Yu. A. Bondarenko

Effect of the method of producing Ni3Al-based alloy single crystals on the macro- and microhomogeneity of component distribution, structure, and properties

The mechanisms of hardening heterophase Ni3Al-based cast alloys, which are thermally stable natural eutectic composites, are studied in the operating temperature range. The distribution of basic and alloying elements and impurities in macrovolumes along the height of a charge billet prepared in a vacuum induction furnace is analyzed. The effect of the deviation of the axis of intermetallic alloy single crystals from the 〈111〉 orientation on their mechanical properties is considered. It is shown that the deviation from this orientation within 2.5°–5.4° does not affect the short-term strength characteristics and substantially affects the ductility characteristics of the single crystals. The effect of the method of introducing basic components and refractory reaction- and surface-active alloying elements in the alloys on the structure-phase state of Ni3Al-based alloys and their service life is investigated.

Structure, Chemical Composition, and Phase Composition of Intermetallic Alloy VKNA-1V After High-Temperature Heat Treatment and Process Heating

Single-crystal preforms from intermetallic alloy VKNA-IV with different crystallographic orientations (CGO) are studied. The mode of heat treatment is shown to affect the microstructure of the preforms, ultimate rupture strength, yield strength, and long-term strength (the time before failure). Process heatings used in soldering also affect these properties.

Structure and mechanical properties of a nonmagnetic high-nitrogen corrosion-resistant 05Kh22AG15N8M2F cast steel produced by high-gradient directional solidification

The structure and properties of an austenitic high-nitrogen corrosion-resistant 05Kh22AG15N8M2F cast steel produced by high-gradient directional solidification (HGDS) and equiaxed-grain solidification (ES) have been studied and compared. In contrast to ES, HGDS allows one to substantially decrease the degree of dendritic segregation of alloying elements, to eliminate porosity, and to increase the strength and plasticity of the steel.

Effect of directional solidification on the structure and properties of Ni3Al-based alloy single crystals alloyed with W, Mo, Cr, and REM

The effect of the solidification gradient (G = 60 and 150°C/cm) at a solidification rate R = 10 mm/min on the structural parameters and the short- and long-term strength characteristics of blade-type single-crystal workpieces made of a heterophase γ′ + γ VKNA-1V-type γ′(Ni3Al)-based alloy with low contents of refractory metals is studied. The single crystals have a cellular-dendritic structure: dendrites are heterophase and consist of thin discontinuous nickel-based γ solid solution layers between γ′(Ni3Al)-matrix regions. Primary γ′-phase precipitates are located in the interdendritic space. An increase in solidification gradient G from 60 to 150°C/cm (by a factor of 2.5) at a solidification rate R = 10 mm/min leads to a decrease in the dendrite arm spacing by ∼1.5 times, the size of primary γ′-phase precipitates by 2.5–3 times, and the refinement of γ′ regions between γ layers in dendrite arms and at the periphery of dendrites by 2–3 times. The strength characteristics of the single crystals grown at G = 150°C/cm are higher than those of the single crystals grown at G = 60°C/cm by 10%. An increase in gradient G weakly affects the long-term strength of the single crystals. During long-term high-temperature tests under loading, secondary disperse γsec′ particles precipitate in the discontinuous γ solid solution layers forming inclusions in two-phase γ′ + γ dendrites, and the morphology of the γ layers changes (they become thicker and shorter). The 〈111〉 VKNA-1V alloy single crystals grown at G = 150°C/cm and R = 10 mm/min have a set of the required properties, namely, a high high-temperature strength over the entire temperature range, moderate high-temperature plasticity, and the absence of the plasticity drop at 800°C (which is characteristic of single crystals with other crystallographic orientations). These properties make 〈111〉 VKNA-1V alloy single crystals promising for working and nozzle gas turbine engine blades, including the blades in “blisk” assembly units.

Properties of high-temperature alloys of the system Ni-Nb with a unidirectional eutectic structure

Conclusions1.The possibility of using alloys with a unidirectional eutectic structure from the Ni-Al-Nb system as high-temperature materials has been demonstrated. Alloys containing 21–23% Nb and 2.0–2.5% Al after directional crystallization under thermal gradient conditions of 70–80 deg/cm and a crystallization rate of 0.3–0.4 mm/min have a unidirectional (composite) structure consisting of alternating parallel plates of γ- and δ-phases.2.Time to failure for alloys of the Ni-Al-Nb system with a unidirectional structure in stress-rupture tests in a vacuum at 1100°C and a stress of σ=120 MPa is 14–24 h, and σf20=910–950 MPa.3.As an example of alloying with chromium it has been demonstrated that on making additions to eutectic alloys it is necessary to evaluate the tendency of the alloy towards orientated phase growth. Addition of 2–4% Cr to alloy with 23% Nb and 2–2.5% Al increases its time to failure to 69–81 h with the same test conditions.

Structural heat-resistant β-NiAl + γ′-Ni 3 Al alloys of the Ni–Al–Co system: I. Solidification and structure

When analyzing the ternary Ni–Al–M phase diagrams, where M is a group VI–VIII transition metal, we chose the Ni–Al–Co system, where the γ′ and γ phases are in equilibrium with the β phase, as a base for designing alloys with the following physicochemical properties: a moderate density (≤7.2 g/cm3) and satisfactory heat resistance at temperatures up to 1300°C. The structure formation in heterophase β + γ′ alloys during directional solidification is studied. It is found that, in contrast to cobalt-free β + γ′ alloys (where the γ′-Ni3Al aluminide forms according to the peritectic reaction L + β ⇄ γ′), the alloys with 8–10 at % Co studied in this work during directional solidification at 1370°C contain the degenerate eutectic L ⇄ β + γ. The transition from the β + γ field to the β + γ′ + γ field occurs in the temperature range 1323–1334°C, and the γ′ phase then forms according to the reaction β + γ ⇄ γ′.

In situ formation of the composite structure of a eutectic Nb–Si alloy during directional solidification in a liquid-metal coolant

The results of investigation of the structure of a heat-resistant eutectic niobium–silicon alloy, which was prepared by directional solidification using a liquid-metal coolant, are reported. The typical areas of the macrostructure of an ingot undergone directional solidification are considered, and the composition and the volume fractions of the Nb–Si composite have been determined.

Directional Solidification, Structure, and Mechanical Properties of a Eutectic Nb–Si Alloy with a Natural Composite Structure for GTE Blades

Directional solidification in a liquid-metal coolant and the formation of a natural composite structure in a eutectic niobium–silicon alloy are studied to produce GTE blades in ceramic molds. The microstructure and the phase composition of the alloy are analyzed in parts of variable sections. The shortand long-term strengths of the niobium–silicon composite material are measured at a temperature of 1200°C.

Formation of the Structure of a Eutectic Alloy of the Nb – Si System During Directed Crystallization with Liquid-Metal Coolant

Peculiarities of the structure of a refractory eutectic alloy of the Nb – Si system, formed by the method of directed crystallization with liquid-metal coolant, have been studied. Characteristic zones of microstructure of the ingot obtained upon directed crystallization are considered, the alloy composition is analyzed, and volume fractions of phases in the Nb – Si composite are determined.

Effect of high-gradient directional solidification on the structure and mechanical properties of high-strength VNS-72 and VKS-12 steels

The structure and mechanical properties of high-strength structural VKS-12 and corrosion-resistant VNS-72 steels have been studied after remelting in a vacuum induction furnace and high-gradient directional solidification (HGDS). The HGDS method is shown to give better results for both steels, since it provides a deformed structure having a very small grain size and high ductility and fracture-toughness characteristics at a high strength.