Search

Hydrogen is gaining traction as a promising alternative fuel in aviation due to its high energy density per unit mass and eco-friendly characteristics. This study delves into the realm of physical and material-based hydrogen storage tailored for aeronautical purposes. Key hurdles include achieving substantial hydrogen storage capacities, ensuring safety standards, aligning with aircraft design specifications, optimizing round-trip energy efficiency, and overcoming constraints regarding weight and volume. Various material-based storage technologies, including metal hydrides, carbon-based materials, and innovative nanostructured materials, have been explored, albeit at a fundamental stage. However, the transition from these initial material-centric investigations to the development of functional fuel tank systems is yet to be realized. Conversely, conformal graphene-based composite tanks present a promising solution for hydrogen storage in aircraft. Their flight readiness represents a significant milestone in the quest to decarbonize aviation and mitigate the environmental impact of air travel. [ABSTRACT FROM AUTHOR]

Using animate nouns to refer to entities in the world involves a complex interaction of ontology, cognition and language. The present study evaluates two accounts of the use of animate nouns, with Mandarin Chinese as the vehicle for testing between the competing accounts. One account was proposed by Cheng et al. (2008. How universal is the Universal Grinder? In Marjo van Koppen & Bert Botma (eds.), Linguistics in the Netherlands, 50–62. Amsterdam & Philadelphia: John Benjamins). These researchers contend that the count interpretation is basic for Mandarin animate nouns, due to a lexical blocking effect. To access the alternative, mass interpretation requires some kind of pragmatic coercion. A second account was proposed by Pelletier, based on English (1975. Non-Singular reference: Some preliminaries. Philosophia 5(4). 451–465; 2012. Lexical nouns are both +MASS and +COUNT, but they are neither +MASS nor + COUNT. In Diane Massam (ed.), Count and mass across languages, 9–26. Oxford: Oxford University Press). We extend this account to Mandarin animate nouns, proposing that they are encoded in the mental lexicon with both a count sense and a mass sense. To adjudicate between the accounts, we conducted four experiments that were designed to assess the interpretation assigned to animate nouns by Mandarin-speaking children and adults. The experimental conditions manipulated both the syntactic structures of the sentences and the non-linguistic contexts in which those sentences were presented. The experimental findings support our proposal that both mass and count interpretations of animate nouns are available to children and adults when sentences are presented in contexts that are congruent with these interpretations. The findings also suggest that syntactic structure is an even more critical factor in determining the interpretation that is assigned to animate nouns in Mandarin. [ABSTRACT FROM AUTHOR]

The Asian citrus psyllid (ACP) is the main vector of Citrus Huanglongbing, the most damaging citrus disease, causing significant financial losses in the citrus industry. Global warming has expanded the habitat of this pest, allowing it to continue its northward migration to China. Population genetic information of ACP is fundamentally essential for species management. This study investigated the genetic diversity and population structure of Chinese ACP using the mitochondrial cytochrome oxidase subunit I gene by dataset comprised 721 sequences from 27 geographic sites in China. Low haplotype diversity (0.323 ± 0.022) and low nucleotide diversity (0.00071 ± 0.00007) were observed in the entire population, which may indicate recent founder events. Twenty-three haplotypes were identified and clustered into 2 haplogroups: haplogroup I and haplogroup II. Haplogroup II included only 2 unique haplotypes, which occurred exclusively in the Southwest China ACP population. Genetic differentiation analyses were also indicative of Southwest China population was significantly differentiated from the remaining populations. Demographic history analysis showed that ACP population in China has experienced demographic expansion. Our results provided a better understanding of the genetic distribution patterns and structures of ACP populations in China. [ABSTRACT FROM AUTHOR]

Metal ion doping is the most widely used means to improve the photocatalytic performance of semiconductor materials, which can adjust the band gap, broaden the range of optical response and construct impurity levels. The high efficiency modified NaTaO3 perovskite catalyst with good structural and catalytic properties was synthesized by a simple hydrothermal reaction method. A variety of analysis and testing techniques, such as XRD, SEM, DRS, XPS and EPR, were used to analyze the structure properties of the prepared materials. The results show that the influence mechanism of different metal introduction on the structure and properties of the NaTaO3 perovskite was different. Metal doping promoted the bond angle of Ta-O-Ta close to 180°, which restrains the recombination of the photogenerated electron-holes in the crystal. As Ce is introduced into the perovskite, the CeO2 forms and agglomerates around the perovskite, which improves the electron transport performance. With the narrower band gap, the Ce-modified perovskite shows that the degradation rate of ARS is 84% after 180 min of photoreaction. The species of h+, O2− and ·OH play different roles in improving the performance of the photocatalytic degradation process. [ABSTRACT FROM AUTHOR]

Taking into account the complexity involved in the issue of superordinates, the present study investigates superordinates and their interpretation in Mandarin, as compared to the interpretation of superordinates in English, which is a typical language with number marking. Thus, Mandarin superordinates are mostly used in bare forms; furthermore, Mandarin superordinates are used much more often with mass classifiers than count classifiers. 5 Our account on Mandarin superordinates Our account follows from the grammatical account proposed in the literature for the interpretation of Mandarin nouns in general (e.g., [11]; [31]; [32]; [39]; [49]). Keywords: child language; count-mass semantics; Mandarin Chinese; superordinate collectives EN child language count-mass semantics Mandarin Chinese superordinate collectives 933 972 40 07/05/22 20220701 NES 220701 1 Introduction The study of superordinate collectives has been the subject of much debate in the literature. [Extracted from the article]

Seven isolates of a putative cytorhabdovirus (family Rhabdoviridae, order Mononegavirales) designated as citrus-associated rhabdovirus CiaRV) were identified in citrus, passion fruit. and paper bush from the same geographical area in China. CiaRV, bean-associated cytorhab-dovirus (Brazil), and papaya virus E (Ecuador) should be taxonomically classified in the species Papaya cytorhabdovirus. Due to natural mutations, the glycoprotein (G) and P4 genes were impaired in citrus-infecting isolates of CiaRV, resulting in an atypical rhabdovirus genome organization of 3' leader-N-P-P3-M-L-5' trailer. The P3 protein of CiaRV shared a common origin with begomoviral movement proteins (family Geminiviridae). Secondary structure analysis and trans-complementation movement-deficient tomato mosaic virus and potato virus X mutants by CiaRV P3 supported its function in viral cell-to-cell trafficking. The wide geographical dispersal of CiaRV and related viruses suggests an efficient transmission mechanism, as well as an underlying risk to global agriculture. Both the natural phenomenon and experimental analyses demonstrated presence of the "degraded" type of CiaRV in citrus, in parallel to "undegraded" types in other host plant species. This case study shows a plant virus losing the function of an important but nonessential gene, likely due to host shift and adaption, which deepened our understanding of course of natural viral diversification. [ABSTRACT FROM AUTHOR]

In addition to serving as question markers with interrogative force,wh-words such asshenme‘what’ in Mandarin Chinese have a noninterrogative meaning. For the noninterrogative meaning, these words have been typically analyzed as negative polarity items, i.e., aswh-pronouns that are similar in meaning to the English NPIanyand to its Mandarin counterpartrenhe. This accounts for the None reading that is generated in negative statements withwh-words. However, negative sentences with thewh-wordshenme‘what’ can also be assigned another reading, in certain circumstances. We refer to this as the Insignificance (not much) reading. This reading is not possible for sentences with the NPIrenhe. The None reading is the default interpretation for negative sentences with eitherrenheorshenmebecause the Insignificance reading of the negatedshenmesentences requires contextual support. Like English “not much,” the Insignificance reading of negatedshenmesentences in Mandarin makes a sentence true in a broader range of circumstances than the corresponding sentence with the NPIrenhe. Both the fact that the Insignificance reading requires contextual support and considerations of language learnability in the absence of negative evidence lead us to expect the Insignificance reading to emerge later than the None reading in the course of language development. An experimental study of Mandarin-speaking children of different ages supported this expectation. The youngest group of children only assigned the None reading to negative sentences withshenmeas well as to sentences withrenhe. However, older children and adults accessed the Insignificance reading. [ABSTRACT FROM AUTHOR]

Highlights: [•] We show that wh-pronouns in Mandarin Chinese are not homogeneous. [•] The concept of numericity is involved in the interpretation of the numerical wh-pronoun ji-ge ‘how many-Classifier’, but not in other wh-pronouns. [•] Ji-ge receives three readings, including ‘proform-N’, ‘at least two’ and ‘a few’. [•] The three readings of ji-ge emerge in Mandarin-speaking children in three distinct developmental stages. [Copyright &y& Elsevier]

Huanglongbing (HLB) is a plant disease mainly spread by the insect-borne citrus psyllid. It is the most destructive citrus pathosystem worldwide. To understand the impact of sexual transmission on HLB dynamics, we propose a host–vector–HLB compartment model incorporating two transmission routes. The basic reproduction number ℛ 0 is derived. Various interventions of the disease are assessed. We also investigate the effect of different incidence functions to simulate sexual transmission. For the case of sublinear incidence functions, the disease-free equilibrium is globally asymptotically stable (GAS) provided ℛ 0 < 1. For mass action incidence of sexual transmission, the endemic equilibrium is GAS provided ℛ 0 > 1. However, under nonlinear incidence, it is proved that the model may exhibit backward bifurcation. Theoretical and numerical studies reveal that (i) different forces of infection between heterosexual psyllids in the model may have a distinct impact on disease dynamics; (ii) sensitivity analysis shows that for ℛ 0 , the transmission rate between host and vector is more sensitive parameter than that between heterosexual psyllids; (iii) if the sexual transmission is ignored, the disease burden is likely to be underestimated in comparison with realistic scenarios; (iv) in the absence of chemical insecticides, the combined use of yellow sticky traps and injection of nutrient solutions can be more effective in suppressing the spread of HLB. These findings provide valuable insights for public policymakers to determine the long-term viability of implemented HLB management strategies and highlight the urgency of finding sustainable HLB solutions. [ABSTRACT FROM AUTHOR]

Abstract: Samples of Ti46Al8Nb have been cooled from the alpha phase field at 4°C/min and subsequently oil quenched; others have been end-quenched. The microstructures have been examined using optical and analytical scanning and transmission electron microscopy. It has been found that cooling to only 30°C below the transus results in the formation of significant amounts of grain boundary gamma. This grain boundary gamma can grow into the alpha matrix; it can nucleate alpha/gamma lamellae, or massive gamma, or gamma/gamma lamellae; it can influence the fracture behaviour in massively transformed samples that have been heat treated to refine the microstructure. The factors that influence which structure is associated with the grain boundary gamma are investigated and it is clear that the cooling rate is the dominant factor. The significance of these observations is discussed in terms of the properties of cast samples which have been heat treated by precipitating alpha within the massive gamma. [Copyright &y& Elsevier]

It is shown that the modest pressures used in hot isostatic pressing alter the equilibrium proportions and thus the properties of phases in Ti–46Al–8Nb. These results are interpreted in terms of the atomic volumes of the phases and of the potential of pressure to modify the properties of alloys. [Copyright &y& Elsevier]

Transition metal Fe, Co, Ni and Cu doped strontium titanate‐rich SrTiO3@TiO2 (STO@T) materials were prepared by hydrothermal method. The prepared doped materials exhibit better photocatalytic CO2 reduction to CH4 ability under visible light conditions. Among them, Fe‐doped and undoped SrTiO3@TiO2 under visible light conditions CO2 reduction products only CO, while M‐STO@T (M=Co, Ni, Cu) samples converted CO2 to CH4. The average methane yield of Ni‐doped STO@T samples are as high as 73.85 μmol g−1 h−1. The production of methane is mainly due to the increase in the response of the doped samples to visible light. And the increase in the separation rate of photogenerated electrons and holes and the efficiency of electron transport caused by the generation of impurity levels. The impurity level caused by Ti3+ plays an important role in the production of methane by CO2 visible light reduction. Ni doping effectively improves the photocatalytic performance of STO@T and CO2 reduction mechanism were explained. [ABSTRACT FROM AUTHOR]

In this article, the author focuses on interpretation and acquisition of three polarity-sensitive items in Mandarin Chinese including renhe 'any,' shenme 'what,' and ji-ge 'how many-classifier' in Mandarin speaking children. It mentions complexity and nonuniformality of polarity-sensitive items in Mandarin in both adult grammar and child grammar.

• The article offers novel data on Mandarin adpositions, localisers, spatial nouns. • It explores these data at an intra- and inter-sentential level. • The account is the first to capture these data. • The analysis has potentially cross-linguistic applications. • General considerations are offered for a theory of spatial categories. The goal of this paper is to show that Mandarin localisers and spatial nouns (e.g. qian 'front' and qian-mian 'front-side', respectively) are part of a nominal super-category but display complementary discourse properties. At the sentential level, both categories can be combined with prepositions (e.g. zai zhuozi hou 'behind the table'), and form phrases and sentences describing the location of an entity under discussion. At the discourse level, however, only spatial nouns can act as anaphors to previous prepositional phrases, thereby licensing ground NP ellipsis. We show that their differing discourse properties depend on their grammatical properties, and determine how anaphoric relations are established: spatial nouns always introduce direct reference to discourse-relevant locations. We offer a formal account based on a combination of Lexical Syntax with Discourse Representation Theory, and discuss the consequences of this account for a theory of spatial categories in Mandarin. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened (ODS) nickel (Ni)‐based superalloys are advanced materials known for their outstanding tensile and creep performance at temperatures exceeding 1000 °C. Nevertheless, their conventional synthesis presents a longstanding challenge in cost‐effectively producing intricate components for critical applications. In this work, electrostatic self‐assembly (ESA) of powders with the laser powder bed fusion (LPBF) process are successfully combined to produce yttria ODS Inconel 718 (IN718) alloy for the first time. This approach demonstrates a significant contribution of yttria to the strength of IN718 after the solid solution heat treatment, as evidenced by ≈50% improvement in room temperature yield strength with a 0.5 wt.% yttria addition. The addition of yttria by this process leads to a heterogeneous microstructure. This heterogeneous microstructure comprises two distinct grain areas with varying amounts of yttria nanoparticles and dislocation storage. The results show that the yield strength increase can be predicted by the combination of both Y2O3 dispersion strengthening and dislocation strengthening mechanisms. These findings offer an effective approach to tailor heterogeneous microstructures, unlocking new opportunities for cost‐effectively producing high‐performance ODS Ni‐based superalloy products with excellent mechanical properties. [ABSTRACT FROM AUTHOR]

• A novel mathematical model for HLB infection is proposed and global dynamics are analyzed. • The optimal control problem of the HLB model is formulated and solved. • The sensitivity and uncertainty analysis are conducted to examine the sensitivity of R0 to the uncertainty of parameters. • Insecticide treatment combined with HLB-symptomatic trees removal is the most cost-effective strategy. Huanglongbing (HLB) is currently one of the most devastating citrus plant diseases. To better understand the spread of HLB disease, the stage-structured compartmental model is formulated to describe the transmission dynamics of HLB between the citrus trees and Asian citrus psyllid (ACP). Based on strict mathematical derivations, the explicit expression for the basic reproduction number (R 0) of HLB is derived. The dynamics of the model are rigorously analyzed by using the theory of dynamical system. The theoretical results show that the disease-free equilibrium is globally asymptotically stable if R 0 < 1 , and if R 0 > 1 the system is uniformly persistent. By applying the global sensitivity analysis of R 0 , we can obtain some parameters with the most significant influence on the transmission dynamics of HLB. Moreover, the optimal control theory is used to investigate the corresponding optimal control problem of the epidemic model. Numerical simulations are conducted to reinforce the analytical results. Using the cost-effectiveness analysis, the superiority of various intervention strategies is compared by calculating Incremental Cost-Effectiveness Ratio (ICER) value. The findings imply that coupled control strategy involving insecticide spraying treatment and HLB-symptomatic trees removal is the most cost-effective strategy and belongs to long-term intervention measures, and it is recommended to take this strategy to control the disease in the whole process. On the contrary, nutrient solution treatment and yellow sticky trap control are short-term intervention measures, which can be used at the initial stage of disease outbreak but discontinued at the later stage due to cost considerations. These findings provide us potential decision-making tools that allow managers to choose better control strategies of HLB. [ABSTRACT FROM AUTHOR]

Platform heating is one of the effective strategies used in laser powder bed fusion (LPBF) to avoid cracking during manufacturing, especially when building relatively large-size components, as it removes significant process-induced residual strains. In this work, we propose a novel and simple method to spare the elaborate post-processing heat treatment typically needed for LPBF Al-Sc alloys without compromising the mechanical properties. We systematically investigated the effects of LPBF platform heating at 200 °C on the residual stress relief, microstructure, and mechanical performance of a high-strength Al-Mn-Sc alloy. The results reveal that LPBF platform heating at 200 °C is sufficient to largely relieve the process-induced residual stresses compared to parts built on an unheated 35 °C platform. Meanwhile, the platform heating triggered the dynamic precipitation of uniformly dispersed (1.5–2 nm) Sc-rich nano-clusters. Their formation in a high number density (1.75 × 1024 m−3) resulted in a ~20% improvement in tensile yield strength (522 MPa) compared to the build on the unheated platform, without sacrificing the ductility (up to 18%). The improved mechanical properties imply that platform heating at 200 °C can strengthen the LPBF-synthesised Sc-containing Al alloys via in situ aging, which is further justified by an in situ measurement study revealing that the developing temperatures in the LPBF part are within the aging temperature range of Al-Sc alloys. Without any post-LPBF treatments, these mechanical properties have proven better than those of most Al-Sc alloys through long-time post-LPBF heat treatment. [ABSTRACT FROM AUTHOR]

A Laser Powder Bed Fusion Inconel 718 produced with intentionally non‐optimized parameters is investigated to understand the role of defects and microstructure on the high‐cycle fatigue life. Samples from three built directions and three heat treatments were used for fatigue tests at room and 650°C under R=0.1. Printing orientation has a minor effect on fatigue life at both temperatures. Most samples failed from lack of fusion defects, carefully analyzed by scanning electron microscope (SEM) observations. Surface defect leads to transgranular fracture surface, while subsurface initiation leads to crystallographic fracture surface. S−N curves related to hot isostatic pressure condition shown that defects have higher influence at 20°C than at 650°C. Kitagawa diagrams are plotted for both temperatures to quantify the influence of defect size on fatigue limit. Natural cracks are observed at the surface in order to discuss the relative part of initiation life in the whole fatigue life. Highlights: Fatigue is governed by lack of fusion (LoF) ranging from 200 to 600 μmThe fatigue limit is higher at high temperature compared with ambient temperatureHot isostatic pressure (HIP) treatment improves the fatigue resistanceNatural crack initiated from LoF propagates in a very similar way compared with long crack [ABSTRACT FROM AUTHOR]

Purpose: Limited research has attempted to reveal the different modes of the melt pool formation in additive manufacturing. This paper aims to study the mechanisms of surface roughness formation, especially on the aspect of melt pool formation which determine the surface profile and consequently significantly influence the surface roughness. Design/methodology/approach: In this study, the conditions under which different modes of melt pool formation (conduction mode and keyhole mode) occur for the case of as-fabricated Hastelloy X using direct metal laser solidification (DMLS) are derived and validated experimentally. Top surfaces of uni-directionally built samples under various processing conditions are cut, grinded, polished and etched to reveal their individual melt pool morphologies. Similarly, up-skin (slope angle < 90°) and down-skin (slope angle > 90°) melt pool morphologies are also investigated to compare the differences. Surface tension gradients and resultant Marangoni flow, which dominate the melt flow in the melt pool, is also calculated to help better evaluate the melt pool shape forming. Findings: Two types of melt pool formation modes are dominating in DMLS: conduction mode and keyhole mode. Melt pool formed by conduction mode generally has an aspect ratio of 1:2 (depth vs width) and is in elliptical shape. Appropriate selection of scanning laser power and speed are required to maintain a low characteristic length and width ratio to prevent ballings. Melt pool formed by keyhole mode has an aspect ratio of 1:1 or less. High-energy contour promotes formation of key-hole-shaped melt pool which fills the gaps between layers and smoothens the up-skin surface roughness. Low-energy contour scan is necessary for down-skin surface to form small melt pool profiles and achieve low Ra. Originality/value: This paper provides valuable insight into the origins of surface quality problem of DMLS, which is a very critical issue for upgrading the process for manufacturing real components. This paper helps promote the understanding of the attributes and capabilities of this rapidly evolving three-dimensional printing technology and allow appropriate control of processing parameters for successful fabrication of components with sound surface quality. [ABSTRACT FROM AUTHOR]

Purpose: Selective laser melting (SLM) process is an additive manufacturing method that uses computer-aided design to fabricate complex components layer-by-layer. Surface roughness is one of the primary drawbacks of SLM process; hence, the purpose of this paper is to present a parametric study and optimisation of fundamental parameters, including scan power, speed, inclined angle and layer thickness on surface roughness during selective laser melting of Hastelloy X. Design/methodology/approach: Parametric significance on surface finish was analysed using analysis of variance and response surface methodology. General agreement between predicted and measured values was achieved. Surface characteristics of both up-skin and down-skin with various angles were covered within the investigated range. Findings: Both experimental and statistical analysis showed that surface roughness of up-skin was primarily influenced by scan power, inclined angle and layer thickness while down-skin was more affected by the former two factors. Melt pool shape and staircase size were found to determine the up-skin surface, whereas attached particles were responsible for down-skin surface roughness. Originality/value: As per our understanding, this manuscript provides valuable insight into the surface quality problem of SLM, which is a very critical issue for up-grading the process for manufacturing real components. This manuscript helps promote improved knowledge and understanding of the attributes and capabilities of this rapidly evolving 3D printing technology. Moreover, it establishes usable processing window and helps obtain optimal conditions, thus offering useful information to professionals working in this field. By combining experiments with statistical analysis, both practice and theory relevant to SLM process are further developed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of grain oxidation on high-temperature high-cycle-fatigue performance of laser powder bed fusion Hastelloy X was analyzed. • The high-temperature high-cycle-fatigue performance of LPBF HX, in this study, is superior to that of Cast HX. • The presence of annealing twins increases the resistance to the initiation and propagation of fatigue cracks. • Dynamic recrystallized grains formed during the fatigue loading process, further increasing the crack propagation resistance. High-temperature fatigue properties are critical for laser powder bed fusion (LPBF) fabricated Nickel-based superalloy Hastelloy-X (HX) used in aero engines. In this study, superior high-temperature high-cycle fatigue properties of LPBF HX were achieved. The detailed investigations show that the grain boundary oxidation promoted by the different deformation modes between neighboring grains, despite the reduced oxygen-related damage in the coarser LPBF HX microstructures, are the potential causes for the inter-granular fatigue crack initiation and the subsequent crack coalescence. In the meantime, the crack propagation could be hindered by the refined carbides and annealing twins with Σ3 misorientation (60°/〈1 1 1〉) in LPBF HX. Furthermore, the recrystallized grains formed ahead of the crack tip due to the severe deformation within the plastic zone and high testing temperature have different crystallographic orientations, which leads to the crack propagation path changes and increases the fatigue crack propagation resistance. [ABSTRACT FROM AUTHOR]

Although massive transformation has been increasingly observed in titanium alloys, the decomposition mechanism of the massive transformation product (α m) is still unclear. Here, the β→α m →α+β continuous phase transformation in Ti-6Al-4V alloy during cooling was studied. We found that massive transformation occurs at a moderate cooling rate below 291.5 °C/s, forming irregular featureless α m. The thermodynamically unstable α m is supersaturated with β stabilizers, and it tends to decompose into ultrafine α+β structure during the continuous cooling at ever-lower cooling rates and temperatures. In the initial stage of α m decomposition, misfit dislocations appear as a predecessor and split α m into strips. Accompanied by the elemental redistribution, misfit dislocations are accommodated and replaced by β phase. Both the formation and decomposition of α m follow the typical Burgers orientation relationship. [Display omitted] [ABSTRACT FROM AUTHOR]

Haynes 188 alloy with a combination of strength and ductility is of significance in aircraft engines and recent development in additive manufacturing significantly increases potential applications of this material. However, understanding the microstructure and tensile properties of Laser Powder Bed Fusion (LPBF) Haynes 188 alloy is limited. Here, a crack-free Haynes 188 alloy is successfully fabricated. The LPBF specimens are observed in two different directions: perpendicular and parallel to the building direction, referred to as "LPBF-H" and "LPBF-V" sections, respectively. To investigate the anisotropy of LPBF specimens, tensile tests were conducted on LPBF Haynes 188 alloy with different observed sections. The vertical sections show lower yield strength than the horizontal sections due largely to an elongated columnar structure. The effects of solute, grain size and dislocation on the strengthening mechanism are discussed thoroughly. The synergy effects of the grain size and the dislocation increase the strength of the LPBF alloys compared to wrought and casting equivalents. For LPBF specimens, the dislocation cellular structure is particularly investigated. To better understand the plasticity, the fracture morphology is also analyzed. The developed understanding on the microstructure and mechanical properties of Haynes 188 alloys in this work could also be applicable to other Co-based superalloys. • A Haynes 188 alloy with superior mechanical properties is successfully fabricated using the LPBF process. • LPBF Haynes 188 alloys show better mechanical strength compared to wrought and cast specimens. • The strengthening mechanism of LPBF Haynes 188 is disscussed thoroughly. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) is an emerging additive manufacturing technique that is currently adopted by a number of industries for its ability to directly fabricate complex near-net-shaped components with minimal material wastage. Two major limitations of LPBF, however, are that the process inherently produces components containing some amount of porosity and that fabricated components tend to suffer from poor repeatability. While recent advances have allowed the porosity level to be reduced to a minimum, consistent porosity-free fabrication remains elusive. Therefore, it is important to understand how porosity affects mechanical properties in alloys fabricated this way in order to inform the safe design and application of components. To this aim, this article will review recent literature on the effects of porosity on tensile properties, fatigue life, impact and fracture toughness, creep response, and wear behavior. As the number of alloys that can be fabricated by this technology continues to grow, this overview will mainly focus on four alloys that are commonly fabricated by LPBF—Ti-6Al-4 V, Inconel 718, AISI 316L, and AlSi10Mg. [ABSTRACT FROM AUTHOR]

In this study, the influence that porosities play on the mechanical properties of Ti-6Al-4V parts fabricated by laser powder bed fusion (LPBF) was investigated with the aim of improving process efficiency of the LPBF process by establishing the resulting trade-offs to component quality. It was found that build times can be substantially reduced by using higher layer thickness parameters without a significant detriment to mechanical properties. Where porosities formed, spherical pores tend to have a marginal effect on Young's modulus, yield strength, tensile strength, and uniform elongation as these properties can be approximated linearly using the rule of mixtures assuming null strength pores. However, such pores were found to be otherwise more detrimental to total elongation and toughness. Conversely, lack of fusion pores are extremely detrimental and should be avoided. Thus, it is proposed that when building a component, different process parameters can be used at different regions of the component to maximize process efficiency without compromising its overall function. For instance, for surfaces, a highly optimized parameter set with lower layer thickness can be used. At regions with minimal stress distribution during service, a large layer thickness parameter set where the resulting mechanical properties is sufficient can be used. [ABSTRACT FROM AUTHOR]

The β→α transformation is a crucial and fundamental phase transformation in titanium and its alloys. This work investigated the effect of elastic compressive stress (ECS) on the microstructure and mechanical property during cooling from β phase region to α + β phase region in Ti-6Al-4V alloy. Results indicated that ECS in this process results in significant refinement and increased aspect ratios of α lamellae (α L) and α colonies (α C). These changes are attributed to the enhanced phase transformation driving force to promote nucleation of α lamellae. The ECS-cooling induced alloy exhibits higher hardness than the stress-free counterpart, mainly resulting from the refined microstructure. This work provides a potential method to tailor the microstructure and improve the mechanical properties of Ti alloys. [Display omitted] • The phenomena of α L refinement are for the first time identified under elastic stress, and the formation mechanism of such phenomena was elucidated. • The elastic compressive stress influences Gibbs free energy are the main reasons for the refinement and variant selection of α lamellae and α colony in Ti-6Al-4V alloys. [ABSTRACT FROM AUTHOR]

For SLMed Ti–6Al–4V- x O (x = 0.11, 0.16, 0.21, and 0.25 wt%) alloys, both microstructure and mechanical properties are sensitive to oxygen content. The α′ martensites in as-built state transform to a 'bimodal' microstructure containing α lamellae interspersed with β transformed regions after 2 h annealing at 800 °C, 850 °C, 900 °C, and 950 °C followed by air cooling. The α lamellar width decreases and the β phase volume fraction increases with increasing oxygen content, due to reduced diffusivity of Al and V. The solid solution hardening effect of oxygen was quantified as: σ 0 = 472 MPa + 2159 c 0.5 , where σ 0 is the lattice frictional stress and c is oxygen atomic fraction of the alloy. Increased oxygen content causes reduced fracture toughness and higher fatigue crack growth rate in the unstable growth regime, and the appearance of bilinear growth rate of the Paris regime at high annealing temperatures. The absence of the bilinear behaviour in the low oxygen content alloy and for annealing at low temperatures was interpreted in terms of changes in microstructural characteristics caused by oxygen impeding the diffusion of Al and V. [ABSTRACT FROM AUTHOR]

In this work, the effects of post-LPBF (laser powder bed fusion) heat treatments on microstructure evolution, tensile and Charpy properties of Ti-6Al-4V have been investigated. The results show that the original martensitic microstructure in the LPBF sample has converted to a lamellae mixture of α and β phases when post heat-treatment temperatures are below the β-transus (800°C, 850°C and 900°C) with air cooling. On this basis, a good balance of tensile strength and ductility was obtained from sample post heated at 800°C for 6 h followed by air-cooling, with an increase of ~42% in ductility and a significant toughness enhancement (almost 100% increase) compared to the as-built sample. The relationship betweenα lamellaethickness, β volume fraction and post-LPBF heat treatment has been established. Both α lamellae thickness and β volume fraction increase with the heat-treatment temperature. [ABSTRACT FROM AUTHOR]

Co-based and Ni-based superalloys have been widely used in aerospace, with much attention given to additive manufactured Ni-based superalloys. However, the equally important Co-based superalloys have received less attention. In this work, a Co-based Haynes 188 superalloy is fabricated using Laser Powder Bed Fusion (LPBF). This research shows the impressive mechanical properties of Haynes 188 superalloy before and after heat treatment at both room and high temperatures for the first time. In the as-built specimen, arrayed stacking faults, Lomer–Cottrell locks, dislocations, and M 6 C/M 23 C 6 eutectic carbides are found. The yield strength, ultimate tensile strength, and elongation of the as-built specimen are 642 MPa, 928 MPa, and 57.3 %, respectively. For the heat-treated specimen, the grain size increases, dislocation density reduces and the eutectic carbides dissolve into the matrix, which reduces the yield strength to 488 MPa. However, annealing twins are found in the heat-treated specimen, and the twin-twin interaction networks further enhance the pile-up of dislocations and work hardening ability during the deformation, which leads to an increase in the ultimate tensile strength and elongation to 1002 MPa and 68.1 %, respectively. This work provides an effective method to improve the mechanical properties of Co-based superalloys by additive manufacturing, which is essential for the development of high-performance superalloys and their manufacturing methods. [ABSTRACT FROM AUTHOR]

• The influence of the GB-α on the fatigue behavior of LPBF Ti–64 was investigated. • HCF property is improved due to low aspect ratio α lath and discontinuous GB-α. • Discontinuous GB-α could improve the crack propagation resistance. • α lath with a low aspect ratio inhibits the crack initiation at the interface. High cycle fatigue (HCF) performance of additive manufactured (AM) titanium products is of great significance for its structural and functional applications. However, tying fatigue performance to the complex microstructures in AM titanium alloys is challenging. The work here carried out a thorough investigation into the influence of microstructures (particularly the grain boundary α-phase (GB-α) with varied morphologies) on the fatigue performance of laser powder bed fusion (LPBF) Ti–6Al–4V (Ti-64). Results showed that the improvement in the high-cycle fatigue life of LPBF Ti-64 could be achieved by the formation of low aspect ratio α lath and discontinuous GB-α via optimized post-fabrication heat treatment. Discontinuous GB-α could fully accommodate the deformation, improving the fatigue crack propagation resistance. Moreover, α lath with a low aspect ratio could lead to less strain accumulation on the interface between adjacent α lath, and thereby inhibit the crack initiation at these interfaces. This study enhances the understanding of how LPBF-induced complex microstructures influence fatigue behavior, and provides a pathway for the improvement of fatigue performance of additive manufactured titanium alloy. [ABSTRACT FROM AUTHOR]

• Defects control in SLMed A357 is achieved with optimised processing parameters. • Microstructure homogenisation with Si particle modification is achieved with optimised heat treatment procedures. • Tensile ductility is significantly improved without the presence of large defects. • Fatigue property is substantially improved with defect elimination and Si particle modification. The relationship between defects and mechanical properties, especially fatigue properties, of selective laser melted (SLMed) Al-7Si-0.6Mg alloy built with different processing parameters has been investigated. With relatively high densities, although the tensile strength is not affected, ductility and fatigue properties vitally vary with different defects. Furthermore, an excellent fatigue performance with the run-out stress of 200 MPa has been achieved with optimised processing parameters, which is by far the best fatigue performance in SLMed Al-Si alloys. Microstructure and fractography are characterised by different methods, demonstrating that defects and Si particles are the main controlling factors for the fatigue properties. [ABSTRACT FROM AUTHOR]

Coaxial Electron Beam Wire-feed Additive Manufacturing (CAEBWAM), which is a novel additive manufacturing process, can produce fully dense alloy components with equiaxed β grains (EGβ) and isotropical mechanical properties and is considered as a potential manufacturing method for large-scale complex components. However, actual complex components inevitably include bonding regions, which are similar to welded joints, in the wire-feed deposition process, and limited knowledge is available on the microstructures and mechanical properties for this kind of regions. This work thoroughly studied the microstructures and mechanical properties of the Ti-6Al-4V alloy cruciform structure fabricated by CAEBWAM. It was found that the microstructure at the Bonding Zone (BZ) was composed of coarse columnar β grains (CGβ), continuous grain boundary α (α GB) phase, and coarse α laths due to a higher temperature and poor heat dissipation condition. The average width of α lath in the BZ region was larger and the hardness was lower compared with those in the EGβ region. Tensile properties and fracture behaviours of the tensile samples extracted at cruciform structure were examined. The fracture tended to occur at the BZ region and exhibited a mixed fracture mode with trans- and inter-granular fractures. This work will improve the understanding of microstructures and mechanical properties for representative cruciform structure in wire-feed AMed components, which would be conducive to further progress of the actual complex components. [Display omitted] • The microstructure and mechanical properties of the Ti-6Al-4V cruciform structure were investigated. • The formation of inhomogeneous microstructure and the tensile behaviour were elucidated. • Coarse columnar β grains, continuous grain boundary α phase, and coarser α-lath were formed in the Bonding Zone (BZ). • The fracture tends to occur at the BZ region and exhibits a mixed fracture mode with trans- and inter-granular fractures. [ABSTRACT FROM AUTHOR]

Quasi-static tensile and stress-controlled high cycle fatigue tests of solution heat-treated (SHT) Hastelloy X manufactured by electron beam powder bed fusion (PBF-EB) and laser-based power bed fusion (PBF-LB) process were performed at room temperature and 750 °C. Post-fabrication SHT was ineffective in overcoming the microstructural anisotropy observed within as-built specimens, with the grains still maintaining its columnar architecture along the build direction. A significant drop in ductility was observed in tensile specimens tested at 750 °C, which was attributed to the carbide precipitation and grain boundary sliding. Upon investigating the influence of microstructural evolution as a function of test duration, a significant increase in precipitation was observed with an increase in test duration. A notable decrease in the fatigue strength was observed at elevated temperature. The long columnar grain structure within vertically build PBF-EB specimens was found to offer higher resistance against fatigue at 750 °C, owing to its reduced grain boundary area perpendicular to the loading direction. The corresponding fatigue damage mechanisms were investigated via fractographic analysis of the fracture surfaces and longitudinal cross-sections of the fractured specimens. Irrespective of the build orientation and test conditions, the fatigue cracks that resulted in final failure were found to initiate from the specimen surface. Also, the grain boundary precipitates were found to result in intergranular cracking during elevated temperature fatigue tests. • Tensile and fatigue behaviour of PBF-EB and PBF-LB HX were compared at RT and 750 °C. • PBF-LB HX showed higher tensile strength and fatigue behaviour at room temperature. • Vertical PBF-EB HX exhibited significant resistance to fatigue degradation at 750 °C. • Cleavage facets and intergranular fracture observed after tensile test at 750 °C. • Intergranular cracks observed in PBF-EB and PBF-LB HX after fatigue tests at 750 °C. [ABSTRACT FROM AUTHOR]

Additive manufacturing, or 3D printing, has brought tremendous opportunities for the design and making of metallic components with high geometrical complexity. However, in order to maximize the performance and functionality of a specific part, the additive manufacturing industry currently still faces fundamental issues of material processability and limited mechanical properties. Here, we report a high strength in-process and post-process friendly Al alloy specifically developed for the selective laser melting (SLM) process, one of the most commonly used additive manufacturing techniques. We found that the introduction of Mn and Sc as major strengthening elements significantly improved the processability of the Al alloy and its corresponding mechanical properties due to the rapid solidification nature of the SLM process. The developed alloy demonstrates an exceptional high thermal stability, which enables the utilization of a very simple post heat treatment to relieve the residual stresses generated during the SLM process, maintain a high solid solution strengthening effect from Mn and simultaneously achieve exceptional precipitation strengthening from a high density of nano-sized Al 3 Sc precipitates. We created a new high strength Al alloy with a yield strength of up to 560 MPa and a ductility of about 18% after a simple industrially desirable post heat treatment of 5 h at 300 °C. The highly enhanced alloy properties, good processability and simple post heat treatment of the developed alloy offers tremendous benefits for the fabrication of complex high performance lightweight engineering components made by SLM. Image 1 [ABSTRACT FROM AUTHOR]

Abstract The ageing responses of selective laser melted Al-7Si-0.6Mg alloy with different solid solution treatment times are investigated in this work. Silicon particles with random crystallographic orientations are the dominant precipitates at the direct aged condition. With 1 or 8 h solid solution treatment, the precipitation sequence resembles that of cast/wrought Al-Si-Mg alloys. However, the main precipitates at the peak-aged condition are different and are premature B′ (1 h) and β″ (8 h), respectively. These unusual precipitation pathways are attributed to the uniaxial strains in the Al matrix, suggesting new heat treatment procedures required for selective laser melted alloys. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

A357 alloy was manufactured by selective laser melting (SLM) and subjected to different heat treatments, by considering the stress relief step as critical, to establish the microstructure-mechanical property relationship and model the yield strength. For the as-SLM processed condition, the imposed fast cooling rate refines and limits the amount of Fe-rich intermetallic and eutectic Mg 2 Si phases, and enables a higher level of supersaturation of solutes. The latter leads to significant yield strength contributions from solid solution strengthening and natural ageing. The inter-cellular Si network within the columnar grains remains unchanged but small Si-rich particles appear within cells after direct ageing. The Si network breaks up during stress relieving, leading to high ductility. The lower ductility for the vertically-built samples under as-SLM processed, directly aged, and stress relieved conditions is due mainly to the finer Si networks brittle nature. Porosity resulting from trapped hydrogen gas enlarges significantly with solutionisation, deteriorating the ductility. Grain growth is not obviously observed with heat treatment. Si particles coarsen preferentially at grain boundaries initially, however, they distribute more evenly by coarsening within the grains as well during prolonged solutionisation. Anisotropy in both yield strength and ductility subsequently disappears when a more homogeneous microstructure is obtained. [ABSTRACT FROM AUTHOR]

AlScZr and AlErZr alloys with Sc or Er additions of ~0.6 at.% were prepared by a novel wedge mould casting and laser remelting methodology. Precipitation strengthening and thermal stability were studied using hardness testing and transmission electron microscopy. After ageing, the AlScZr alloy achieved a peak hardness of 113 HV 0.5 and possessed pronounced thermal stability, while the AlErZr alloy obtained a maximum hardness of 84 HV 0.5 and experienced relatively rapid over-ageing. Compared with Sc, the lower solubility of Er even after laser remelting and its more rapid diffusivity are responsible for the relatively lower ageing response and poorer thermal stability. [ABSTRACT FROM AUTHOR]

The as-Selective Laser Melted (as-SLMed) Ti-6Al-4V generally has a martensitic microstructure. In the present study, martensite decomposition was investigated in various annealed samples by XRD, SEM and TEM. It has been found that annealing at 700 °C or 800 °C for 2 h was not sufficient to obtain a fully decomposed microstructure. The amount of martensite did reduce greatly and volume fraction of β phase increased significantly when the annealing temperature increased from 700 to 800 °C. However, the best combination of mechanical property was not obtained. It is to be noted that annealing at 800 °C for 2 h is widely used for SLMed Ti-6Al-4V as reported in literature. Detailed SEM and TEM analysis revealed the presence of residual martensite containing twins and a high density of dislocations even in the 800 °C/2 h annealed sample. The twin was determined as { 10 1 ¯ 1 } < 10 1 ¯ 2 > type, which are retained twin formed in martensitic transformation during the cooling in SLM. Annealing at 800 °C for 6 h or more provided a fine equilibrium α + β microstructure, which provided a strong and ductile SLMed Ti-6Al-4V. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) has been increasingly used by industries to produce metal components. However, there remains a challenge to improve the productivity of the LPBF process, especially for high-volume production. In this study, we used Hastelloy-X (HX) as an example and demonstrated a hybrid approach of using a core-shell structured (0.5 mm thick dense shell + fast scanned porous core) part combining hot isostatic pressing (HIP) to improve the LPBF productivity. The microstructure evolution, mechanical properties, and the production rate of the parts built with and without the core-shell structure are compared and discussed in this work. The as-built core-shell HX showed a porous core enclosed by a dense shell, the density was restored through HIP. The HIP-processed core-shell HX revealed an artificially induced grain size gradient (large to small) from the shell to the core, while the HX without the core-shell structure presented uniformly distributed larger grains in the microstructure after HIP. The mechanical properties were studied using microhardness tests and uniaxial tensile tests. The core-shell HX showed an increment of the microhardness from the shell to the core, and the corresponding tensile properties were superior to the HX without the core-shell structure. The LPBF production rate using the core-shell approach was largely improved than the equivalent solid production route. The findings herein demonstrate the feasibility of using the core-shell approach to improve the productivity of the LPBF HX without sacrificing the tensile properties. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effects of varied process parameters on the defect, molten pool morphologies, microstructures, and hardness of HX, and established the correlation based on the Hall-Petch relationship. The formation mechanism of different types of defects, which are formed by increasing energy density, is systematically explained. The dendritic/cellular structure analysis via detailed Scanning electron microscope (SEM) examination found that the size of dendritic arm spacing was affected significantly by varied energy densities. Higher energy input reduces the temperature gradient and solidification rate, which results in the increase of primary dendritic arm spacing (PDAS). In addition, the grain boundaries of dendrite can improve the mechanical properties, especially the hardness. The hardness test results show that the hardness value increased with the decrease of PDAS, which exhibited this linear relationship illustrated by the Hall-Petch relationship. [ABSTRACT FROM AUTHOR]

Post heat treatment is essential for additively manufactured alloys to eliminate residual stress and in some cases further improve mechanical performance. This study systematically investigated the hardening response of a Ti-6Al-2Sn-4Zr-6Mo alloy processed by laser powder bed fusion (LPBF) to a one-step heat treatment. The results revealed significant hardening at both 500 °C and 650 °C. Most notably, an ultra-high peak-hardness of 563VHN was achieved within 5 mins of heat treatment at 650 °C due to a unique martensite-decomposed α+β microstructure consisting of alternating long β laths that are ∼5 nm thick and α laths that are ∼35 nm thick, and within the α laths are also short β laths that are ∼2 nm thick with an ∼11 nm inter-spacing. The influence of both types of β laths on the α lath thickness was established and related to the ultra-high hardness observed, which provides new insight for the design of new metastable LPBF-processed Ti alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

• A mixed equiaxed + columnar prior-β grain microstructure was achieved by 0.05 wt% boron addition. • High-cycle fatigue property was improved significantly in Ti-64-0.05B. • Fatigue crack propagation resistance was reduced due to the prior-β grain size reduction and the TiB particle precipitation. Boron is a powerful grain solute that promotes substantial microstructural refinement in titanium alloys produced by additive manufacturing. However, the fatigue performance of boron refined additive manufactured titanium alloys remained unknown. In this study, a thorough investigation into the high-cycle fatigue life and crack propagation rates of laser direct energy deposited Ti-6Al-4V with a trace boron addition was carried out. The high-cycle fatigue life was significantly improved, as the refined microstructure increased the crack initiation resistance. However, the crack propagation resistance estimated from spectrum loading was reduced, due to the refined prior-β grains and TiB particles. [ABSTRACT FROM AUTHOR]

The sliding behavior of two titanium alloys processed by laser powder bed fusion, with and without heat treatment, was investigated alongside two as-received conventionally-processed versions of these alloys. These samples presented a wide range of microstructures often encountered in Ti alloys. Oxidative, abrasive and adhesive wear always occurred when sliding against steel. However, wear rates were similar regardless of the friction and hardness if material removal mainly occurred through abrasion and/or adhesion. Martensitic phases decomposed during sliding while nano-crystalline grains enhanced oxidative wear which reduced friction. With a stable nanocrystalline microstructure that confers ultrahigh hardness, wear rate and friction can be substantially reduced by promoting oxidative over abrasive or adhesive wear. • Dry sliding of two conventionally- and LPBF-processed Ti alloys was investigated. • A nano-crystalline microstructure enhances oxide formation which reduces friction. • α′ or α″ is unstable in the presence of frictional heat and oxygen diffusion. • A stable ultrahard nanocrystalline microstructure can reduce both wear and friction. • This microstructure promotes oxidative wear and minimizes adhesion/abrasion. [ABSTRACT FROM AUTHOR]

[Display omitted] • A macroscale thermal modelling strategy has been developed by combining a published characteristic time-based heat input (CTI) model with an adaptive mesh re-mapping method. • The strategy is capable to accurately capture the peak temperatures of the thermal cycles induced by deposited tracks. • The predicted temperature histories agree well with in-situ measurements by thermocouples in both the printed part and powder bed. • Case studies demonstrate that our strategy can improve computational efficiency at least 6 times. Numerical modelling is an effective tool to investigate the rapid temperature cycling in laser powder bed fusion. However, the high computational cost limits the modelling of part-scale components due to the significantly different scales between the highly local energy input region and the global field response region. This study presents a macroscale finite element thermal simulation strategy with a track-scale resolution by combining the recently developed characteristic time-based heat input (CTI) model with a currently proposed adaptive mesh re-mapping method. Due to the uniformly distributed power density along the scan direction in the CTI model, the optimized mesh strategy allows one element to capture the temperature solutions over the majority of a scan track except at the two ends. The adaptive mesh re-mapping method is used to map simulated results from a previous scan track model to a current scan track model with a new mesh configuration. This strategy has been implemented for a Ti-6Al-4V part with the dimensions of 20 × 40 × 3 m m 3. The predicted temperature histories agree well with the in-situ measurements at the points in both the printed part and powder bed. Three case studies demonstrate that our strategy can improve computational efficiency between 6 and 30 times. [ABSTRACT FROM AUTHOR]

[Display omitted] • Powder-fed laser-based directed energy deposition of Beta-C was successful. • Due to a high dislocation density, the Beta-C alloy had a fast-ageing response. • Higher strength was achieved compared to conventionally-processed aged Beta-C. • The ageing response was further accelerated by carbon additions. • With added carbon, the alloy was harder, less ductile but strength was unchanged. This work investigates the viability of fabricating Ti-3Al-8V-6Cr-4Mo-4Zr (Beta-CTM) using laser-based and powder-fed directed energy deposition. To determine an appropriate ageing strategy, heat treatments were conducted at 440 °C and 480 °C over different periods of time and their effectiveness were determined through hardness testing. After identifying an optimal ageing treatment, tensile properties were investigated on the samples in the as-built and aged conditions. The microstructure, hardness and tensile properties of the as-built sample was found to resemble that of a conventionally-manufactured and solution-treated alloy. However, as compared to conventionally-manufactured Ti-3Al-8V-6Cr-4Mo-4Zr subjected to the same ageing temperature, the ageing process was much quicker with the DED-processed alloy because of its high dislocation density. Furthermore, the latter can also achieve much higher strength while also having comparable ductility. To achieve a similar ageing response and tensile behavior, conventionally-manufactured Ti-3Al-8V-6Cr-4Mo-4Zr would require cold-working prior to ageing. Carbon additions were also investigated to further accelerate the ageing response and to refine the β grain size. While the ageing response was much quicker and a much harder alloy can be produced, the carbon amount added was insufficient for β grain refinement, which resulted in reduced ductility without a change in strength. [ABSTRACT FROM AUTHOR]

In this work, we presented an investigation into the deformation behavior of laser powder bed fusion (LPBF) Ti-6Al-4V (Ti64), particularly how microstructure characteristics determined the grain deformation behavior by using in-situ SEM tensile characterization. Results demonstrated that α laths with their elongation directions 45° to the tensile loading axis and α laths with the larger thickness could induce severe strain accumulation during the uniaxial tensile process. Crystallographic orientations and grain morphologies of α lath were considered the key factors that could influence the deformation behavior. The strain localization was observed in the α laths dominated by multiple slip systems. Furthermore, the α laths with their elongation directions 45° to the tensile loading axis had the longest effective slip length, which could make α laths favorable for deformation. The dislocations multiplication of coarse α laths was much greater than in fine α laths, which could also result in strain localization. These findings could shed light on the deformation behavior related to lamellar structure in LPBF Ti64 and could further help the mechanical property manipulation. • Strain distribution of LPBF Ti64 during the tensile process was characterized by using in-situ SEM tensile testing. • Crystallographic orientations and grain morphologies of α lath could determine the deformation behavior. • The strain localization was observed in the α laths dominated by both prismatic and pyramidal slip systems. • The α laths with elongation directions 45° to the tensile loading axis could make them favorable for deformation. • The dislocations multiplication of coarser α laths is more rapid than in fine α laths. [ABSTRACT FROM AUTHOR]

An Al-Mn-Mg-Sc-Zr alloy was additively manufactured and subsequently deformed to investigate the effect of high defect densities on the precipitation behavior, work hardening capability and ductility. For this, the LPBF-fabricated alloy was deformed by rotary swaging up to a true strain of 2.5 following a laser powder bed fusion (LPBF) process. Compared to the LPBF condition, swaging results in a refinement of the microstructure by one order of magnitude and an increased hardness and ultimate tensile strength (UTS) which is mainly attributed to the finer microstructure of the swaged alloy. By annealing, a higher peak-aging hardness of (209 ± 2) HV0.1 and UTS of (717 ± 2) MPa of the swaged alloy at a lower peak-aging temperature of 300 °C (1 h) was obtained. Significant improvement of uniform elongation by enhanced work hardening capability of the swaged and annealed alloy is obtained for annealing temperatures above 300 °C while strength is only moderately affected. The significant improvement of aging kinetics is discussed alongside a profound microstructural characterization of the heterogeneous grain structure and precipitate distribution. • Work hardening of high strength Al alloys is improved by deformation prior ageing. • Enhanced uniform ductility is obtained. • UTS of (612 ± 9) MPa at a uniform strain of (1.4 ± 0.2) % is found. • Heterogeneous microstructure by additive manufacturing resists cold work. [ABSTRACT FROM AUTHOR]

The defects remain a significant issue for additive manufactured titanium alloys, which hinders their further market penetration. In this work, we proposed a new understanding of the inhomogeneous microstructure formation affected by defects with detailed EBSD characterization, and how the defects and inhomogeneous microstructures determined the strain accumulation behavior by in-situ SEM tensile testing. Smaller prior β grains and coarser α laths were identified around the defects. In-situ tensile behavior investigations revealed that irregularly-shaped and elongated defects with high stress intensity factor ( Δ K I) could induce severe strain accumulation, showing that the defect morphology was the primary factor that could determine the strain accumulation behavior. In the meantime, the inhomogeneous microstructures around the defects could further contribute to the strain accumulation, with the coarser α laths more favorable for deformation and stronger microtexture for easier slip transmission. In addition, microcracks were found initiated from a spherical pore with small loading, and arrested due to the negligible strain accumulation. Further characterization showed that oxidation, which was found more probable in spherical pores, was the cause of this microcrack initiation. [Display omitted] [ABSTRACT FROM AUTHOR]

Heat treatment (HT) is an effective way to attain the desired microstructure and mechanical properties in laser powder bed fusion (LPBF) Ti–6.5Al–2Zr–1Mo–1V (TA15). However, previous studies only obtained the high tensile ductility of LPBF TA15 but were accompanied by a large loss of strength, which was unable to achieve balanced mechanical properties. Here, we evaluated the tensile properties of LPBF TA15 at their usage temperatures (500 °C), and a superior combination of high-temperature strength and ductility in LPBF TA15 was successfully achieved via a single-step heat treatment. After the heat treatment close to the β transus temperature (950 °C as used in this study), the tensile strength of the sample was ∼30% higher than that of as-cast TA15, accompanied by the obvious enhancement of ∼67% in elongation. The high strength originated mainly from the secondary α-phase and discontinuous grain boundary α-phase (GB-α), whereas the large ductility correlates to the complete decomposition of brittle α' martensite. Discontinuous GB-α could inhibit crack initiation at the grain boundary and the fine secondary α-phase impeded the dislocation motion, which could enhance the tensile strength. Meanwhile, the α lath directions after heat treatments were far away from the 45° of the load direction, which also avoided the localized deformation within α laths and thus improved the fracture resistance of LPBF TA15. [ABSTRACT FROM AUTHOR]

[Display omitted] • With the transverse loading direction, the strain localization was found within the continuous grain boundary α-phase. • Discontinuous grain boundary α-phase could fully accommodate uniform deformation together with the matrix microstructure. • An effective approach that eliminates the anisotropy in additive manufactured Ti-6Al-4V was provided. Grain boundary α-phase (GB-α) in titanium alloys is the vulnerable site for failure, while the correlation between deformation behavior and local dislocation motion is still ambiguous. In this study, we made a detailed investigation into the deformation behavior of GB-α with different morphologies in a laser powder bed fusion (LPBF) fabricated Ti-6Al-4V (Ti-64) by using in-situ and interrupted tensile testing, and discussed the underlying mechanisms of dislocation motion. The deformation-induced dislocations were found severely accumulated within the continuous GB-α with the transverse loading direction, which corresponds to the strain localization, while uniformly distributed between the continuous GB-α and surrounding grains with the perpendicular tensile loading. In contrast, discontinuous GB-α could fully accommodate uniform deformation with the matrix microstructure under both loading directions. The new understanding of dislocation motions in GB-α provides a novel perspective to effectively eliminate the tensile property anisotropy with the columnar microstructure present in LPBF Ti-64. [ABSTRACT FROM AUTHOR]