Roughening improves hydrogen embrittlement resistance of Ti-6Al-4V

Polished surfaces of Ti-6Al-4V, the most commonly used titanium alloy, were observed to suffer from hydride growth and associated embrittlement during hydrogen charging, whereas rough surfaces suffered no such susceptibility. Direct microscopic analyses of recombined hydrogen bubbles and thermal desorption spectroscopy (TDS) revealed that the surface roughening promotes recombination of atomic hydrogen to molecular hydrogen, in turn, reducing the relative amount of atomic hydrogen uptake. Subsurface time-of-flight secondary-ion mass spectrometry (ToF-SIMS) further revealed that the high defect density underneath the roughened surface impedes hydrogen diffusion into the bulk. These combined effects mean that, unexpectedly, roughening significantly reduces hydrogen uptake into Ti-6Al-4V and enhances its resistance against hydrogen embrittlement – all resulting from a simple surface treatment

Genome Analysis Reveals Interplay between 5′UTR Introns and Nuclear mRNA Export for Secretory and Mitochondrial Genes

In higher eukaryotes, messenger RNAs (mRNAs) are exported from the nucleus to the cytoplasm via factors deposited near the 5′ end of the transcript during splicing. The signal sequence coding region (SSCR) can support an alternative mRNA export (ALREX) pathway that does not require splicing. However, most SSCR–containing genes also have introns, so the interplay between these export mechanisms remains unclear. Here we support a model in which the furthest upstream element in a given transcript, be it an intron or an ALREX–promoting SSCR, dictates the mRNA export pathway used. We also experimentally demonstrate that nuclear-encoded mitochondrial genes can use the ALREX pathway. Thus, ALREX can also be supported by nucleotide signals within mitochondrial-targeting sequence coding regions (MSCRs). Finally, we identified and experimentally verified novel motifs associated with the ALREX pathway that are shared by both SSCRs and MSCRs. Our results show strong correlation between 5′ untranslated region (5′UTR) intron presence/absence and sequence features at the beginning of the coding region. They also suggest that genes encoding secretory and mitochondrial proteins share a common regulatory mechanism at the level of mRNA export

Effects of production parameters on the structure of resol type phenolic resin/layered silicate nanocomposites

Polymer/layered silicate nanocomposites belong to one of the most promising group of materials of the past few decades and most probably for the near future. Following the pioneering works of Toyota Research Group in the 1980s, the interest on these materials increased rapidly and research is now being carried out world wide, using all kinds of polymers as base material. In this present study, the aim was to investigate the effects of several different production parameters; on the morphology of resol type phenol formaldehyde based layered silicate nanocomposites produced by mixing and casting. For this purpose; two different liquid resol type phenolic resins (PF76 and PF76TD), two different curing methods (heat cure route and acid cure route), two different montmorillonite clays (unmodified Cloisite Na+ and modified Rheospan), two different clay sources (Wyoming-USA and Tokat-Turkey), and five different clay amounts (0.5%, 1%, 1.5%, 3%, 10%) were used. XRD, SEM, TEM analyses and mechanical tests indicated that resol type phenolic resins lead to better structures when they were modified with ethylene glycol and cured by the use of an acidic curing agent. It was also observed that use of modified clay with no more than 1.5 wt% in the phenolic matrix lead to certain degree of exfoliation consequently better structure and higher mechanical performance

Preventing damage and redeposition during focused ion beam milling: the “umbrella” method

\u3cp\u3eFocused ion beam (FIB) milling has enabled the development of key microstructure characterization techniques (e.g. 3D electron backscatter diffraction (EBSD), 3D scanning electron microscopy imaging, site-specific sample preparation for transmission electron microscopy, site-specific atom probe tomography), and micro-mechanical testing techniques (e.g. micro-pillar compression, micro-beam bending, in-situ TEM nanoindentation). Yet, in most milling conditions, some degree of FIB damage is introduced via material redeposition, Ga\u3csup\u3e+\u3c/sup\u3e ion implantation or another mechanism. The level of damage and its influence vary strongly with milling conditions and materials characteristics, and cannot always be minimized. Here, a masking technique is introduced, that employs standard FIB-SEM equipment to protect specific surfaces from redeposition and ion implantation. To investigate the efficiency of this technique, high angular resolution EBSD (HR-EBSD) has been used to monitor the quality of the top surface of several micro-pillars, as they were created by milling a ringcore hole in a stress-free silicon wafer, with or without protection due to an “umbrella”. HR-EBSD provides a high-sensitivity estimation of the amount of FIB damage on the surface. Without the umbrella, EBSD patterns are severely influenced, especially within 5 µm of the milled region. With an optimized umbrella, sharp diffraction patterns are obtained near the hole, as revealed by average cross correlation factors greater than 0.9 and equivalent phantom strains of the order 2 × 10\u3csup\u3e−4\u3c/sup\u3e. Thus, the umbrella method is an efficient and versatile tool to support a variety of FIB based techniques.\u3c/p\u3