RU2569444C2 - Diffusion welding of thin-wall laminar titanium structures - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention can be used for production of titanium laminar structures, for example, complex 3D structures, in particular, cellular fillers, fan blades, air intakes, outlets of accelerators. First, welding pressure is determined to be applied to titanium alloy work pieces to be compressed in steel tooling. This is performed to get workpiece creeping at the rate equal to that of unstressed workpiece of the same titanium alloy at pressure of physical contact between their surfaces. Welding pressure is defined with due allowance for relative height of welding sections and hardening of workpiece titanium alloy under compression at welding temperature.

EFFECT: lower contact friction between steel tooling and titanium parts of the structure being welded.

3 dwg, 3 ex

Description

The invention relates to diffusion welding and can be used in the manufacture of titanium thin-walled layered structures with a contact surface, which is a combination of simple shapes with a small cross section, for example, complex three-dimensional structures in aerospace applications, such as a honeycomb core, a fan blade, an air intake, and also an exhaust windows in accelerator technology.

A known method of diffusion welding of a bag for the manufacture of a hollow fan blade by superplastic molding, comprising assembling a bag of three blanks of the composition Ti-6Al-4V with a thickness of 1.0 mm with marked areas subjected to joining with a width of 8 mm and 20 mm and not subject to joining, and subsequent placement package in the heating block of the press between the flat plates. When implementing the method of diffusion welding using modes characterized by known values of temperature and pressure. In particular, after heating to a temperature of 850 ° C and reaching a vacuum depth of at least 1.33 Pa, a press force is applied to the bag, providing a pressure of 2 MPa, and is kept under pressure for 2 hours to carry out the diffusion welding process (description of patent RU 2291019 C2, IPC B21D 53/78 (2006.01), B21D 26/02 (2006.01), published January 10, 2007).

There is a method of diffusion welding of a bag for the manufacture of a honeycomb core made of titanium alloys, in which the material that impedes welding is applied to sections of sheet blanks made of foil that are not to be joined, and technological nitrided sheet gaskets with honeycomb width are placed in areas to be joined. Sheet blanks with gaskets are collected in a bag, placed in a stamp, under vacuum, heated to the polymorphic transformation temperature of the titanium alloy of the workpiece material and squeezed in two stages. At the first stage, corrugations are formed on the blanks by settling the honeycomb packet until the gaskets are closed in height. At the second stage, the honeycomb blanks are connected and the compressive force is selected from the conditions for creating gaskets on the connected pressure sections of 2 MPa. Upon completion of the diffusion welding process, steel gaskets are removed from the preformed cells of the obtained semi-finished product, and the semi-finished product is stretched to obtain a honeycomb block with finally formed cells (description to patent RU 2397054 C1, IPC B23K 20/18 (2006.01), B23K 101/02 (2006.01) published on 08/20/2010).

A disadvantage of the known methods is the use for diffusion welding of modes characterized by known values of temperature and pressure in accordance with the titanium alloy of the workpiece material.

In the known methods, tooling is used from steel sheets having, during diffusion welding, a higher resistance to high-temperature deformation than welded titanium billets. In this case, titanium elements of a layered structure can be considered as a plastic (soft) layer located between the "rigid" steel tooling.

In the conditions of diffusion welding, when titanium comes in contact with steel equipment, due to the presence of friction, the steel deters titanium deformation, i.e. the so-called "contact hardening" of titanium occurs. Since the formation of a diffusion joint is based on the high-temperature deformation of the welded workpieces under the action of compressive pressure, the development of “contact hardening” can lead to a decrease in the creep rate of titanium and a deterioration in the quality of the diffusion joint.

The degree of “contact hardening” (limited deformation) for the case of compression of a “plastic” titanium layer located between two “hard” steel layers depends both on the technological parameters of the test (temperature, applied pressure) and on the geometric dimensions of the “plastic” layer — its relative height λ (λ = h / d, where h is the height, d is the diameter or width of the layer).

Thus, when developing the technology of diffusion welding of titanium thin-walled layered structures, it is necessary to adjust the welding conditions, and in particular the welding pressure, taking into account the relative height λ of the welded sections under conditions of high temperature deformation and the development of contact hardening in the welded titanium billets.

The objective of the utility model is to improve the quality of the welded joint by improving the diffusion welding technology using steel tools in the manufacture of titanium thin-walled layered structures with a combination of small sections and a relative height λ of the welded layers of less than 2.0.

EFFECT: reduced contact friction between steel tooling and titanium parts of a welded structure.

The technical result is achieved by the fact that in the method of diffusion welding of thin-walled layered titanium structures with a relative height λ, the welded sections are less than 2.0, in which the package of welded workpieces is placed in a steel tool, the assembly is heated and under vacuum conditions, pressure welding isothermally held in the temperature range of the polymorphic transformation of the workpiece material, characterized in that the welding pressure p _y is determined from the condition:

where p is the pressure of physical contact between the surfaces of the workpieces with λ≥2.0, MPa; k _y is a numerical coefficient taking into account the relative height of the welded sections and hardening of the titanium alloy of the workpiece material under compression at the welding temperature, 1.0 <k _y <5.64; n is an empirical coefficient characterizing the effect of welding pressure on the change in creep rate of a titanium alloy of the workpiece material.

Condition (1) is established experimentally and allows you to determine the pressure p _y , which must be applied to titanium billets in cramped conditions (λ <2.0) to ensure their creep with a speed έ _y equal to the creep rate έ of billets from that titanium alloy in a free state (k≥2.0) at a known pressure p of the formation of physical contact.

Figure 1 shows a hollow fan blade; figure 2 - element of the air intake; figure 3 is a section of the exhaust window of the electron accelerator.

Examples of calculation of welding pressure during diffusion welding of thin-walled layered titanium structures with a relative height λ of welded sections of less than 2.0.

For these structures, the numerical value of k _{y was} calculated from the experimentally established dependence k _y = 0.954 + 0.197 / (0.042 + λ) ² . The value of the coefficient n was determined experimentally for each titanium alloy, taking it equal to the approximating coefficient in the equation for changing the creep rate of the form έ = k · p ⁿ · exp (E / RT), where k is the proportionality coefficient, sec ^-1 ; p is the numerical value of the welding pressure measured in MPa; n is an empirical coefficient characterizing the creep of the workpiece material; E is the activation energy, J / mol; R is the gas constant, J / (K · mol); T is the heating temperature, K.

Example 1

Package for the manufacture of a hollow fan blade (Fig. 1) from billets 1, 2, 3 of the composition of the VT6 alloy (Ti-6Al-4V) with a thickness of 1.0 mm (h / 2) with sections 4 subjected to the connection of a minimum width of 8 mm (d ) The relative height of the welded sections is λ = (1.0 + 1.0) / 8 = 0.25.

The quantity of the welding pressure p _y determined, taking for computing the estimated value of the coefficients k _y = 3,41 and n = 0,9 and p = pressure of 2 MPa. According to a numerical calculation according to dependence (1), p _y = 3.41 ^{1 / 0.9} · 2 = 3.91 · 2 = 7.82 MPa.

The diffusion welding process is carried out according to the mode:

heating to a welding temperature T = 990 ° C; welding pressure p _y = 7.82 MPa is maintained for 60 minutes.

Example 2

The air intake element (Fig. 2) from OT4 alloy blanks with a thickness of 0.3 mm (h / 2), consisting of a corrugated sheet 5 with corrugations 6 mm wide (d) at the junctions with a flat sheet 6. Relative height of the welded sections λ = (0 , 3 + 0.3) / 6 = 0.1.

The value of the welding pressure p _{y was} determined by taking the calculated values of the coefficients k _y = 2.92 and n = 1.2 and the pressure p = 2 MPa for calculations. According to a numerical calculation, p _y = 2.92 ^{1 / 1.2} · 2 = 2.44 · 2 = 4.88 MPa.

The diffusion welding process is carried out according to the mode:

heating to a welding temperature T = 950 ° C; welding pressure p _y = 4.88 MPa is maintained for 50 minutes.

Example 3

Section of the exit window of the electron accelerator (Fig. 3) from VT14 alloy blanks, consisting of two support grids 7, 8 1.2 mm thick with oval holes and jumpers 9 with a minimum width d of 2.0 mm at the junctions with the foil 10 thick 0.08 mm located between them. The relative height of the welded sections is λ = (1.2 + 1.2 + 0.08) / 2.0 = 1.24.

The value of the welding pressure p _{y was} determined by taking the calculated values of the coefficients k _y = 2.02 and n = 1.2 and the pressure p = 2 MPa for calculations. According to a numerical calculation, p _y = 2.02 ^{1 / 1.2} · 2 = 2.44 · 2 = 3.6 MPa.

The diffusion welding process is carried out according to the mode:

heating to a welding temperature T = 950 ° C; welding pressure p _y = 3.6 MPa is maintained for 65 minutes.

Claims (1)

The method of diffusion welding of thin-walled layered titanium structures, including placing a package of welded billets of titanium alloy in a steel tool, heating the assembly and welding under pressure in a vacuum during isothermal holding in the temperature range of polymorphic transformation of titanium alloy billets, characterized in that the welding pressure p _{I have} to be applied to the workpiece of the titanium alloy being in compression conditions in steel tooling of conditions ensuring creep έ blanks at a rate _in equal to έ creep speed in free state blanks from the same titanium alloy at a pressure p of the physical contact between their surfaces, wherein the welding pressure is determined from the condition:
P _y ⁼ pk _y ^{1 / n} , MPa, where
k _y is a numerical coefficient equal to 1.0 <k _y <5.64, taking into account the relative height of the welded sections λ = h / d, where h is the height, d is the diameter or width of the welded layer, and hardening of the titanium alloy of the workpieces under compression at welding temperature
n is an empirical coefficient characterizing the influence of the welding pressure on the creep rate έ of the titanium alloy of the billets, which is determined experimentally for each titanium alloy, taking it equal to the approximating coefficient in the equation for changing the creep rate of the titanium alloy έ = k · p ⁿ · exp (E / RT ), where
k is the coefficient of proportionality, sec ^-1 ;
p is the numerical value of the welding pressure, MPa;
E is the activation energy, J / mol;
R is the gas constant, J / (K · mol);
T is the heating temperature, K.

Images