Compositions of Gamma and Gamma Prime Phases in an As-Cast Nickel-Based Single Crystal Superalloy Turbine Blade

The core and the interdendritic regions of an as-cast nickel based single crystal turbine blade were observed by electron microscopy to understand the microstructural development during an investment casting process. The dendrite core region shows an irregular morphology of gamma prime in gamma due to a relatively short casting time, which prevented the development of gamma prime expected in a solution heat-treated microstructure. By comparison, the interdendritic region comprises three different regions composed of: several elongated gamma prime particles, relatively tiny and irregular gamma prime, and gamma prime with relatively regular morphology. The chemical analysis of these phases showed that, regardless of the analysis point in the core or the interdendritic region, almost the same compositions were acquired in the regular type of gamma and gamma prime phases. This result suggests that if the gamma prime forms in the gamma matrix, the composition of gamma prime is almost uniform regardless of the region and prevailing general chemical composition. In contrast, the composition of the elongated gamma prime in the interdendritic region was slightly different depending on the analysis point even within the same elongated particle

Precipitation of Topologically Closed Packed Phases during the Heat-Treatment of Rhenium Containing Single Crystal Ni-Based Superalloys

Continual development of nickel-based superalloys for single-crystal turbine applications has pushed their operating temperatures higher and higher, most notably through the addition of rhenium. However, this has left them susceptible to the precipitation of topologically closed packed phases (TCPs), which are widely considered detrimental. Whilst these have long been reported as an end-of-life phenomenon in in-service components, they have more recently been observed during the manufacture of turbine blades. Several rhenium-containing alloys (CMSX-4, CMSX-10K, and CMSX-10N) were cast into single-crystal test bars and studied at different times along their solution heat-treatment process to discern if, when, and where these TCPs precipitated. It was seen that all alloys were susceptible to TCPs at some point along the process, with the higher rhenium-containing alloy CMSX-10N being the most prone. They occurred at the earliest stages of the solution process; this was attributed to aluminium diffusion from the segregated interdendritic regions into the dendrite core, causing the concentration of rhenium into the ɣ-matrixes until sufficient potential was achieved for TCP precipitation. As the samples became more homogeneous, fewer TCPs were observed; however, in the case of CMSX-10N, this took longer than the typical 24-h solution time used in industry, leading to components entering service with TCPs still present.</p

The analysis of SATS results as a measure of pupil progress across educational transitions

Within any Educational System the transition of pupils from one stage to the next, and often the associated transition from one educational establishment to another, is an area of interest for educational establishments, educationalists and educational authorities due to the effects of this movement on pupil progress, their academic achievement and performance measures for schools. The National Curriculum Assessments (NCA) are used in England as a nationally administered examination to evaluate pupil progress and academic achievement at the transition from one Key Stage to another. Also within England different schools can have differently aged cohorts, for example Primary Schools cover ages 4 to 11 years whereas Infant Schools cover ages 4 to 7 years and Junior Schools 7 to 11 years. This investigation has examined the significance of type of primary school (i.e., all-age primary, 4 to 11 years, versus junior, 7 to 11 years) for achievement at age 11 years. Using national statistics, it was shown that junior and primary schools perform equivalently in terms of academic achievement at the end of the pupils’ time in the schools but primary schools seem to outperform junior schools in terms of the improvement in the pupils’ ability (value added) during their time in Key Stage 2. This work has shown that on average a junior school will have a lower value added score at Key Stage 2 to equivalently performing primary schools and that this difference, whilst small, is both statistically, and in terms of league table position, significant. Also, the data were compared to the much smaller group of schools which provide education from Key Stage 1 through to Key Stage 4 and beyond. These schools showed the same rate of progress (value added) through Key Stages 1 and 2 as the general population of schools but with lower points scores per student

The analysis of SATS results as a measure of pupil progress across educational transitions

Within any Educational System the transition of pupils from one stage to the next, and often the associated transition from one educational establishment to another, is an area of interest for educational establishments, educationalists and educational authorities due to the effects of this movement on pupil progress, their academic achievement and performance measures for schools. The National Curriculum Assessments (NCA) are used in England as a nationally administered examination to evaluate pupil progress and academic achievement at the transition from one Key Stage to another. Also within England different schools can have differently aged cohorts, for example Primary Schools cover ages 4 to 11 years whereas Infant Schools cover ages 4 to 7 years and Junior Schools 7 to 11 years. This investigation has examined the significance of type of primary school (i.e., all-age primary, 4 to 11 years, versus junior, 7 to 11 years) for achievement at age 11 years. Using national statistics, it was shown that junior and primary schools perform equivalently in terms of academic achievement at the end of the pupils’ time in the schools but primary schools seem to outperform junior schools in terms of the improvement in the pupils’ ability (value added) during their time in Key Stage 2. This work has shown that on average a junior school will have a lower value added score at Key Stage 2 to equivalently performing primary schools and that this difference, whilst small, is both statistically, and in terms of league table position, significant. Also, the data were compared to the much smaller group of schools which provide education from Key Stage 1 through to Key Stage 4 and beyond. These schools showed the same rate of progress (value added) through Key Stages 1 and 2 as the general population of schools but with lower points scores per student

Investment casting of Ti–46Al–8Nb–1B alloy using moulds with CaO-stabilized zirconia face coat at various mould pre-heat temperatures

AbstractCasting of titanium based alloys presents considerable problems including the extensive interactions that occur between the metal and refractory. An investigation was undertaken to develop a zirconia facecoat suitable to replace current zircon/silica facecoat used in investment casting titanium aluminide alloys. The stability of the zirconia slurry was assessed using pH, viscosity and plate weight, and the mould properties such as friability, strength and permeability were measured. The interaction between the zirconia face coat and a Ti–46Al–8Nb–1B alloy was studied by centrifugal investment casting at three mould pre-heating temperatures. Computer simulation of metal cooling profiles during casting was also carried out to assist the analysis. In this work, a stable zirconia slurry was developed, and the moulds produced using a zirconia facecoat have comparable mechanical properties and better permeability than those made of the traditional zircon/silica facecoat. The friability of the zirconia facecoat was much improved in comparison to that made of yttria face coat. During casting, metal non-fill defects were presented at a low preheat mould temperature of 500°C. The interaction products found between the metal and mould included a combined (Ti, Zr)5(Si, Al)3 and ZrAl2 phases, a re-precipitated ZrO2 phase, and a Al2O3 film at the interface. The interaction between mould and metal also caused a high hardness at the interface due to oxygen penetration, which varied with samples using different mould pre-heat temperatures. The suggestion has been made that the mould pre-heat temperature should be less than 1200°C

El aprendizaje del estudiante o la experiencia del estudiante: el cambio de la facultad tradicional a la no tradicional en la educación superior

Trends in higher education indicate transformations from teachers to facilitators, mentors, or coaches. New classroom management requires diverse teaching methods for a changing population. Non-traditional students require non-traditional faculty. Higher education operates similar to a traditional corporation, but competes for students, faculty, and funding to sustain daily operations and improve academic ranking among peers (Pak, 2013). This growing phenomenon suggests the need for faculty to transform the existing educational culture, ensuring the ability to attract and retain students. Transitions from student learning to the student experience and increasing student satisfaction scores are influencing facilitation in the classroom. On-line facilitation methods are transforming to include teamwork, interactive tutorials, media, and extending beyond group discussion. Faculty should be required to provide more facilitation, coaching, and mentoring with the shifting roles resulting in transitions from traditional faculty to faculty-coach and faculty mentor. The non-traditional adult student may require a more hands on guidance approach and may not be as self-directed as the adult learning theory proposes. This topic is important to individuals that support creation of new knowledge related to non-traditional adult learning models.Las tendencias en educación superior indican que los profesores se están transformando en mediadores, tutores o coaches. La nueva gestión del aula requiere diversos métodos de enseñanza para una población que está en constante cambio. Los estudian­tes no convencionales necesitan de profesores no tradicionales. La educación superior funciona de forma similar a una corpora­ción tradicional, pero compitiendo por los estudiantes, los profe­sores y la financiación para mantener su funcionamiento diario y mejorar en el ranking académico de universidades (Pak, 2013). Este fenómeno en aumento sugiere la necesidad de que la facul­tad transforme su cultura educativa, asegurándose la capacidad de atraer y retener a los estudiantes. Las transiciones del apren­dizaje del estudiante a la experiencia del estudiante y los índices de satisfacción creciente de los alumnos están influyendo en el proceso de facilitación de la clase. La facultad debería estar obli­gada a proporcionar más facilitación, coaching y asesoramiento con los cambios de roles que surgen en la transición de la facul­tad tradicional a la facultad coach y a la facultad mentora. El estu­diante adulto no convencional puede necesitar de más ayuda en el enfoque de la orientación y puede que no sea tan autodirigido como propone la teoría del aprendizaje de adultos. Este tema es importante para las personas que apoyan la creación de nuevos conocimientos relacionados con los modelos de aprendizaje para adultos no tradicionales