RU2613003C1 - Manufacturing method for parts from titanium alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: load carrying components are made of VT8 titanium alloy. Then heat treatment is sequentially performed in three stages. The first is carried out at temperature from 600 to 650 °C, at which the titanium silicides are released from supersaturated solid solutions -α and -phases β. The second is carried out at temperature from 850 °C and above, which is characterized by conversion of the phase composition from α- to β-. The third is conducted at temperature from 950 to1100 °C. At 1100 °C the phase composition of the alloy is represented only by β-phase.

EFFECT: improved strength characteristics of VT8 titanium alloy parts.

Description

The invention relates to the field of metallurgy, mainly to methods for producing parts or products with a regulated structure, and can be used to optimize the technological molding of products of complex shape.

The task of obtaining a certain distribution of the structure of the material over the volume of the product is usually solved on the basis of great practical experience and the results of specially conducted experiments. One of the successfully applied ways of stably obtaining a given material structure in mass-produced products is the use of the superplasticity effect.

Titanium alloys with high specific structural strength and corrosion resistance are used for the manufacture of a wide range of products, and a technological process based on the superplasticity effect can significantly expand the scope of new titanium alloys.

Titanium alloys are classified according to various criteria. The most common classification by phase composition [Metallography of titanium alloys / Under. ed. S.G. Glazunova, B.A. Kolacheva. - M .: Metallurgy, 1980; B.K. Wulf. Heat treatment of titanium alloys. M .: Metallurgy, 1969]. It is most suitable for analyzing the rheological properties of alloys and includes:

1) α-alloys, the structure of which is represented by the α-phase;

2) pseudo - α-alloys, the structure of which is represented by the α-phase and a small amount of β-phase or intermetallic compounds (not more than 5%);

3) (α + β) alloys whose structure is represented by α and β phases. Alloys of this type may contain a small amount of intermetallic compounds (up to 1%);

4) pseudo - β-alloys with the structure represented by one β-phase after quenching or normalization from the β-region. The structure of these alloys in the annealed state is represented by the α phase and a large amount of β phase;

5) β-alloys, the structure of which is represented by a thermodynamically stable β-phase;

6) alloys based on intermetallic compounds.

Α-class alloys (VT1, VT1-0, VT5, etc.) are alloyed with aluminum and neutral hardeners (tin and zirconium). Compared to titanium, alloys of this class are characterized by increased strength and heat resistance, high thermal stability, low tendency to cold brittleness, and good weldability. The good weldability of α-alloys is due to their single-phase structure even with a significant aluminum content, and therefore the weld metal and the heat-affected zone are not embrittled. Titanium α-alloys are not thermally hardened - the only type of heat treatment is complete annealing (to sufficiently remove the hardening) or incomplete (to relieve residual stresses).

Pseudo α-alloys (OT4, OT4-1, OT4V, etc.) contain small amounts of aluminum and low concentrations of β-stabilizers, which allows preserving high processability during pressure processing. These alloys are well welded by all types of welding. Pseudo - α-alloys are not thermally hardened, they are used in the annealed state.

Alloys of the (α + β) class (VT6, VT6C, VT8, VT14, VT23, etc.) have a wide range of properties, since they include materials containing in the annealed state from about 5 to 60% of the β phase. Great possibilities for controlling the properties of these alloys are determined not only by the mortar hardening of the α and β phases, but also by their ability to heat harden by quenching and aging. The mechanical properties of alloys of the (α + β) -class are very sensitive to the type and parameters of the microstructure. To ensure a high level of ductility and resistance to cyclic loads, it is necessary to strive for an equiaxed fine-grained structure.

Pseudo - β-titanium alloys (VT35, VT19, VT32, etc.) are highly alloyed alloys in which the total content of alloying elements reaches 25% or more. The advantages of these alloys include:

1) high processability in the hardened state, which allows some pressure treatment operations even at room temperature;

2) a large effect of thermal hardening, which is associated with a high degree of supersaturation of the hardened phase with alloying elements (Mo, Cr, Zr, V);

3) a high depth of hardenability;

4) high fracture toughness with significant strength characteristics;

5) high fatigue resistance.

Known methods for the manufacture of large stampings from titanium alloys (VT3-1, VT6, VT22, VT23, etc.) by superplastic deformation (AS USSR 1577378, C22F 1/04, 1988; AS USSR 1759583, V23K 20/14, 1990; UK patent No. 1301987, 1978).

The closest set of essential features is the technical solution for US patent No. 3920175, 1977, which was adopted by the authors for the closest analogue.

The disadvantage of this method is that when using titanium billets from VT8 alloy (blades, disks, impellers of compressors, etc.), the technology used does not allow to achieve the necessary strength of the finished products (impact strength, crack resistance, heterogeneity). This is due to the fact that the plates of one α-colony are deformed identically, and dynamic polygonization and dynamic recrystallization in the β phase at temperatures of the (α + β) region occur more easily than in the α phase under the same conditions.

The technical task is to improve the mechanical properties of titanium billets from VT8 alloy (blades, disks, impellers of compressors) by improving the morphology and rheological characteristics of the starting material.

The method is carried out by the method of superplastic deformation, including gas molding of parts from high-strength titanium alloy VT8 at temperatures from 870 ° to 1000 ° C.

Next, heat treatment is carried out sequentially in three stages. The first (low temperature) is carried out at a temperature from 600 ° to 650 ° C, at which titanium silicides are released from supersaturated solid solutions of α and β phases.

The second one occurs at a temperature of 850 ° C, which is characterized by the transformation of the phase composition from α- to β-.

The third - occurs at a temperature of 950 ° ... 1100 ° C. At a temperature of 1100 ° C, the phase composition of the alloy is represented only by the β phase.

Thus, due to the fact that the sensitivity of titanium alloys to the type and parameters of the structure allows one to obtain a different combination of strength, plastic and service properties of other alloys on one alloy, i.e. Using the three-stage heat treatment of VT8 alloy, it is possible to replace high-alloy pseudo-β-class alloys (VT19, VT32, VT35, etc.), which are unusually expensive in production, thermally unstable due to their high density, and have a wide variation in mechanical properties.

Claims (1)

A method of manufacturing parts from titanium alloys by the method of superplastic deformation, including gas molding of parts at temperatures from 870 ° to 1000 ° C, characterized in that after gas molding, the parts are subjected to heat treatment at a temperature of from 600 ° to 650 ° C to release titanium silicides from supersaturated solid solutions of α- and β-phases, followed by heat treatment at a temperature of more than 850 ° C until the phase composition of α- turns into a β-phase with the transition to the third stage of heat treatment at a temperature of from 950 ° to 1100 ° C until β-phase.