Evaluation of the microstructure and mechanical properties of a new modified cast and laser-melted AA7075 alloy

The mechanical properties and microstructure of as-cast and homogenized AA7075 were investigated. This alloy was modified by adding transition elements 0.3%Sc + 0.5%Zr, 1%Ti + 0.2%B, and 1%Fe + 1%Ni for use in additive manufacturing applications. After adding Ti + B and Sc + Zr, the structure became uniform and finer with the formation of the Al3(Sc, Zr) and TiB2 phases. Coarse structures were obtained with the formation of an extremely unfavorable morphology, close to a needle-like structure when Fe + Ni was added. The mechanical properties of the modified alloys were increased compared to those of the standard alloy, where the best ultimate tensile strength (UTS) and yield strength (YS) were obtained in the AA7075-TiB alloy compared to the standard alloy in as-cast and homogenized conditions, and the highest hardness value was provided by Fe + Ni additives. The effect of the laser melting process on the microstructure and mechanical properties was investigated. Single laser melts were performed on these alloys using 330 V and a scanning speed of 8 mm/s. During the laser melting, the liquation of the alloying elements occurred due to non-equilibrium solidification. A change in the microstructures was observed within the melt zone and heat-affected zone (HAZ). The hardness of the laser-melted zone (LMZ) after adding the modification elements was increased in comparison with that of the standard alloy. Corrosion testing was performed using a solution of 100 mL distilled water, 3.1 g NaCl, and 1 mL HCl over 5, 10, and 30 min and 1 and 2 h. The corrosion resistance of the alloy modified with FeNi was low because of the non-uniform elemental distribution along the LMZ, but in the case of modification with ScZr and TiB, the corrosion resistance was better compared to that of the standard alloy. © 2019 by the authors.Ministry of Science and Higher Education of the Russian FederationThe author (Asmaa M. Khalil) gratefully acknowledges financial support from the Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of MISiS (Support project for young research engineers)

Influence of Adding Modifying Elements and Homogenization Annealing on Laser Melting Process of the Modified Alznmgcu with 4%si Alloys

AlZnMgCu, the high-strength aluminum alloy, is unsuitable for laser melting applications due to its high hot cracking sensitivity and large solidification temperature range. Adapting this alloy for laser melting processing is a high-demand research issue for extending its use. Thus, this paper investigates the effect of adding 4%Si, 4%Si-Sc + Zr, 4%Si-Ti + B, and homogenization annealing on the laser melting process (LMP) of AlZnMgCu alloy. Homogenization annealing at 500◦ C for 6.5 h was selected to dissolve most of the low melting temperature phases into the grain matrix and perform stable alloys for the LMP. The pulsed laser melting process (PLM) was performed on the as-casted and the homogenized samples. The microstructures of the as-casted, the homogenized alloys, and after the LMP were evaluated. In addition, the hardness of the base metal (BM) and laser melted zone (LMZ) were measured. The results revealed that the microstructure was enhanced and refined in the as-cast state by adding the modifiers due to the increasing nucleation potency of solidification sites and the formation of primary Al3 (Ti, Zr, Sc) phases. The average grain size was decreased by 15.6 times when adding 4%Si + 0.4%Zr + 0.29%Sc, while it decreased by 10.2 times when adding 4%Si + 1%Ti + 0.2%B. The LMZ of the as-casted samples exhibited a non-uniform distribution of the grains and the elements after the LMP. This was attributed to the evaporation of Zn, Mg during the high laser power process besides the non-uniform distribution of elements and phases in samples during casting. After the laser treating of the homogenized samples with 4%Si-Sc + Zr, uniform columnar grains were formed in the direction of the laser. The presence of Ti and B changed the crystallization nature, resulting in the LMZ with very fine and equiaxed grains due to forming many nucleation centers during solidification. The hardness values have positively increased due to Si addition and adding a combination of Ti + B and Sc + Zr. The maximum hardness was 153.9 ± 5 HV achieved in the LMZ of the homogenized samples of 4%Si + 1%Ti + 0.2%B. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This research was partially funded by Russian Foundation for Basic Research (RFBR) with project number 19-38-60037

Type II restriction endonuclease R.Eco29kI is a member of the GIY-YIG nuclease superfamily

<p>Abstract</p> <p>Background</p> <p>The majority of experimentally determined crystal structures of Type II restriction endonucleases (REases) exhibit a common PD-(D/E)XK fold. Crystal structures have been also determined for single representatives of two other folds: PLD (R.BfiI) and half-pipe (R.PabI), and bioinformatics analyses supported by mutagenesis suggested that some REases belong to the HNH fold. Our previous bioinformatic analysis suggested that REase R.Eco29kI shares sequence similarities with one more unrelated nuclease superfamily, GIY-YIG, however so far no experimental data were available to support this prediction. The determination of a crystal structure of the GIY-YIG domain of homing endonuclease I-TevI provided a template for modeling of R.Eco29kI and prompted us to validate the model experimentally.</p> <p>Results</p> <p>Using protein fold-recognition methods we generated a new alignment between R.Eco29kI and I-TevI, which suggested a reassignment of one of the putative catalytic residues. A theoretical model of R.Eco29kI was constructed to illustrate its predicted three-dimensional fold and organization of the active site, comprising amino acid residues Y49, Y76, R104, H108, E142, and N154. A series of mutants was constructed to generate amino acid substitutions of selected residues (Y49A, R104A, H108F, E142A and N154L) and the mutant proteins were examined for their ability to bind the DNA containing the Eco29kI site 5'-CCGCGG-3' and to catalyze the cleavage reaction. Experimental data reveal that residues Y49, R104, E142, H108, and N154 are important for the nuclease activity of R.Eco29kI, while H108 and N154 are also important for specific DNA binding by this enzyme.</p> <p>Conclusion</p> <p>Substitutions of residues Y49, R104, H108, E142 and N154 predicted by the model to be a part of the active site lead to mutant proteins with strong defects in the REase activity. These results are in very good agreement with the structural model presented in this work and with our prediction that R.Eco29kI belongs to the GIY-YIG superfamily of nucleases. Our study provides the first experimental evidence for a Type IIP REase that does not belong to the PD-(D/E)XK or HNH superfamilies of nucleases, and is instead a member of the unrelated GIY-YIG superfamily.</p

Features of Structure Formation in an Al–Fe–Mn Alloy upon Crystallization with Various Cooling Rates

Abstract: Specific features of the microstructure formation of an Al–2.5% Fe–1.5% Mn alloy owing to the cooling rate during casting and during laser melting are studied in this work. An analysis of the microstructure in the molten state shows that, with an increase in the cooling rate during crystallization from 0.5 to 940 K/s, the primary crystallization of the Al6(Mn,Fe) phase is almost completely suppressed and the volume of the nonequilibrium eutectic increases to 43%. The microstructures of the Al–2.5% Fe–1.5% Mn alloy after laser melting are characterized by the presence of crystals of an aluminum matrix of a dendritic type with an average cell size of 0.56 μm, surrounded by an iron-manganese phase of eutectic origin with an average plate size of 0.28 μm. The primary crystallization of the Al6(Mn,Fe) phase is completely suppressed. The formation of such a microstructure occurs at cooling rates of 1.1 × 104–2.5 × 104 K/s, which corresponds to the cooling rates implemented in additive technologies. At the boundary between the track and the base metal and between the pulses, regions were revealed consisting of primary crystals of the Al6(Mn,Fe) phase formed by the epitaxial growth mechanism. The size of the primary crystals and the width of this zone depends on the size of the eutectic plates and the size of the dendritic cell located in the epitaxial layer. After laser melting, the Al–2.5% Fe–1.5% Mn alloy has a high hardness at room temperature (93 HV) and, after heating up to 300°C, it has a high thermal stability (85 HV). The calculated yield strength of the Al–2.5% Fe–1.5% Mn alloy after laser melting is 227 MPa. The combination of its ultrafine microstructure, high processibility during laser melting, hardness at room and elevated temperatures, and high calculated yield strength make the Al–2.5% Fe–1.5% Mn alloy a promising alloy for use in additive technologies. © 2021, Allerton Press, Inc

ПРОБЛЕМЫ ОБЕСПЕЧЕНИЯ ИНФЕКЦИОННОЙ БЕЗОПАСНОСТИ ОРГАННОГО И ТКАНЕВОГО ДОНОРСТВА ПРИ ЛАБОРАТОРНОЙ ДИАГНОСТИКЕ ГЕМОКОНТАКТНЫХ ВИРУСНЫХ ИНФЕКЦИЙ

It provided data on the prevalence, clinical signifi cance and methods of laboratory diagnostics for occult forms of blood-borne viral infections (BBVIs). It considered causes of such forms of infection and their signifi cance for clinical transplantation. We analyzed the existing algorithm of laboratory screening of a potential organ donor for BBVIs in Russia. It is shown that the current screening algorithm doesn’t allow detecting hidden forms of BBVIs.Представлены данные о распространенности, клинической значимости и методах лабораторной диагностики скрытых форм гемоконтактных вирусных инфекций (ГВИ). Рассмотрены причины возникновения таких форм инфекции и их значимость для клинической трансплантологии. Проанализирован существующий алгоритм лабораторного обследования потенциального донора органов на ГВИ в РФ. Показано, что действующий алгоритм скрининга доноров на ГВИ не позволяет выявлять скрытые формы инфекции

Evaluation of Microstructure and Hardness of Novel Al-Fe-Ni Alloys with High Thermal Stability for Laser Additive Manufacturing

The microstructure and phase composition of cast and laser-melted Al-Fe-Ni alloys were investigated.Two main phases—Al3(Ni,Fe) and Al9FeNi—were formed in the as-cast state. A fine microstructure without porosity or solidification cracks was observed in the Al-Fe-Ni alloys after laser treatment. The hardness of the laser-melted alloys was 2.5–3 times higher than the hardness of the as-cast alloys owing to the formation of an aluminum-based solid solution and fine eutectic particles. The formation of the primary Al9FeNi phase was suppressed as a result of the high cooling rate. Annealing these alloys at temperatures less than 300°C demonstrated the high thermal stability of the microstructure while maintaining the hardness. The Al-Fe-Ni alloys investigated in this study are promising heat-resistant materials for additive manufacturing because of their fine, stable structure, and the low interdiffusion coefficients of Fe and Ni. © 2020, The Minerals, Metals & Materials Society.Loginova I.S. would like to thank Dr. Solonin A.N. for valuable discussions regarding the structure formation process. This project and all the experiments were funded by RFBR, Project Number 19-38-60037

Влияние Zr, Sc, Ti, B Fe и Ni на микроструктуру сплава aa7075 при лазерной обработке

In the present work the wrought aluminium alloy AA7075 modified with 0,3%Sc+0,5%Zr, 1%Тi+0,2 %B and 1%Fe+1%Ni to refine and uniform the grain structure, to decrease the effective solidification range to decrease the hot crack formation during rapid solidification after laser processing was studied.В настоящей работе исследован высокопрочный сплав AA7075, дополнительно легированный 0,3%Sc+0,5%Zr, 1%Ti+0,2%B и 1%Fe+1%Ni для повышения сопротивляемости сплава образованию горячих трещин и однородности структуры

СТРУКТУРА ОБРАЩЕНИЙ ПАЦИЕНТОВ СО СМЕШАННЫМИ ФОРМАМИ ГЕМОКОНТАКТНЫХ ВИРУСНЫХ ИНФЕКЦИЙ В МНОГОПРОФИЛЬНОМ СТАЦИОНАРЕ

We retrospectively analyzed the number and causes of hospitalizations in patients with mixed types of blood-borne viral infections (BBVIs) in specialized departments of a general hospital in 2010– 2014. We revealed an increase in detection of mixed BBVIs from 1.39 up to 1.50% (χ2 =1.192, df=1, p&gt;0.05), particularly hIV/hCV and hIV/hBV/hCV. The majority of patients with co-infections had different medical and social deviations. The highest incidence of mixed infection occurred among men, mainly in the age group of 31–40 years (χ2 =5.46, df=1, p&lt;0.05). Departments with the highest degree of the epidemic hazard for transmission of mixed BBVIs were the department of intensive care and resuscitation with a small operating room for emergency detoxification, departments of acute poisoning for the mentally ill patients, the department of resuscitation and intensive care for emergency patients and somato-psychiatric department.Ретроспективно проанализирована динамика количества и причин госпитализации пациентов с микст-формами гемоконтактных вирусных инфекций (ГВИ) в специализированные отделения стационара общесоматического профиля за период с 2010 по 2014 г. Зафиксирован рост выявляемости сочетанных форм инфекций с 1,39 до 1,50% (χ2 =1,192, df=1, p&gt;0,05), преимущественно HIV+HCV и HIV+HBV+HCV. Большинство пациентов с сочетанными формами инфекций имели разного рода медико-социальные девиации. Наибольшая частота встречаемости микст-инфекций зафиксирована у мужчин, преимущественно в возрастной группе 31–40 лет (χ2 =5,46, df=1, p&lt;0,05). К подразделениям с высокой степенью эпидемической опасности распространения микст-форм ГВИ относились: отделение реанимации и интенсивной терапии с малой операционной для экстренной детоксикации, отделения острых отравлений для психических больных, отделение реанимации и интенсивной терапии для экстренных больных, а также соматопсихиатрическое отделение

Fused eco29kIR- and M genes coding for a fully functional hybrid polypeptide as a model of molecular evolution of restriction-modification systems

<p>Abstract</p> <p>Background</p> <p>The discovery of restriction endonucleases and modification DNA methyltransferases, key instruments of genetic engineering, opened a new era of molecular biology through development of the recombinant DNA technology. Today, the number of potential proteins assigned to type II restriction enzymes alone is beyond 6000, which probably reflects the high diversity of evolutionary pathways. Here we present experimental evidence that a new type IIC restriction and modification enzymes carrying both activities in a single polypeptide could result from fusion of the appropriate genes from preexisting bipartite restriction-modification systems.</p> <p>Results</p> <p>Fusion of <it>eco29kIR </it>and <it>M </it>ORFs gave a novel gene encoding for a fully functional hybrid polypeptide that carried both restriction endonuclease and DNA methyltransferase activities. It has been placed into a subclass of type II restriction and modification enzymes - type IIC. Its MTase activity, 80% that of the M.Eco29kI enzyme, remained almost unchanged, while its REase activity decreased by three times, concurrently with changed reaction optima, which presumably can be caused by increased steric hindrance in interaction with the substrate. <it>In vitro </it>the enzyme preferentially cuts DNA, with only a low level of DNA modification detected. <it>In vivo </it>new RMS can provide a 10²-fold less protection of host cells against phage invasion.</p> <p>Conclusions</p> <p>We propose a molecular mechanism of appearing of type IIC restriction-modification and M.SsoII-related enzymes, as well as other multifunctional proteins. As shown, gene fusion could play an important role in evolution of restriction-modification systems and be responsible for the enzyme subclass interconversion. Based on the proposed approach, hundreds of new type IIC enzymes can be generated using head-to-tail oriented type I, II, and III restriction and modification genes. These bifunctional polypeptides can serve a basis for enzymes with altered recognition specificities. Lastly, this study demonstrates that protein fusion may change biochemical properties of the involved enzymes, thus giving a starting point for their further evolutionary divergence.</p

ЛЕКАРСТВЕННО-РЕЗИСТЕНТНЫЕ ВАРИАНТЫ ВГС СУБТИПА 1B, ЦИРКУЛИРУЮЩИЕ НА ТЕРРИТОРИИ РОССИЙСКОЙ ФЕДЕРАЦИИ: АНАЛИЗ АМИНОКИСЛОТНЫХ МУТАЦИЙ В БЕЛКАХ NS5A И CORE

Aim. To determine the prevalence of amino acid substitutions in hepatitis C virus NS5a and core proteins which are associated with resistance to direct-acting antivirals and interferon in genotype 1b (HCV-1b) strains circulating in Russia. Materials and methods. Nucleotide sequences of NS5a (n=93) and core (n=30) of HCV-1b were obtained using direct sequencing of respective amplified genome fragments. The search for resistance associated substitutions was performed for amino acid positions 28, 29, 30, 31, 32, 58, 62, 92, 93 of NS5a, and 70 and 91 amino acid positions of core proteins, respectively. Results. The total proportion of HCV-1b strains carrying resistance associated substitutions in NS5a was 22,6% (21/93). The total detection rate of L31M and Y93H substitutions that are associated with resistance to the majority of NS5a inhibitors was 10,8%. Less clinically significant substitutions L28M, R30Q, P58S/T, A92T were detected too. The proportion of infections caused by HCV-1b strains that are potentially resistant both to interferon and NS5a inhibitors was 10% (10/30). Conclusion. Testing of HCV-1b infected patients for background resistance profile could be a useful tool to prevent the choosing of initially ineffective treatment regimen.Цель: определение распространенности штаммов вируса гепатита С субтипа 1b (ВГС-1b) на территории Российской Федерации, несущих аминокислотные мутации в белках NS5a и core, ассоциированные с лекарственной резистентностью к ингибиторам NS5a и препаратам интерферона соответственно. Материалы и методы: определение нуклеотидной последовательности белка NS5a (n=93), а также белка core (n=30) ВГС-1b проводилось методом прямого секвенирования амплифицированных фрагментов генома. Поиск мутаций, ассоциированных с лекарственной резистентностью, проводился в аминокислотных позициях 28, 29, 30, 31, 32, 58, 62, 92, 93 белка NS5a и аминокислотных позициях 70 и 91 белка core ВГС-1b. Результаты: 22,6% (21/93) исследованных изолятов ВГС-1b несли мутации, ассоциированные с лекарственной резистентностью к ингибиторам NS5a. В 10,8% последовательностей были выявлены замены L31M и Y93H, связанные с устойчивостью к большинству ингибиторов NS5a, а также менее значимые с клинической точки зрения замены L28M, R30Q, P58S/T, A92T. Доля лиц, инфицированных штаммами ВГС-1b, потенциально резистентными одновременно к препаратам интерферона и ингибиторам NS5a, составила 10% (10/30). Заключение: полученные данные свидетельствуют в пользу целесообразности предварительного исследования профиля резистентности ВГС-1b перед назначением терапии для предотвращения выбора заведомо неэффективного препарата