RU2471879C1 - Heatproof titanium alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention may be used in production of components of rocket engines operated at high loads and temperatures approximating to 800°C. Proposed titanium alloy contains the following components in wt %: aluminium 6.0-7.5, zirconium 3.0-5.0, tungsten 6.0-7.5, hafnium 2.5-4.0, tantalum 2.5-4.0, titanium making the rest.

EFFECT: decreased weight, higher reliability, durability and strength.

2 cl, 1 tbl

Description

The invention relates to the field of metallurgy of titanium alloys and can be used for the manufacture of parts of rocket engine assemblies operating under high loads at temperatures up to 800 ° C, including a long time.

When using alloys in these structures, the following mandatory requirements should be considered:

- alloys should have a fairly stable phase composition, eliminating the possibility of embrittlement during prolonged loading and provide high strength and creep resistance at operating temperatures;

- alloys must have high heat resistance, ensuring the exclusion of penetrating oxidation during long-term operation, at operating temperatures.

The prior art known deformed heat-resistant certified titanium alloy VT18U (Ilyin A.A., Kolachev B.A., Polkin I.S. Titanium alloys. Composition, structure, properties. Reference book. - M .: VILS-MATI, 2009. , p.66, 74 [1]) used in the aviation industry for blades, disks of engine compressors, having the following chemical composition, wt.%:

Aluminum 6.2-7.3; Molybdenum 0.4-1.0; Zirconium 3.5-4.5; Niobium 0.5-1.0; Silicon 0.05-0.2; Tin 2.0-3.0; Titanium rest

However, an α-phase-based alloy (pseudo α-alloy) is operational up to a temperature of 600 ° C and for a short time up to 650 ° C. A significant drawback of the alloy is its thermal instability during long-term operation; rather low processability during hot deformation due to a rather high aluminum content in combination with tin and low heat resistance: the alloy is intensively oxidized when heated above 600 ° C.

Known titanium alloy (patent RU 2405849 C1, C22C 14/00, 12/10/2010 [2]), having the following chemical composition, wt.%:

Aluminum 10.5-12.5; Niobium 38.0-42.0; Molybdenum 0.3-0.6; Zirconium 1.5-2.5; Silicon 0.1-0.25; Tungsten 0.5-1.0; Tantalum 0.7-1.5; Carbon 0.03-0.08; Titanium rest

Based on the presence of a large amount of aluminum in the alloy, it should be attributed to two-phase α + α ₂ (Ti ₃ Al) alloys with a small content of an additional β phase (due to the high content of β stabilizers Nb, Mo, Ta, W). This circumstance allows us to state that the alloy cannot be thermally stable in phase composition during oxidation at high temperatures and will be brittle. Another disadvantage of the alloy is the low technological ductility during hot deformation, which makes it possible to use the alloy only in the cast state or possibly in the form of granules with subsequent gas conditioning, which is economically disadvantageous. And, finally, the alloy is not sufficiently heat-resistant: it is intensively oxidized at temperatures above 700 ° C.

The closest analogue (prototype) is a heat-resistant titanium alloy (patent RU 2396366 C1, C22C 14/00, 08/10/2010, [3]) characterized by the following chemical composition, wt.%:

Aluminum 5.0-7.5; Zirconium 3.0-5.0; Tungsten 5.0-7.5; Hafnium 0.005-0.2; Titanium rest

The alloy was used in turbopump units of liquid rocket engines in the form of rotors operating for a short time at temperatures of 750-800 ° C. The disadvantages of this alloy are the inability to use it at a temperature of 800 ° C for a long time and significant oxidation at temperatures above 780 ° C.

The objective of the invention is the creation of high-tech high-temperature and heat-resistant titanium alloy, operating at temperatures up to 800 ° C under continuous loading.

The technical result is an improvement in the weight characteristics of the alloy, ensuring the reliability of titanium parts - products at temperatures up to 800 ° C for a long time, providing high strength and creep resistance in the absence of embrittlement during operation.

The problem is achieved in that the heat-resistant and heat-resistant titanium alloy containing aluminum, zirconium, tungsten, hafnium, titanium is additionally delegated by tantalum in the following ratio of components, wt.%:

Aluminum 6.0-7.5; Zirconium 3.0-5.0; Tungsten 6.0-7.5; Hafnium 2.5-4.0; Tantalum 2.5-4.0; Titanium rest

This increase in the hafnium content and the introduction of tantalum into the alloy makes it possible to increase the heat resistance of the alloy due to the fact that both of these elements are significantly more refractory than titanium and, therefore, have a higher level of interatomic bonds, which will reduce the diffusion mobility of atoms at high temperatures. At the same time, the indicated amounts of hafnium and tantalum should significantly increase the oxidation resistance of the titanium alloy at operating temperatures. For the same purpose, the lower limits of the content of aluminum and tungsten in the alloy were increased to 6.0 wt%.

It should also be noted that hafnium and tantalum, being a neutral hardener with respect to titanium and a β-isomorphic element, respectively, should stabilize the phase constancy of the alloy and thereby increase its technological plasticity both at room and at elevated temperatures, which is very important for titanium alloys high in aluminum.

Zirconium is an essential component of the titanium alloy of the present invention, and this titanium alloy contains in an amount of 3.0-5.0% by weight for the reason that when its content is less than 3.0% by weight, it is impossible to obtain a satisfactory effect of suppressing the absorption of hydrogen, and when its content is more than 5.0% by weight, such a characteristic as lightness (low density) may deteriorate.

According to the nomenclature and content of alloying elements, the proposed alloy should be classified as martensitic type pseudo α-alloys (a small amount (β-phase).

The alloy can be melted according to the technology generally accepted for serial titanium alloys using ligatures and pure alloying elements by the triple remelting method in vacuum arc furnaces, including skull furnaces.

For experimental verification of the claimed composition by triple remelting in a vacuum arc furnace, several alloy compositions were smelted in the form of ingots, from which ⌀16 mm rods were made by free forging, then annealed at 800 ° C for 1 hour, followed by cooling in air .

Samples were made from rods for mechanical tests at room and elevated temperatures, as well as for evaluating heat resistance on a derivatograph at the maximum temperature to which no metal oxidation was observed (by weight gain).

Table 1 presents the results of tensile tests, impact bending, long-term strength, creep and heat resistance of the developed composition, with different levels of alloying, including lower and higher than stated. For comparison, the properties of the prototype alloy are given.

From table 1 it follows that the heat-resistant and heat-resistant alloy of the proposed composition (3-5) significantly exceeds the known titanium alloy (prototype) in terms of strength and heat-resistant characteristics at room and elevated temperatures. The maximum heating temperature without oxidation is 860-920 ° C. At the same time, the alloy is distinguished by a sufficiently high ductility and toughness, which guarantees its successful operation in highly loaded structures.

In addition, based on the experience of using a similar phase composition and alloying level in titanium alloy designs, it can be concluded that the inventive titanium alloy can be welded, which puts it in a number of technological titanium alloys of wide application.

Alloy test results.

Table 1 No. p / p Alloy composition Test temperature 20 ° C 800 ° C Maximum heating temperature without oxidation, ° С σ _0.2 , MPa σ ⁱⁿ
MPa δ,
% ψ,
% KCU, J / cm ² σ _in , MPa σ ₂ , MPa σ ₂ , E <1% MPa σ ₁₀₀ , MPa σ ₁₀₀ , E <1% MPa one 2 3 four 5 6 7 8 9 10 eleven 12 13 one Prototype 1078-1226 1128-1324 6-16 11-36 25-31 343-412 176-216 137-187 - - 800-861 2 Ti, 5.5 Al, 2.5 Zr, 5.5 W, 2.4 Hf, 2.3 Ta 1105 1178 17 32 36 371 194 159 - - 845 3 Ti, 6.2 Al, 3.5 Zr, 6.1 W, 2.9 Hf, 2.8 Ta 1159 1260 16 32 32 399 234 184 198 157 861 four Ti, 6.5 Al, 4.2 Zr, 6.7 W, 3.5 Hf, 3.3 Ta 1180 1395 8.5 thirty 31 432 260 210 228 200 894 5 Ti, 7.1 Al, 4.8 Zr, 7.2 W, 3.8 Hf, 3.9 Ta 1252 1400 7.5 12 28 468 298 244 256 220 918 6 Ti, 7.7 Al, 5.5 Zr, 7.8 W, 4.5 Hf, 4.2 Ta 1347 1443 3.8 7 16 495 318 274 281 248 948

The table shows that the proposed alloy significantly exceeds the known titanium alloys in terms of strength and heat resistance at temperatures up to 800 ° C. At the same time, the alloy provides a sufficiently high level of plastic and viscous properties, which determines its reliable operation in highly loaded structures.

Using the claimed technical solution will allow:

- to reduce the weight characteristics of product units operating at temperatures of ≥800 ° C, by 1.5-1.8 times due to the replacement of highly loaded parts from heat-resistant nickel alloys;

- to provide increased reliability of titanium products at a temperature of ≥800 ° C due to the exclusion of the process of penetrating oxidation of the metal;

- to optimize the manufacturing technology of parts and assemblies, including welded ones, due to the possibility of heat treatment in air, excluding vacuum and thermal equipment with a protective atmosphere.

Thus, this invention provides improved weight characteristics by replacing highly loaded parts of heat-resistant nickel alloys, increasing strength and creep resistance in the absence of embrittlement during operation at elevated temperatures up to 800 ° C. In addition, the implementation of the invention provides a stable high heat resistance and heat resistance at elevated temperatures.

Claims (2)

1. Heat-resistant and heat-resistant titanium alloy containing aluminum, zirconium, tungsten, hafnium, titanium, characterized in that it additionally contains tantalum in the following ratio of components, wt.%:
Aluminum 6.0-7.5 Zirconium 3.0-5.0 Tungsten 6.0-7.5 Hafnium 2.5-4.0 Tantalum 2.5-4.0 Titanium Rest 2. Heat-resistant and heat-resistant titanium alloy according to claim 1, characterized in that it is obtained by the method of triple vacuum-arc remelting.