RU2523049C1 - Method of gamma-aluminide titanium-based alloys production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed process comprises production of the mix of powders, forming the pellet therefrom and execution of self-propagating high-temperature synthesis. Obtained the mix of pure metals containing titanium, aluminium, niobium and molybdenum in the following amount, it wt %: aluminium - 40-44, niobium - 3-5, molybdenum - 0.6-1.4, titanium making the rest. This pellet is compacted to relative density of 50-85% and subjected to thermal vacuum processing at 550-560°C for 10-40 min, heating rate of 5-40°C/ min and pressure of 10^-1-10^-3 Pa while SPS is performed at initial temperature of 560-650°C.

EFFECT: preset shape of casts, high mechanical properties.

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Description

The invention relates to the field of metallurgy, in particular to methods for producing castings from alloys based on gamma titanium aluminide (γ-TiAl), and can be used to produce critical products operating at temperatures up to 700 ° C, in particular gas turbine engine blades.

Casting alloys based on gamma aluminide titanium TiAl (hereinafter gamma alloys) are among the most promising materials for producing blades of gas turbine engines of a new generation. These alloys should possess not only high casting properties, but also a complex of various mechanical properties: strength, ductility, fatigue properties, heat resistance, etc. [Ilyin AA, Kolachev BA, Polkin IS Titanium alloys. Composition, structure, properties. Directory. M .: VILS-MATI, 2009, 520 p.]. A feature of gamma alloys is the high sensitivity of their phase composition and, as a consequence, operational properties even to small changes in the concentrations of alloying elements and to the parameters of the process.

For the manufacture of shaped castings from gamma-alloys, initially, as a rule, billets are obtained in the form of ingots by their repeated melting [Appel F., Paul JDH, and Oehring M. “Gamma Titanium Aluminum Alloys: Science and Technology)), Wiley-VCH Verlag & Co. KGaA, 2011, 745 p.]. This is a time-consuming and energy-intensive process, which leads to a significant increase in the cost of the final product. In particular, a known method for producing castings from gamma alloys is disclosed in US Pat. No. 6,174,495 (2001). According to this method, a titanium-based melt containing from 31.3 to 32.0 wt.% Aluminum, as well as other additives, is poured into a mold (including a complex configuration: “precision”) and cooled at normal speed. The disadvantage of this method is that to obtain the melt using the workpiece in the form of an ingot.

It is possible to reduce the energy required to obtain a preform by using the method of self-propagating high-temperature synthesis (SHS), which is discussed in a number of patents.

A known method of producing powder materials based on nickel aluminide or titanium aluminide in the SHS mode (http://naT.RU 2354501). This method includes preparing an exothermic mixture by mixing powders of aluminum and nickel or titanium oxide in an amount taken to produce stoichiometric nickel or titanium aluminide and at least one additive selected from the range consisting of magnesium, magnesium perchlorate, calcium peroxide, chloride sodium, alumina, placing the mixture in the SHS reactor, initiating the combustion process in an inert atmosphere under an inert gas pressure of not higher than 1 MPa, followed by isolation of the target product by chemical treatment webs of reaction products of combustion in a dilute solution of hydrochloric or sulfuric acid at a temperature of 60-80 ° C with continuous stirring. The final product obtained by this method is a powder with a particle size of less than 3 microns. To obtain the finished product requires additional operations (compaction, pressing, processing by cutting), which is the main disadvantage of the proposed method.

Closest to the proposed is a method for producing a cast alloy based on titanium aluminides in a combustion mode, which is disclosed in patent RU 2320744 (publ. March 27, 2008). This method includes preparing a reaction mixture of powders containing titanium oxide, niobium oxide, aluminum, at least one energy additive selected from the series: calcium peroxide, magnesium, barium, placing the mixture in a refractory form coated on the inside with a functional protective layer of refractory inorganic compounds, placing the mold on a centrifuge, igniting the mixture and carrying out synthesis in the combustion mode with centrifugal acceleration of 200-1000 g, followed by separation of the cast alloy from the synthesis product, etc. This preparation is carried out from an initial composition of the mixture, mass.%. Using this method, you can get an ingot with a uniform structure and high heat resistance (up to 700 ° C). Its disadvantage is that to obtain products of complex shape requires additional labor-intensive operations.

The objective of the invention is to provide a new method for producing castings of a given configuration from alloys based on gamma titanium aluminide in order to achieve a high level of mechanical properties at elevated temperatures.

The problem is achieved in the proposed method for producing a cast alloy based on gamma titanium aluminide intended for producing shaped castings, including obtaining a mixture of powders containing titanium, aluminum and niobium, obtaining a briquette, conducting self-propagating high temperature synthesis (SHS), characterized in that the mixture is obtained from powders of pure metals, and SHS is carried out at an initial temperature of 560-650 ° C, the relative density of the mixture briquette 50-85%, thermal vacuum treatment of the briquette at a temperature of 550-65 0 ° C for 10-40 minutes, heating rates of 5-40 ° C / min and a pressure of 10 ^-1 -10 ^-3 Pa.

In a private embodiment, the method is characterized in that the cast alloy is obtained from a mixture of powders, additionally containing molybdenum, in the following ratio of components, mol.%:

Aluminum 40-44 Niobium 3-5 Molybdenum 0.6-1.4 Titanium rest

The essence of the invention lies in the fact that the billet obtained by the SHS method in the optimal mode has a uniform structure, which minimizes the melting time before casting into a mold with a given configuration. This can significantly reduce the time to obtain the final cast parts with high performance properties, in particular heat resistance.

Carrying out SHS at an initial temperature below 560 ° C does not allow to realize a stationary combustion regime, which significantly impairs the quality of the synthesized preform.

Carrying out SHS at an initial temperature above 650 ° C leads to the implementation of combustion in the thermal explosion mode in the initial briquette, which also affects the quality of the synthesized preform.

The relative density of the briquette mixture of less than 50% does not provide sufficient strength of the initial briquette, reduces the burning rate, which leads to increased residual porosity of the workpiece.

The relative density of the mixture briquette of more than 85% leads to the formation of closed porosity in the initial briquette, which prevents the most complete degassing during thermal vacuum treatment and leads to the formation of delamination cracks in the synthesized preform.

Thermo-vacuum treatment of the briquette at a temperature below 550 ° C, for less than 10 minutes, at a pressure of more than 10 ^-1 Pa, at a speed above 40 ° C / min does not ensure the completeness of the degassing process, which increases the residual porosity of the synthesized preforms, and therefore increases the content of impurities in the final product.

Thermo-vacuum treatment of the briquette at temperatures above 650 ° C leads to spontaneous ignition of the initial briquette and premature occurrence of the SHS reaction directly in the chamber of the vacuum furnace.

Thermo-vacuum treatment of the briquette for more than 40 minutes at a pressure of less than 10 ^-3 Pa and a heating rate of less than 5 ° C / min is not advisable, because this does not lead to a further increase in the degree of degassing of the initial briquette and does not increase the quality of the workpiece.

EXAMPLE 1

We considered 5 options for obtaining a workpiece from a mixture of metal powders of the following composition, mol.%: Aluminum - 42, niobium - 4, molybdenum - 1, titanium - the rest. The SHS modes are given in Table 1.

After receiving the preform (Figure 1), it was remelted in a vacuum induction furnace at a temperature of 650 ° C, and then the melt was poured into molds with a given configuration, obtaining a shaped casting (Figure 2). After the HIP treatment of castings at a temperature of 1250 ° C and a pressure of 100 MPa for 3 hours, samples were cut from them for compression tests at 700 ° C. The yield strength (σ _0.2 ) and the relative shortening (ε) were determined.

The results shown in table 1 show that only in the SHS 2-4 modes corresponding to the claimed method, high strength is achieved. In this case, there is no destruction of the samples (when shortening to 10% inclusive), which indicates a sufficiently high ductility of the tested materials. Modes 1 and 5 lead to a decrease in strength and ductility, since in the process of SHS refractory conglomerates are formed, which adversely affect the final structure of castings.

Table 1 Parameters for producing gamma alloy billets by SHS method and mechanical properties of castings obtained from billets No. Mode Settings ¹ Compression mechanical properties F% T ₁ , ° C t min V, ° C / min P, Pa T ₀ ° C σ _0.2 , MPa ε,% one thirty 500 5 2 10 480 450 ² 0 2 fifty 550 10 5 10 ^-1 560 720 > 10 3 72 600 25 22 10 ^-2 640 755 > 10 four 85 650 40 40 10 ^-3 720 715 > 10 5 90 800 60 60 10 ^-4 790 320 ² 0 ¹ F is the relative density of the mixture, T ₁ and t are the temperature and time of thermal vacuum treatment of the mixture, V is the heating rate, P is the pressure, T ₀ is the initial temperature of the SHS; ² Brittle fracture (yield strength not achieved)

EXAMPLE 2

According to the mode of preparation of preform 3 (see Table 1), 5 variants of mixtures were prepared (Table 2). Shaped castings were obtained from these mixtures under conditions similar to Example 1.

The results shown in table 2 show that only compositions 2-4 allow to achieve high values of σ _0.2 and ε. In this case, there is no destruction of the samples (when shortening to 10% inclusive), which indicates a sufficiently high ductility of the tested materials.

Composition 1 has a reduced strength, which is associated with lower concentrations of niobium and molybdenum. Composition 5 has a reduced strength and ductility, which is associated with increased concentrations of niobium and molybdenum.

table 2 Compositions of mixtures for producing gamma alloy billets by the SHS method and mechanical properties of castings obtained from these billets No. Concentration, mol. % Compression mechanical properties Al Nb Mo Ti σ _0.2 , MPa ε,% one 38 2 0.3 Rest 650 > 10 2 40 3 0.6 Rest 730 > 10 3 42 four 1,0 Rest 745 > 10 four 44 5 1.4 Rest 725 > 10 5 46 6 1.7 Rest 715 5

Claims (1)

A method of producing a cast alloy based on gamma titanium aluminide for shaped castings, comprising obtaining a mixture of powders, forming a briquette from it and conducting self-propagating high temperature synthesis (SHS), characterized in that a mixture of powders of pure metals containing titanium, aluminum, niobium and molybdenum is obtained in the amount, mol.%: aluminum 40-44, niobium 3-5, molybdenum 0.6-1.4, titanium - the rest, the briquette is formed with a relative density of 50-85% and subjected to thermal vacuum treatment at a temperature of 550-650 ° C for 10-40 minutes, heating rates of 5-40 ° C / min and a pressure of 10 ^-1 -10 ^-3 Pa, and the SHS is carried out at an initial temperature of 560-650 ° C.

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