Analysis of the Alloying System in Ni-Base Superalloys Based on &lt;i&gt;Ab Initio&lt;/i&gt; Study of Impurity Segregation to Ni Grain Boundary

Vsevolod I Razumovskiy,Igor M Razumovskii,Andrei V Ruban,A.Y Lozovoi

doi:10.4028/www.scientific.net/amr.278.192

Analysis of the Alloying System in Ni-Base Superalloys Based on <i>Ab Initio</i> Study of Impurity Segregation to Ni Grain Boundary

Vsevolod I Razumovskiy, Igor M Razumovskii + Show 2 more

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https://doi.org/10.4028/www.scientific.net/amr.278.192

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Abstract

A new approach to the design of Ni-based polycrystalline superalloys is proposed. It is based on a concept that under given structural conditions, the performance of superalloys is determined by the strength of interatomic bonding both in the bulk and at grain boundaries of material. We characterize the former by the cohesive energy of the bulk alloy, whereas for the latter we employ the work of separation of a representative high angle grain boundary. On the basis of our first principle calculations we suggest Hf and Zr as “minor alloying additions” to Ni-based alloys. Re, on the other hand, appears to be of little importance in polycrystalline alloys.

Highlights

Ni-base superalloys (NBS) are key materials for the manufacturing of aerospace engines
Taking into account the well known thermodynamic similarity between open and internal interfaces in metals, we sought for the strengthening elements for polycrystalline NBS among transition metals that segregate to the surface above all
The main purpose of our study is to evaluate the segregation energies of some typical alloying elements (W, Ta, Re, Hf, Zr, B) and other impurities (S, Bi) to some representative grain boundaries (GBs) and the respective free surface using first principles calculations

Summary

Introduction

Ni-base superalloys (NBS) are key materials for the manufacturing of aerospace engines. The main purpose of our study is to evaluate the segregation energies of some typical alloying elements (W, Ta, Re, Hf, Zr, B) and other impurities (S, Bi) to some representative GB and the respective free surface using first principles calculations These are combined with (somewhat improved) previous calculations of the partial cohesive energies [1,2] which determine the contribution of each element into the bonding strength in the bulk, to arrive at some suggestion on impurities suitable for microalloying in NBS. The Σ5 (210)[100] tilted symmetric grain boundary was selected as a representative high angle grain boundary in NBS as its energy falls in the midrange of special GBs in pure Ni [9] Equilibrium structure of this boundary used in the present work (Fig. 1) coincides with the structure used in other studies

Calculated grain boundary energy γ

Es seg

Comparing respective

Segregation energies of impurity atoms to the free surface

Conclusion