RU2526657C1 - Refractory alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: refractory alloy contains the following element in wt %: titanium 20-35, vanadium 20-35, niobium 20-35, aluminium 5-15, tantalum 2-10, zirconium 1-15. Magnitude of the alloy formation configuration entropy corresponds to the following ratio: ΔS_mix=R∑Ci·lnC_i≥11.2, where ΔS_mix is configuration entropy, J/(mole·K), R is universal gas constant equal to 8.31 J/(mole·K), C_i is concentration of i^th element, at. %.

EFFECT: better manufacturability, higher plasticity, low density, higher strength.

4 cl, 2 tbl

Description

The invention relates to the field of metallurgy and can be used for the manufacture of parts of the hot zone of aircraft engines, heat-loaded elements of rockets and for the production of parts of special equipment.

Modern heat-resistant materials do not always meet the requirements of developers and designers. A particularly tense situation has developed in the development of materials with a low specific gravity, which are represented by heat-resistant titanium alloys (operating temperature up to 600-700 ° C) and materials based on titanium aluminide (-900 ° C). Therefore, the search for new heat-resistant materials becomes relevant.

Alloys and composite materials based on intermetallic compounds, primarily titanium and nickel aluminides, are one of the promising heat-resistant materials. They have high heat resistance and oxidation resistance, but they have significant disadvantages, such as low mechanical properties at low temperatures, limited heat resistance for titanium aluminide and a sufficiently high specific gravity for nickel aluminide, low processability.

The most promising in this direction are highly entropic alloys (WES), which are multicomponent (n≥4) alloys, the main components of which are introduced in equal shares or close to equal shares. The structure and properties of wind farms are largely determined by high configurational entropy, which, by reducing the Gibbs energy for solid solutions, stabilizes them. The combination of an ultra-high alloyed solid solution, a nanostructured state, and precipitates of strengthening phases (most often multicomponent intermetallic compounds) determines a high complex of properties. Wind farms have high mechanical characteristics, heat resistance, high corrosion resistance and oxidation resistance.

Heat-resistant alloys with high configurational entropy are known, containing niobium, titanium, vanadium and zirconium and are characterized by low density (~ 6.5-6.7 g / cm ³ ), high microhardness (up to 4.0 GPa) and high oxidation resistance at high temperatures.

(See ON Senkov, SV Senkova, S. Woodward, DV Miracle. Low-density multi-principal element alloys of the Cr-Nb-Ti-V-Zr system: Microstructure and phase analysis // Acta Materialia. No. 61. - 2013. - P.1545-1557.)

The disadvantage of these materials is their low ductility during tensile tests and low technology, which limits their use as a structural material.

The closest in technical essence and the achieved result is an alloy of the NbTiVTaAl _x system containing 23.53 at.% Of titanium, vanadium, niobium and tantalum, as well as 5.88 at.% Aluminum with a density of 8.8 g / cm ³ .

(X. Yang, Y. Zhang, PK Liaw "Microstructure and Compressive Properties of NbTiVTaAl _x High Entropy Alloys" / Procedia Engineering. No. 36. - 2012. - P.292-298.)

The disadvantage of this alloy is its high density and high cost due to the excessively high content of tantalum, which limits its use as a structural material in aviation and rocket technology.

The objective and technical result of the invention is the creation of a high-tech and ductile (δ _o > 3%) heat-resistant alloy with low density and high strength characteristics.

The technical result is achieved in that the heat-resistant alloy contains titanium, vanadium, niobium, aluminum, tantalum and zirconium in the following ratio of components, at.%:

titanium 20-35 vanadium 20-35 niobium 20-35 aluminum 5-15 tantalum 2-10 zirconium 1-15

the value of the configurational entropy of alloy formation corresponds to the following relationship:

ΔS _mix = R∑Ci · lnC _i ≥11.2, where

ΔS _mix - configurational entropy, J / (mol · K),

R is the universal gas constant equal to 8.31 J / (mol · K),

C _i - the concentration of the i-th element, at.%,

n is the number of components in the alloy.

The technical result is also achieved in that the alloy contains niobium, titanium and vanadium in equal concentrations or concentrations, differ from the equal by no more than 25 at.%; aluminum in an amount not exceeding 0.5 of the content of one of the main components: niobium, titanium or vanadium, and the aluminum content exceeds the tantalum content by two or more times.

High configurational entropy of more than 11.2 J / (mol · K), along with the specified concentrations of the components, provides an alloy with a structure of a highly alloyed solid solution, and allows to increase the strength and heat resistance of the alloy with sufficient ductility.

Titanium, niobium and vanadium form the basis of a highly entropic alloy. These elements have close atomic radii and small differences in electronegativity, which creates the prerequisite for creating an alloy with a solid solution structure. The introduction of these components in equal or close to equal proportions is justified by the need to obtain sufficient configurational entropy with a relatively small number of components. When obtaining configuration entropy values of less than 11.2 J / (mol · K), the properties of the alloy do not reach the required values of strength characteristics at normal and elevated temperatures.

A slight increase in the content (but not more than 25 at.%) Of titanium and vanadium is possible in order to reduce the density of the alloy or to reduce the content of vanadium in order to improve heat resistance

The optimum aluminum content depends on the content of the main components and from the point of view of strength and ductility is in the range of 0.20-0.25 from the content of Ti, V, Nb. An additional introduction of aluminum reduces the density of the alloy and increases its heat resistance, however, the strength and ductility of the alloy decrease. Given these factors, the aluminum content is limited to half the content of the main components.

Tantalum is the most refractory element of the system and during crystallization plays the role of the “leading bcc metal”, since the crystallization of the alloy begins with the formation of a Ta-based solid solution. This determines high strength properties and sufficient ductility. The optimum tantalum content is about 0.2 atomic fractions of the content of the main components, however, the tantalum content is limited depending on the aluminum content to produce alloys with a density not exceeding 6.5 g / cm ³ .

The introduction of zirconium increases the hardness and strength of the alloy. However, when its content exceeds 15 at.%, Zirconium sharply reduces the strength, ductility, and manufacturability of the alloy.

The invention can be illustrated by the following example.

The alloy of the invention TiVNbZrAl _0.25 Ta _0.1 was made by plasma arc melting.

Pure charge materials were placed in the crystallizer so that the most refractory components were located directly in the area of the plasma jet.

Melting was carried out at a residual pressure of the order of 10 ^-2 Pa in an argon atmosphere. The liquid bath was maintained for at least 5 minutes at each re-melting. After the next remelting, the ingot was turned over and the next remelted. To ensure homogeneity, remelting was repeated 5-7 times.

As a result, ingots weighing 1.2-6 kg were obtained. The ingots had a shiny surface. Chemical analysis of the ingots showed their homogeneity in the basic elements and the correspondence of the chemical composition of the alloys to the specified one.

The ingots were cut by waterjet cutting, while demonstrating a fairly good machinability. No significant macroscopic structural defects were detected.

Samples of this alloy were subjected to hot deformation by free forging at temperatures of 1300-1100 ° C. The alloy showed good ductility for heat resistant materials. However, the behavior of the alloy indicates that the optimum deformation temperatures are higher, and pressing or extrusion may be the optimal processing method.

Samples for structural studies and tests were obtained from ingots and deformed billets. The blanks were cut by hydroabrasive or EDM, subjected to machining (turning, planing, milling) and then grinded. The alloy showed satisfactory machinability with carbide tools.

Samples of alloys in the cast and hot-deformed state were subjected to structural studies, tests of mechanical properties and tests for heat resistance.

Calculation of the configurational entropy of alloy formation was carried out according to the formula: ΔS _mix = R∑Ci · lnC _i ≥11.2, where

ΔS _mix - configurational entropy, J / (mol · K),

R is the universal gas constant equal to 8.31 J / (mol · K),

C _i - the concentration of the i-th element, at.%,

n is the number of components in the alloy.

The calculations showed that the configurational entropy for all obtained variants of the alloy according to the invention is more than 11.2 J / (mol · K), which indicates the production of an alloy with a structure of a highly alloyed solid solution with high strength and heat resistance with sufficient ductility.

; $${\sigma }_{в}^{700}=590-615МПа$$

; $${\sigma }_{в}^{1100}=100-120МПа$$

), пластичностью (δ²⁰⁺4-12%), высокой микротвердостью (более 4,5 ГПа) и высокой стойкостью к окислению при высоких температурах.From the data presented in the tables it follows that the heat-resistant alloy according to the invention is characterized by low density (~ 6.49 g / cm ³ ), high strength at low and high temperatures ( $${\sigma }_{\mathrm{at}}^{\mathrm{twenty}}=1067-1090MP\mathrm{but}$$

; $${\sigma }_{\mathrm{at}}^{700}=590-615MP\mathrm{but}$$

; $${\sigma }_{\mathrm{at}}^{1100}=\mathrm{one\; hundred}-120MP\mathrm{but}$$

), ductility (δ ²⁰⁺ 4-12%), high microhardness (more than 4.5 GPa) and high oxidation resistance at high temperatures.

Table 1 The chemical composition and density of the alloy according to the invention The content of elements,% at Ti Zr V Nb Al That Cr density, g / cm ³ Known Alloy TiVNbTaAl _0.25 * 23.53 23.53 23.53 5.88 23.53 - 8.78 TiZrVNbTa _0.1 Al _0.25 29.86 1.01 29.83 29.85 7.46 2.99 - 6.49 TiZr _0.25 VNbTa _0.1 Al _0.25 27.78 6.94 27.77 27.76 6.94 2.78 - 6.49 TiZr _0.5 VNbTa _0.1 Al _0.25 25.97 12,99 25.97 25.97 6.49 2.60 - 6.49

table 2 Characteristics of the alloys according to the invention Alloy / Test Type TiVNbAl _0.25 Ta _0.1 TiVNbZr _0.25 Al _0.25 Ta _0.1 TiVNbZr _0.5 Al _0.25 Ta _0.1 Density, g / cm ³ 6.49 6.49 6.49

), МПаTensile strength at room temperature ( $${\sigma }_{\mathrm{at}}^{\mathrm{twenty}}$$

), MPa 1067-1090 1120-1135 1156-1171 Tensile Strength at 700 ° C ( $${\sigma }_{\mathrm{at}}^{700}$$

), MPa 590-615 611-617 629-639 Tensile Strength at 1100 ° C ( $${\sigma }_{\mathrm{at}}^{1000}$$

), MPa 109-117 119-125 129-135 Relative elongation at room temperature (δ ²⁰ ),% 6-12 5-7 4-6 Long-term strength at 700 ° C ( $${\sigma }_{\mathrm{one\; hundred}}^{700}$$

), MPa no less than 300 * no less than 300 * no less than 300 * Endurance limit σ _-1 , based on N = 10 ⁷ cycles at 20 ° C, MPa no less than 150 * no less than 150 * not less than 150 Hardness at room temperature, GPa 3.9-4.2 4.2-4.3 4.4-4.5 * - confirmed values.

Claims (4)

1. Heat-resistant alloy containing titanium, vanadium, niobium, aluminum and tantalum, characterized in that it additionally contains zirconium in the following ratio of components, at.%:
titanium 20-35 vanadium 20-35 niobium 20-35 aluminum 5-15 tantalum 2-10 zirconium 1-15
the value of the configurational entropy of alloy formation corresponds to the following relationship:
ΔS _mix = R∑C _i · lnC _i ≥11.2, where
ΔS _mix - configurational entropy, J / (mol · K),
R is the universal gas constant equal to 8.31 J / (mol · K),
C _i - concentration of the i-th element, at.%. 2. The heat-resistant alloy according to claim 1, characterized in that it contains niobium, titanium and vanadium in equal concentrations or concentrations differing by no more than 25% from each other. 3. The heat-resistant alloy according to claim 1, characterized in that the concentration of aluminum in the alloy does not exceed 0.5 concentration of niobium, titanium or vanadium. 4. The heat-resistant alloy according to claim 1, characterized in that the concentration of aluminum exceeds the concentration of tantalum by two or more times.