Ab initio Calculations of Elastic Constants of Superalloys

• Using the-state-of-the-art ab initio method we have studied elastic constants of alloys potentially interesting for high temperature applications. We have shown that Cr substitutes the Al sublattice in B2 NiAl at concentration up to 40 at. %, but at higher Cr content it prefers the Ni-sublattice. Alloying of NiAl with Cr yields reduced strength but improves the ductility of the alloys. Alloying of NiAl with W which substitutes the Al sublattice, leads to a strong decrease of the shear modulus, and near 50 at.% of W the alloy becomes mechanically unstable as elastic constant C is negative. This is in agreement with our phonon calculations where we found soft modes along the [110] direction for B2 NiW. According to our calculations in (Ru,Ni)Al alloys the shear modulus is almost constant up to 40 at.% of Ni, at higher Ni concentrations it is drastically reduced. We have shown that the changes in elastic properties of (Ru-X)Al alloys are due to electronic topological transitions.

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