Abstract
Twin boundaries (TBs) in Ni-based superalloys are vulnerable sites for failure in demanding environments, and a current lack of mechanistic understanding hampers the reliable lifetime ...prediction and performance optimisation of these alloys. Here we report the discovery of an unexpected γ″ precipitation mechanism at TBs that takes the responsibility for alloy failure in demanding environments. Using multiscale microstructural and mechanical characterisations (from millimetre down to atomic level) and DFT calculations, we demonstrate that abnormal γ″ precipitation along TBs accounts for the premature dislocation activities and pronounced strain localisation associated with TBs during mechanical loading, which serves as a precursor for crack initiation. We clarify the physical origin of the TBs-related cracking at the atomic level of γ″-strengthened Ni-based superalloys in a hydrogen containing environment, and provide practical methods to mitigate the adverse effect of TBs on the performance of these alloys.
The path-constrained moving target search problem has been subject to research since 1979 and is still investigated due to its important application, namely: search missions. This review paper ...provides an overview of the two main research branches. We cover approaches for path-constrained searchers, as well as approaches for kinematics-constrained searchers such as aerial search platforms. Besides an extensive overview of the literature, an overview of properties that are typical for search optimization approaches is given. A tabular summary of the approaches and their properties is provided for easy comparison and efficient lookup of applicable methods. Finally, we identify a main research gap and propose a promising type of algorithm for efficiently solving moving target search optimization problems.
Display omitted
•Successfully imaged H concentrations in δ phase and carbonitrides, and at their interfaces with the matrix using NanoSIMS in alloy 718.•δ attracts a higher concentration of H than ...the matrix while carbonitrides adsorb much less. No H segregation was observed at the interfaces.•The higher vulnerability of δ in H induced cracking is attributed to its higher capacity in H adsorption, and vice versa for carbonitrides.
Here we report imaging of hydrogen/deuterium concentrations in δ phase and carbonitrides, and at their interfaces with the matrix in a nickel-based superalloy using Nanoscale Secondary Ion Mass Spectrometry. It is found that δ phase attracts a higher concentration of hydrogen than the matrix during cathodic charging, while carbonitrides adsorb much less. No hydrogen segregation was observed at the interfaces. Detailed electron microscopy analysis of the H-charged samples after tensioning to failure demonstrates that the higher vulnerability of δ in hydrogen induced cracking is largely attributed to its higher capacity in hydrogen adsorption, and vice versa for carbonitrides.
Objective To assess whether breastmilk feeding is associated with a reduced risk of bronchopulmonary dysplasia (BPD). Secondary outcome measures analyzed were retinopathy of prematurity (ROP) and ...necrotizing enterocolitis (NEC). Study design In an ongoing multicenter cohort study, the data of 1433 very low birth weight infants born before 32 weeks of gestation and discharged in 2013 were analyzed. We compared growth and neonatal complications of infants who received breastmilk exclusively (N = 223) with those who received formula feedings exclusively (N = 239). Logistic regression models were estimated for BPD, ROP, and NEC using nutrition as an independent variable. The Firth logistic regression model and Lasso were used for sensitivity analyses. Results Exclusively breastmilk-fed infants gained less weight compared with formula-fed infants. SDS for weight decreased between birth and discharge (median (Q1-Q3): formula −0.9 (−1.4 to −0.5) vs breastmilk −1.1 (−1.7 to −0.6)). Exclusive formula feeding of very low birth weight infants was associated with increased risks of BPD (OR 2.6) as well as NEC (OR 12.6) and ROP (OR 1.80) after controlling for known risk factors. Conclusions Exclusive breastmilk feeding was associated with lower growth rates and a reduced risk of BPD as well as NEC and ROP.
Micro slip activation and localization in Ti-6Al-4V deformed in tension have been examined quantitatively using high-resolution (HR) digital image correlation (DIC), HR-electron backscatter ...diffraction (EBSD) and crystal plasticity finite element modelling. The measured polycrystal slip, strain, lattice rotation and geometrically necessary dislocation (GND) density distributions are generally well captured by the a priori crystal plasticity model based on the rate-sensitive properties of α-titanium. An overall slip trace analysis showed over 80% agreement between HR-DIC and crystal plasticity modelling of the primary slip activation. The texture beneath the characterised free-surface has been found to affect the local slip, stress distribution, lattice curvature and GND density and three texture variations have been considered. Grain-level slip trace analysis shows that the crystal plasticity modelling can capture single (straight) slip, multiple slip activation and complex wavy slip. The latter has been found to result from the interaction of independently activated basal and prismatic slip systems with common slip direction. Initial inter-granular misorientations greater than about 5° have been shown to influence the subsequent micromechanical grain behaviour including slip, lattice rotation and GND density. This work contributes to the understanding of slip localization and load shedding in dwell fatigue in polycrystalline hexagonal materials.
•Quantitative analysis of microscale slip shows reasonable agreement between experiments and crystal plasticity modelling.•The subsurface grain orientations affect the lattice curvature and GND density, and the bounds on behaviour have been given.•The complex wavy slip results from the interaction of different slip modes (basal and prismatic) with common slip direction.•Initial intra-granular misorientations greater than about 5° influence the subsequent micromechanical grain behaviour.•Crystal plasticity modelling and HR-DIC both suggest that most of the plastic strain is associated with prismatic slip.
A specimen of Ti–4Al deformed in-situ to about 0.7% compressive strain using neutron diffraction, and showing early stages of twinning, has been investigated in 3D using synchrotron X-ray diffraction ...contrast tomography (DCT). A cylindrical volume of 900 μm × 400 μm diameter was observed using DCT, containing about 400 grains of which almost 60 grains were identified to have twinned predominantly by {101¯2} 〈1¯011〉 011 tensile twinning. To consider possible twin nucleation criteria, non-twinned grains of similar orientation to the twinned grains were compared against the family of twinned grains. Such comparison highlights that the twinned grain family has a grain size distribution shifted to a higher mean value than the corresponding family of grains that has not twinned. An initial neighbourhood analysis did not reveal any significant differences of the two grain families. However, complex twin chains and clusters were identified forming a slightly imperfect network demonstrating the importance of the 3D analysis. Analysis of the parent grain orientations within those chains/clusters using the Luster-Morris parameter revealed a significantly higher propensity of prismatic 〈a〉 slip transfer compared to the neighbourhood of the non-twinned grain family while no difference was observed for the likelihood of twin shear transfer. The findings suggest that grain chains/clusters with high ability of prismatic 〈a〉 slip activity and slip transfer does promote formation and clustering of twins, which is likely associated with the build up of tensile intergranular strain along the 〈c〉 axis perpendicular to the loading direction recently suggested by crystal plasticity modelling.
Display omitted
Mixed austenitic and ferritic steel powders consolidated via the hot isostatic pressing process present a bimodal microstructure and interesting properties.
Display omitted
•Functional grading by hot ...isostatic pressing of mixed austenitic and ferritic steel powders has been studied.•Joining dissimilar metal components while minimising excessive grain growth has been achieved via the hot isostatic pressing.•Diffusional processes during hot isostatic pressing at various temperatures have been comprehensively investigated.•Significant increase in hardness only with a limited lath constituent in a soft austenitic matrix achieved.•A model has been proposed for predicting the microstructure of mixed powder specimens depending on the processing conditions.
Functional grading of a ferritic steel (SA508 grade 3) and austenitic stainless steel (316L) powder via hot isostatic pressing (HIP) consolidation is investigated as an alternative to dissimilar welding. Fundamental aspects of this method such as the development of microstructure and diffusional processes during the HIP process of such mixed powder are studied in this work. A change of the post-HIP α to γ ratio with HIP temperature was observed in mixed powder specimens, combined with the formation of a ferritic lath zone which affects the properties of the specimens (throughout this work the term ferritic laths refers to a ferritic phase of unknown structure which is likely to consist of martensite, bainite or a mixture of both). These effects were attributed to extensive diffusion of alloying elements from 316L into SA508 grade 3. Simulation and experimental quantification of diffusion in diffusion couple experiments were applied to derive an empirical model for estimating α-Fe boundary migration and the formation of the ferritic lath zone and phase fractions for various temperatures and dwell times of the HIP process.
To evaluate lowest mean arterial blood pressure during the first 24 h of life (minMAP(24)) in very-low-birthweight (VLBW) infants and to identify associations between hypotension and short-term ...outcome.
Retrospective cohort analysis of the minMAP(24) of 4907 VLBW infants with a gestational age <32 weeks in correlation with clinical data. Hypotension was defined as minMAP(24) being lower than the median value of all patients of the same gestational age.
MinMAP(24) values correlated with gestational age. Median minMAP(24) values of VLBW infants ≤29 weeks' gestation were 1-2 mm Hg lower than gestational age in completed weeks. Hypotensive infants had a higher rate of intraventricular haemorrhage (IVH, 20.3% vs 15.9%, p<0.001), bronchopulmonary dysplasia (BPD, 19.2% vs 15.1%, p<0.001) and death (5.2% vs 3.0%, p<0.001). Multivariate logistic regression analyses, including potential confounders, confirmed these data. MinMAP(24) was an independent risk factor for IVH (OR 0.97/mm Hg, 95% CI 0.96 to 0.99, p=0.003), BPD (OR 0.96/mm Hg, 95% CI 0.94 to 0.98, p<0.001) and mortality (OR 0.94/mm Hg, 95% CI 0.90 to 0.98, p=0.003).
Hypotension during the first 24 h of life is associated with adverse outcomes in VLBW infants. This underlines the need for randomised controlled trials on the use of vasoactive drugs in this vulnerable patient cohort.
We compare the dislocation substructure within macrozone and non-macrozone regions of hot-rolled Ti–6Al–4
V. Hough-based and cross-correlation-based analysis of electron backscatter diffraction ...(EBSD) patterns are used to establish the grain orientations and intra-granular misorientations, respectively. The set of geometrically necessary dislocations (GNDs) that support measured lattice curvatures and minimize the total GND line energy are calculated. The GND content in the macrozone is approximately twice that in the non-macrozone region, and 〈
a〉 GNDs are present at densities ∼10 times higher than
〈c
+
a
〉 GNDs.
Melanocortin 4 receptor (MC4R) deficiency, caused by mutations in MC4R, is the most common cause of monogenic forms of obesity. However, these mutations have often been identified in small-scale, ...case-focused studies. Here, we assess the penetrance of previously reported MC4R mutations at a population level. Furthermore, we examine why some carriers of pathogenic mutations remain of normal weight, to gain insight into the mechanisms that control body weight.
We identified 59 known obesity-increasing mutations in MC4R from the Human Gene Mutation Database (HGMD) and Clinvar. We assessed their penetrance and effect on obesity (body mass index BMI ≥ 30 kg/m2) in >450,000 individuals (age 40-69 years) of the UK Biobank, a population-based cohort study. Of these 59 mutations, only 11 had moderate-to-high penetrance and increased the odds of obesity by more than 2-fold. We subsequently focused on these 11 mutations and examined differences between carriers of normal weight and carriers with obesity. Twenty-eight of the 182 carriers of these 11 mutations were of normal weight. Body composition of carriers of normal weight was similar to noncarriers of normal weight, whereas among individuals with obesity, carriers had a somewhat higher BMI than noncarriers (1.44 ± 0.07 standard deviation scores SDSs ± standard error SE versus 1.29 ± 0.001, P = 0.03), because of greater lean mass (1.44 ± 0.09 versus 1.15 ± 0.002, P = 0.002). Carriers of normal weight more often reported that, already at age 10 years, their body size was below average or average (72%) compared with carriers with obesity (48%) (P = 0.01). To assess the polygenic contribution to body weight in carriers of normal weight and carriers with obesity, we calculated a genome-wide polygenic risk score for BMI (PRSBMI). The PRSBMI of carriers of normal weight (PRSBMI = -0.64 ± 0.18) was significantly lower than of carriers with obesity (0.40 ± 0.11; P = 1.7 × 10-6), and tended to be lower than that of noncarriers of normal weight (-0.29 ± 0.003; P = 0.05). Among carriers, those with a low PRSBMI (bottom quartile) have an approximately 5-kg/m2 lower BMI (approximately 14 kg of body weight for a 1.7-m-tall person) than those with a high PRS (top quartile). Because the UK Biobank population is healthier than the general population in the United Kingdom, penetrance may have been somewhat underestimated.
We showed that large-scale data are needed to validate the impact of mutations observed in small-scale and case-focused studies. Furthermore, we observed that despite the key role of MC4R in obesity, the effects of pathogenic MC4R mutations may be countered, at least in part, by a low polygenic risk potentially representing other innate mechanisms implicated in body weight regulation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
PDF
