RU2516204C2 - Diffusion welding of metals with non-metals by electrically blasted interlayers - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention may be used in diffusion welding of metal and non-metal parts. Metal interlayer is arranged between parts to be welded and placed in vacuum chamber. Vacuum 0f 10^-2-10^-3 Pa is created in said chamber. Parts are heated to 200-300°C to pass pulse current through said interlayer produced by capacitor discharge to blast said interlayer. Power of said pulse current is selected to make 5-10 kJ so that interlayer is heated to temperature of fused cluster formation to produce nanostructure of layer of parts material and that of metal interlayer in area of their bonding. Compressive pressure is applied to said parts and cooled in vacuum to a room temperature.

EFFECT: high-quality joint.

5 dwg

Description

The diffusion welding method is mainly used to obtain a strong connection of two or more metal bodies.

Nevertheless, the development and improvement of modern electronics in instrumentation, aviation and other industries cannot be imagined without the use of new structural materials based on ceramics, ceramic, quartz, ferrite and other non-metallic materials. These materials are based on oxides of various elements and have unique physicochemical properties.

Compounds of these materials with metals and with each other are widely used for fastening elements of high-frequency systems, for viewing and waveguide windows, shells and cases of electronic and gas-discharge devices, for photocathodes in night-vision devices, cases of laser gyroscopes, in accelerator technology, and in the manufacture of jewelry etc. Traditional methods for producing such compounds — bonding and soldering — do not always provide high strength, vacuum density, heat resistance, reliable thermal and electrical contact, preservation of properties during long-term storage.

Promising methods for joining dissimilar materials with special physical and mechanical properties at low temperature and pressure - welding using electrically exploded interlayers

An analogue is shock welding in a vacuum developed by V.S. Paton. The connection of metals is carried out as in the present method - in a vacuum chamber. The load is also applied once, but it impulse acts on the metals being joined due to a special impactor located outside the vacuum chamber, therefore, the impulse load is similar to the well-known principle of the application filed. The temperature in the welding chamber is obtained due to radiation heating or induction heating of the parts to be welded. In the application filed, the temperature is reached due to the explosion of the conductor.

The closest analogue of the proposed method is a welding method: welding by a pulsed electric discharge in a liquid (SIEC) invention Yutkina L.A. A.A. Deribas, V.M. Kudinov, F.I. Matvienkov. [copyright certificate SU No. 1309404, No. 1600101]. (The author cites extracts from the book by A. A. Yutkin “Electro-hydraulic effect” 1955 Moscow-Leningrad “Mashgiz.” Circulation 6500.)

(The difference of the claimed method consists in the following: a plate is used as an electrically exploded interlayer, not a wire. The process is carried out in vacuum. Technical parameters also differ from those arising in the form of pulsed ultra-high pressure shock waves in a liquid.)

The essence of the electrodynamic effect is that during a high-voltage pulse discharge in a liquid around a discharge zone, pulsed ultrahigh pressures arise in the form of a shock wave in a liquid that deforms plastic and destroys brittle objects near the discharge zone.

A pulsed electrical discharge within the fluid volume is carried out by a pulsed current generator consisting of a high voltage transformer, a rectifier, a capacitor bank, and a switch. The interelectronic gap in the liquid is closed by a metal wire. When a pulsed discharge current is passed through such a wire, a phenomenon occurs called an electric explosion of the conductor.

The disadvantage of this method can be a significant width of the layer leads to the formation of defects in the joint, to obtain the finished adapter requires mechanical processing.

A known method of diffusion welding in vacuum [copyright certificate SU No. 1303335 dated 12.24.85], which allows to heat-weld dielectrics and semiconductors with metals or with each other. A semiconductor wafer made of a material with negative differential conductivity with metallized contact surfaces is mounted on the surface of the parts to be welded from a dielectric or semiconductor, opposite to the one being welded. The parts are heated, squeezed and high voltage is applied to them through the semiconductor wafer, under the influence of which the semiconductor wafer begins to generate high-frequency and ultrasonic vibrations commensurate with the frequency of atomic vibrations in the lattice of the materials being welded, which activate the process.

The disadvantage of this method is the bulkiness of the installation and the insufficient level of quality of the connections.

A known method of diffusion welding of porous materials through a metal interlayer [certificate of authorship SU No. 1750897 of 05/11/90], which allows a gaseous organometallic substance to be pumped between the surfaces of the porous materials cooled to minus temperatures, during which pyrolysis forms a metal interlayer on the surfaces to be welded. Then the parts are heated from the outside and, after the cessation of the vapor-gas mixture, is squeezed and isothermal exposure is performed. In the welding process, the connection of parts begins from their periphery to the center.

The disadvantage of this method is the limited application. Significant cost of implementation time.

The combination of materials using an electric explosion of interlayers in vacuum (SVzPV) allows us to solve these problems.

The method allows to implement the principle of models and nanotechnologies for connecting structural non-metals with metals and non-metals through electrically exploded interlayers in a vacuum.

Analysis of the results of an electric explosion

For an electric explosion of conductors, an oscillatory circuit with variable resistance is used. The explosion pattern of the interlayer in vacuum is shown in figure 1

Scheme for welding using an electric explosion of conductors:

1 - power source

2 - high voltage pulse capacitor,

3 - circuit breaker,

4 - charging resistance;

5 - exploding conductor,

6 - welded parts,

7 - vacuum chamber,

8 - pumping system,

9 - pressure mechanism.

The temperature and time regime of an electric explosion determines the nanostructure of materials in the joint zone. The temperature at different points of the exploding conductor is different and can range from room temperature to evaporation temperature. The model for determining the average temperature of the conductor is a system of differential equations:

, $$\frac{d}{dt}V\left(t\right)=Y\left(t\right)$$

,

, $$\frac{d}{dt}Y\left(t\right)+\frac{R_O+R_n\left(t,d\right)}{L}\cdot Y\left(t\right)+\frac{\mathrm{one}}{L\cdot C}\cdot V\left(t\right)=0$$

,

, $$c_P\left(t\right)\cdot m\left(d\right)\cdot \frac{d}{dt}T\left(t\right)={\left(C\cdot Y\left(t\right)\right)}^2\cdot R_n\left(t,d\right)-{\epsilon }_n\cdot {\sigma }_c\cdot T{\left(t\right)}^{\mathrm{four}}\cdot S_n-S_n\cdot {\lambda }_O\cdot \frac{T\left(t\right)-T_O}{L_X}$$

,

c _P (t) = a +10 ^-3 · b · T (t) +10 ⁵ · c · T (t) ^-2 ,

where V (t) is the interlayer voltage; R _O is the resistance of the circuit; R (t, d) is the interlayer resistance; L is the inductance of the circuit; C is the capacity of the circuit C _P (t) is the capacity of the interlayer; m _d - mass of the interlayer S _n - interlayer area σ _C - Stefan-Boltzmann constant L _X - characteristic length; λ _O is the coefficient of thermal conductivity of parts; T _O - temperature snap.

The first two equations describe the discharge of a serial RLC circuit. The third is the balance of energy in the conductor: an increase in the internal energy of the conductor is equal to the difference between the supplied electric power and the power consumption for heat sink and thermal radiation. The fourth equation describes the temperature dependence of the heat capacity of the interlayer. From this system of equations, the interlayer stress, the interlayer temperature, and the time derivative of the voltage are determined. The current in the conductor and power are determined by the formulas:

; $$W_n\left(t_k\right)={\displaystyle \underset{O}{\overset{t_k}{\int }}{I}_n{\left(t\right)}^2\cdot R_n\left(t,d\right)dt}$$

$$I_n\left(t\right)=C\cdot Y_U\left(t\right)$$

; $$W_n\left(t_k\right)={\displaystyle \underset{O}{\overset{t_k}{\int }}{I}_n{\left(t\right)}^2\cdot R_n\left(t,d\right)dt}$$

The dependences of voltage, current, and interlayer temperature on time are shown in FIG. The dependence of the interlayer resistance on time was determined from the percolation model and approximated by the formula

, $$R_n\left(t,d\right)=R_{On}\left(d\right)\cdot \exp \left(\frac{t}{{\tau }_r}\right)$$

,

where τ _r = K _r (R _O + R _On (d)) · C is the discharge time constant

Dependence of current, A (a), voltage, V (b), and interlayer temperature, K (c) on time.

The constructed model allows us to determine the average temperature of the interlayer during the explosion, depending on the material of the interlayer and the parameters of the discharge circuit: capacitor capacitance, circuit inductance, interlayer dimensions. High temperatures (up to 30000 K) and short time processes (microseconds) ensure the formation of a nanostructure from the materials of the parts to be connected and the exploding conductor in the joint zone.

Local temperatures in the contact zone were determined from the percolation model. The flat conductor is presented in the form of a grid of resistances with random or regular scatter of resistance values. In the proposed qualitative model, the circuit is calculated by the matrix-topological method according to the following algorithm. Initially, the characteristics of the interlayer material in the solid and liquid states (conductivity, density, specific heat, melting point, boiling point, temperature coefficients, thermal conductivity, molar masses), initial temperature, voltage, element resistances, and interlayer dimensions are set. Further, at each time step, currents, electric capacities, temperature, calculated by the equation of balance of internal and electric energy, are calculated in each branch of the grid. If the evaporation temperature is reached in the branch, it is assumed that the resistance has burned out. Blown resistances form clusters, which, when combined, form a discontinuous cluster that destroys the interlayer and stops the flow of current. The dependence of the interlayer resistance on time R _n (t) was used to calculate the parameters of the electric circuit of the oscillatory circuit. This dependence was approximated by the exponent.

The temperature of the branches for three points in time is shown in figure 3. The "peaks" of temperatures at the grain boundaries are clearly visible.

According to the proposed percolation model and experimental results, the following physical picture of a conductor explosion is presented. Since the resistance of the grain boundaries is much larger than the resistance in the bulk, melting starts from the grain boundary and extends into their depths.

In order to determine the mechanism of interaction of materials during UHFW, the crystallographic aspects of the formation of compounds of dissimilar materials in the solid state at low temperatures, when heterodiffusion or diffusion on the welding surface does not have a noticeable development, are studied. By analogy with diffusion welding, such a joint can be classified as an adhesive type joint.

Studies of diffraction patterns of a metal foil after welding using SVZPV are presented in Fig. 4, and the initial foil from material 47ND in Fig. 5, with vectors of the preferred orientation of the crystallographic planes bounding the foil.

Thus, melting and crystallization have led to a reorientation of the preferred crystallographic directions in the metal interlayer.

The X-ray diffraction studies of the surface of the nickel interlayer after the destruction of the compound along the contact boundary showed a significant change in the intensities of reflections from planes with small Miller indices.

This makes it possible, when using SVzPV, to obtain high-quality compounds of metals and non-metals, as well as non-metals with non-metals (ceramics + ferrites, glass + quartz glass, ruby + ruby, etc.). Welding was carried out at a residual pressure in a vacuum chamber of 10 ^-4 Pa, a welding pressure of 20 ... 30 MPa and a temperature of parts of 500 ... 600 K.

The proposed method of joining materials (metals with metals, metals with non-metals and non-metallic materials with each other) comprising heating the materials to be welded in a vacuum of 10 ^-2 -10 ^-3 Pa (Pascal), primary heating to 200-500 ° C in a vacuum with then passing through a metal interlayer selected by the physicochemical properties close to the materials to be joined (the material is selected when welding metals from the mutual solubility of materials, for example: when connecting copper with molybdenum, these are mutually soluble materials, the interlayer it is selected from nickel, which is mutually soluble with copper and molybdenum; when combined with non-metallic materials, if the interlayer material forms a new chemical compound with non-metal, for example: vacuum dense ceramic VK-1, VK-2 with aluminum or titanium). A pulsed current with a power of 5-10 kilo joules due to the discharge of a capacitor, characterized in that the pulsed current provides heating of the interlayer to the temperature of formation of molten clusters, which, using the electrical conductivity effect, combine to form a discontinuous cluster, destroying the interlayer, with the formation of a nanostructure from materials of joined parts and of an exploding interlayer with a characteristic sound signal (such as an explosion), and stopping the flow of current, immediately after that I compress its pressure, the items in the chamber are cooled to room temperature, this flow process provides forming secure connections by adjusting the crystal lattices of the parts.

Claims (1)

A method for diffusion welding of parts from metallic and nonmetallic materials, including placing between a welded part installed in a vacuum chamber a metal interlayer, heating them, passing a pulsed current through the interlayer obtained by discharging a capacitor with a power sufficient to explode it, applying to the welded parts compression pressure and cooling the parts in the vacuum chamber to ambient temperature, characterized in that in the vacuum chamber a vacuum of 10 ^-2 to 10 ^-3 Pa, the heating parts osuschest They are added to a temperature of 200-300 ° C, and the pulse current power is chosen to be 5-10 kJ from the condition of heating the interlayer to the temperature of formation of molten clusters, which provides a nanostructure of the layer from materials of the welded parts and the metal interlayer in the zone of their connection.

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