Influence of cryomilling on the microstructural features in HVOF-sprayed NiCrAlY bond coats for thermal barrier coatings: Creation of a homogeneous distribution of nanoscale dispersoids

Previous research has revealed that thermal barrier coatings with cryomilled bond coats exhibit improved thermal cycling lifetime by growing a continuous and uniform oxide layer at a slower rate; yet the mechanism controlling the ultimate failure remains unclear. In an effort to provide a foundation for understanding the improved behavior, the influence of cryomilling on the microstructure of the NiCrAlY bond coat material is investigated in this article. Rather than focusing on the alumina scale formation, the microstructural features and their evolution within the high-velocity oxy-fuel (HVOF)-sprayed NiCrAlY bond coats themselves, prepared from conventional powder and cryomilled powder, were carefully compared through extensive scanning electron microscope/energy-dispersive X-ray spectroscopy characterization. In addition, the as-cryomilled NiCrAlY powder is characterized to provide evidence of the direct influence of cryomilling and to exclude the impact from the HVOF spraying. It is found that the essential change in microstructural features resulting from the cryomilling is the creation of a homogeneous distribution of ultrafine (nanoscale) Al-rich oxide/nitride dispersoids, which remain thermally stable even after exposure at 1100°C for 100 h. The TEM study on the as-cryomilled powder, prior to the HVOF spraying, indicates that some Al and Y-rich oxides are already present within the material as a direct result of the cryomilling process.     

Enhancement of hardening and thermal resistance of Mg–Sn-based alloys by addition of Cu and Al

Mg–Sn-based alloys are considered as a promising precipitation-hardening system for applications at elevated temperatures, but the hardening effect is not satisfactory owing to sluggish nucleation and rapid coarsening of the major Mg₂Sn lath precipitates. In this study, Cu and Al are added to a Mg–6Sn–1Mn base alloy. The age-hardening response and the microstructures of these modified alloys have been investigated and are compared to that of the base alloy. The additional elements are found to bring several beneficial effects to the alloys for applications at elevated temperatures. Firstly, a eutectic structure consisting of strong intermetallic phases, i.e. Mg₂Cu in the Mg–6Sn–1Mn–2Cu alloy and Al_0.93Cu_1.07Mg in the Mg–6Sn–1Mn–2Cu–2Al alloy, remains stable along the grain boundaries after solution and ageing heat treatments. Secondly, the precipitate density has been increased significantly and the precipitate size has been refined remarkably during ageing at 200?°C. Moreover, the growth of the precipitates is inhibited remarkably during the over-ageing period. Therefore, the age-hardening response and over-ageing resistance are notably improved.     

Effects of irradiation with electrons of different energies on the dark conductivity and the network of hydrogenated amorphous silicon films

The effects of irradiation with electrons having energies in the range 0.7–1.7 MeV on the dark conductivity and the network of hydrogenated amorphous silicon (a-Si:H) thin films have been studied. The dark conductivity measurements show that electron irradiation leads to a degradation in the dark conductivity, with the degradation being greater at lower electron energies. The Raman results suggest that the irradiation induces structural defects in the a-Si:H films, with the lower energy electrons producing more disorder in the amorphous network.     

Electronegativity difference as a factor for evaluating the thermal stability of Al-rich metallic glasses

This article proposes a factor, the critical electronegativity difference Δx _cri, to correlate alloy composition with thermal stability and glass-forming ability of Al–Ni–RE (RE: Rare Earth element) ternary metallic glasses. The Al-rich metallic glasses with Δx > Δx _cri exhibit glassy behavior, whereas alloys with Δx < Δx _cri are nanocrystalline. Nanoglassy alloys occur when Δx ≈ Δx _cri. The best glass formers are located near Δx _cri. Furthermore, an equation has been deduced to calculate Δx _cri with varying RE covalent atomic radius.     

Efficient atomic packing clusters and glass formation in ternary Al-based metallic glasses

In this article, we propose an efficient atomic packing cluster-based composition protocol to help design Al-based metallic glasses. Its validity is verified by some typical experimental data from the literatures. Furthermore, with this understanding, the Al–Ni–Y alloy system is re-evaluated. As a result, the best glass former Al₈₆Ni₉Y₅ in this system, with the critical thickness of about 500 µm, is successfully fabricated by wedge casting.     

Solubility criterion for sequential disordering in metal-metal multilayers upon solid-state reaction

An n-body Ni-Ti potential is derived and applied in a molecular dynamics simulation to study the maximum supersaturated solubility of the terminal solid solutions and solid-state reaction in a Ni/Ti bilayer. It reveals that during interfacial reaction of the Ni/Ti bilayer the Ti lattice reaches its maximum solubility by dissolving Ni earlier than Ni does through dissolution of Ti, which results in a sequential disordering of first Ti and then Ni, although Ti has a higher melting point than Ni. In the Ni-Zr, Ni-Mo and Ni-Ta systems, however, the Ni lattice collapses more rapidly because it reaches a maximum solubility earlier than its partners, which have higher melting points than Ni. A solubility criterion is thus relevant for all the above cases; the lower the maximum solid solubility the less stable is the lattice of the metal upon solid-state reaction.     

Elastic solutions with arbitrary elastic inhomogeneity and anisotropy

An efficient numerical algorithm is proposed to accurately compute the elastic fields in two-dimensional (2D) or three-dimensional (3D) microstructures with arbitrary elastic inhomogeneity and anisotropy. It combines the equivalent inclusion method of Eshelby, the microelasticity theory of Khachaturyan, and the spectral iterative perturbation method of Hu and Chen. Its efficiency is compared with those of existing approaches in the literature. The method can be conveniently implemented in phase-field modeling of stress-dependent microstructure evolution and/or of mass/electrical transport.     

Desensibilización sistemática,inoculación de estrés y terapia inespecífica en el tratamiento de la ansiedad a las matemáticas

RESUMEN

Las autoras comienzan ofreciendo una panorámica general de las investigaciones sobre el síndrome de fobia a las matemáticas y la ansiedad ante los exámenes, explicando a continuación que el objetivo general de su estudio es desarrollar procedimientos de modificación de conducta que ayuden a estudiantes de Psicología, con una historia previa de conductas de evitación a los exámenes, a enfrentarse a las pruebas de psicología matemática. Más específicamente, se quiere comparar la eficacia de la Desensibilización Sistemática tradicional con un paquete cognitivo complejo desarrollada por ellas siguiendo el modelo de Inoculación de Estrés, y el valor de estas dos intervenciones específicas se compara, a su vez, con un grupo de terapia no orientado al problema. Tras describir el método y resultados, las autoras destacan en la discusión la eficacia de las tres intervenciones y el hecho de que se lograse afectar al rendimiento y no sólo a la ansiedad en matemáticas. Finalmente afirman que sus resultados apoyan la actualidad de la obra de Frank (1973, 1982), quien señala que una parte muy importante de los efectos psicoterapéuticos se debe a factores comunes a todas las terapias, en los que habitualmente no recae el peso explicativo.     

Estudio de las diferencias individuales en gastos atencionales,a partir de una tarea de papel y lápiz

Resumen

En este trabajo, que conjuga la tradición psicométrica con la perspectiva de procesamiento de información, se estudió si las diferencias en rendimiento observadas en los tests están asociados a diferencias individuales en gasto atencional. Fueron seleccionados 4 grupos extremos de sujetos en función de dos factores de inteligencia (verbal y espacial), los cuales realizaron una tarea de verificación de frases (tarea primaria) aisladamente o en conjunción con una de emparejamiento perceptivo (tarea secundaria). Se utilizaron como variables dependientes el número de aciertos de la tarea primaria, en ambas condiciones, y en la tarea secundaria, con tiempo limitado; y el número de errores en ambas tareas, sin límite de tiempo. Los sujetos altos verbales tuvieron más aciertos que los bajos verbales al ejecutar la tarea primaria en solitario, e iguales diferencias se encontraron entre altos y bajos espaciales; no se observaron diferencias en el número de errores. Al realizar ambas tareas concurrentemente, los altos verbales tienen mayor número de aciertos y cometen menos errores, en la tarea primaria, que los bajos verbales; los altos y bajos espaciales se diferencian únicamente en el número de aciertos. Estos resultados son discutidos y comparados con estudios diferenciales recientes.