The Ashbya Genome Database (AGD)—a tool for the yeast community and genome biologists

The Ashbya Genome Database (AGD) is a comprehensive online source of information covering genes from the filamentous fungus Ashbya gossypii. The database content is based upon comparative genome annotation between A.gossypii and the closely related budding yeast Saccharomyces cerevisiae taking both sequence similarity and synteny (conserved order and orientation) into account. Release 2 of AGD contains 4718 protein-encoding loci located across seven chromosomes. Information can be retrieved using systematic or standard locus names from A.gossypii as well as budding and fission yeast. Approximately 90% of the genes in the genome of A.gossypii are homologous and syntenic to loci of budding yeast. Therefore, AGD is a useful tool not only for the various yeast communities in general but also for biologists who are interested in evolutionary aspects of genome research and comparative genome annotation. The database provides scientists with a convenient graphical user interface that includes various locus search and genome browsing options, data download and export functionalities and numerous reciprocal links to external databases including SGD, MIPS, GeneDB, KEGG, GermOnline and Swiss-Prot/TrEMBL. AGD is accessible at http://agd.unibas.c

Intergranular precipitation and chemical fluctuations in an additively manufactured 2205 duplex stainless steel

Fluctuations in energy distribution during additive manufacturing (AM) can result in spatial and temporal thermal transients. These transients can lead to complexities, most significantly when alloys with multi phases are subjected to AM. Here we unveil such complexities in a duplex stainless steel, where we report an unanticipated formation of a Ni-Mn-Si rich phase at grain boundaries and a local fluctuation in Cr and Fe concentrations in regions close to grain boundaries, providing Cr-rich precursors for Cr2N formation after laser powder bed fusion (LPBF). The formation of these phases is believed to be due to severe thermal gyrations and thermal stresses associated with LPBF resulting in a high-volume fraction of ferrite supersaturated with N and Ni, and a high density of dislocations accelerating diffusion and phase transformations

γʹ and γ″ co-precipitation phenomena in directly aged Alloy 718 with high δ-phase fractions

Co-precipitation of γ′ and γ′′ is the main strengthening mechanism that provides superior high-temperature strength in directly aged Alloy 718 aerospace parts. Control of their morphology, fraction, and configuration might allow exposure to more demanding operation environments in next-generation aircraft engines. The density of geometrically necessary dislocations introduced during hot deformation has been shown to significantly affect the co-precipitate morphology of γ′ and γ′′ in materials free of the δ-phase. However, the combined effects of geometrically necessary dislocation density and lower Nb content due to higher δ-phase fractions on co-precipitation behaviour and strengthening remain unknown. We verify these effects by hardness testing as a proxy for high-temperature strength in materials with 4.1 % δ-phase fraction. Deformation at 950 °C yields a remarkable increase of 12 % in hardness after direct ageing, explained by the prevalence of complex co-precipitate configurations. Deformation at 1000 °C decreases the δ-phase fraction and geometrically necessary dislocation density but achieves up to 19 % volume fractions of γ″, leading to a predominance of monoliths and duplet co-precipitates and a better direct ageing response. Atom probe microscopy reveals the flux of elements during co-precipitation. We recommend a δ-annealing treatment before the final forging step for manufacturing stronger Alloy 718 aerospace parts

Engineering Hierarchical Microstructures via Advanced Thermo-Mechanical Processing of a Modern HSLA Steel

Advanced thermo-mechanical processing of mild steels in the ferrite phase field has recently achieved breakthrough in grain refinement into the submicron regime. However, these steels often suffer from grain boundary failure and low rates of work hardening. A potential approach to overcome these challenges is to process modern high-strength low-alloy steels with multi-scale hierarchical microstructures. Thus, the applicability of advanced thermo-mechanical processing for achieving such microstructures in a high-strength low-alloy steel was studied. The microstructural evolution during warm deformation of a martensitic/bainitic starting microstructure using a Gleeble 3500 thermo-mechanical simulator at 600 °C followed by a direct aging step was investigated. The strain rate of 10 s−1led to strain localization and, therefore, the formation of a macroscopic shear band. High-resolution characterization techniques such as electron channeling contrast imaging, electron backscatter diffraction, and transmission electron microscopy were used to reveal the ultrafine grain sizes (~ 0.5 μm) in this shear band. The mechanism behind this refinement is continuous dynamic recrystallization, as the initial grains subdivided into smaller crystallites that are confined by a mix of subgrain and high-angle grain boundaries. Two populations of precipitates were formed. Larger precipitates (mean diameter ~ 150 nm) decorate grain boundaries, whereas smaller precipitates (~ 15 nm) nucleate on dislocations and subgrain boundaries

Additive manufacturing of steels: a review of achievements and challenges

Metal additive manufacturing (AM), also known as 3D printing, is a disruptive manufacturing technology in which complex engineering parts are produced in a layer-by-layer manner, using a high-energy heating source and powder, wire or sheet as feeding material. The current paper aims to review the achievements in AM of steels in its ability to obtain superior properties that cannot be achieved through conventional manufacturing routes, thanks to the unique microstructural evolution in AM. The challenges that AM encounters are also reviewed, and suggestions for overcoming these challenges are provided if applicable. We focus on laser powder bed fusion and directed energy deposition as these two methods are currently the most common AM methods to process steels. The main foci are on austenitic stainless steels and maraging/precipitation-hardened (PH) steels, the two so far most widely used classes of steels in AM, before summarising the state-of-the-art of AM of other classes of steels. Our comprehensive review highlights that a wide range of steels can be processed by AM. The unique microstructural features including hierarchical (sub)grains and fine precipitates induced by AM result in enhancements of strength, wear resistance and corrosion resistance of AM steels when compared to their conventional counterparts. Achieving an acceptable ductility and fatigue performance remains a challenge in AM steels. AM also acts as an intrinsic heat treatment, triggering ‘in situ’ phase transformations including tempering and other precipitation phenomena in different grades of steels such as PH steels and tool steels. A thorough discussion of the performance of AM steels as a function of these unique microstructural features is presented in this review

An Initial Report on the Structure-Property Relationships of a High-Strength Low-Alloy Steel Subjected to Advanced Thermomechanical Processing in Ferrite

2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Advanced thermomechanical processing (aTMP) of high-strength low-alloy (HSLA) steels has been applied to achieve ultrafine ferrite grains decorated with nanoscale precipitates, clusters, and solute segregation, potentially leading to an increase in strength, toughness, and ductility. In our own previous research on a modern Mo-Ti-Nb HSLA steel processed in ferrite, this was only confirmed using hardness testing. Reports on the success of similar aTMP routes in achieving superior mechanical properties so far only provided results from subsize specimens or simpler steels under large strain conditions. Therefore, herein, an initial report on the mechanical properties of the previously studied Mo-Ti-Nb HSLA steel subjected to warm rolling and aging is provided. A reduction of 55% at 650 °C leads to an ultimate tensile strength (UTS) of 650 MPa, a yield to an ultimate tensile strength ratio of 0.95, and a total elongation of 14% in the as-rolled condition, similar to mild steels deformed to larger strains. The low yield to UTS ratio is explained by precipitate coarsening. Delamination occurs in the low-temperature region of Charpy impact testing in both longitudinal and transversal directions. Direct aging significantly increases the room temperature impact energy due to the onset of grain growth

An Initial Report on the Structure-Property Relationships of a High-Strength Low-Alloy Steel Subjected to Advanced Thermomechanical Processing in Ferrite

2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Advanced thermomechanical processing (aTMP) of high-strength low-alloy (HSLA) steels has been applied to achieve ultrafine ferrite grains decorated with nanoscale precipitates, clusters, and solute segregation, potentially leading to an increase in strength, toughness, and ductility. In our own previous research on a modern Mo-Ti-Nb HSLA steel processed in ferrite, this was only confirmed using hardness testing. Reports on the success of similar aTMP routes in achieving superior mechanical properties so far only provided results from subsize specimens or simpler steels under large strain conditions. Therefore, herein, an initial report on the mechanical properties of the previously studied Mo-Ti-Nb HSLA steel subjected to warm rolling and aging is provided. A reduction of 55% at 650 °C leads to an ultimate tensile strength (UTS) of 650 MPa, a yield to an ultimate tensile strength ratio of 0.95, and a total elongation of 14% in the as-rolled condition, similar to mild steels deformed to larger strains. The low yield to UTS ratio is explained by precipitate coarsening. Delamination occurs in the low-temperature region of Charpy impact testing in both longitudinal and transversal directions. Direct aging significantly increases the room temperature impact energy due to the onset of grain growth

2015 EXCELLENCE IN METALLOGRAPHY AWARD EVOLUTION OF STRAIN-INDUCED PRECIPITATES IN A MOLYBDENUM-BASE Mo-Hf-C ALLOY

The powder metallurgy processed molybdenumbase alloy Mo-Hf-C (MHC) Dallinger,**** Helmut Clemens***** and Sophie Primig****** INTRODUCTION The particle-hardened alloy Mo-Hf-C (MHC) is processed via a powder metallurgy (PM) route. It is known for its high strength at elevated temperatures and its high recrystallization temperatures. Its nominal composition of 0.65 at.% Hf and 0.65 at.% C has been derived from various investigations of arc melted and solution-annealed Mo-Hf-C alloys in the 1960s and 70s. In particular, an alloy with a similar composition to MHC exhibited superior properties after swaging. In contrast to PM processed MHC, all the hafnium and carbon content of the solution-annealed material is in solid solution. The carbon and the hafnium contents of MHC are adjusted in order to produce ~1 vol.% hafnium carbide. 1-3 After sintering, the microstructure of MHC consists of a molybdenum matrix, hafnium-oxide particles (5-10 µm diameter), molybdenum carbides decorating the grain boundaries, and large hafnium carbides (1 µm diameter, ~80 nm thick). The residual hafnium content in solid solution is ~0.10-0.15 at.% and the typical microporosity is ~4%. For a full exploitation of the precipitation potential of the MHC alloy, it i