Determination of the five parameter grain boundary character distribution of nanocrystalline alpha-zirconium thin films using transmission electron microscopy

Grain boundary engineering and other fundamental materials science problems (e.g., phase transformations and physical properties) require an improvement in the understanding of the type and population of grain boundaries in a given system – yet, databases are limited in number and spare in detail, including for hcp crystals such as zirconium. One way to rapidly obtain databases to analyze is to use small-grained materials and high spatial resolution orientation microscopy techniques, such as ASTAR™/precession electron diffraction. To demonstrate this, a study of grain boundary character distributions was conducted for α-zirconium deposited at room temperature on fused silica substrates using physical vapor deposition. The orientation maps of the nanocrystalline thin films were acquired by the ASTAR™/precession electron diffraction technique, a new transmission electron microscope based orientation microscopy method. The reconstructed grain boundaries were classified as pure tilt, pure twist, 180°-twist and 180°-tilt grain boundaries based on the distribution of grain boundary planes with respect to the angle/axis of misorientation associated with grain boundaries. The results of the current study were compared to the results of a similar study on α-titanium and the molecular dynamics results of grain boundary energy for α-titanium

A Constitutive Equation Relating Composition and Microstructure to Properties in Ti-6Al-4V: As Derived Using a Novel Integrated Computational Approach

While it is useful to predict properties in metallic materials based upon the composition and microstructure, the complexity of real, multi-component, and multi-phase engineering alloys presents difficulties when attempting to determine constituent-based phenomenological equations. This paper applies an approach based upon the integration of three separate modeling approaches, specifically artificial neural networks, genetic algorithms, and Monte Carlo simulations to determine a mechanism-based equation for the yield strength of α+βprocessed Ti-6Al-4V (all compositions in weight percent) which consists of a complex multi-phase microstructure with varying spatial and morphological distributions of the key microstructural features. Notably, this is an industrially important alloy yet an alloy for which such an equation does not exist in the published literature. The equation ultimately derived in this work not only can accurately describe the properties of the current dataset but also is consistent with the limited and dissociated information available in the literature regarding certain parameters such as intrinsic yield strength of pure hexagonal close-packed alpha titanium. In addition, this equation suggests new interesting opportunities for controlling yield strength by controlling the relative intrinsic strengths of the two phases through solid solution strengthening

Systematic Assessment of the Influence of Mo Concentration on the Oxygen Ingress in Ti–Mo System During High Temperature Oxidation

To understand the role of composition in the oxidation behavior of Ti–Mo system and to evaluate the extent of oxygen ingress into the metal substrate during high temperature exposure, a compositionally graded Ti–xMo specimen (0 ≤ x ≤ 12 wt% Mo) was prepared using an additive manufacturing technique, solutionized and then subjected to oxidation tests at 650 °C for different exposure times. The depth of oxygen diffusion, across the composition range, was assessed via change in the local hardness and the results were coupled with quantitative measurement of the oxygen concentration. The concentration of O in the α phase was reduced by 90 % after a short distance of 16 μm from the metal/oxide interface while it remained more or less the same in β phase. The solubility of Mo in α phase also approached zero near the surface as O changed the partition coefficient of this element between α and β phases. It was shown that the addition of Mo reduces the solubility of O in the metal substrate which in turn retards the transition point from parabolic to the linear oxidation stage

New Records of the Cryptogenic Soft Coral Genus Stragulum (Tubiporidae) from the Eastern Caribbean and the Persian Gulf

The monotypic soft coral genus Stragulum van Ofwegen and Haddad, 2011 (Octocorallia: Malacalcyonacea: Tubiporidae) was originally described from Brazil, southwest Atlantic Ocean. Here, we report the first records of the genus from the eastern Caribbean and the Persian Gulf in the northwest Indian Ocean. We compare the morphological features of specimens, together with molecular data from three commonly used barcoding markers (COI, mtMutS, 28S rDNA) and 308 ultraconserved elements (UCE) and exon loci sequenced using a target-enrichment approach. The molecular and morphological data together suggest that specimens from all three localities are the same species, i.e., Stragulum bicolor van Ofwegen and Haddad, 2011. It is still not possible to establish the native range of the species or determine whether it may be an introduced species due to the limited number of specimens included in this study. However, the lack of historical records, its fouling abilities on artificial substrates, and a growing number of observations support the invasive nature of the species in Brazilian and Caribbean waters and therefore suggest that it may have been introduced into the Atlantic from elsewhere. Interestingly, the species has not shown any invasive behaviour in the Persian Gulf, where it has been found only on natural, rocky substrates. The aim of the present report is to create awareness of this taxon with the hope that this will lead to new records from other localities and help to establish its native range

Oxidation behavior and microstructural evolution of Ti-6Al-4V and Ti-6Al-4V-1B sheet

A direct comparison between the oxidation behavior of Ti-6Al-4V and Ti-6Al-4V + 1B has been conducted to elucidate whether the addition of boron to Ti-6Al-4V impacts the oxidation behavior. Industrially prepared sheet of Ti-6Al-4V and Ti-6Al-4V + 1B were oxidized at temperatures between 650 and 950 °C for holding times of 25 and 50 h. Weight-gain measurements and characterization of surface and near-surface microstructures showed that the addition of 1 wt% B increased the material’s oxidation resistance. Additionally, the ingress of oxygen tends to decrease the solubility of other alloying species in α-Ti and leads to the formation of a distinctive and atypical microstructure with a distinct morphology

Non-native coral species dominate the fouling community on a semi-submersible platform in the southern Caribbean

A coral community was examined on a semi-submersible platform that was moored at the leeward side of Curaçao, in the southern Caribbean, from August 2016 until August 2017. This community included several non-native or cryptogenic species. Among them were two scleractinian corals (Tubastraea coccinea and T. tagusensis) and two octocorals (Chromonephthea sp. and an unidentified Nephtheidae sp.). This is the first reported presence of T. tagusensis in the southern Caribbean, and the genus Chromonephthea in the Caribbean region. An ascidian, Perophora cf. regina, is also reported from the southern Caribbean for the first time, as well as a coral-associated vermetid gastropod, Petaloconchus sp., first recorded in the Caribbean in 2014. Lack of biofouling management could potentially harm indigenous marine fauna through the introduction of non-native species. Therefore monitoring communities associated with semi-submersible platforms is essential to track the presence and dispersal of non-native, potentially invasive species

On the eutectoid transformation behavior of the Ti-Zn system and its metastable phases

To date, Zn has not been used as an alloying addition in structural Ti alloys. The main obstacle has been the disparity between their melting and vaporization temperatures. A novel processing technique was developed to create a Ti-Zn compound. The equilibrium phases and microstructures were studied by electron microscopy and x-ray diffraction techniques. Results show the presence of pearlitic domains of α-Ti (hexagonal closed packed crystal structure) and Ti2Zn (body center tetragonal structure) in regions that have a near eutectoid composition. Solutionizing and water quenching results in the formation of martensite along with intermetallic laths, suggesting that the eutectoid transformation is active

Primary cutaneous aggressive epidermotropic cytotoxic T-cell lymphomas: reappraisal of a provisional entity in the 2016 WHO classification of cutaneous lymphomas.

Primary cutaneous CD8-positive aggressive epidermotropic T-cell lymphoma is a rare and poorly characterized variant of cutaneous lymphoma still considered a provisional entity in the latest 2016 World Health Organization Classification of Cutaneous lymphomas. We sought to better characterize and provide diagnostic and therapeutic guidance of this rare cutaneous lymphoma. Thirty-four patients with a median age of 77 years (range 19-89 years) presented primarily with extensive annular necrotic plaques or tumor lesions with frequent mucous membrane involvement. The 5-year survival was 32% with a median survival of 12 months. A subset of 17 patients had a prodrome of chronic patches prior to the development of aggressive ulcerative lesions. We identified cases with lack of CD8 or αβ T-cell receptor expression yet with similar clinical and pathological presentation. Allogeneic stem cell transplantation provided partial or complete remissions in 5/6 patients. We recommend the term primary cutaneous aggressive epidermotropic cytotoxic T-cell lymphoma as this more broad designation better describes this clinical-pathologic presentation, which allows the inclusion of cases with CD8 negative and/or αβ/γδ T-cell receptor chain double-positive or double-negative expression. We have identified early skin signs of chronic patch/plaque lesions that are often misdiagnosed as eczema, psoriasis, or mycosis fungoides. Our experience confirms the poor prognosis of this entity and highlights the inefficacy of our standard therapies with the exception of allogeneic stem cell transplantation in selected cases

Oxidation behavior and microstructural evolution of Ti-6Al-4V and Ti-6Al-4V-1B sheet

A direct comparison between the oxidation behavior of Ti-6Al-4V and Ti-6Al-4V + 1B has been conducted to elucidate whether the addition of boron to Ti-6Al-4V impacts the oxidation behavior. Industrially prepared sheet of Ti-6Al-4V and Ti-6Al-4V + 1B were oxidized at temperatures between 650 and 950 °C for holding times of 25 and 50 h. Weight-gain measurements and characterization of surface and near-surface microstructures showed that the addition of 1 wt% B increased the material’s oxidation resistance. Additionally, the ingress of oxygen tends to decrease the solubility of other alloying species in α-Ti and leads to the formation of a distinctive and atypical microstructure with a distinct morphology