Anomalous production of vacancy clusters and the possibility of plastic deformation of crystalline metals without dislocations

High-speed heavy plastic deformation of thin foils of fcc metals, including aluminium, is found to produce a high density of small vacancy clusters, in the form of stacking-fault tetrahedra. The dependences of the density of the clusters on the deformation temperature and deformation rate indicate the production of vacancy clusters from deformation-induced dispersed vacancies. Neither dislocations nor any indication of the reaction of dislocations are present in the regions containing a high density of vacancy clusters. A possible model is proposed that describes, at extremely high strain rates where dislocation generation is difficult, how a high concentration of point defects is produced by a large number of parallel shifts of atomic planes without dislocations.     

Observation of phase separation in magnetron sputter-deposited Al–Cu thin films

The microstructures of Al–1.8 to 92.5?at.% Cu thin films prepared by radiofrequency (13.56?MHz) cathodic magnetron sputtering have been investigated by X-ray diffraction (XRD) and transmission electronic microscopy (TEM). A phase separation occurs in films of nominal Al–66.64?at.% Cu composition, consisting of a fcc Al solid solution phase, a fcc Cu solid solution phase and an unexpected sc Cu₃Al ordered phase with a Cu₃Au structure and a lattice parameter of about 0.36?nm.     

Effect of Al-Zr clusters on the thermal stability of Cu-Zr-rich Cu-Zr-Al bulk metallic glasses

The Gibbs free energy of formation, ?G^a, of the amorphous phase of Cu–Zr-rich Cu–Zr–Al bulk metallic glasses (BMGs) has been calculated over a broad composition region to re-evaluate their thermal stability, based on the efficient cluster packing model. It is found that Al–Zr clusters have an important effect on the thermal stability of the Cu–Zr–Al BMGs with the same Cu/Zr content ratio. The crystallisation of the BMGs involves crystallisation of both Al–Zr and Cu–Zr clusters. The results could be useful for predicting the thermal stability and understanding the underlying mechanism of crystallisation of multicomponent metallic glasses.     

Effect of deep cryogenic treatment on carbon segregation in Cr8Mo2SiV tool steel during tempering

Carbon segregation in Cr8Mo2SiV tool steel after common heat treatment (CHT) and deep cryogenic treatment (DCT) has been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) extraction replica and three-dimensional atom probe (3DAP) tests. The XRD results show that most of the retained austenite transformed to martensite after DCT. The TEM results confirm the transformation of blocky retained austenite to twin martensite during DCT. The 3DAP results reveal the segregation of carbon atoms and the maximum carbon fraction in carbon-rich regions increases after DCT. The peak carbon concentration in carbon-rich regions of SDC99 steel after CHT and DCT are 8 at. % and 15 at. %, respectively. The segregated carbon atoms grew into nuclei for nanoscale carbides precipitation on subsequent tempering.     

Three methods of developing MMPI taxonomies of sexual offenders

In a sample of 261 state hospital sexual offenders, Minnesota Multiphasic Personality Inventory (MMPI) profiles did not differ for offenders with adult victims versus offenders with child victims when offender age was controlled. MMPI 2-point analyses for the whole sample revealed five common codes that were independent of victim maturity. The sample was randomly divided in half and subjected to a cluster-analytic procedure which revealed two MMPI clusters. The first cluster was unelevated, with Scale 4 as its high point. The second cluster had multiple elevations, with Scales 8, 4, 2, and 7 as the highest scales. These clusters were replicated in a cluster analysis of the second half of the sample. However, when the sample was recombined, the two clusters were not externally validated basis on demographic and criminological variables. The results suggest that common psychological variables among sexual offenders may have more discriminative value than victim maturity in developing sexual offender taxonomies.     

Nanocrystallization in a Zr 57 Ti 5 Cu 20 Al 10 Ni 8 bulk metallic glass

The first stages of thermal relaxation towards equilibrium in a Zr 57 Ti 5 Cu 20 Al 10 Ni 8 bulk metallic glass have been studied by differential scanning calorimetry, X-ray diffraction, transmission electron microscopy and high-resolution electron microscopy. These coupled experiments rule out for this glass the existence of a phase separation on the nanometric scale preceding the onset of crystallization. The first step of crystallization is of the primary type, that is it consists of the nucleation of nanocrystallites in the amorphous matrix with which they coexist in metastable equilibrium. The very high nucleation rate leads to a nanometric composite structure with a number density of about 7 2 10 24 m -3 of 3-4nm crystallites, occupying a volume fraction of about 15%. These features, as well as the crystallization kinetics observed during isochronal or isothermal heating, are discussed.     

Evolution of grain-boundary character distribution during iterative processing of an austenitic stainless steel

The present article deals with the analysis of grain-boundary character distribution (GBCD) and microstructural characteristics after iterative processing of austenitic stainless steel, AISI 316L. The steel was subjected to iterative cold reduction and subsequent annealings. After an initial decrease in the fraction of Σ3 boundaries, the number of these increases in subsequent steps. The results relate the importance of iterative processing and the mechanism of obtaining a higher fraction of Σ3 boundaries.     

Microstructure and mechanical behavior of nanostructured composite Cu60Fe40 alloy

In this study, bulk nanostructured composite Cu₆₀Fe₄₀ alloy is prepared by a combustion synthesis technique. The prepared Cu₆₀Fe₄₀ alloy consists of Cu(Fe) solid solution and Fe(Cu) solid solution phases. The large-scaled compositional segregation in the Cu-rich and Fe-rich phases is not observed, respectively. A few micron-sized dendrite (Fe(Cu) solid solution) is embedded into the nanostructured matrix (Cu(Fe) solid solution). The grain size of the matrix is in the range 50–300?nm. The yield and fracture strength of the Cu₆₀Fe₄₀ alloy are 540 and 1050?MPa, respectively, and the fracture strain obtained from the compression test is about 20.9%. The Cu₆₀Fe₄₀ alloy displays notable work hardening in the compressive deformation.     

Comparative evaluation of two superior stopping rules for hierarchical cluster analysis

A split-sample replication stopping rule for hierarchical cluster analysis is compared with the internal criterion previously found superior by Milligan and Cooper (1985) in their comparison of 30 different procedures. The number and extent of overlap of the latent population distributions was systematically varied in the present evaluation of stopping-rule validity. Equal and unequal population base rates were also considered. Both stopping rules correctly identified the actual number of populations when there was essentially no overlap and clusters occupied visually distinct regions of the measurement space. The replication criterion, which is evaluated by clustering of cluster means from preliminary analyses that are accomplished on random partitions of an original data set, was superior as the degree of overlap in population distributions increased. Neither method performed adequately when overlap obliterated visually discernible density nodes.This research was supported in part by NIMH grant 5R01 MH 32457 14.     

AC loss density component in electrical steel sheets

This article proposes a new approach to the loss separation issue. The conventional loss separation into three components is abandoned. The dependence of the dynamic component of loss density versus frequency is assumed to be a power law. The model is verified for selected samples of nonoriented and grain-oriented steel.     

Dimensions of Filipino Negative Social Emotions

The interpretation of emotions as cultural categories is possible by investigating emotional experience within the social situations which were expected to produce them. This is afforded by a componential framework of analysis. In this study, 15 Filipino social negative emotion words are clustered and subjected to a componential analysis in focus group discussions. The emotion components that were used to differentiate each cluster were appraisal processes, focal events, emotion regulation, action tendencies and relationships with the other. Three emotion clusters were identified varying in terms of degree of intensity. The highest intensity was associated with emotions that invoke a moral dimension to the actions of the other. The other two clusters are lesser in intensity and involve putting responsibility on the self for experiencing the emotions. The emotions in all clusters are associated with varying forms of changes in the relationships with the other.     

筛选性决策和选择性决策的信息利用

在构像理论中,用来证明决策分为筛选和选择两个独立阶段的证据存在于：筛选阶段的信息在选择阶段不再被使用。本研究以构像理论为基础,设计实验室模拟实验,以实验情境中越来越苛刻的限制条件,迫使决策者在选择决策阶段不利用筛选信息,以此来检验决策者在选择决策阶段是否利用筛选信息,以及利用的程度和条件。实验情境的设计遵循这样一个原则：从信息最容易获得,记忆负荷最小的决策情境,过渡到信息最难以获得,记忆负荷最大的决策情境。研究得到以下结论：（1）筛选信息在大部分决策者进行选择性决策的时候得到了利用,用以选择最终的备择项;（2）随着选择决策过程中对于筛选信息的记忆负荷,以及认知负荷的增加,筛选信息在选择阶段被利用的可能性有所减少。     

Formation of omega and Ti2Ni phases in a residual Ti–Ni–Ti multilayer between stainless steel and zirconia after bonding at 1173 K

Stainless steel (316L) and 8 mol pct Y₂O₃-stabilized zirconia (8Y-ZrO₂) were bonded using a Ti–Ni–Ti multilayer at 1173 K (900 °C) for 1 h. Cross-sectional transmission electron microscopy specimens were prepared by an innovative focused ion beam plus lift-out technique. In addition to acicular α-Ti, the dissolution of Fe, Cr, and Ni diffusing outwards from 316L into β-Ti led to the precipitation of the omega (ω) phase with different variants in the residual Ti foil between 316L and Ni. The ω-phase was not found in the residual Ti foil between Ni and 8Y-ZrO₂, while Ti₂Ni precipitates were precipitated in some α-Ti grains owing to the exclusion of Ni from the β-Ti.     

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.     

Amorphization under fracture surface in hydrogen-charged and low- temperature tensile-tested austenitic stainless steel

ABSTRACT

The microstructure just below the fracture surface in hydrogen-charged stable austenitic SUS 316L stainless steel, which was subjected to a low strain rate tensile test at ?70°C, was studied by a combination of the focused-ion-beam method and transmission electron microscopy. An amorphous region with a chemical composition almost identical to that of the polycrystalline region was found under the lath-like structure on the fracture surface, although no deterioration of tensile properties by hydrogen appeared. In the amorphous region, band-like regions with wavy contrasts were observed, which were often accompanied by cracks at the boundaries. The presence of the amorphous region with band-like regions implies that amorphization occurred due to high-density vacancies accompanied by agglomerations of excess vacancies in the hydrogen-charged SUS 316L stainless steel that was tensile-tested at low temperatures.     

Electropulsing-induced strengthening of steel at high temperature

Electropulsing usually promotes a metastable phase to evolve towards its equilibrium state. This work reports an alternative case, where electropulsing promotes the decomposition of the stable δ-phase in duplex stainless steel at high temperature. This decomposition enables both the γ-phase and the σ-phase in the steel to survive and hence to strengthen it at high temperature. The hardness of the quenched sample with electropulsing treatment is 49.4% higher than that without electropulsing treatment. A fundamental understanding of the observation is developed.     

Accumulation of geometrically necessary dislocations near grain boundaries in deformed copper

Cross-correlation-based analysis of electron backscatter diffraction patterns has been used to map the distribution of geometrically necessary dislocation (GND) density in deformed polycrystalline copper. Patterning of the dislocations into high-density cell walls and low-density cell interiors was readily observed at the micron scale. Patterning at the longer length scale of the grain size was also evident with high-density regions (GND hot spots) tending to be in clusters, often found close to some but not all grain boundaries and triple junctions.     

Attainment of an exceptionally high strength in low-carbon steel along with modest ductility through a novel heat treatment route

ABSTRACT

Over the last few decades, the use of steel (the most significant structural engineering material) is facing a significant challenge due to its replacement by other materials (such as composites) possessing higher strength-to-weight ratio/specific strength. This necessitates further enhancement in the strength of steel. In particular, low-carbon steel, in the annealed condition, suffers from inherent problems of poor strength and discontinuous yielding. In this research work a novel heat treatment route of incomplete austenitisation-based cyclic ice-brine quenching has been adopted on low-carbon steel (AISI 1010 steel containing 0.1 wt.% C) without considering any costly alloying or thermo-mechanical treatment. Accordingly, exceptionally high strength (UTS?=?1.7?GPa) and specific strength (226?MPa?g^?1cm³) are achieved after three cycles along with a modest ductility (% Elongation?=?9). This is the highest strength reported so far for low-carbon steel containing 0.1 wt.% C. Yield point phenomenon is also eliminated. This is attributed to a novel microstructure consisting of highly sub-structured fine plate martensite crystals containing internal twin and dislocation tangles along with dispersion of nano-sized cementite particles and clusters of cementite particles.     

Associations Between Time Since Event and Posttraumatic Growth Among Military Veterans

Despite efforts to understand the antecedents, correlates, and consequences of posttraumatic growth (PTG), the role of time since a traumatic event (time since event) vis-à-vis PTG is not well understood. Part of a larger project exploring experiences following emotionally distressing events among military veterans (N = 197) using Amazon’s Mechanical Turk (Mturk), in the current study, we sought to clarify associations between the time since event and PTG. We used cluster-analytic techniques and analyses of variance to (a) determine the number of clusters, and (b) assess differences in core constructs of PTG and participant characteristics across clusters. Results revealed 4 significantly different groups (i.e., clusters) characterized by differential associations between PTG and time since event. These groups also differed significantly in challenge to core beliefs, level of PTSD symptoms, intrusive and deliberate rumination, and age. The immediate moderate-growth group (Cluster 1) experienced moderate levels of PTG over shorter periods of time, severe PTSD symptoms, and was significantly younger. The low-growth group (Cluster 2) was characterized by minimal PTG, regardless of time, the least challenge to core beliefs, and low amounts of intrusive and deliberate rumination. The long-term small-growth group (Cluster 3) was primarily characterized by small amounts of PTG over longer periods of time. The high-growth group (Cluster 4) was characterized by high PTG, regardless of time, greater challenge to core beliefs, the highest amount of deliberate rumination, and the highest number of PTSD symptoms. Findings underscore heterogeneity within military veterans’ experiences of PTG over time.     

Dynamic balance between grain refinement and grain growth during high-pressure torsion of Cu powders

High-pressure torsion (HPT) was applied to unmilled coarse-grained (CG) Cu powders with low initial dislocation density and cryomilled nanocrystalline (nc) Cu powders with high initial dislocation density, with identical processing parameters. HPT of unmilled CG Cu powders resulted in exceptional grain refinement and increase in dislocation density, whereas significant grain growth and decrease in dislocation density occurred during HPT of cryomilled nc Cu powders. Equilibrium structures were achieved under both conditions, with very similar stable grain sizes and dislocation densities, suggesting dynamic balances between deformation-induced grain refinement and grain growth, and between deformation-induced dislocation accumulation and dislocation annihilation. The equilibrium structures are governed by these two dynamic balances.