Impact of coherent and incoherent twin boundaries on the microhardness of annealed nanocrystalline Ni–W alloys

The microstructural evolution of nanocrystalline Ni–W alloys with annealing temperature and more specifically grain boundary (GB) character is investigated through several techniques and correlated with the hardening behaviour. It is shown that two distinct regions can be identified in relation to the annealing temperature and the microstructural evolution. At temperatures below 550 °C (Regime I), a small increase in grain size is observed and is accompanied by a significant hardening and an increase in the fraction of Σ3 incoherent twin boundaries. At temperatures above 550 °C (Regime II), the thermal stability is overcome and important grain growth occurs with a decrease in both the volumic fraction of GBs and the microhardness. It is suggested that the microhardness evolution during heat treatment is influenced by two opposing processes: an increase in the fraction of incoherent twin boundaries (hardening effect) and grain growth (softening effect). Both aspects are directly associated with the mean free path of mobile dislocations.     

Pinning of grain boundary migration by a coherent particle

We studied single-particle pinning of grain boundary (GB) migration during grain growth. A phase-field model was formulated to simulate the pinning by a coherent particle and validated quantitatively by comparison with analytical prediction. A study of GB migration velocity using this model revealed that second-phase coherent particles have a previously unknown restraining effect over the whole of the GB-particle interaction range, which is qualitatively different from the interaction between GB and incoherent particles.     

Enhanced grain growth in yttria-doped zirconia thin film structures synthesized under photon irradiation

Enhanced grain growth in ultra-thin yttria-doped zirconia (YDZ) films synthesized under ultraviolet (UV) irradiation is reported. The mean grain size in UV-synthesized 7.5 mol% YDZ films nearly 56 nm thick increased to 85 nm upon annealing in an oxygen-rich ambient at 900°C for 1 h, while in thermally grown YDZ they grew only to ～15 nm under identical annealing conditions. In situ electron microscopy kinetic studies reveal an enhanced kinetic constant and self-limiting grain growth behaviour in the UV-synthesized oxide films. The difference between UV and thermally grown films was not significant in undoped films when compared to the case of 7.5 mol% YDZ.     

Novel fabrication of bulk Al with gradient grain size distributions via powder metallurgy

We describe a novel approach to synthesize gradient microstructures, defined hereafter as containing a broad but continuous distribution of grain sizes. These microstructures extend the concept of a bimodal grain size distribution and the ability to design with multiple length scales. We demonstrate the proposed approach via experiments involving cryogenic ball milling of Al–4.5Mg–0.4Mn–0.05Fe and Al–50Mg powder followed by subsequent consolidation. Our results reveal that the grains in the consolidated powder present a gradient size distribution ranging from <100 nm to >3 μm. Moreover, phase composition analysis revealed a unique “interfingered” structure where the two starting phases were intermixed in a complex three-dimensional mesh. Hardness studies of this gradient microstructure show average Vickers hardness values of 200 ± 2.6, 204 ± 4.3 and 266 ± 50 for macrohardness, microhardness and nanoindentation, respectively. The standard deviation values highlight that the gradient microstructure is disordered locally, but homogenous macroscopically.     

Grain orientation effects on dynamic strength of FCC multicrystals at low shock pressures: a hydrodynamic instability study

Variability in local dynamic plasticity due to material anisotropy in polycrystalline metals is likely to be important on damage nucleation and growth at low pressures. Hydrodynamic instabilities could be used to study these plasticity effects by correlating measured changes in perturbation amplitudes at free surfaces to local plastic behaviour and grain orientation, but amplitude changes are typically too small to be measured reliably at low pressures using conventional diagnostics. Correlations between strength at low shock pressures and grain orientation were studied in copper (grain size?≈?800 μm) using the Richtmyer–Meshkov instability with a square-wave surface perturbation (wavelength = 150 μm, amplitude = 5 μm), shocked at 2.7 GPa using symmetric plate impacts. A Plexiglas window was pressed against the peaks of the perturbation, keeping valleys as free surfaces. This produced perturbation amplitude changes much larger than those predicted without the window. Amplitude reductions from 64 to 88% were measured in recovered samples and grains oriented close to 〈0 0 1〉 parallel to the shock had the largest final amplitude, whereas grains with shocks directions close to 〈1 0 1〉 had the lowest. Finite element simulations were performed with elastic-perfectly plastic models to estimate yield strengths leading lead to those final amplitudes. Anisotropic elasticity and these yield strengths were used to calculate the resolved shear stresses at yielding for the two orientations. Results are compared with reports on orientation dependence of dynamic yielding in Cu single crystals and the higher values obtained suggest that strength estimations via hydrodynamic instabilities are sensitive to strain hardening and strain rate effects.     

Grain orientation effects on delamination during fatigue of a sensitized Al–Mg alloy

Fatigue crack growth experiments were conducted in humid air (RH~45%) at 25 °C on 29-mm-thick plate samples of an aluminium–magnesium (Al–Mg) 5083-H131 alloy in the long transverse (LT) direction. Samples were tested in both the as-received condition and after sensitization at 175 °C for 100 h. Delamination along some grain boundaries was observed in the short transverse plane after fatigue testing of the sensitized material, depending upon the level of ΔK and K_max. Orientation microscopy using electron backscattering diffraction and chemical analyses using transmission electron microscopy and energy dispersive spectroscopy of grain boundaries revealed that Mg segregation and the orientation of grains had key roles in the observed grain boundary delamination of the sensitized material.     

On the AlN precipitation and grain refinement in the Al(N)-added medium C–Mn steels

The precipitation of AlN particles and grain refinement in the Al(N)-added medium C–Mn steel have been studied using a Gleeble hot-deformation simulator and extraction replica TEM technique. No significant grain refinement occurs during either hot-rolling or hot-deformation/isothermal-holding, which is due to the absence of AlN precipitation; the lack of precipitation is caused by an unusually high-energy barrier for nucleation. Abrupt grain refinement occurs on reheating because of the copious precipitation of AlN during reheating. The copious precipitation of AlN during reheating is possible because thermally unstable Fe-rich sulphides act as precursors for AlN precipitation during reheating.     

Associations of depression status and hopelessness with blood pressure: a 24-year follow-up study

Hypertension is estimated to cause 12.8% of all deaths worldwide. Both literature and well-supported cognitive models indicate that hopelessness predicts depressive symptoms. This study aimed to test whether high levels of hopelessness are associated with increased blood pressure, as well as whether depression acts as a mediator between hopelessness and blood pressure. Data from the original 24-year longitudinal Baltimore Epidemiologic Catchment Area Study (ECA) were analyzed via linear regression (N = 917; 60.3% female; 62.9% European American; mean age = 42.96 years, SD = 16.94). Hopelessness was found to have a significant direct relationship with systolic blood pressure (SBP, p < .05), but not with diastolic blood pressure (DBP, p > .05); while depression had no significant direct relationship with SBP or with DBP. Overall, findings indicated that hopelessness has a significant relationship with SBP. Limitations and implications are discussed.     

Effect of initial texture on deformation-induced grain growth in pulsed electrodeposited microcrystalline copper

Owing to the presence of large fraction of grain boundaries, deformation-induced grain growth is commonly observed in fine-grained electrodeposited metals. Here we demonstrate that microcrystalline copper (d～1–10?µm) with different textures produced by electrodeposition exhibit significant deformation-induced grain growth in tension by coalescence along with twin boundary migration and detwinning. Oriented growth with the formation of a cube texture was noted in the deformed samples. There was an increased fraction of twin boundaries with large angular deviation from Brandon's criterion during deformation.     

Reducing Identity Distress: Results of an Identity Intervention for Emerging Adults

Emerging adulthood is a transitional period between adolescence and adulthood where positive and negative life trajectories tend to diverge, with issues surrounding identity formation playing a key role. The present study evaluated the Miami Adult Development Project, a self-facilitated identity-focused intervention. The sample consisted of 141 emerging adults (19?29 years old; M = 23.08) who completed pretest and posttest assessments. Results indicated participation in the intervention relative to the comparison group was associated with lower levels of identity distress and higher levels of well-being via the reduction of identity distress and the development of a consolidated identity (commitment and synthesis). The present study provides evidence for the effectiveness of positive identity interventions during emerging adulthood.     

Microstructure evolution and hardness variation of pack-rolled nanocrystalline nickel

The microstructure evolution and hardness of nanocrystalline nickel during pack rolling at room temperature have been investigated. It was found that the roll-bonding side (R) and non-roll-bonding side (NR) behaved quite differently. The hardness of side R is higher than that of side NR. No obvious work softening was observed in either side R or side NR until the strain reached ~ 0.611. Quantitative X-ray diffraction analysis indicated that the grain size in side NR increases faster than that in side R, a result confirmed by transmission electron microscopy. Texture analysis showed that (2 0 0) preferred orientation first strengthens but then weakens in both sides NR and R, while a strong (2 2 0) preferred orientation emerges, particularly in side R. Further texture analysis suggests that dislocation slip is responsible for the texture discrepancy between side NR and side R. The dislocation activity, grain rotation and grain growth are discussed based on the experimental results.     

Kinetic study of static recrystallization in an Fe–Al–O ultra-fine-grained nanocomposite

A nearly abrupt coarsening of grains is observed in a newly developed Fe–Al–O ultra-fine-grained nanocomposite with a significant volume fraction (4%) of alumina nano-precipitates. The microstructure of the alloy was analysed in different states (as-received and annealed) by means of scanning electron microscopy, transmission electron microscopy (TEM) and hardness. The initial grain size 150–200 nm increases up to 50 μm during annealing 1000 °C/8 h and thereafter demonstrates saturation. A linear correlation between volume fraction of coarse grains and hardness was found. It was identified by TEM that alumina nano-precipitates stabilize the dislocation microstructure against recovery very effectively and the grain coarsening is due to fast growth of very few dislocation free grains. Thus, the observed grain coarsening has the attributes of static recrystallization.     

Grain boundary phase observed in Al–5 at.% Zn alloy by using HREM

The nature and behaviour of grain boundary (GB) phases is very important since they can control strength, plasticity, resistivity, grain growth, corrosion resistance, etc, especially in nanocrystalline materials. For nanocrystalline Al-based light alloys, extremely high plasticity has been observed in restricted temperature and concentration intervals close to the solidus line. This phenomenon is not fully understood. It can be explained by formation of GB phases not included in the bulk phase diagram. Therefore, the structure of GB phases, as well as thermodynamic conditions for their existence, has to be carefully studied. In this work the structure and composition of GBs and GB triple junctions in Al–5 at.% Zn polycrystals annealed in the temperature region above and below the bulk solidus line were studied by high-resolution electron microscopy and analytical transmission electron microscopy. Evidence has been obtained that a thin layer of a liquid-like phase exists in GBs and GB triple junctions slightly below the bulk solidus line.     

Identifying long-term patterns of work-related rumination: associations with job demands and well-being outcomes

The aim of this 2-year longitudinal study was to identify long-term patterns of work-related rumination in terms of affective rumination, problem-solving pondering, and lack of psychological detachment from work during off-job time. We also examined how the patterns differed in job demands and well-being outcomes. The data were collected via questionnaires in three waves among employees (N = 664). Through latent profile analysis (LPA), five stable long-term patterns of rumination were identified: (1) no rumination (n = 81), (2) moderate detachment from work (n = 228), (3) moderate rumination combined with low detachment (n = 216), (4) affective rumination (n = 54), and (5) problem-solving pondering (n = 85), both combined with low detachment. The patterns differed in the job demands and well-being outcomes examined. Job demands (time pressure, cognitive and emotional demands) were at the highest level across time in patterns 3–5 and lowest in pattern 1. Patterns 3 and 4 were associated with poorer well-being outcomes (higher job exhaustion and more sleeping problems, and lower work engagement) across time. By contrast, pattern 5 showed positive outcomes, especially high level of work engagement. Thus, the different patterns of work-related ruminative thoughts suggest diverse relationships with job demands and well-being.     

Shaping achievement goal orientations in a mastery-structured environment and concomitant changes in related contingencies of self-worth

Across three time-points spanning 9 months, changes in achievement goal orientations and contingencies of self-worth were assessed as a function of participating in a mastery-structured academic program for high-ability adolescents (N = 126). Endorsement of mastery goal orientations increased during the program and remained high even after students returned to their home learning environments. In contrast, performance-approach and performance-avoidance goal orientations decreased during the summer program, but returned to previous levels when assessed 6 months later. Latent growth curve models assessed the covariation of performance goal orientations and two contingencies of self-worth (outperforming others and others’ approval) hypothesized to represent elements of performance goal orientations. Changes in the contingency of self-worth based on outperforming others positively covaried with observed changes in both performance goal orientations; however, changes in self-worth contingent on others’ approval did not. Results are discussed in terms of mastery-structured environments’ potential to alter achievement goal orientations via their underlying psychological processes. Implications for achievement goal theory and the design of achievement-oriented environments are discussed.     

Is it Push or Pull? Recent Evidence from Migration into Bangalore, India

Given urban areas contribute to more than 65 % of India’s gross domestic product (GDP), the sustainability of the rapid 8–9 % GDP growth India has experienced in the last decade, is dependent to a large extent on urban areas. With migration being one of the important factors contributing to the growth of urban population, we attempt to understand whether it is push (out of the rural area) or pull (toward the urban area due to its perceived benefits) which explains migration in India, taking the case of Bangalore, which has one of the largest proportions of in-migrants to total population. An examination of these factors is done using a primary survey of migrants in Bangalore. Using a probit model, we find that the lower the level of education of the migrant, the greater the importance of the push factors whereas with increasing level of education of the migrant, pull factors become more important in migration. Women are more likely to be “pulled” toward urban areas. We find migrants from within Karnataka are “pushed”. This suggests that nonfarm employment opportunities have to be increased, rural infrastructure improved, and the development of small and medium towns encouraged.     

Microstructure and phase evolution in spark-plasma-sintered Al86Ni6Y4.5Co2La1.5 glassy alloy

Al₈₆Ni₆Y_4.5Co₂La_1.5 amorphous powders synthesized after 200 h of mechanical alloying were spark plasma sintered at 25 and 400 MPa at 400 °C for 15 min. The sample sintered at 25 MPa showed precipitation of FCC-Al grains of sub-micron size attributed to a higher amount of localized high-temperature regions which favoured faster long-range atomic diffusion. On the contrary, the 400-MPa sintered sample showed the presence of nanocrystals (5–20 nm) distributed in an amorphous matrix. This is attributed to higher pressure sintering favouring local and short-range atomic redistributions. The higher amount of retained amorphous phase in the 400-MPa sintered sample could be accounted for by a smaller amount of localized high-temperature regions in comparison to those in 25-MPa sintered sample. High-pressure sintering induces shear fracturing and fragmentation of the brittle amorphous particles and provided better surface contact and packing density. The retention of a larger amount of amorphous phase and a higher relative density (96%) contributes to high microhardness (278 Hv) and nanoindentation hardness (3.7 GPa) of the 400-MPa sintered sample.     

Grain boundary networks in high-performance,heteroepitaxial, YBCO films on polycrystalline,cube-textured metals

Grain boundaries (GBs) in high-temperature superconductors suppress the critical current density (J _c) dramatically, with the J _c decreasing exponentially with GB angle, especially when GB misorientation exceeds 4°. To reduce the number of high-angle GBs, fabrication of biaxially textured, superconducting wires via heteroepitaxial growth on cube-textured metals has been widely investigated worldwide. Such wires exhibit very high J _c in applied magnetic fields despite having a majority of GBs with total misorientations in the range 4–8°. Here, we show that GB networks in these wires have numerous GBs with out-of-plane misorientations greater than 4° but few boundaries having in-plane misorientations greater than 4°. Transport measurements on bicrystal GBs show that GBs with out-of-plane tilts between 4° and 8° are well linked. Together, these results explain the high performance of superconducting films on cube-textured metals.     

Design strategy for microalloyed ultra-ductile magnesium alloys

This article describes a design strategy deployed in developing ultra-ductile Mg alloys based on a microalloying concept, which aims to restrict grain growth considerably during alloy casting and forming. We discuss the efficiency of the design approach, and evaluate the resulting microstructural and mechanical properties. After processing, the so-designed alloys ZQCa3 (Mg–3Zn–0.5Ag–0.25Ca–0.15Mn, in wt.%) and ZKQCa3 (Mg–3Zn–0.5Zr–0.5Ag–0.25Ca–0.15Mn, in wt.%) reveal very fine grains (<10 µm), high ductility (elongation to fracture of up to 30%) at moderate strength or high strength (ultimate tensile strength of up to 350 MPa) at reasonable ductility. These properties are explained based on thermodynamic modelling, microstructure analysis including transmission electron microscopy studies, and microstructural and mechanical testing after annealing, and are compared to a related commercial alloy (ZK31).