Dr Alessandro Mottura, School of Metallurgy & Materials, University of Birmingham

From Ni-based to Co-based superalloys: planar faults energies to order
When Nov 11, 2013
from 02:00 PM to 03:00 PM
Where LR8
Contact Name
Contact Phone 01865-283302
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In 2006, an intermetallic phase based on the L12 crystal structure was observed in the Co-Al-W ternary system. This new intermetallic phase (γʹ), together with the high-temperature phase of pure Co (γ), can form the typical γ/γʹ microstructure observed in single-crystal Ni-based superalloys. Thanks to higher melting temperatures, this new class of γʹ-strengthened Co-based superalloys may become suitable substitutes for conventional Ni-based superalloys in the hottest sections of gas turbines and jet engines. Initial investigations of their creep properties revealed a pronounced anomalous yield strength at high temperatures, and examination of dislocation structures within the γʹ precipitates indicates dramatic differences when compared to their Ni-based relatives. This can, in part, be attributed to the various planar fault energies in the γʹ phase. The possible presence of a continuous γʹ phase field stretching from the Ni- to the Co-based systems may lead to new hybrid alloys with diverse properties. In this work, ab initio methods coupled with the axial next-nearest-neighbour Ising model and special quasi-random structures are used to study the effect of wider chemical changes on the relevant planar fault energies, with the objective of exploring the possibility of hybrid Ni-Co-based superalloys.