RU2834114C1 - Method for electroexplosive sputtering of electroerosion-resistant composite coating containing matrix based on silver and nickel with inclusions of titanium diboride on copper electrical contact - Google Patents

Abstract

FIELD: coating metallic material.

SUBSTANCE: invention relates to a method for electroexplosive sputtering of an electroerosion-resistant composite coating on a copper electrical contact. Electric explosion of double-layer conductor is performed. One of the layers of the above conductor consists of silver foil with mass of 100-400 mg, and the second one – of nickel foil with mass equal to 0.05-0.1 of the mass of the first layer. On the surface of the double-layer conductor there is a powder of titanium diboride weighing 0.5-1.5 of the mass of silver foil. Pulsed multiphase plasma jet is formed from explosion products. Surface of copper electric contact is melted by it at absorbed power density of 4.5-5.5 GW/m² with deposition of explosion products on surface of copper electric contact with formation of electroerosion-resistant composite coating. Said coating contains a matrix based on silver and nickel with inclusions of titanium diboride.

EFFECT: obtaining a coating having high electrical erosion resistance, electrical conductivity and stability of operation in conditions of switching electrical networks.

1 cl, 4 dwg, 2 ex

Description

The invention relates to a technology for applying coatings to metal surfaces using concentrated energy flows, in particular, to a technology that ensures an increase in the electroerosion resistance of electrical contacts, in particular switching electrical contacts made of copper, by producing coatings on their surface containing a matrix based on silver and nickel with inclusions of titanium diboride, which can be used in electrical engineering as electroerosion-resistant coatings with high operational stability under conditions of switching electrical networks.

A method is known for applying electrical erosion-resistant coatings based on titanium diboride and copper to copper electrical contacts (RU No. 2539138, IPC C23C 4/12, C23C 14/14, C23C 4/10, C23C 14/32, H01H 1/02, published 10.01.2015). A method for applying electrical erosion-resistant coatings based on titanium diboride and copper to copper electrical contacts involves an electrical explosion of a composite electrically exploded conductor consisting of a two-layer flat copper shell weighing 60-360 mg and a core in the form of titanium diboride powder weighing 0.5-2.0 times the shell mass, forming a pulsed multiphase plasma jet from the explosion products, melting the surface of a copper electrical contact with it at an absorbed power density of 4.5-6.5 GW/ ^m2 , depositing the explosion products on the surface, forming a composite coating of the _TiB2 -Cu system on it, and subsequent pulse-periodic electron beam treatment of the coating surface at an absorbed energy density of 40-60 J/ ^cm2 , a pulse duration of 150-200 μs, and a number of pulses of 10-30 imp.

The disadvantage of the method is low electrical erosion resistance, electrical conductivity and stability of the coating based on titanium diboride and copper under the conditions of switching electrical networks. Another disadvantage of the method is the two-stage formation of the coating, including electroexplosive spraying and electron beam processing.

The closest to the claimed invention is the method of electroexplosive spraying of an electroerosion-resistant coating based on titanium diboride and silver onto a copper electrical contact (RU No. 2806954, IPC C23C 4/10, C23C 4/126, published 08.11.2023). A method for electroexplosive spraying of an electroerosion-resistant coating based on titanium diboride and silver onto a copper electrical contact, characterized in that an electrical explosion of silver foil weighing 100-400 mg with titanium diboride powder placed on it weighing 0.5-1.5 times the foil mass is carried out, a pulsed multiphase plasma jet is formed from the explosion products, the surface of the copper electrical contact is melted with it at an absorbed power density of 4.5-5.5 GW/ ^m2 with the deposition of explosion products onto the surface of the copper electrical contact with the formation of an electroerosion-resistant composite coating containing a matrix based on silver with inclusions of titanium diboride.

The disadvantage of this method is the low electrical erosion resistance, electrical conductivity and stability of the coating based on titanium diboride and silver under the conditions of switching electrical networks.

The technical problem solved by the claimed invention is the production of a coating containing a matrix based on silver and nickel with inclusions of titanium diboride on a copper electrical contact, which has high electrical erosion resistance, electrical conductivity and operational stability under conditions of switching electrical networks.

The existing technical problem is solved by creating a method for electroexplosive spraying of an electroerosion-resistant composite coating containing a silver- and nickel-based matrix with titanium diboride inclusions onto a copper electrical contact, characterized in that an electrical explosion of a two-layer conductor is carried out, one of the layers of which consists of silver foil weighing 100-400 mg, the second layer - of nickel foil weighing 0.05-0.1 of the mass of the first layer, with titanium diboride powder weighing 0.5-1.5 times the mass of silver foil placed on the surface of the two-layer conductor, a pulsed multiphase plasma jet is formed from the explosion products, the surface of the copper electrical contact is melted with it at an absorbed power density of 4.5-5.5 GW/m ² with the deposition of explosion products onto the surface of the copper electrical contact with the formation of an electroerosion-resistant composite coating containing a silver- and nickel-based matrix with diboride inclusions titanium.

The technical result obtained by implementing the invention is that, during an electrical explosion of a two-layer conductor, one of the layers of which consists of silver foil, the second layer - of nickel foil, with titanium diboride powder placed on the surface of the two-layer conductor, the destruction products form a plasma jet, which serves as a tool for forming an electroerosion-resistant composite coating on the surface of a copper electrical contact, containing a matrix based on silver and nickel with inclusions of titanium diboride. The advantage of the claimed method compared to the prototype is the formation of a coating that has better electroerosion resistance, electrical conductivity and operational stability under switching conditions of electrical networks. Adding nickel to electroexplosive coatings containing a silver-based matrix with inclusions of titanium diboride makes it possible to achieve this. The structure of the resulting electroexplosive coating is a matrix based on silver and nickel with inclusions of titanium diboride. Achieving this result is ensured by adding nickel. The combination of better electrical conductivity and hardness of the silver-nickel matrix compared to silver allows for the formation of a pair of electrical contacts that have better performance characteristics. This allows for increased electrical erosion resistance, electrical conductivity, and operational stability in electrical network switching conditions for composite coatings containing a silver-nickel matrix with titanium diboride inclusions compared to coatings containing a silver-based matrix with titanium diboride inclusions.

The use of this coating reduces the transient resistance of electrical contacts and maintains the constancy of electrical parameters (on time, proper on time, proper off time, total circuit off time, time-current characteristic, off current, on current, resistance to through currents, mechanical wear resistance, switching wear resistance, recovery voltage, switching position diagram) due to a combination of characteristics of the structure and phase composition. The proposed electrical erosion-resistant composite coating is a silver and nickel matrix containing titanium diboride inclusions and has a bimodal structure: submicrocrystalline (confirmed by the results of scanning electron microscopy) and nanocrystalline (confirmed by the results of transmission electron microscopy). The strength characteristics of the proposed coating allow for rapid running-in of electrical contacts, so no final abrasive treatment of the coating surface is required before use.

Studies using the scanning electron microscopy method have shown that during electroexplosive spraying on a copper electrical contact by means of an electrical explosion of a two-layer conductor, one of the layers of which consists of silver foil weighing 100-400 mg, the second layer of nickel foil equal to 0.05-0.1 of the mass of the first layer, with titanium diboride powder weighing 0.5-1.5 of the mass of silver foil placed on the surface of the two-layer conductor, a pulsed multiphase plasma jet is formed from the explosion products, the surface of the copper electrical contact is melted with it at an absorbed power density of 4.5-5.5 GW/ ^m2 with the deposition of explosion products on the surface of the copper electrical contact with the formation of an electroerosion-resistant composite coating containing a matrix based on silver and nickel with inclusions of titanium diboride, the formation of a coating structure representing a matrix based on silver and nickel with inclusions of titanium diboride was confirmed. The specified mode, in which the absorbed power density is 4.5-5.5 GW/ ^m2 , is established empirically and is optimal, since at an impact intensity below 4.5 GW/ ^m2, no relief is formed between the coating and the substrate made of copper electrical contact, as a result of which peeling of the coating is possible, and at an impact intensity above 5.5 GW/ ^m2, an intensive scattering of explosion products occurs, which leads to a decrease in the content of a silver-nickel-based matrix with titanium diboride inclusions in the electrical erosion-resistant composite coating compared to the state in the original materials by 5%. When the mass of silver foil is less than 100 mg, it becomes impossible to place titanium diboride powder on its surface due to a decrease in the area of the two-layer conductor. If the silver foil mass value is more than 400 mg, the electroerosion-resistant composite coating containing a silver-nickel matrix with titanium diboride inclusions has a large number of defects on the surface of copper electrical contacts. In this case, the defects are represented by fragments of silver foil that did not break down during the electrical explosion, but only partially melted and stuck to the coating surface. If the nickel foil mass value is less than 0.05 of the mass of the first layer of silver foil, the coating properties do not increase due to the addition of nickel, i.e., adding nickel in such an amount is insufficient. If the nickel foil mass value is more than 0.1 of the mass of the first layer of silver foil, the coating properties deteriorate due to the excess of nickel, i.e., adding nickel in such an amount is excessive and impractical. If the titanium diboride powder mass value is less than 0.5 of the mass of silver foil, the electroerosion resistance and stability of the coating under electrical network switching conditions are reduced. Titanium diboride, when forming an electrical erosion-resistant composite coating containing a silver-nickel matrix with titanium diboride inclusions, is a phase with a high melting point and hardness. A decrease in the titanium diboride concentration does not affect the increase in electrical erosion resistance and the stability of the coating under electrical network switching conditions. When the titanium diboride powder mass is more than 1.5 of the silver foil mass, the explosion products are not transferred to the surface of the copper electrical contact. In this case, the excess mass of titanium diboride powder does not allow the pulsed plasma jet to form, therefore, the coating is not formed.

The proposed method is illustrated by figures, where:

Fig. 1 shows the cross-sectional structure of the surface layer of an electrical erosion-resistant composite coating containing a matrix based on silver and nickel with inclusions of titanium diboride - the coating was obtained on electrical copper grade M00;

Fig. 2 shows the cross-sectional structure of the surface layer of an electrical erosion-resistant composite coating containing a matrix based on silver and nickel with inclusions of titanium diboride with the superposition of characteristic X-ray emissions of boron (yellow), silver (pink), copper (blue), nickel (green) and titanium (red) - the coating was obtained on electrical copper grade M00;

Fig. 3 shows an enlarged image of the cross-sectional structure of the surface layer of an electrical erosion-resistant composite coating containing a matrix based on silver and nickel with inclusions of titanium diboride - the coating was obtained on electrical copper grade M00;

Fig. 4 shows an enlarged image of the cross-sectional structure of the surface layer of the electrical erosion-resistant composite coating containing a matrix based on silver and nickel with inclusions of titanium diboride with the superposition of characteristic X-ray emissions of nickel (orange), nitrogen (yellow) [nitrogen is present in an amount of less than 0.01 at.%, but since nitrogen is determined automatically with all other identified elements, its designation cannot be removed in the resulting image], titanium (pink), silver (blue) and boron (red) - the coating was obtained on electrical copper grade M00;

Examples of specific implementation of the method:

Example 1.

The contact surface of the copper electrical contact of the KKT 61 command controller with an area of 1.5 cm was subjected to processing.², copper grade M00. A two-layer conductor was used, one of the layers of which consisted of silver foil weighing 100 mg, the second layer - of nickel foil weighing 5 mg, which is 0.05 of the mass of the first layer. Titanium diboride powder weighing 50 mg was placed on the surface of the two-layer conductor, which is 0.5 of the mass of silver foil. The formed plasma jet melted the surface of the copper electrical contact at an absorbed power density of 4.5 GW/m²and formed on it an electroexplosive electroerosion-resistant composite coating containing a matrix based on silver and nickel with inclusions of titanium diboride. Electroexplosive spraying was performed using the electroexplosive spraying unit "EVU 60/10M" of the scientific laboratory of electroexplosive spraying of highly reliable coatings of the Siberian State Industrial University, Novokuznetsk (https://www.sibsiu.ru/universitet/podrazdeleniya/otdely/?ELEMENT_ID=21392). The mode of thermal force action on the irradiated surface was set by selecting the charging voltage of the capacitive energy storage unit of the unit, according to which the absorbed power density was calculated. Additional process parameters: time of plasma action on the sample surface ~ 100 μs, pressure in the shock-compressed layer near the irradiated surface ~ 12.5 MPa, residual gas pressure in the working chamber ~ 100 Pa; plasma temperature at the exit of the silver nozzle ~10⁴K. A pulse plasma accelerator was used, consisting of coaxial electrodes and a compression chamber with a guide nozzle, and devices used for rigid fastening of a copper electrical contact relative to the accelerator nozzle, placed in the process chamber. During the charging of the capacitor bank, a low vacuum (100 Pa) was created in it using a forevacuum pump. A two-layer conductor, one layer of which consisted of silver foil, the second layer of nickel foil with a suspended titanium diboride powder was placed between the coaxial electrodes. The peculiarity of the end coaxial circuit for discharging a capacitive energy storage device through the foil of the exploded material is that the foil is pressed against the ends of the electrodes, one of which (external) is made in the form of a ring, and the other (internal) in the form of a coaxial current-carrying rod. In this case, the current flows from the center of the foil to its periphery. The formed jets can be characterized as multiphase, since they include, along with plasma, condensed particles in the form of droplets of varying dispersion.

A coating with high electrical erosion resistance, electrical conductivity and high stability of operation under conditions of switching of electrical networks was obtained. Copper contacts, strengthened by the claimed method, showed an increased resource of switching wear by 2.15...2.41 times compared to serial contacts.

Example 2.

The copper electrical contact surface of the contacts of the PVI-320A starters with an area of 0.8 ^cm2 , copper grade M00, was subjected to processing. A two-layer conductor was used, one of the layers of which consisted of silver foil weighing 400 mg, the second layer - of nickel foil weighing 40 mg, which is 0.1 of the mass of the first layer. Titanium diboride powder weighing 600 mg was placed on the surface of the two-layer conductor, which is 1.5 of the mass of silver foil. The formed plasma jet was used to melt the surface of the copper electrical contact at an absorbed power density of 5.5 GW/ ^m2 and an electroexplosive electroerosion-resistant composite coating was formed on it, containing a matrix based on silver and nickel with inclusions of titanium diboride. Electroexplosive spraying was performed using the EVU 60/10M electroexplosive installation of the scientific laboratory of electroexplosive spraying of highly reliable coatings of the Siberian State Industrial University, Novokuznetsk (https://www.sibsiu.ru/universitet/podrazdeleniya/otdely/?ELEMENT_ID=21392). The mode of thermal force action on the irradiated surface was set by selecting the charging voltage of the capacitive energy storage device of the installation, which was used to calculate the absorbed power density. Additional process parameters: plasma action time on the sample surface ~ 100 μs, pressure in the shock-compressed layer near the irradiated surface ~ 12.5 MPa, residual gas pressure in the working chamber ~ 100 Pa; the plasma temperature at the silver nozzle exit is ~10 ⁴ K. A pulsed plasma accelerator was used, consisting of coaxial electrodes and a compression chamber with a guide nozzle, and devices used for rigid fastening of a copper electrical contact relative to the accelerator nozzle, placed in the process chamber. During the charging of the capacitor bank, a low vacuum (100 Pa) was created in it using a forevacuum pump. A two-layer conductor, one layer of which consisted of silver foil, the second layer of nickel foil with a suspended titanium diboride powder, was placed between the coaxial electrodes. The peculiarity of the end coaxial circuit for discharging a capacitive energy storage device through the foil of the exploded material is that the foil is pressed against the ends of the electrodes, one of which (external) is made in the form of a ring, and the other (internal) is in the form of a coaxial current-carrying rod. In this case, the current flows from the center of the foil to its periphery. The formed jets can be characterized as multiphase, since they include, along with plasma, condensed particles in the form of drops of varying dispersion.

We obtained a coating with high electrical erosion resistance, electrical conductivity and high stability of operation under conditions of switching of electrical networks. Copper contacts, strengthened by the claimed method, showed a resource of switching wear 2.53 times higher than serial contacts of PVI-320A starters.

Microhardness, elastic modulus, and bending strength were measured. The microhardness value of the electroerosion-resistant composite coating formed by the electroexplosive spraying method and containing a silver-nickel matrix with titanium diboride inclusions is 5.611 GPa (the standard microhardness values of titanium diboride, silver, and nickel are 32.000, 0.251, and 0.638 GPa, respectively). The elastic modulus of the formed coating was 26900 kgf/mm² (standard values of the elastic modulus of titanium diboride and silver are 47927 - 50986 and 8430 kgf/mm², respectively, and for annealed silver - 8200 kgf/mm², the corresponding value for nickel is 21414 kgf/mm²), the bending strength was 45.2 MPa (standard values of the bending strength of titanium diboride, silver and nickel are 500 - 600, 17 and 20 MPa, respectively).

As a result of studying the obtained coatings using complementary methods of coating research: scanning electron microscopy and micro-X-ray spectral analysis of the coating surface and straight sections, X-ray phase analysis and layer-by-layer analysis using transmission electron microscopy, the following was established. Using scanning electron microscopy and micro-X-ray spectral analysis of the coating surface, it was established that the coating surface is uniform, and the distribution of elements on it is represented only by atoms of the elements from which the coating was formed: titanium, boron, silver and nickel. A study of the elemental composition of the coating by its thickness showed that the main elements of the coating are also titanium, boron, silver and nickel. These results of studying the structure of the coating on a transverse section are completely consistent with the results of the study of the coating surface presented above. The method of mapping in characteristic X-ray radiation of elements was used to visualize the distribution of elements in the volume of the coating, according to which clearly defined areas of the coating measuring 0.5-2.5 μm with a predominant location of titanium and boron can be noted. The combination of these elements indicates the formation of the titanium diboride phase. These formations are located in a matrix that is a composition based on silver and nickel (this is also confirmed by the method of mapping in characteristic X-rays of silver and nickel). The formed coatings do not contain pores.

The X-ray phase analysis and transmission electron microscopy methods established the content of TiB ₂ , Ag and Ni phases in the coating. The conducted studies of the structure, phase and elemental compositions did not reveal oxide phases (as a rule, oxides can form in electroexplosive coatings in case of air penetration into the working space), which reduce the electrical conductivity of the coating. Also, during the electroexplosive spraying process, the titanium diboride phase remains stable, without transformation into other borides and chemical compounds. Titanium diboride has better electrical conductivity, microhardness, elastic modulus, bending strength and other characteristics compared to other titanium borides. Thus, the conducted comprehensive complementary studies of electroexplosive coatings confirm the formation of a coating structure representing a matrix based on silver and nickel with inclusions of titanium diboride, which provides the best level of properties of the created coatings among possible combinations of titanium, silver and nickel borides.

The electrical erosion resistance of the coatings obtained by the claimed method under arc erosion conditions was measured on the contacts of electromagnetic starters of the PMA 4100 brand. Tests for switching wear resistance in the AC-4 mode according to GOST [GOST 2933-83. Testing for mechanical and switching wear resistance. Low-voltage electrical apparatuses. Test methods. - M .: Publishing house of standards, 1983. - 26 p.] were carried out on the test complex of the Federal State Budgetary Educational Institution of Higher Education "Siberian State Industrial University" (Novokuznetsk) at a switching current of 378 A, which was 6 times higher than the nominal current, and cosϕ = 0.35. The number of on-off cycles until complete destruction was ~ 11100-12100. This exceeds the requirements of GOST, according to which the number of on-off cycles before complete destruction for such contacts should be 10,000.

The tests of the coatings for electrical erosion resistance under spark erosion conditions were carried out with point contact. The current was 3 A and the voltage was 220 V. After 10,000 on-off cycles, the sample mass loss was measured. The coatings formed in the proposed method have greater electrical erosion resistance under spark erosion conditions compared to electrical copper grade M00. Relative change in electrical erosion resistance under spark erosion conditions of coatings based on titanium diboride and silverm/m _eh is 9.67, wherem _eh- loss of mass of copper grade M00, taken as a standard, during 10,000 on-off cycles.

The electrical conductivity of the coatings was measured using a digital conductivity tester Sigma 2008B1 (made in China, model 2023). Ten sections were selected on the coating surface, after which the electrical conductivity was measured and averaged. The electrical conductivity of the formed electrical erosion-resistant composite coatings containing a silver-nickel matrix with titanium diboride inclusions is 62.5 MS/m. The obtained high electrical conductivity value is ensured by the use of silver with the addition of nickel, strengthened by the refractory phase of titanium diboride, which has high electrical conductivity and at the same time hardness, wear resistance and electrical erosion resistance.

The proposed method allows to form a coating which, according to the combination of properties, structural characteristics and phase composition, allows to increase the service life of copper electrical contacts of various types that switch electrical circuits and to expand the area of practical application.

Claims (1)

A method for electroexplosive spraying of an electroerosion-resistant composite coating containing a silver- and nickel-based matrix with titanium diboride inclusions onto a copper electrical contact, characterized in that an electrical explosion of a two-layer conductor is carried out, one of the layers of which consists of silver foil with a mass of 100-400 mg, the second layer - of nickel foil with a mass equal to 0.05-0.1 of the mass of the first layer, with titanium diboride powder with a mass of 0.5-1.5 of the mass of silver foil placed on the surface of the two-layer conductor, a pulsed multiphase plasma jet is formed from the explosion products, the surface of the copper electrical contact is melted with it at an absorbed power density of 4.5-5.5 GW/ ^m2 with the deposition of explosion products onto the surface of the copper electrical contact with the formation of an electroerosion-resistant composite coating containing a silver- and nickel-based matrix with titanium diboride inclusions.