Method of thermo-mechanical treatment of two-phase titanium alloys

FIELD: metallurgy; mechanical engineering; aircraft engine manufacture; medicine.

SUBSTANCE: proposed method includes intensive plastic deformation of blank in crossing vertical and horizontal channels at temperature of 600°C at stored logarithmic degree of deformation no less than 2. Heat treatment performed before intensive plastic deformation includes hardening from temperature of polymorphous transformation of minus 10°C in water and high-temperature aging at temperature of 675-700°C continued for 4 hours at cooling in air; after intensive plastic deformation, blank is subjected to extrusion performed in several passes at temperature of 300°C and drawing coefficient no less than 1.2.

EFFECT: improved strength characteristics (ultimate strength, yield point, fatigue range); enhanced homogeneity at retained satisfactory ductility.

1 tbl, 1 ex

 

The invention relates to thermo-mechanical processing with the change of the mechanical properties of the material and can be used in mechanical engineering, aircraft engine industry and medicine in the manufacture of semi-finished products of two-phase titanium alloys.

Known methods of processing two-phase titanium alloys to improve their mechanical properties.

For example, the mode of deformation of the workpieces in overlapping horizontal and vertical channels (see Wmel, Vigaplus, Viesnica "a plastic structure formation metals", Minsk: Nauka and Technica, 1994, p.26) allows you to consolidate the metal due to the intense shear strain.

A method of processing workpieces, including severe plastic deformation of the blank in overlapping horizontal and vertical channels pressurized in the latter, which was carried out at the initial and final stages of the deformation process (patent RF N 2139164, the IPC 21 J 5/00, publ. 10.10.1999,).

There is a method of deforming the workpiece in the intersecting vertical and horizontal channels at a temperature of 600°With (To S.Y., Jang BC, Tires DH, Li S. Effect of temperature and initial microstructure on equal channel angular extrusion alloy Ti-6Al-4V, Script, materialia, No. 48, 2003, s-202).

Known methods do not allow to obtain the required is provided by the uniform strength characteristics, including indicators of fatigue.

The closest to the invention is a method of deforming the workpiece in the intersecting vertical and horizontal channels at 600° (Yapici GG, Karaman, I., Z.P. Luo, Rivers, Microstructure and mechanical properties of powder alloy Ti-6Al-4V, intensely deformed using equal-channel angular pressing, Script, materialia, No. 49, 2003, s-1027).

This method can be used to enhance the strength characteristics of the processed material, but insufficient to be used in critical structures. In addition, the known method does not provide the uniformity of structure and mechanical properties over the cross section of the workpiece.

The invention is aimed at increasing the level and uniformity of strength and fatigue characteristics of two-phase titanium alloys while maintaining ductility.

This object is achieved by a method of obtaining ultrafine-grained billets, including severe plastic deformation of the blank in overlapping vertical and horizontal channels at a temperature of 600°With accumulated logarithmic degree of deformation e≥2. Unlike the prototype before severe plastic deformation conduct heat treatment, which includes quenching from a temperature of polymorphic transformation mi the us 10° With water and high-temperature aging at 675-700°C for 4 hours, air cooling, and after severe plastic deformation perform extrusion in several cycles at a temperature of 300°With drawing ratio not less than 1.2.

Preliminary thermal treatment of two-phase titanium alloys allows you to create a structure that is favorable for improving the uniformity of the obtained characteristics.

Extrusion used after severe plastic deformation in intersecting vertical and horizontal channels, allows you to create a strain pattern, similar to the conditions of all-round compression that provides increased deformability of such hard materials, such as two-phase titanium alloys. For example, processes such as drawing or rolling, under the same temperature and time conditions and degrees of deformation can not provide the high deformability of the materials due to the implementation of less favourable for its improvement schemes deformation.

The combination of intensive plastic deformation in an intersecting channels and extrusion in these modes provides additional refinement of the structure of the workpieces, and a preliminary heat treatment can improve the uniformity of the obtained structures is, which leads to the increase of the level and uniformity of strength and fatigue characteristics while maintaining ductility.

The method is as follows.

Preparation of two-phase titanium alloy in the form of a rod subjected to quenching from the temperature of polymorphic transformation minus 10°With water and high-temperature aging at 675-700°C for 4 hours with cooling. This time-temperature regime of heat treatment provides an intermediate strength compared with the properties of annealed material and increased ductility compared with high-strength condition (Kolachev B.A., Polkin I.S., Talalaev E Titanium alloys in different countries: a Handbook. - M.: VILS, 2000. 316 C.). This allows subsequent intensive plastic deformation of two-phase titanium alloys. In addition, the specified heat treatment is a mixed microstructure, which contains a large globular α-phase (no more than 20%) and lamellar β-developed structure. This morphology ensures uniformity of ultrafine-grained structure in the cross section of the workpiece. After the heat treatment is carried out intensive plastic deformation in the intersecting channels. The deformation is carried out at a temperature of 600°With few consequences which subsequently passes, between which the rod rotate around the longitudinal axis by 90°. The number of passes is determined by the accumulated achievement of the logarithmic strain e≥2.

After deformation in an intersecting channels, the workpiece is subjected to the edit processing on a lathe to remove the defective layer.

In the next step, the workpiece is subjected to extrusion in a few cycles with a gradual decrease in diameter and increase the length of the workpiece with a set of drawing ratio of 1.2. The temperature of extrusion 300°was determined empirically and is a temperature at which the billet is formed ultrafine-grained structure that provides a combination of properties: high strength and fatigue properties while maintaining ductility. After this stage they control the mechanical properties in tension at room temperature and the control of the microstructure.

An example of a specific implementation.

Took the rod of the alloy Ti-6Al-4V with a diameter of 40 mm and length 120 mm Temperature of polymorphic transformation of the alloy Ti-6Al-4V was 960°C. the Rod was tempered in water with a temperature of 950°and were subjected to aging at a temperature of 675°C for 4 hours with cooling. Thereafter, the rod was subjected to severe plastic deformation by the above method. Hugo is the intersection of the channels f=120° . Temperature deformation 600°C. the Number of consecutive passes of n=2. After editing and processing on a lathe, the workpiece diameter was 36 mm

In the next step, the rod was subjected to extrusion at a temperature of 300°C. the Number of cycles of extrusion was 6, resulting in the workpiece diameter is reduced from 36 to 20 mm, and the length of the workpiece is increased from 120 to 300 mm was Further carried out the control of the homogeneity of the microstructure in the cross section of the workpiece. The control of mechanical properties in tension at room temperature showed the values shown in table 1. For comparison, the table shows the mechanical properties of the alloy to thermomechanical processing on the proposed method, and properties after processing by a known method prototype.

Table 1.

The mechanical properties of the alloy Ti-6Al-4V in different States
Mechanical

properties of alloy
Status alloy
Before processing, the proposed methodAfter processing by the method prototypeAfter treatment by the proposed method
Tensile strength, MPa94012841370
Yield strength, MPa 84010421270
Elongation, %16711
Relative narrowing, %453537
The limit of endurance, MPa550650695

Thus, the proposed method of thermomechanical processing of two-phase titanium alloys can significantly improve the level and uniformity of strength and fatigue characteristics of the processed material while maintaining ductility.

The method of thermomechanical processing of two-phase titanium alloys, including severe plastic deformation of the blank in overlapping vertical and horizontal channels at a temperature of 600°With accumulated logarithmic degree of deformation of at least two, wherein before severe plastic deformation conduct heat treatment, which includes quenching from a temperature of polymorphic transformation minus 10°With water and high-temperature aging at a temperature of 675-700°C for 4 h with cooling, and after severe plastic deformation perform extrusion billet in multiple passes at a temperature of 300°With drawing ratio not less than 1.2.



 

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