RU2613829C2 - Method for producing of deformed semifinished products from intermetallides titanium alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method for producing deformed semifinished products from gamma alloy Ti-43Al-3Nb-2W-0.5Si includes heating and a two-stage compression of cast billet in the metal clad. The cast billet is coated by thermal layer from fiberglass and/or kaolin fiber with softening temperature ≥1150°C and placed in a shell from the titanium alloy with a thickness δ, defined by the expression δ= (0.02-0.05)×∅, where ∅ - billet diameter in mm. Then the billet is heated and subjected to premoulding at temperatures 1250-1380°C with a deformation degree of 25-40%, the deformation rate of 50-60 mm/s, and then the final compression with deformation degree 96-98%, followed by cooling of compressed semifinished products upto the room temperature.

EFFECT: obtaining the billet uniform structure, which provides high values of stress limit and elongation at the room temperature, heat resistance at temperatures up to 800°C.

4 cl, 1 dwg, 2 tbl, 6 ex

Description

The invention relates to the field of non-ferrous metallurgy, specifically to hot pressure treatment of alloys based on titanium intermetallic TiAl (gamma alloys), and can be used in the manufacture of parts for gas turbine engines.

A known method of processing titanium alloys based on intermetallic compounds Ti ₃ Al [Ti-25Al-5Nb (wt.%)] (SU 1235244, C22F 1/18, publ. 08.28.2015), which includes:

- homogenizing annealing of the workpieces at temperatures of 1000-1200 ° C, holding at these temperatures for 2-5 hours and cooling to room temperature;

- packaging the heat-treated preform in a container with a wall thickness of (0.01-0.08) × ∅, where ∅ is the diameter of the preform, mm;

- heating the container to temperatures of 1050-1200 ° C and holding at these temperatures for 2-8 hours, carrying out prepressing with a degree of deformation of 5-30% and a speed of deformation of 10-50 mm / s, final pressing with a degree of deformation of 20-85% at a strain rate of 10-50 mm / s.

The disadvantage of this method is the many hours of homogenizing annealing of the workpieces before pressing and the need to use effective protection against oxidation during heating at elevated temperatures.

The closest analogue taken as a prototype is a method for producing semi-finished products from titanium-based alloys containing Ti-36Al (wt.%) (SU 1408805, C22F 1/18, publ. 08.28.2015), which includes:

- the formation of a heat-insulating layer by heating to temperatures of 1200-1250 ° C, holding at these temperatures for 2-2.5 hours and cooling the workpiece to room temperature at a speed of 5-7.5 degrees per second;

- packaging the obtained preform in a metal shell, heating it to temperatures of 1290-1360 ° C, prepressing in a press container for a degree of deformation of 29-38% and subsequent pressing at a speed of 50-60 mm / s and a degree of deformation of 62-71% with a total degree of deformation of 90-94%. Subsequent cooling of the resulting semi-finished products is carried out in air.

Despite the good quality of the obtained semi-finished products (fine-grained structure and high mechanical properties), the method is economically expensive, since it requires preliminary heating of the workpiece to create a heat-insulating layer, which does not provide the required performance of the operation.

An object of the invention is to develop a method for producing pressed semi-finished products from cast billets of gamma-alloy Ti-43Al-3Nb-2W-0.5Si (at.%).

The technical result is the production of semi-finished extruded semi-finished products with a homogeneous structure and an increased set of mechanical properties — tensile strength and elongation at room temperature — from a hardly deformable Ti-43Al-3Nb-2W-0.5Si alloy (at.%).

To achieve the technical result, a method for producing deformed semi-finished products from a Ti-43Al-3Nb-2W-0.5Si gamma-alloy is proposed, which includes heating and two-stage pressing of a cast billet in a metal shell, while the cast billet is coated with a heat-insulating coating of fiberglass and / or kaolin fiber with a softening temperature ≥1150 ° C and placed in a shell of titanium alloy with a thickness δ, determined by the expression δ = (0.02-0.05) × ∅, where - ∅ the diameter of the workpiece in mm, then the workpiece is heated and subjected support ssovke at temperatures of 1250-1380 ° C at a degree of 25-40% strain, strain rate of 50-60 mm / s, followed by a final pressing with the strain of 96-98%, followed by cooling of extruded semifinished to room temperature.

Preferably, titanium alloys with a phase transition temperature (T _pp ) of 1000-1050 ° C. are used as the metal shell.

The choice of shell thicknesses is associated with a decrease in contact stresses in the surface layers of the workpiece during pressing and using the shell as an additional lubricant.

The choice of glass fiber or kaolin fiber as a heat-insulating coating is due to the production of a gas-tight plastic layer on the external surface of the coated preform at extrusion temperatures, which reduces the oxidizability of the preform during heating, ensures that the pre-set heating temperature is stored in the preforms, eliminating their cooling during pressing, and forms a process lubricant that reduces stress pressing blanks.

The selected heat-insulating coating based on fiberglass and / or kaolin fiber has similar softening temperatures and thermal conductivity at temperatures of 1250-1380 ° C, so the quality of the heat-insulating coating of the cast billet will be the same for each individual and their mixture.

Preferably, the cast billets with a heat-insulating coating in a titanium alloy sheath are heated in a gas medium consisting of 75 ± 1 vol.% Hydrogen and 25 ± 1 vol.% Nitrogen, with an oxygen content of ≤0.004 vol.% And water vapor ≤0.001 vol. .% at dew point temperature ≤ -60 ° С.

The proposed billet heating medium provides increased technological ductility of the cast alloy, reduces the high-temperature oxidation of the billets, and ensures the explosion safety of the operation, since heating the billets in a pure hydrogen medium increases the risk of explosive combustion causing destruction of the furnace structure.

Preferably, the cooling of the pressed semi-finished products is carried out at a speed of 10-20 deg./s to room temperature. The proposed cooling regimes for billets are associated with a decrease in thermal stresses causing warping of pressed semi-finished products (especially thin-walled profiles) during cooling from deformation temperatures.

As shown in tables 1 and 2 (options 1 and 5), when applied to the workpieces of a metal shell with a thickness of less than 0.02 × ∅, the resulting tensile stresses cause the destruction of the metal shell, exposure of the surface of the workpieces and their cooling, which leads to the appearance of surface tears and cracks. With coating thicknesses of more than 0.05 × ∅, tensile stresses do not destroy the metal shell, they can preserve the temperature of the workpiece and ensure normal material flow. Despite the advantages of thick coatings, their use reduces the yield of suitable material, increases the cost of semi-finished products, and there are problems with the disposal of used thermal insulation coatings and shells.

The figure 1 presents the dependence of the influence of the temperature of pressing and the permissible degree of deformation during prepressing on the quality of the resulting semi-finished products. It can be seen from these dependences that when the degree of prepressing is less than 25% (region I), a loss of technological plasticity of the material is observed due to cooling of the workpiece and the appearance of high flow stresses, which leads to the formation of deep tears and cracks. With a degree of pre-pressing the workpieces of more than 40% (region III), the workpieces are subject to significant plastic deformation, which causes strong heating of the workpieces and an increase in temperature to the area with intensive recrystallization and grain growth. The optimal temperature range of pressing, providing increased processability of the alloys, is region II, which is presented in figure 1.

Examples of implementation.

The alloy ingots of the composition Ti-43Al-3Nb-2W-0.5Si (at.%) Were made according to the technology adopted in the production of serial titanium alloys. The following charge materials were used - titanium sponge, ligatures with the specified alloying elements. The manufacture of ingots included the production of a consumable electrode, smelting of ingots by vacuum-arc remelting, and machining of ingots. Cast billets with a diameter of 150 mm and a length of 180 mm were coated with a heat-insulating material and packaged in a shell of a titanium alloy with a phase transformation temperature (T _pp ) in the range of (1000-1050) ° С (for example, an alloy of the grade BT20). The prepared billets in a shell made of a titanium alloy with a heat-insulating coating were immediately heated to the specified pressing temperatures and subjected to hot pressure treatment by two-stage pressing to obtain the final semi-finished products. Pressed semi-finished products were cut into billets, from which samples were made to study the structure (determine the size of the micrograin) and test the mechanical properties at room temperature. Table 1 presents the results of experiments on two-stage pressing of Ti-43Al-3Nb-2W-0.5Si alloy blanks (at.%) According to the proposed method (options No. 2-4) and the prototype method (option No. 6).

Table 2 presents the grain sizes (d _W ) and mechanical properties (σ _B , σ _0.2 and δ) at a temperature of 20 ° C of the pressed alloys Ti-43Al-3Nb-2W-0,5Si (at.%) By the proposed method (options No. 2-4) and the prototype method (option No. 6).

As can be seen from tables 1 and 2, the proposed method for producing semi-finished products from an alloy Ti-43Al-3Nb-2W-0.5Si (at.%), In comparison with the prototype method, provides an increase in the technological plasticity of the alloy, expands the range of allowable deformation values during pre-pressing (25-40)% instead of (29-38)%. This creates the opportunity for a favorable flow of material in the matrix, which provides high values of the total deformation at the final stages of pressing. Such phenomena lead to the formation of high-quality fine-grained billets with a smaller grain size by 23.6% and increased mechanical properties at a temperature of 20 ° C - tensile strength by 18.8% and elongation by 58%.

The proposed method for the manufacture of pressed semi-finished products from the Ti-43Al-3Nb-2W-0.5Si gamma-alloy (at.%) Allows to obtain deformed fine-grained preforms with enhanced mechanical properties at room temperature. The resulting semi-finished products with such a structure and mechanical properties can be used in the final operations of manufacturing parts with fewer transitions and machining allowances, providing increased values of the metal utilization factor (CMM) and reducing the cost of machining.

Claims (4)

1. A method of obtaining a deformed semi-finished products from a Ti-43Al-3Nb-2W-0.5Si gamma alloy, comprising heating and two-stage pressing of a cast billet in a metal shell, characterized in that the cast billet is coated with a heat-insulating coating of glass fiber and / or kaolin fiber with softening temperature ≥1150 ° C and placed in a shell of titanium alloy with a thickness δ, determined by the expression δ = (0.02-0.05) × ∅, where ∅ is the diameter of the workpiece in mm, then the workpiece is heated and pre-pressed at temperatures 1250-1380 ° С with the degree of deformation cation of 25-40%, a strain rate of 50-60 mm / s, and then final pressing with a degree of deformation of 96-98%, followed by cooling the pressed semi-finished products to room temperature. 2. The method according to p. 1, characterized in that as the metal shell using titanium alloys with a phase transition temperature (T _PP ) of 1000-1050 ° C. 3. The method according to p. 1 or 2, characterized in that the heating of cast billets with a heat-insulating coating in a shell of titanium alloy is carried out in a gas medium consisting of 75 ± 1 vol.% Hydrogen and 25 ± 1 vol.% Nitrogen, with the content oxygen ≤0.004 vol.% and water vapor ≤0.001 vol.% at dew point temperature ≤ -60 ° C. 4. The method according to p. 1 or 2, characterized in that the cooling of the pressed semi-finished products is carried out at a speed of 10-20 deg./s to room temperature.

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