RU2804232C1 - High entropy heat-resistant alloy (embodiments) - Google Patents

Abstract

FIELD: alloy metallurgy.

SUBSTANCE: invention is related to high-entropy heat-resistant alloys operating under conditions of short-term exposure to high temperatures of 1200°C and which can be used for the manufacture of elements and structural parts of aircraft and rocket engines. The alloy contains components in the following ratio, at.%: aluminium 18.0, molybdenum 7.5, niobium 16.0, tantalum 7.77, titanium 15.3, zirconium 15.4, vanadium 15.0, silicon 5, 0, a rare earth metal selected from the group including lanthanum, cerium, yttrium and neodymium, or a mixture of rare earth metals selected from the group including lanthanum, cerium, yttrium and neodymium, 0.03, while in the case of a mixture, the content of each of the rare earth metals is more than 0.001.

EFFECT: alloy has a reduced density and increased strength characteristics at temperatures up to 1200°C.

2 cl, 1 tbl

Description

The invention relates to the field of alloy metallurgy, namely, to high-entropy heat-resistant alloys that operate under short-term exposure to high temperatures of 1200°C and which can be used for the manufacture of elements and structural parts of aircraft and rocket engines.

A heat-resistant alloy is known for the manufacture of parts of the hot zone of aircraft engines and heat-loaded elements of rockets, containing 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. In this case, the value of the configuration entropy of alloy formation corresponds to the following ratio:

Where

ΔSmix - configuration entropy, J/(mol⋅K),

R is the universal gas constant equal to 8.3 1 J/(mol⋅K),

Ci is the concentration of the i-th element, at. %,

(RU 2526657, С23С 30/00, published 08/27/2014)

A heat-resistant high-entropy alloy AlNbTiVZrx is known, containing titanium, niobium, vanadium, zirconium and aluminum in the following ratio of components, at. %; titanium 24-24.6, niobium 22.4-23.6, vanadium 21.9-22.8, zirconium 3.3-6.7, the rest is aluminum, with x taking values from 0.1 to 0, 25. The known alloy is operational at temperatures up to 800°C.

(RU 2631066, С22С 30/00, published 09/18/2017)

High-entropy alloys with a bcc structure are known: ZrAlNbTiMoV, ZrAl _0.5 NbTiMoV, ZrAl _0.5 NbTiMo _0.5 V, containing zirconium, aluminum, niobium, titanium, molybdenum and vanadium in amounts from 5 to 35 at. % each. In this case, the known alloy may contain silicon and yttrium Υ in an amount of 0.01-5 at. %, which, as elements with a small cross-sectional area for neutron absorption, are introduced into the alloy to strengthen the solid solution. Known alloys are designed to operate at temperatures up to 1000°C under conditions of exposure to neutron irradiation.

(US 2016326616 (A1), B22F 3/105; B22F 3/15; С22С 1/02; С22С 1/04; С22С 14/00; С22С 16/00; С22С 21/00; С22С 27/02; С22С 27/ 04; С22С 27/06; С22С 30/00; G21C 1/02; G21C 11/08, published 11/10/2016)

The mechanical properties of known heat-resistant alloys at high temperatures are insufficient for their use for the manufacture of products operable at temperatures up to 1200°C.

The closest technical solution is a high-entropy alloy with a bcc structure AlMo _0.5 NbTa _0.5 TiZr, containing aluminum, molybdenum, niobium, tantalum, titanium and zirconium with the following ratio of components at. %: aluminum 20.4, molybdenum 10.5, niobium 22.4, tantalum 10.1, titanium 17.8, zirconium 18.8. The density of the known alloy is 7.4 g/cm ³ .

The well-known alloy ΑlΜο _0.5 ΝbΤa _0.5 TiΖr has the following mechanical properties

O.N. Senkov, S.V. Senkova, S. Woodward. Effect of aluminum on the microstructure and properties of two refractory high-entropy alloy. / Acta Materialia. 2014, V, 68, p. 214-228.

The known alloy has high strength characteristics at high temperatures, but also a fairly high density and insufficiently high corrosion resistance, which limits its use for the manufacture of elements and structural parts of aircraft and rocket engines.

The objective and technical result of the invention is to create a high-entropy heat-resistant alloy with reduced density and increased strength characteristics at temperatures up to 1200°C.

The technical result is achieved by the fact that the high-entropy heat-resistant alloy contains aluminum, molybdenum, niobium, tantalum, titanium and zirconium, while it additionally contains vanadium, silicon, and a rare earth metal selected from the group: lanthanum, cerium, yttrium, neodymium; with the following ratio of components, at. %:

aluminum 18.0 molybdenum 7.5 niobium 16.0 tantalum 7.77 titanium 15.3 zirconium 15.4 vanadium 15.0 silicon 5.0 rare earth metal 0.03

The technical result is also achieved by the fact that the alloy contains a mixture of rare earth metals selected from the group: lanthanum, cerium, yttrium, neodymium; in an amount of more than 0.001 wt. % of each, and their total content in the mixture is 0.03 wt. %

Aluminum, silicon and titanium provide a decrease in density and improved ductility, and molybdenum in the amount of 7.5 at. %, tantalum in the amount of 7.77 at. %. as well as niobium and zirconium provide increased strength characteristics of the alloy at elevated temperatures.

Although Al is an fcc metal, it has high solubility in many bcc metals and can stabilize the disordered structure with space group Im-3m. Aluminum in a concentration of 18 at. % also promotes the formation of a protective oxide film, which improves the alloy's resistance to high-temperature oxidation and corrosion.

Titanium in a concentration of 15.3 at. %, zirconium in a concentration of 15.4 at. %, as well as niobium (16.0 at.%), have complete solubility in each other. At the stated concentrations, zirconium, titanium and niobium exist in the bcc phase at high temperatures (up to 1600°C) and in the entire solid-state range (up to 2000°C), respectively. This combination of elements shows strong ordering tendencies in the presence of aluminum, and also shows separation tendencies due to positive interaction parameters between zirconium and niobium and between titanium and niobium. The presence of aluminum, as well as zirconium, and titanium in the alloy also contributes to the formation of not only bcc-type phases, but also a large amount of Ti ₃ Al intermetallic compounds enriched in Mo, Nb, Ta and Al ₂ Zr ₃ . Since the high-temperature bcc phase is characteristic of these elements and their alloys, the probability of the formation of a single phase with high entropy is very high.

Increased strength at high temperatures is also associated with the presence of silicon in an amount of 5 at. % due to the formation of silicide. Silicon has a beneficial effect on the heat resistance of the alloy. When combined with aluminum, it forms a denser protective oxide film, which improves resistance to high temperature oxidation and significantly increases corrosion resistance.

Vanadium in the amount of 15.0 at. % in combination with titanium and niobium create the basis of a high-entropy alloy. These elements have close atomic radii and slight differences in electronegativity, which creates the prerequisites for creating an alloy with a solid solution structure. The introduction of these components in equal shares or shares close to equal is justified by the need to obtain sufficient configuration entropy.

Vanadium is responsible for the refractory and strength characteristics of the material and at the selected content of 15.0 at. % has a positive effect on the heat resistance of the alloy.

Alloying with molybdenum in the amount of 7.5 at. % provides the alloy with increased corrosion resistance and a high level of strength due to hardening; solid solution, and the viscoplastic properties of steel also increase. A higher molybdenum content is not economically feasible. Alloying with molybdenum, along with increasing heat resistance, also increases ductility during short-term and long-term tests.

Addition of rare earth metals REM lanthanum, cerium, yttrium and neodymium in an amount of 0.03 at. % leads to an increase in the distortion of the matrix alloy lattice and its strengthening due to grain refinement in the presence of rare earth metals.

REM exhibit their positive strengthening properties in amounts greater than 0.001 wt. % of each and their total content in the mixture is 0.03 at. %.

The compositions of the alloy according to the invention AlSiMoNbTaTiZrREM meet all of the above criteria established for assessing whether a given combination of elements can form HEAs, and are disordered single-phase solid solutions with a bcc-type structure.

The invention can be illustrated by the following example.

The alloys according to the invention, AlSiMoNbTaTiZrREM, were produced by plasma-arc melting.

Clean, charge materials were placed in the crystallizer in such a way that the most refractory components were located directly in the area of influence of the plasma jet.

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

As a result, ingots weighing 0.5 kg were obtained. The ingots had a shiny surface. Chemical analysis of the ingots showed their homogeneity in the main elements and the correspondence of the resulting chemical composition to the specified composition.

The ingots were cut using waterjet cutting and demonstrated fairly good machinability. No significant macroscopic structural defects were identified.

Alloy samples were subjected to hot deformation by free forging at temperatures of 1200-1300°C. The alloys demonstrated ductility that is quite good for heat-resistant materials. However, the behavior of the alloy indicates that the optimal deformation temperatures are higher, and the optimal processing method may be pressing or extrusion.

Samples for structural studies and testing were obtained from ingots and deformed billets. The workpieces were cut using a waterjet or electroerosive method, subjected to cutting processing (turning, planing, milling) and then polished. The alloys demonstrated satisfactory machinability with carbide tools.

Alloy samples in the cast and hot-deformed state were subjected to structural studies, mechanical properties tests, and heat resistance tests.

Calculation of the density of the TiSiVNbAlTaMoZrY alloy

Density of titanium - 4.505 g/ ^cm3 , vanadium - 6.11 g/ ^cm3 , silicon - 2.33 g/ ^cm3 , niobium - 8.57 g/ ^cm3 , aluminum - 2.7 g/ ^cm3 , zirconium - 6.51 g/cm ³ , yttrium - 4.47 g/cm ³ , tantalum - 16.65 g/cm ³ , molybdenum - 10.22 g/cm ³ , cerium - 6.40 g/cm ³ , lanthanum - 6.7 g/cm ³ , neodymium - 6.90 g/cm ³ .

Alloy Density: 15.3x3.505+5.0x2.33+15.0x6.11+16.0x8.57+18.0x2.7+7.77x15.65+7.5x10.22+15.4x6.51 +0.03x4.47=6.55 g/ ^cm3 .

The density of the TiSiVNbAlTaMoZrY alloy was 6.55±10% g/cm ³ .

The resulting alloys have hardness up to 620HV and mechanical properties under compression: at room temperature σ _0.2 to 2100 MPa, at 800°C, σ _0.2 to 1600 ΜPa; at 1000°C, σ _0.2 to 750 MPa; at 1200°C, σ _0.2 to 250 MPa.

The test results showed that the alloys according to the invention have an advantage in density while maintaining high strength compared to the known alloy. The alloy according to the invention has a finer grain, which is ensured by the selected ratio of components. The corrosion resistance of the invention is also superior to that of the known alloy. The alloy has increased resistance to high-temperature oxidation.

Claims (5)

1. A high-entropy heat-resistant alloy containing aluminum, molybdenum, niobium, tantalum, titanium and zirconium, characterized in that it additionally contains vanadium, silicon and a rare earth metal selected from the group including lanthanum, cerium, yttrium and neodymium, with the following ratio of components , at.%: aluminum 18.0 molybdenum 7.5 niobium 16.0 tantalum 7.77 titanium 15.3 zirconium 15.4 vanadium 15.0 silicon 5.0 rare earth metal 0.03 2. A high-entropy heat-resistant alloy containing aluminum, molybdenum, niobium, tantalum, titanium and zirconium, characterized in that it additionally contains vanadium, silicon and a mixture of rare earth metals selected from the group including lanthanum, cerium, yttrium and neodymium, in the following ratio components, at.%: aluminum 18.0 molybdenum 7.5 niobium 16.0 tantalum 7.77 titanium 15.3 zirconium 15.4 vanadium 15.0 silicon 5.0 a mixture of rare earth metals of 0.03, with the content of each of the rare earth metals being more than 0.001.