RU2369662C2 - Method of thermo-mechanical treatment of titanium alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to non-ferrous metallurgy and can be implemented in aerospace and rocket engineering for producing details and units of landing gears of aircraft and docking units of rockets operating under conditions of cyclic loads. The technical object of the invention is increased low-cycle fatigue (LCF) determined by number of cycles (N) up to destruction at ratios of concentration K_t=4.0 (r_H=0.1 mm) and K_t=2.2 (r_H=0.75 mm). Treatment of titanium alloys is carried out in eleven stages with heating to temperature above and below the temperature of polymorphic transformation and deformation. In stages from the first to the third deformation is carried out in four steps with cooling of alloy and changing direction of deformation to 90° alternating shortening and drawing. Deformation is executed in one step alternating direction of deformation at 90° from two to seven times in stages from the fourth to the eighth. Heating with conditioning from 2 to 10 hours is performed in the eleventh stage.

EFFECT: invention increases resource and reliability of parts and units of aircraft.

1 tbl, 3 ex

Description

The invention relates to the field of non-ferrous metallurgy, in particular to the thermomechanical processing of titanium alloys, and can be used in aerospace and rocket technology to create parts and components of the landing gear of aircraft and docking nodes of rockets operating under cyclic loads.

A known method of thermomechanical processing of titanium alloys, including:

- heating to a temperature of (1050-1200) ° C (T _pp + 120 ÷ T _pp +270) ° C, deformation during cooling to 850 ° C (T _pp -80) ° C;

- heating to a temperature of (880-1050) ° C (T _pp -50 ÷ T _pp +120) ° C, cooling during deformation to a temperature of 750 ° C (T _pp -180) ° C, where T _pp = 920 ° C (Alexandrov V.K., Anoshkin N.F., Belozerov A.P. “Semi-finished products from titanium alloys. M., ONTI VILS, 1996, p. 371).

There is also known a method of thermomechanical processing used in the manufacture of products from titanium alloys, including heating in the β-region above the temperature of the polymorphic transformation, deformation during cooling to a temperature of 30-70 ° C below the temperature of the polymorphic transformation, cooling, reheating in a two-phase region, repeated deformation in this area during cooling, re-cooling, final heating into a two-phase region, holding and cooling, characterized in that in order to increase the mechanical solid deformation is carried out in β- and (α + β) -regions with the same degree of 40-60%, reheating is carried out to a temperature of 20-40 ° C below the polymorphic transformation temperature, repeated deformation is carried out with a degree of 25-35% when cooled to temperatures 100-130 ° C below the temperature of the polymorphic transformation, re-cooling after deformation is carried out to a temperature of 180-280 ° C below the temperature of the polymorphic transformation, after which the last cycle of heating and deformation is repeated during cooling under the same conditions, and cooling e after deformation in this cycle is carried out to room temperature, the final heating is carried out to a temperature of 100-300 ° C below the temperature of the polymorphic transformation (a.c. USSR No. 1740487).

The disadvantage of this method is the low level of cyclic strength of titanium alloys.

The closest analogue taken as a prototype is a method for thermomechanical processing of titanium alloys, including multiple heating to a temperature above and below the polymorphic transformation temperature and deformation during cooling to a temperature below the polymorphic transformation temperature, exposure and cooling, in which thermomechanical processing is carried out in six stages, while in the first five stages carry out:

- heating to a temperature of (T _pp + 120 ÷ T _pp +270) ° C, deformation with a degree of 50-70% upon cooling to (T _pp -40 ÷ T _pp -100) ° C;

- heating to a temperature of (T _pp + 60 ÷ T _pp +160) ° C, deformation with a degree of 40-60% upon cooling to (T _pp -100 ÷ T _pp -180) ° C;

- heating to a temperature of (T _pp -20 ÷ T _pp -40) ° C, deformation with a degree of 10-30% upon cooling to (T _pp -140 ÷ T _pp -160) ° C;

- heating to a temperature of (T _pp + 20 ÷ T _pp +50) ° C, deformation with a degree of 40-60% upon cooling to (T _pp -110 ÷ T _pp -130) ° C;

- heating to a temperature of (T _pp + 20 ÷ T _pp +50) ° C, deformation with a degree of 30-70% upon cooling to (T _pp -110 ÷ T _pp -130) ° C;

then, at the sixth stage, heating is carried out to a temperature of (T _pp -400 ÷ T _pp -500) ° C with holding for 5-20 hours, where T _pp is the temperature of the complete polymorphic transformation (RF patent No. 22219280).

The alloy processed in this way has lower low-cycle fatigue values at various stress concentrators.

An object of the invention is to increase low-cycle fatigue (MCU), determined by the number of cycles (N) to failure at concentration coefficients K _t = 4.0 (r _n = 0.1 mm) and K _t = 2.2 (r _n = 0, 75 mm).

The stated technical problem is achieved by the fact that the proposed method of thermomechanical processing of titanium alloys, including multiple heating to a temperature above or below the temperature of the polymorphic transformation and deformation during cooling to a temperature below the polymorphic transformation, exposure and cooling, in which the thermomechanical treatment is carried out in eleven stages, this:

at the first stage, heating is carried out to a temperature of (T _pp + 290 ÷ T _pp +370) ° C, deformation in four stages upon cooling to a temperature of (T _pp + 100 ÷ T _pp -70) ° C with a change in the direction of deformation by 90 ° at alternating draft and drawing with a degree of deformation of 20 ÷ 50% at each stage;

at the second stage - heating to a temperature of (T _pp + 180 ÷ T _pp +270) ° C, deformation in four stages when cooling to a temperature of (T _pp + 50 ÷ T _pp -90) ° C with a change in the direction of deformation by 90 ° C when alternating precipitation and drawing with a degree of deformation of 20 ÷ 50% at each stage;

at the third stage - heating to a temperature of (T _pp + 80 ÷ T _pp +170) ° C, deformation in four stages when cooling to a temperature of (T _pp -30 ÷ T _pp -200) ° C with a change in the direction of deformation by 90 ° C when alternating precipitation and drawing with a degree of deformation of 20 ÷ 50% at each stage;

at the fourth stage - heating to a temperature (T _pp -20 ÷ T _pp -40) ° C, deformation with a degree of 15-60%;

at the fifth stage - heating to a temperature (T _pp + 30 ÷ T _pp +60) ° C, deformation with a degree of 30-60%;

at the sixth stage, heating to a temperature (T _pp -20 ÷ T _pp -40) ° C, deformation with a degree of 20-40% during cooling to a temperature (T _pp -110 ÷ T _pp -130) ° C;

at the seventh stage, heating to a temperature (T _pp + 20 ÷ T _pp +50) ° C, deformation with a degree of 30-60% during cooling to a temperature (T _pp -110 ÷ T _pp -130) ° C;

at the eighth stage - heating to a temperature (T _pp -20 ÷ T _pp -40) ° C, deformation with a degree of 20-60% during cooling to a temperature (T _pp -110 ÷ T _pp -130) ° C;

at the ninth stage - heating to a temperature (T _pp + 80 ÷ T _pp +150) ° C, deformation during rolling with a degree of 40-70%;

at the tenth stage, heating to a temperature of (T _pp -20 ÷ T _pp -50) ° C, deformation during rolling with a degree of 30-60%;

then at the eleventh stage, heating is carried out to a temperature of (T _pp -320 ÷ T _pp -520) ° C with a holding time of 2-10 hours, where T _pp is the temperature of the polymorphic transformation;

while the deformation in stages four through eight is carried out in one stage with a change in the direction of deformation by 90 ° from two to four times.

In the first three stages, a comprehensive deformation is carried out after heating in the β-region, which ensures the preparation of a workpiece (slab) that is homogeneous in chemical composition, macro- and microstructure. Lowering the temperature of the beginning and end of deformation at each subsequent stage ensures a decrease in the β-grain size and the creation of an ultrafine-grained β-structure. The end of the deformation at a lower temperature than the beginning of the deformation creates a hot hardening, which increases the dispersion of the phase upon subsequent heating in the β-region.

Upon subsequent heating and deformation, a homogeneous structural and phase state is created due to three phase recrystallizations, which consist of deformation in the α + β region at the fourth, sixth and eighth stages and heating in the β region at the fifth, seventh and ninth stages. During deformation in the α + β region, more intense deformation occurs in zones with a smaller grain size, and upon heating in the β region, the process of recrystallization and grain growth proceed more intensively in these zones. In other areas with larger grains, the deformation is less intense and the recrystallization process is proceeding at a slower rate. Thus, the alignment of the structure occurs. With three phase recrystallizations, a homogeneous ultrafine-grained structure is achieved.

A preform with such a structure has a shallow oxidation depth along the grain boundaries, and therefore requires a lower depth of surface machining before rolling the plates in the ninth and tenth stages.

Deformation during rolling at the tenth stage in the α + β-region provides grinding of the intragranular structure and the creation of discontinuity and serration of the boundaries.

In the last eleventh treatment stage (aging), the decomposition of metastable phases and dispersion hardening are achieved.

The implementation of the eleven stages of processing provides high values of low-cycle fatigue at various stress concentrators.

Examples of implementation

Samples were made of titanium alloys, for example, VT-23 and VT-43, processed by the proposed method of thermomechanical processing (1-3) and the prototype method (4), which were subjected to mechanical tests.

Example 1

at the first stage, heating is carried out to a temperature of (T _pp +290) ° C, deformation in four stages upon cooling to a temperature of (T _pp +100) ° C with a change in the direction of deformation by 90 upon alternating draft and drawing with a degree of deformation of 20% for each stage;

at the second stage - heating to a temperature of (T _pp +180) ° C, deformation in four stages upon cooling to a temperature of (T _pp +50) ° C with a change in the direction of deformation by 90 ° C with alternating precipitation and drawing with a degree of deformation of 20% at every stage;

at the third stage - heating to a temperature of (T _pp +80) ° C, deformation in four stages upon cooling to a temperature of (T _pp -30) ° C with a change in the direction of deformation by 90 ° C with alternating precipitation and drawing with a degree of deformation of 20% at every stage;

at the fourth stage - heating to a temperature (T _pp -20) ° C, deformation with a degree of 15%;

at the fifth stage - heating to a temperature (T _pp +30) ° C, deformation with a change in the direction of deformation by 90 ° with a degree of 30% (first change of direction);

at the sixth stage, heating to a temperature of (T _pp -20) ° C, deformation with a change in the direction of deformation by 90 ° with a degree of 20% during cooling to a temperature of (T _pp -110) ° C (second change of direction);

at the seventh stage - heating to a temperature of (T _pp +20) ° C, deformation with a degree of 30% during cooling to a temperature of (T _pp -110) ° C;

at the eighth stage, heating to a temperature of (T _pp -20) ° C, deformation with a degree of 20% during cooling to a temperature of (T _pp -110) ° C;

at the ninth stage, heating to a temperature (T _pp +80) ° C, deformation during rolling with a degree of 40%;

at the tenth stage - heating to a temperature (T _pp -20) ° C, deformation during rolling with a degree of 30%;

then, at the eleventh stage, heating is carried out to a temperature of (T _PP -320) ° C with a holding time of 2 hours, where T _PP is the temperature of the polymorphic transformation.

In this case, the deformation in stages four through eight is carried out in one stage with a change in the direction of deformation by 90 two times (in stages 5 and 6).

Example 2

at the first stage, heating is carried out to a temperature of (T _pp +370) ° C, deformation in four stages upon cooling to a temperature of (T _pp -70) ° C with a change in the direction of deformation by 90 ° when alternating draft and drawing with a degree of deformation of 50% every stage;

at the second stage - heating to a temperature of (T _pp +270) ° C, deformation in four stages upon cooling to a temperature of (T _pp -90) ° C with a change in the direction of deformation by 90 ° C with alternating precipitation and drawing with a degree of deformation of 50% at every stage;

at the third stage - heating to a temperature of (T _pp +170) ° C, deformation in four stages upon cooling to a temperature of (T _pp -200) ° C with a change in the direction of deformation by 90 ° C with alternating precipitation and drawing with a degree of deformation of 50% at every stage;

at the fourth stage - heating to a temperature (T _pp -40) ° C, deformation with a degree of 60%;

at the fifth stage - heating to a temperature (T _pp +60) ° C, deformation with a change in the direction of deformation by 90 ° with a degree of 60% (first change);

at the sixth stage, heating to a temperature of (T _pp -40) ° C, deformation with a change in the direction of deformation by 90 ° with a degree of 40% during cooling to a temperature of (T _pp -130) ° C (second change);

at the seventh stage, heating to a temperature of (T _pp +50) ° C, deformation with a change in the direction of deformation by 90 ° with a degree of 60% during cooling to a temperature of (T _pp -130) ° C (third change);

at the eighth stage, heating to a temperature of (T _pp -40) ° C, deformation with a degree of 60% during cooling to a temperature of (T _pp -130) ° C;

at the ninth stage - heating to a temperature (T _pp +150) ° C, deformation during rolling with a degree of 70%;

at the tenth stage - heating to a temperature (T _pp -50) ° C, deformation during rolling with a degree of 60%;

then, at the eleventh stage, heating is carried out to a temperature of (T _PP -520) ° C with a holding time of 10 hours, where T _PP is the temperature of the polymorphic transformation;

In this case, the deformation in stages four through eight is carried out in one stage with a change in the direction of deformation by 90 ° three times (at stages 5, 6 and 7).

Example 3

at the first stage, heating is carried out to a temperature of (T _pp +320) ° C, deformation in four stages upon cooling to a temperature of (T _pp +20) ° C with a change in the direction of deformation by 90 ° when alternating draft and drawing with a degree of deformation of 30% every stage;

at the second stage - heating to a temperature of (T _pp +220) ° C, deformation in four stages upon cooling to a temperature of (T _pp -20) ° C with a change in the direction of deformation by 90 ° C with alternating precipitation and drawing with a degree of deformation of 30% at every stage;

at the third stage - heating to a temperature of (T _pp +120) ° C, deformation in four stages upon cooling to a temperature of (T _pp -110) ° C with a change in the direction of deformation by 90 ° C with alternating precipitation and drawing with a degree of deformation of 30% at every stage;

at the fourth stage - heating to a temperature (T _pp -30) ° C, deformation with a change in the direction of deformation by 90 ° with a degree of 30 (first change);

at the fifth stage - heating to a temperature (T _pp +45) ° C, deformation with a change in the direction of deformation by 90 ° with a degree of 40% (second change);

at the sixth stage, heating to a temperature of (T _pp -30) ° C, deformation with a change in the direction of deformation by 90 ° with a degree of 30% during cooling to a temperature of (T _pp -120) ° C (third change);

at the seventh stage - heating to a temperature of (T _pp +30) ° C, deformation with a degree of 40% during cooling to a temperature of (T _pp -120) ° C;

at the eighth stage, heating to a temperature of (T _pp -30) ° C, deformation with a change in the direction of deformation by 90 ° with a degree of 40% during cooling to a temperature of (T _pp -120) ° C (fourth change);

at the ninth stage, heating to a temperature of (T _pp +110) ° C, deformation during rolling with a degree of 50%;

at the tenth stage - heating to a temperature (T _pp -30) ° C, deformation during rolling with a degree of 40%;

then, at the eleventh stage, heating is carried out to a temperature of (T _PP -420) ° C with a holding time of 6 hours, where T _PP is the temperature of the polymorphic transformation. In this case, the deformation in the fourth to eighth stages is carried out in one stage with a change in the direction of deformation by 90 ° four times (at stages 4, 5, 6 and 8).

The proposed method of thermomechanical processing of titanium alloys allows an order of magnitude to increase low-cycle fatigue at various stress concentrators.

The application of the proposed method of thermomechanical processing will increase the resource and reliability of parts and components of aircraft.

Table VT23 (T _pp = 920 ° C) σ _B = 1300 MPa σ _{max cycle} = 600 MPa VT43 (T _pp = 910 ° C) σ _B = 1400 MPa σ _{max cycle} = 600 MPa K _t = 2.2 (r _n = 0.75 mm) K _t = 4.0 (r _n = 0.1 mm) K _t = 2.2 (r _n = 0.75 mm) K _t = 4.0 (r _n = 0.1 mm) one 30000 130,000 55,000 210000 2 35,000 250000 60,000 270000 3 32000 170000 57000 240000 four 3000 13000 5000 25,000

Claims (1)

A method for thermomechanical processing of titanium alloys, including multiple heating to a temperature above or below the temperature of polymorphic transformation and deformation during cooling to a temperature below polymorphic transformation, exposure and cooling, characterized in that the thermomechanical treatment is carried out in eleven stages, while the first stage is heated to a temperature _(BTT + 290 ÷ _BTT +370) ° C, the deformation in four stages with cooling to a temperature _(BTT + 100 ÷ _BTT -70) ° C with a variation in the deformation direction at 90 ° with eredovanii precipitation and drawing with the strain of 20-50% at each stage, the second stage - heating to a temperature _(BTT + 180 ÷ _BTT +270) ° C, the deformation in four stages with cooling to a temperature _(BTT + 50 ÷ _BTT -90) ° C with a variation in the deformation direction at 90 ° C with alternating precipitation and drawing with the degree of deformation of 20-50% in each stage, in the third step - heating to a temperature _(BTT + 80 ÷ _BTT +170) ° C, deformation in four stages when cooled to a temperature of (T _pp -30 ÷ T _pp -200) ° C with a change in the direction of deformation by 90 ° C when alternating precipitation and drawing with degrees deformation of 20-50% at each stage, at the fourth stage - heating to a temperature (T _pp -20 ÷ T _pp -40) ° C, deformation with a degree of 15-60%, at the fifth stage - heating to a temperature
(T _pp + 30 ÷ T _pp +60) ° C, deformation with a degree of 30-60%, at the sixth stage - heating to a temperature (T _pp -20 ÷ T _pp -40) ° C, deformation with a degree of 20-40% during cooling to a temperature of (T _pp -110 ÷ T _pp -130) ° C, at the seventh stage, heating to a temperature of (T _pp + 20 ÷ T _pp +50) ° C, deformation with a degree of 30-60% during cooling to a temperature (T _pp -110 ÷ T _pp -130) ° C, at the eighth stage - heating to a temperature (T _pp -20 ÷ T _pp -40) ° C, deformation with a degree of 20-60% during cooling to a temperature ( T _{claims BTT} -110 ÷ -130) ° C, the ninth stage - heating to a temperature _(BTT + 80 ÷ _BTT +150) ° C, a deformation at n okatke with a degree of 40-70% at the tenth step - heating to a temperature _{(BTT BTT} -20 ÷ -50) ° C, deformation during rolling with a degree of 30-60%, followed by the eleventh step is carried out heating to a temperature _(BTT -320 ÷ T _pp -520) ° C with a holding time of 2-10 hours, where T _pp is the temperature of the polymorphic transformation, while the deformation in stages four to eight is carried out in one stage with a change in the direction of deformation by 90 ° from two to four times .