169,882 research outputs found
Microstructural evolution of René N4 during high temperature creep and aging
No full textThe main scope of this work is to describe the microstructure evolution of single-crystal (SX) superalloy René N4 during creep and static aging at high temperatures, in function of time, stress and temperature. During creep at high temperatures, SX microstructure evolves from a dense and ordered distribution of cuboidal γ′ particles to a configuration characterized by alternate rafts of γ′ phase and γ matrix, through a process known as rafting. The microstructural evolution of superalloys is very important to derive models able to predict service conditions of a component through microstructural analysis. In this work two microstructural parameters were identified and analyzed for René N4: matrix channels width w along the [001] lattice direction and periodicity width λ, given by the sum of w and the width of the γ′ precipitates along [001]. Both parameters were measured on some creep-damaged and some statically aged specimens, as well as on the virgin material to analyze their trends in function of time, temperature and stress. In particular, the parameter Δλ looks independent of both the stress level and the microstructural morphology and could be used in future works to develop microstructural evolution model of René N4 in function of service time and temperature. Keywords: Single-crystal, Superalloy, Microstructure, René N
On the Effects of the Rejuvenation Treatment on Mechanical and Microstructural Properties of IN-738 Superalloy
No full textThe main scope of this paper is to show the effects of a specific rejuvenation treatment studied for IN-38 on both the microstructure and the mechanical properties of the creep-damaged superalloy and to compare the tests results with the virgin material and with the recovery obtained through the standard heat treatment. This work will show that this rejuvenation treatment is able to recover the microstructure of creep-damaged specimens and that the creep and tensile properties of the rejuvenated alloy are even better than the virgin material for the tests performed. Moreover, it will be shown that the standard heat treatment provided for IN-738 is not able to fully recover the microstructure and that the creep properties of the superalloy during the tests have been lower than the virgin material
Effects of Multiple Rejuvenation Cycles on Mechanical Properties and Microstructure of IN-738 Superalloy
No full textThe scope of this work is to show the effects of multiple applications of a rejuvenation treatment studied for IN-738 on both the microstructure and the mechanical properties of the creep-damaged superalloy and to check the recovery obtained after one and two rejuvenation cycles through creep and tensile tests, whose results will be compared with the performance of the virgin material. This work will show that this rejuvenation treatment is able to recover the microstructure of creep-damaged specimens after one and two applications and that the mechanical properties of the rejuvenated alloy are very similar to the virgin material even after two rejuvenation cycles
Hydrogen diffusion and segregation during solid phase epitaxial regrowth of preamorphized Si
No full textThe redistribution of hydrogen during solid phase epitaxial regrowth (SPER) of preamorphized silicon has been experimentally investigated, modeled, and simulated for different H concentrations and temperatures. H was introduced by H implantation and/or infiltration from the sample surface during partial thermal anneals in air in the 520-620 degrees C temperature range. We characterized the time evolution of the H redistribution by secondary ion mass spectrometry and time resolved reflectivity. The good agreement between all experimental data and the simulations by means of full rate equation numerical calculations allows the quantitative assessment of all the phenomena involved: in-diffusion from annealing atmosphere and the H effect on the SPER rate. We describe the temperature dependence of microscopic segregation of H at the amorphous/crystal (a-c) interface. Only a fraction of H atoms pushed by the a-c interface can be incorporated into the crystal bulk. We propose an energetic scheme of H redistribution in amorphous Si. The segregation of H at the a-c interface is also considered for (110) and (111) orientated substrates. Our description can also be applied to other material systems in which redistribution of impurities during a solid-solid phase transition occurs. (C) 2016 AIP Publishing LLC
Participatory action research in the age of social media: Literacies, affinity spaces and learning
No full textThis article summarizes the developments, methodological design, and some of the theories framed within a PhD research about the integration of social media in higher education. Its aims are to determine significant issues, challenges and opportunities that emerge when social media are integrated into learning environments in higher education. ‘Doing Online Relearning through Information Skills’ (DORIS) is proposed as a research framework to address the aims, objectives, and research questions of this study. It was conceived from a Participatory Action Research perspective. This approach is intended to help discover and reflect upon teaching and learning practices in a technologically mediated educational setting. Furthermore, the concept of affinity spaces is discussed, together with its distinction from the concept of communities of practice. The data collection methods planned to conduct the study are: diagnostic questionnaire, blog, social learners' input and reports, a second questionnaire, and semi-structured interviews. The theory of affinity spaces offers a powerful way of thinking about teaching and learning processes mediated by different technologies. The heuristics that will focus the data collection and analysis are: a) on the function of content, and b) on the function of participants’ interactions with the content and/or with one another. DORIS is proposed as a powerful way to organize learning interventions through the structure of information literacy skills. It is grounded on action research and on constructivist, blended, and problem based learning. Researchers, librarians or educators can adapt this model for teaching, learning and researching about and with social media or for other technologically mediated learning environments, or could be adapted for information literacy programs
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