Papers by Author: Igor M. Razumovskii

Abstract: Effect of comprehensive alloying system (W, Ta, Nb, Mo, V, Hf, Ti, Zr, Ni) and impurity N on cohesive properties of the bulk and the special high-angle grain boundary (GB) Σ5 (210)[100] in Cr-base alloys, as well as segregation behavior of impurities at the GB and the (210) free surface are studied by first principles calculations. The analysis of the data obtained allows us to single out W, Ta as the best and nitrogen as the worst interatomic bond strengthening elements for both the bulk and GB in Cr-base alloys. To verify these theoretical results by means of experiment, we investigated an influence of W (up to 10 wt. %), and (Ta, Nb, Hf and Zr) on mechanical properties of Cr-base alloy. We observed an increasing of the strength properties due to W addition and increasing of the plasticity as a result of (Ta, Nb, Hf, Zr) adding.

Abstract: The effect of B, Si, P, Cr, Ni, Zr and Mg on cohesive properties of Al and the special grain boundary (GB) Σ5 (210)[100], as well as their segregation behavior at the GB and the (210) surface are studied by first principles method. The analysis of these parameters allows us to single out Ni as the best and phosphorus as the worst interatomic bond strengthening alloying elements.

Abstract: Typical defects of the cast engine blades from Ni base superalloys in the as-cast state and after long operation were investigated: the cast porosity, internal and external microcracs. The initial cast porosity and voids, which have appeared during long operation, reduce the fatigue and other service characteristics of the blades from Ni base superalloys. Hot isostatic pressing (HIP) reduces the size and number of micropores in the cast blades from Ni base superalloys with a polycrystalline (alloy GS6U) and single crystal (alloy GS32) structures. As a result, HIP improves the mechanical properties of the blades. Application of the HIP, together with the standard heat treatment in the renovation of the blades after long operation can provide a virtually complete restoration of their structure and efficiency.

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.

Abstract: The effect of γ’ particle size upon the mechanical properties of Ni base superalloy EP741NP obtained by powder metallurgy was investigated. The particle size of γ’ phase in γ-γ’ microstructure was varied by changing the cooling rate V from the temperature of the solid solution treatment at 1200 °C (V = 80, 200 and 400 °C \ min.). After solid solution treatment billets were subjected to aging in the standard mode. It was established that as V increases from 80 to 200 °C \ min., the average particle’s size of γ’ phase decreases from 0.54 microns to 0.22 microns in the aged state. This improves the characteristics of creep and low cycle fatigue at 650°C: time to rupture under load 1000 MPa increased from 132 hours to 416 hours and low cycle fatigue increased from 42,215 to 82,016 cycles.