OJSC “Kompozit”

A. G. Beresnev, Chief Executive Officer

A. V. Logachev, Head of a Division

I. M. Razumovskii, Chief Researcher, e-mail: razumovskii@yahoo.com

Department of Мaterials Science and Engineering, Royal Institute of Technology

V. I. Razumovskiy, Post Graduate Student

There is suggested a new approach to chose the alloying system of high-temperature nickel alloys with a polycrystalline structure. This approach is based on a concept, in which, the creep-resistance of hightemperature alloys is mainly determined by interatomic bonding in the bulk of γ-matrix and on the grain boundaries. The work of separation (W_sep) parameter is introduced as the fundamental characteristics of the mechanical durability of the boundary. This parameter is also introduced for finding the contribution of each alloying element in the grain boundaries' durability. The χ parameter is introduced for the estimation of the alloying elements on the bond strength of atoms in matrix. This parameter represents the partial molar energy of the matrix cohesy. On the basis of the results of the first principles' calculations, the value of the energy of grain boundary segregation of elements is analyzed: W_sep and χ parameters in the alloys of Ni – X system, where X is a typical alloying (W, Re, Ta, Zr, Hf, Nb) or microalloying (B) element or impurity (S, Bi) in high-temperature nickel alloys. The alloying elements, which have both large values of the parameter χ and the largest positive effect on the W_sep of Ni – Х alloys are classified as the “low alloying elements” and are found among the alloying elements under consideration. According to the researched approach, the “low alloying elements” are the elements with high tendency to obtain the grain boundary segregation. These elements also make the grain boundaries more durable and at the same time fixate the atom relations in the bulk of the matrix. A sum of low alloying elements (Σ = Zr + Hf + Nb + Ta) is introduced into the new high-temperature alloy, which is obtained by method of the granular metallurgy. The rest of the alloying elements have been chosen in order to fulfill a number of requirements for: a) lattice constants of γ- and γ’-phase (misfit); b) the γ’-phase solvus temperature; c) propensity to form the topologically close packed phases. The mechanical properties of the new alloy within the high temperatures exceed the mechanical properties of one of the best Russian alloys EP741NP (nickel high-temperature granulate alloy ЭП741НП).

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