadcasting for Satellite (DVB-S) protocol. This analysis comprises 14 geostationary platforms encompassing over 100 million square kilometers of combined coverage area. Using less than €300 of widely available equipment, we demonstrate the ability to identify individual satellite customers, often down to full name and address, and their web browsing activities. Moreover, we find that these vulnerabilities may enable damaging attacks against critical infrastructure, including power plants and SCADA systems. The paper concludes with a discussion of possible confidentiality protections in satellite broadband environments and notes a need for further cryptographic research on link-layer encryption for DVB-S broadband

Hyperstabilization of martensites

The effect of hyperstabilization of martensite implies that the reverse martensitic transformation proceeds in two well separated stages. Namely, a small fraction of martensite (of the order of 10%) retransforms upon heating into the parent phase over a temperature range slightly higher than the nominal reverse transformation temperature, whereas the rest of the martensite retransforms through a renucleation of fine lamellae of the parent phase. The renucleation stage of the transformation is well defined and requires strong overheating of the order of 300 K with respect to the nominal transformation. In this letter, the results are discussed of a study of the hyperstabilization effect in different martensitic structures: faulted β'1 martensite in Cu–Al–Be system and twinned martensite in ferromagnetic Ni–Fe–Ga crystals by means of differential scanning calorimetry, transmission electron microscopy and internal friction. The conclusion has been drawn that hyperstabilization implies a severe blocking of the motion of interphase boundaries during the reverse transformation, which can be produced either due to a high concentration of highly mobile quenched-in defects ("sweeping" of defects during the reverse transformation) or due to a creation of obstacles by preliminary plastic deformation. The former mechanism requires very intense diffusion of quenched-in defects assisted by dislocations/interfaces, which has been confirmed by internal friction studies. It has been shown that the renucleation stage, which occurs at around 600 K for different alloys, is preceded by a relaxation internal friction peak. A possible role of this relaxation in renucleation of the parent phase is discussed.status: publishe