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High resolution electron microscopy of superalloys
If you have a question about this talk, please contact Ms Helen Gardner.
Superalloys are Nickel based alloys containing substantial additions of up to 12 elements used at well over half the homologous melting temperature in the aerospace industry. High-resolution scanning transmission electron microscopy (HR STEM ) in a variety of instruments including the Titan microscope has been used to study the structure of dislocations and other precipitates in both single crystal alloys for blade applications and the discs which support their rotation. In single crystal High Pressure turbine blades the first rotating part after the combuster the single crystal blades are cooled by a complex system of cooling channels and the load is principally carried by the inner cores at temperatures of about 750ºC. Deformation in this temperature range is associated with extended dislocations cutting the coherent precipitates. The study has revealed the detailed structure of these dislocations as they shear and this has important implications for the mobility of the dislocations. Another observation was the segregation of alloying elements with high atomic mass to the stacking faults during shear. In a newly-introduced polycrystalline disc alloy Allvac718Plus, High resolution microscopy has enable us to identify the details structure of precipitates added to inhibit the growth of grains and improve the resistance to crack growth. These results reveal how and under what conditions these grains grow and assist in producing the optimum microstructures.
This talk is part of the Engineering Department Micromechanics Seminars series.
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