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We do Density Functional Theory based total‐energy calculations of the normalL12 phase in Co3X and Ni3X compounds, X being a transition metal element. The lattice parameters, magnetic moments and formation enthalpies are determined and compared with the available experimental data. The (111) superlattice intrinsic stacking fault energy (SISF), a crucial factor affecting materials strength and their mechanical behavior, is calculated using the axial interaction model. We have applied the quasiharmonic Debye model in conjunction with first‐principles in order to establish the temperature dependence of the lattice parameters and the (111) SISF energies. We investigate our prediction of a low formation enthalpy in the system Ni −25 at.%Zn by doing auxiliary simulations for the fcc random alloy at the composition 25 at.%Zn. Our simulations indicate that the elements Ti, Zr, Hf, Nb, and Ta can help stabilizing the promising and extremely important Co3Al0.5W0.5 alloy.
CFD calculations were carried out on a number of frustum geometries from the experimental literature on freckling of superalloys. The effects of two imposed thermal fields were investigated, flat and inclined. Experiments document that when thermal fields are inclined the cold side is more prone to formation of freckles; our results conclude that rising liquid plumes in advance of the solidification front, which can correlate to freckles, are more abundant and intense on the cold side. Also, modelled plume activity is greater in inward sloping frustum geometries as opposed to outward sloping ones, which also agrees with established literature. Complex flow patterns were observed in inclined geometries and there is a clear interplay and competition between both the thermal and solutal aspects of flow, with flow being significantly changed, sometimes reversed in direction in some capacity. Our results also offer insight into the incubation length for plume and resultant freckle formation after the transition between frustums, with some critical distance of advance of the solidification front necessary to initiate and establish other plumes that feed into the main one circulating liquid flow which is locally intense enough to potentially create a freckle.
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Take down policyWhile the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive.
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