Microstructure characterisation and creep modelling of HP40 alloys

The efficiency of steam reforming depends strongly on the creep resistance of the material used for the reformer tubes. The currently most widely used reformer tube material is HP40 (25 Cr, 35Ni, 40 Fe and 0.4C) austenitic stainless steel. A further improvement in the creep resistance of HP40 is needed for efficiency improvement and for a cost reduction in steam reforming. In order to develop a next generation creep resistant alloy, three HP40-based alloys, namely Alloy A, B and C, with different chemical compositions and/or solidification rate, were studied. Previous tests at 1000 oC and 40 MPa have shown that the creep properties of Alloy C are slightly better than those of Alloy B, both being significantly better than Alloy A. The microstructures of three alloys, under as-cast, crept and heat treated conditions, have been analysed so as to understand their relative creep performance. The small intragranular M23C6 may have contributed significantly to the smaller creep rate, and thus a longer creep life for Alloy B and Alloy C as compared with Alloy A. A microstructure-based climb-glide bypass creep model was described to predict the creep behaviour of HP40. Suggestion on the next generation HP40 alloy has been made

Antimicrobial and Aging Properties of Ag-, Ag/Cu-, and Ag Cluster-Doped Amorphous Carbon Coatings Produced by Magnetron Sputtering for Space Applications

Inside a spacecraft, the temperature and humidity, suitable for the human crew onboard, also creates an ideal breeding environment for the proliferation of bacteria and fungi; this can present a hazard to human health and create issues for the safe running of equipment. To address this issue, wear-resistant antimicrobial thin films prepared by magnetron sputtering were developed, with the aim to coat key internal components within spacecrafts. Silver and copper are among the most studied active bactericidal materials, thus this work investigated the antibacterial properties of amorphous carbon coatings, doped with either silver, silver and copper, or with silver clusters. The longevity of these antimicrobial coatings, which is heavily influenced by metal diffusion within the coating, was also investigated. With a conventional approach, amorphous carbon coatings were prepared by cosputtering, to generate coatings that contained a range of silver and copper concentrations. In addition, coatings containing silver clusters were prepared using a separate cluster source to better control the metal particle size distribution in the amorphous carbon matrix. The particle size distributions were characterized by grazing-incidence small-angle X-ray scattering (GISAXS). Antibacterial tests were performed under both terrestrial gravity and microgravity conditions, to simulate the condition in space. Results show that although silver-doped coatings possess extremely high levels of antimicrobial activity, silver cluster-doped coatings are equally effective, while being more long-lived, despite containing a lower absolute silver concentration

5′-end surveillance by Xrn2 acts as a shared mechanism for mammalian pre-rRNA maturation and decay

Ribosome biogenesis requires multiple nuclease activities to process pre-rRNA transcripts into mature rRNA species and eliminate defective products of transcription and processing. We find that in mammalian cells, the 5′ exonuclease Xrn2 plays a major role in both maturation of rRNA and degradation of a variety of discarded pre-rRNA species. Precursors of 5.8S and 28S rRNAs containing 5′ extensions accumulate in mouse cells after siRNA-mediated knockdown of Xrn2, indicating similarity in the 5′-end maturation mechanisms between mammals and yeast. Strikingly, degradation of many aberrant pre-rRNA species, attributed mainly to 3′ exonucleases in yeast studies, occurs 5′ to 3′ in mammalian cells and is mediated by Xrn2. Furthermore, depletion of Xrn2 reveals pre-rRNAs derived by cleavage events that deviate from the main processing pathway. We propose that probing of pre-rRNA maturation intermediates by exonucleases serves the dual function of generating mature rRNAs and suppressing suboptimal processing paths during ribosome assembly

Mammalian DEAD Box Protein Ddx51 Acts in 3′ End Maturation of 28S rRNA by Promoting the Release of U8 snoRNA ▿ §

Biogenesis of eukaryotic ribosomes requires a number of RNA helicases that drive molecular rearrangements at various points of the assembly pathway. While many ribosome synthesis factors are conserved among all eukaryotes, certain features of ribosome maturation, such as U8 snoRNA-assisted processing of the 5.8S and 28S rRNA precursors, are observed only in metazoan cells. Here, we identify the mammalian DEAD box helicase family member Ddx51 as a novel ribosome synthesis factor and an interacting partner of the nucleolar GTP-binding protein Nog1. Unlike any previously studied yeast helicases, Ddx51 is required for the formation of the 3′ end of 28S rRNA. Ddx51 binds to pre-60S subunit complexes and promotes displacement of U8 snoRNA from pre-rRNA, which is necessary for the removal of the 3′ external transcribed spacer from 28S rRNA and productive downstream processing. These data demonstrate the emergence of a novel factor that facilitates a pre-rRNA processing event specific for higher eukaryotes

Effect of stoichiometry on shape memory properties of Ti-Ni-Hf-Cu-Nb shape memory alloys manufactured by sus-pended droplet alloying

A novel Ti-Ni-Hf-Cu-Nb shape memory alloy has been developed by a new combinatorial alloy synthesis method, the Suspended Droplet Alloying. The influence of alloying elements on the transformation temperature, the microstructure and the shape memory effect of this alloy have also been studied. It was found that Cu has a greater negative influence on the transformation temperature of Ti-Ni-Hf-CuX alloys (about −5 K/at.%) than on the Ti-Ni-CuX alloys (−0.67 K/at.%). In addition, the negative effect intensifies with increasing Hf content. The transformation temperature rapidly decreases with increasing Nb composition in the Ti-Ni-Cu-Nb and Ti-Ni-Hf-Cu-Nb alloys, with the solid solution of Nb in the matrix being 1 at.%. A Ti-Ni-Cu-Hf-Nb alloy with high thermal cycle stability has been developed, where the alloying elements affect the transformation behaviour via altering the slipping energy and forming different types of precipitations