Multi-scale modelling of high-temperature deformation mechanisms in Co-Al-W-based superalloys.

Since their discovery nearly ten years ago, Co-Al-W-based superalloys have emerged as the frontrunner materials to replace the ubiquitous Ni-based superalloys used in gas turbines. The study of deformation mechanisms in these alloys is of paramount importance for accelerating the identification of optimal alloy compositions, saving both time and money during the development process. The chemical ordering present in the γ' intermetallic phase precipitates, which grant the superalloys their superb high-temperature strength, gives rise to complex dislocation interactions. Dislocation configurations can feature a variety of possible planar fault structures, and their associated surface energies can play key role in defining the observed mechanical properties. In order to accurately model this complexity, we have calculated Gamma-surfaces for Co-Al-W superalloys using the Density Functional Theory, as implemented in CASTEP. Also known as Generalised Stacking Fault energies, these 2D energy surfaces describe the energy cost of associated with local atomic displacements at the dislocation core. The effect of composition on the Gamma-surface topography was also studied. These ab initio data were incorporated into a Phase Field Dislocation Dynamics model to investigate the meso-scale interactions of the dislocations with the microstructure of the alloys over a range of loading conditions. The phase field approach has also been extended to investigate the effects of solute atom segregation to the site of the stacking faults during high-temperature creep and the resulting influence on the deformation resistance.