Method for manufacturing forgings from titanium alloys with pseudo-monocrystalline structure

Abstract

FIELD: metal forming.SUBSTANCE: invention can be used in aviation and power engineering in the production of forgings from titanium alloys for critical applications. The forging is obtained from a blank in the form of an ingot that has undergone deformation at a temperature above Tp.p., with a total relative deformation in the range of 0.9<ε∑<1.0.EFFECT: obtaining forgings that are thermally resistant to thermal cycling and have a high level of mechanical and fatigue properties.2 cl, 3 dwg, 1 ex

Description

[0001] The invention relates to the production of forgings from titanium alloys for critical applications, such as gas turbine engine (GTE) blades, by metal pressure treatment, and can be used in aviation and power engineering.

[0002] A method is known for manufacturing gas turbine engine blades from OT4 titanium alloy by heating the blank, stamping it to obtain a forging with a feather and lock parts, hot and cold rolling of the blade feather (see Russian Federation Patent No. 1210314 IPC B21K 3 / 04. Published October 20, 1995).

[0003] The disadvantage of this method is that it cannot be applied to titanium alloys, as their cold rolling leads to the formation of cracks and destruction of the blade feather.

[0004] A method is known for manufacturing forgings of gas turbine engine blades from the iron-nickel alloy EI718, including a locking and feather parts, in which the feather part is subjected to cold rolling (see Russian Federation Patent No. 2256527 IPC B21K 3 / 04. Published July 20, 2005).

[0005] EI718 alloy is a high-tech alloy suitable for pressure processing in both hot and cold states, while heat-resistant titanium alloys are not subjected to cold rolling due to low ductility in the cold state.

[0006] A known method for processing semi-finished products from titanium alloys with a two-phase structure, including heating in the β-region and deformation, cooling to the temperature of the (α + β)-region, subsequent heating and deformation, final cooling, wherein heating to the temperature of the β-region is carried out at a rate of 1-20 ° C / min, then holding for 1-8 hours, and deformation is carried out with a degree of 70-98% during cooling to a temperature of 40-200 ° C below the polymorphic transformation temperature, then subsequent heating to a temperature in the temperature range of 50 ° C below and 30 ° C above the polymorphic transformation temperature is carried out at a rate of 10-50 ° C / min and deformation with a degree of 10-50% during cooling to a temperature of 60-200 ° C below the polymorphic transformation temperature, after which heating is carried out to a temperature in the range of 30°C below and 150°C above the temperature of polymorphic transformation at a rate of 10-50°C / min and hold for 2-30 min,and the deformation is carried out at a speed of 0.5-50 mm / s with tension of the semi-finished product with a force of 3-35 kg / mm, 2 during cooling to a temperature 100-400°C below the polymorphic transformation temperature (see Russian Federation Patent No. 2617188 IPC C22F 1 / 18. Published 20.04.2017. Bulletin No. 11).

[0007] The disadvantage of this method is its inapplicability in industrial conditions of mass production and its high labor intensity.

[0008] A method is known for manufacturing blades from two-phase titanium alloys, including shaping a blank in the form of a rod and subsequent volume stamping of the heated blank with the formation of the blade airfoil and its edges in two passes, characterized in that the shaping of the blank is performed by extrusion in two passes with an extrusion coefficient of no more than 4 in the first pass and a degree of deformation of 30-40% along the central part of the profile from the root to the boss in the second pass, ensuring the same degree of deformation along the central part of the blade airfoil, and stamping is performed in the first pass with a degree of deformation of 40-50% along the profile of the blade airfoil, ensuring a proportional allowance along the sections of the profile, and in the second pass - with a degree of deformation of 25-35% along all sections of the central part and on the edges of the blade airfoil.

[0009] In this case, heating for extrusion and bulk stamping is carried out to temperatures below A3 (see Russian Patent No. 2759280 IPC B21K 3 / 04. Published 11.11.2021. Bulletin No. 32).

[0010] The disadvantage of this method is that with an “extrusion coefficient of no more than 4 (relative deformation of no more than 0.5) at the first transition and a deformation degree of 30-40% along the central part of the profile from the root to the boss at the second transition”, it is impossible to obtain a deformation texture directed along the blade feather and the maximum strength properties of the alloy in this direction.

[0011] A known method for manufacturing blades from titanium alloys includes casting blanks consisting of a lock part and a part under the airfoil, heating the cast blanks to a temperature 10-30 °C below the polymorphic transformation temperature of the alloy, deformation in one pass, characterized in that the blanks are cast with a lock part thickness equal to 1.45-2.00 of the lock thickness, and a airfoil thickness equal to 1.65-3.35 of the airfoil thickness of the finished blades, and the deformation is carried out under isothermal conditions with subsequent cooling of the stampings at a rate of less than 15 °C / s. And the heating of the cast blank for isothermal stamping is carried out to a temperature below A3 (see Russian Federation Patent No. 2019359 IPC B21K 3 / 04. Published on September 15, 1994).

[0012] Under such thermomechanical deformation conditions, the directional fibrous structure in the blade airfoil will not be achieved. The maximum mechanical properties of the alloy will not be achieved.

[0013] There are known methods for stamping forgings from titanium alloys with strict regulation of the stamping temperature below T п.п. (See AVIATION MATERIALS. - Volume 5. - magnesium and titanium alloys. VIAM - ONTI. - 1973. - 583 p. Instructions No. 685 - 76 Wrought titanium alloys. Heat treatment of semi-finished products and parts. Moscow: VIAM - VILS. - 1976). Since when stamping from temperatures above T п.п. In the blade forgings, a significant increase in the alloy grain size is observed, leading to a decrease in its plasticity and toughness.

[0014] Improving the mechanical properties of gas turbine engine blades made from heat-resistant alloys is currently being done in two directions of their manufacture:

[0015] - in single-crystal design (see Shalin R.E., Svetlov I.L., Toloraya V.N. Single crystals of nickel heat-resistant alloys. - M.: Mashinostroenie, 1997. - 321 p., E.N. Kablov, I.V. Petrushin, E.S. Elyutin Single-crystal heat-resistant alloys for gas turbine engines. Bulletin of Bauman Moscow State Technical University. - Series "Mashinostroenie". - 2011. - Pp. 38-51);

[0016] - in nano-microcrystalline design (see Lyakishev N.P., Alymov M.I., Dobatkin S.R. Bulk nanomaterials for structural purposes / / Metals. - 2003. - No. 3. - pp. 3-16., Gusev A.I. Nanomaterials, nanostructures, nanotechnologies. Moscow: Fizmatgiz. - 2007. - 417 p., Chuvildeev V.N., Nokhrin A.V., Lopatin Yu.G. et al. On the ultimate strength and ductility at room temperature of nano- and microcrystalline metals obtained by methods of severe plastic deformation. The effect of simultaneous increase in strength and ductility / / Heavy engineering. - 2011. - No. 1. - pp. 2-12). It is believed that metals and alloys with such a structure exhibit unusually high and useful physical and mechanical properties.

[0017] However, at the current stage of scientific and technological development, producing single-crystal titanium alloy gas turbine engine blades is impossible. Nanocrystalline versions are characterized by significant grain boundary non-equilibrium (see V.N. Chuvildeev, Nonequilibrium Grain Boundaries in Metals: Theory and Applications, Moscow: Fizmatlit, 2004, 304 p.), leading to thermal instability. This is unacceptable for gas turbine engines, given thermal cycling and temperature fluctuations within the structure.

[0018] Moreover, "nanotechnology is the science of matter, and not just another phase of materials science development" (Joachim K., Plewer L. Nanosciences. Invisible Revolution. - Moscow: KoLibri, 2009. - 252 p.). That is, not just a structure with a grain size of less than 100 nm, but with a different atomic structure. Which is unattainable by known methods of metal pressure processing, including "severe plastic deformation". And, according to N.G. Kolbasnikov, Doctor of Engineering Sciences, Professor at the St. Petersburg Polytechnic University, nano-microcrystalline structures obtained by "severe plastic deformation" have not lived up to the expectations placed on them for application in mechanical engineering.

[0019] Research (Movchan B.A. Crystallite boundaries in cast metals and alloys. - Kyiv: Tekhnika, 1970. - 212 p., Titanium alloys. Melting and casting of titanium alloys / Andreev A.L., Anoshkin N.F., Bochvar A.G. et al. / - Moscow: Metallurgy, 1994.- 386 p.) showed that in titanium alloys and non-ferrous metal alloys, crystallites (macrograins) in ingots are surrounded by a macroshell of an amorphous alloy. The chemical composition of which ("shell" - intergranular boundaries) coincides with the chemical composition of the matrix (grain).

[0020] The applicant's research (Onishchenko A.K. Theory of Industrial Forging of Steel and Alloys / Ed. by A.K. Onishchenko. Moscow: "Sputnik+", 2021. - 305 p., ill. 2nd revised and supplemented ed.) showed that after forging an ingot from VT8 alloy in the temperature range of 1100 ÷ 950 ° C and a total relative deformation close to 1.0 (A.K. Onishchenko Calculation of the total deformation of an ingot (blank) in metal forming operations / / Heavy Engineering. - 2021. - No. 9. - pp. 18-21), the original cast dendritic structure is transformed into a mechanical mixture. That is, amorphization of the structure occurs (Fig. 1). And, unlike nano- and microcrystalline structures obtained by "severe plastic deformation" (usually in a cold or semi-hot state), this structure remains unchanged after recrystallization annealing. That is, it is thermally stable at temperatures exceeding the maximum operating temperature in a high-pressure compressor (600–650°C) during gas turbine operation.

[0021] The technical result that the invention is aimed at achieving is the production of gas turbine engine forgings from titanium alloys with a pseudo-single-crystal structure, thermally resistant to thermal cycling and with a high level of mechanical and fatigue properties.

[0022] The specified technical result is achieved by the fact that the method for manufacturing forgings from titanium alloys with a pseudo-single-crystal structure, characterized by the fact that the forging is obtained from blanks in the form of an ingot that has undergone deformation at a temperature exceeding the temperature T п.п. , with a total relative deformation ε Σ , in the range 0.9<ε Σ <1.0.

[0023] In this case, the value of the total relative deformation of the workpiece in the form of an ingot (ε Σ ) is calculated using the formula: ε Σ =ε1+(1-ε1)*ε2+[1-ε1-(1-ε1)*ε2]*ε3+{1-[1-ε1-(1-ε1)*ε2]*ε3}*ε4+…<1, where ε1-ε n - relative deformation in the deformation transition number.

[0024] At a machine-building plant, the method is carried out as follows.

[0025] A bar obtained through cooperation with a certificate, for example, for stamping blade forgings, is checked not only for macro-microstructure data, ultrasonic testing and mechanical properties (longitudinal direction) according to OST, but also for the total relative deformation of the ingot ε Σ . And it is used to determine the required relative deformation of the bar blank for forming blade forgings using stamping operations (e.g., extrusion - preliminary stamping of the forging - final stamping of the forging; or only extrusion of the blade forging). To obtain and maintain a pseudo-single-crystal structure in the blade forging, heating and stamping of the blanks are carried out at a temperature above T п.п. After the forging is manufactured, it undergoes recrystallization annealing.

[0026] As an example of the application and effectiveness of the proposed method, forgings of high-pressure cylinder blades for an exported aircraft engine were manufactured using VT18U and VT8M1 alloys. Until now, these blades have been manufactured from 18 mm diameter rods of 14Kh17N2 martensitic-ferritic steel. The technical specifications and forging drawings only specify requirements for a hardness of HRC 23–32. However, OST 90176 also stipulates the following level of mechanical properties for stampings made from this steel: yield strength, σ 0,2 - not less than 85 kgf / mm 2 ; tensile strength, σ B - not less than 110 kgf / mm 2 ; relative elongation, δ - not less than 10%.

[0027] Using serial production technology, these blade forgings are manufactured from 14Kh17N2 steel in a single operation: extruding a 18x23 mm diameter blank in a die heated to 1150°C and producing the blade forging (with the blade and key sections). After extrusion and compression, the relative deformation in the key and key sections of the forging is 0.65.

[0028] Forgings of the same blades from titanium alloys were manufactured using serial technology - heating and extrusion from a temperature of 1150°C, which is higher than the temperature T п.п. , respectively, of both alloys (1030°C - VT18U and 1020°C - VT8M1) by more than 100°C. And, as noted above, not permitted by the technical specifications of VIAM.

[0029] Rods of ∅18 mm and 3000 mm length of titanium alloys VT18U and VT8M1, supplied by VSMPO, obtained after deformation of the ingot by VAR (crystallizers ∅250-450 mm) in the temperature range of 1180-950 °C, are supplied, approximately, with a total relative deformation (ε ∑ ) not less than 0.95.

[0030] Taking into account the extrusion operation (the next transition) at a temperature of 1150°C and a relative deformation of 0.65, the total relative deformation of the blade forging was:

[0031] .

[0032] After recrystallization annealing of blade forgings of both alloys at a temperature of 950°C, the following data on mechanical properties were obtained: σ 0,2 =115.8 kgf / mm 2 ; σ B =128.0 kgf / mm 2 ; δ=15.2% and HRC=35.4 (on VT18U alloy) and σ 0,2 =112.1 kgf / mm 2 ; σ B =125.6 kgf / mm 2; δ=14.5%) and HRC=32.6 (on VT8M1 alloy). That is, exceeding the requirements of the drawing and OST 90176. At the same time, the mass of these blades (up to 100 pcs. per compressor stage) reduces the mass of the high-pressure compressor disc with blades by more than 40% (specific gravity of 14Kh17N2 steel ρ=7.75 g / cm 3 , and titanium alloys VT18U and VT8M1 ρ=4.45 g / cm 3 ).

[0033] Fig. 2 (VT18U alloy) and 3 (VT8M1 alloy) show the macro- and microstructures of longitudinal sections (along the blade feather) of blade forgings after extrusion and annealing.

[0034] Thus, the obtained data from the study of the mechanical properties and structure of high-pressure turbine blades made of titanium alloys confirm not only the novelty of the proposed technical solution, but also the effectiveness of its use in aviation and power engineering.

Claims

1. A method for producing forgings from titanium alloys with a pseudo-single-crystal structure, characterized by the fact that the forging is obtained from a blank in the form of an ingot that has undergone deformation at a temperature exceeding the temperature T п.п. , with a total relative deformation ε Σ in the range 0.9<ε Σ <1.

0.

2. The method according to paragraph 1, characterized in that the value of the total relative deformation of the workpiece in the form of an ingot ε Σ calculated using the formula: ε Σ = ε1+ (1 - ε1) ⋅ ε2+ [1 - ε1- (1 - ε1) ⋅ ε2] ⋅ ε3+ {1 - [1 - ε1- (1 - ε1) ⋅ ε2] ⋅ ε3} ⋅ ε4+ … < 1, where ε1-ε n - relative deformation in the deformation transition number.

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