Abstract Electric contacts are the essential components of electric equipment. In the past, the silver-cadmium oxide is used as the materials contacts. However, because it generates the poison cadmium gas during the service, which causes the cancer, the silver-cadmium oxide will be prohibited in the near future. Now the silver-tin oxide is often used as the materials of the electrical contacts. To oxidize pure tin more easily,¡AIn2O3 is usually added as the auxiliary oxide agent. However, In2O3 is expensive. Hence, in this study, the other metal oxide agents are added to the silver-tin oxide to investigate the agent effect on the erosion characteristics (such as the erosion amount, the contact resistance, the arc energy, etc). This study uses the powder metallurgy to produce the electrical contacts, where the sizes of pure silver powder and tin oxide powder are 2~3£gm and 4~5£gm, respectively. The doping agents are made of 3~4£gm tungsten oxide and 3~5£gm molybdenum oxide, respectively. The powder are mixed in a suitable proportion to produce electrical contacts. The effect of metal oxide on the erosion of electrical contacts is investigated under different electric conditions. Results show that when the tin oxide powder is added to the pure sil-ver, the splashing of material can be prevented efficiently, and the erosion of electrical contacts can be reduced. Among the materials of silver-tin oxide, the contacts have the minimum erosion at the concen-tration of 5wt%. In order to reduce the cost of electrical con-tacts, the concentration of tin oxide is increased to 10wt% to investigate the influence of the doping agent. Results show that the addition of 0.3wt%WO3 has the minimum erosion. This electrical contact has lower erosion than the commercial ones. Furthermore, the regions, where the electrical contact has lower erosion than the commercial pure silver contacts and the silver-cadmium oxide, respectively, are established. These re-gions will be the best usable regions of silver tin oxide, and it will be the basis for the choice and the application of silver-tin oxide electrical contacts.

Ohmic nanoswitches have been recently regarded to complement transistors in applications where electrical current leakage is becoming a problem. Although the solid state metal oxide silicon field effect transistor (MOSFET) has fueled a global technology revolution, it is now reaching its performance limits because of device leakage. To avoid electric field-induced damage in MOSFETs, operating voltage and hence threshold voltage must be reduced as linewidth is reduced. However, below a limit, the current cannot be turned off. The ohmic switch approach solves this problem because an air gap that separates the electrical contacts provides excellent electrical isolation when the relay is open. Some applications require these relays to perform billions to trillions of cycles, yet typical devices that are exposed to ambient environment degrade electrically after just a few thousand cycles. A critical challenge here is that trace amounts of volatile hydrocarbons in air adsorb on the electrical contact surfaces for a large variety of coating materials, causing an insulating deposit to form that prevents signal transmission during switch closure. We address this challenge by exploring the interactions of hydrocarbon contaminants with contact materials and operating environment on device lifetime. Our materials of choice are Pt, a common contact material in switch applications due to its resistance to wear, and RuO2, which is believed to be somewhat resistant to hydrocarbon adsorption. We test our devices in N2 and O2 background environments with controlled hydrocarbon contaminant concentrations. We illustrate that the insulating hydrocarbon deposit can be electrically broken down and its resistance lowered. We show how electrical contacts that have degraded electrically due to contamination can have their performance restored to the original level by actuating them in clean N2-O2 environment. It is then shown how this process creates a highly conductive carbonaceous deposit that protects the contact from wear. It is also v demonstrated that RuO2 does not exhibit contaminant-induced degradation even at very high hydrocarbon presence, as long as O2 is also present. These results show that even though the contaminant is ubiquitous in the environment, there are many ways to reduce its effect on ohmic switches.

La sollicitation de fretting apparait comme un processus de dégradation très pénalisant dans les multiples systèmes industriels (aéronautique, industrie automobile, industriels du nucléaire, transports ferroviaires etc. …). Ce processus d’usure engendre dans la plupart des cas soit une réparation (rechargement) des surfaces soit le remplacement des composants (situation la plus souvent observée). La sollicitation de fretting est associée à des micro-déplacements alternés entre deux surfaces en contact. On observe généralement ce type de sollicitation dans tous les contacts soumis à des vibrations ou à des cycles thermiques. La sollicitation de fretting usure dans les contacts électriques est particulièrement pénalisante. Outre l’endommagement des surfaces, ce processus induit une augmentation significative de la résistance électrique des contacts et une perte de fonctionnalité du connecteur en particulier dans les connecteurs basses tensions très sensibles aux fluctuations de la résistance électrique. Pour palier ce problème les industriels de la connectique et leurs clients (industriels de l’automobile) cherchent à mettre en place de nouveaux dépôts palliatifs pour résoudre ces problèmes tout en limitant les surcouts liés à l’utilisation de dépôts nobles tels que l’or.Le sujet de cette thèse porte sur cette problématique avec pour objectif de mettre en place une méthodologie de choix des dépôts pour optimiser la durée de vie des connecteurs. L’étude aborde essentiellement l’influence des conditions de chargements mécaniques et plus particulièrement l’amplitude de débattement / The degradation by fretting appears as a very troublesome process in many industrial systems (spatial, automotive, nuclear industry, railway systems etc. …). This wear process makes it necessary to repair or to replace the destroyed component. The process of degradation by fretting is associated with the micro-displacement between two surfaces in contact. This type of degradation is observed in all types of contacts subjected to the vibrations or thermal variations. The degradation by fretting in electrical contact is particularly dangerous. The wear of the contacting surfaces causes a significant increase of the electrical resistance of the contact and the decay of the functional properties of the connector. This situation concerns especially the low tension connectors very sensible to the fluctuations of the electrical resistance. In order to avoid this situation the automotive industry and its suppliers, the manufacturers of the electrical connectors, are looking for new materials and coatings.The objective of this thesis consists to develop the methodology of choice of the coating materials in order to optimise the lifetime of the electrical contact. The study focuses mainly on the influence of the mechanical conditions, the displacement amplitude in particular, on the performance of the electrical connector.

Dans une automobile, les composants électriques sont alimentés par un type de générateur électrique particulier : l’Alternateur. Entraîné par le moteur du véhicule, il lui prélève donc de la puissance mécanique. Dans les périodes de chasse au gramme de CO2 que nous connaissons, la puissance prélevée au moteur doit être minimisée pour ne pas pénaliser sa consommation. Or les besoins électriques du réseau de bord et des systèmes (éclairage, ventilation, servitudes, contrôle moteur, etc.) sont imposés par l’équipement du véhicule. Il est apparu que dans les cas où l’alternateur est fortement sollicité, des pertes de performances peuvent être imputées au circuit d’excitation de la machine. Il comporte deux contacts électriques glissants balai-bague qui ont été incriminés. Du point de vue théorique aucun élément ne permettait d’expliquer les augmentations brutales de résistance de ces contacts, nous avons donc développé une méthode de mesure originale destinée à rechercher des paramètres influents sur leurs variations. Il nous a été impossible de faire une mesure de l’épaisseur film de transfert et d’identifier les quantités de graphite, nature et quantité des oxydes en présence dans le film. Cependant, nous avons estimé la pertinence de l’hypothèse du rôle de l’oxydation et avons surtout pu isoler le rôle du film de transfert dans l’expression des résistances de contact. Nous avons, de plus, mis en évidence la corrélation existant entre les résistances de contact et le coefficient de frottement pour les deux contacts. / The Alternator is an electrical generator especially designed to supply current to the vehicle electrical components. It is powered by the engine and takes off a part of its power. Currently, car makers are more than willing to minimize the power losses of this device in order to save fuel and reduce CO2 emissions, but the electrical need depend only on the vehicle equipment and use. Sometimes when the alternator runs at full load, the performance could be diminished by unpredictable resistance changes in the electrical sliding contacts of the excitation circuit. There was no theory capable of explaining these phenomena. The analysis limits were the impossibility to measure transfer film thickness and to determine the amount of graphite and the nature and volume of oxides into the film. We developed an experimental method adapted to contact resistance and friction measurements with the aim to find influencing parameters. A dedicated software has been created to extract data from these measurements. We appreciated the relevancy of oxidation hypothesis and we added a study on transfer film, gauging its contribution to contact resistance. Moreover we found a significant correlation between contact resistance and friction, meaning that there are some influent hidden parameters between brush and disc/ring.

Contatos elétricos são aplicados na área de geração, manuseio e distribuição de energia elétrica, sendo fabricados em metais condutores como: cobre eletrolítico e suas ligas. Através de alguns métodos de brasagem, pastilhas com propriedades de condutividade, elétrica e térmica, mais apuradas são brasadas sobre estas bases condutoras. Em função da substituição do cádmio por um elemento menos nocivo ao homem e ao meio ambiente, o estanho vem se difundindo com rapidez, apoiado por iniciativas internacionais. O objetivo deste trabalho é avaliar a brasabilidade de um metal de adição na liga 40%Ag-21%Zn- 20%Cd-19%Cu, sobre metais de base em: cobre eletrolítico, latão (65%Cu-35%Zn), prata pura e prata-óxido de estanho (90%Ag-10%SnO2) através dos ensaios da gota séssil e da cunha. As amostras foram caracterizadas metalograficamente. Os resultados mostraram que a brasabilidade para todos os substratos empregados estava dentro de valores de ângulo de contato menores que 10o, com exceção do substrato prata-óxido de estanho. Para este material ocorreu o demolhamento, dificultando a caracterização da sua molhabilidade. / Electrical contacts are manufactured with conductive metals, like electrolytic copper and its alloys. These products are used in electric circuits to manage the electrical energy. Electrical contacts assemblies can be built up by brazing joining methods, which improves electrical and thermal conductivity in non-ferrous substrates. The cadmium oxide, present into electrical contact alloys, has been replaced by tin oxide due to environmental issues, to meet the actual internationals agreements. The objective of this work is to evaluate the brazeability of a filler metal 40%Ag-21%Zn-20%Cd-19%Cu, on non-ferrous substrates, like: electrolytic copper, brass (65%Cu-35%Zn), silver and silver tin-oxide (90%Ag- 10%SnO2) using sessile drop and edge tests. The results showed that the brazeability of all non-ferrous substrates depicted contact angles less than 10º, except for the silver-tin oxide substrate. For silver-tin oxide substrate dewetting took place and the measurement of contact angles was impossible.

<p>Nickel based coatings were deposited on copper substrates by two different sputtering techniques from a nickel alloy based target. The substrates used were commercially available copper based substrates for low duty electrical contacts. The coatings were analyzed and evaluated as copper diffusion barriers for electrical contact applications. In addition two types of commercially available electroplated nickel coatings (referred to as type A electroplated coatings and type B electroplated coatings) were characterized for comparison. The Technique I sputtered coatings were deposited using three different substrate bias voltages and two different working gas pressures. The Technique II coatings were deposited using two different substrate bias voltages and two different working gas pressures. All sputtered coatings were deposited at a temperature of 200° C. The quality of the barriers was investigated by analyzing their composition, microstructure, stress, mechanical properties , and surface roughness. The results show that sputtered coatings have polycrystalline structures while the two plated films had (200) orientation and (111) orientation. Both plated coatings contained impurities that originate from chemicals used in the plating baths. The surface of the sputtered coatings reflects the substrate surface, while the electroplated samples on the same substrate (type A coatings) show a smooth mirror like surface and the type B electroplated coatings show a rough surface.</p><p>Technique II sputtered coatings showed the highest hardness in the amount of 13 GPa, followed by electroplated type A coatings with a hardness of about 9 GPa while the Technique I coatings showed hardness of 6-8 GPa. All sputtered coatings exhibited compressive stress while the electroplated type A coatings exhibited tensile stress of almost twice the magnitude.</p><p>In this study it is shown that sputtered nickel based coatings sputtered nickel based coatings are a promising more environmental friendly alternative to electroplated nickel coatings.</p>

Nickel based coatings were deposited on copper substrates by two different sputtering techniques from a nickel alloy based target. The substrates used were commercially available copper based substrates for low duty electrical contacts. The coatings were analyzed and evaluated as copper diffusion barriers for electrical contact applications. In addition two types of commercially available electroplated nickel coatings (referred to as type A electroplated coatings and type B electroplated coatings) were characterized for comparison. The Technique I sputtered coatings were deposited using three different substrate bias voltages and two different working gas pressures. The Technique II coatings were deposited using two different substrate bias voltages and two different working gas pressures. All sputtered coatings were deposited at a temperature of 200° C. The quality of the barriers was investigated by analyzing their composition, microstructure, stress, mechanical properties , and surface roughness. The results show that sputtered coatings have polycrystalline structures while the two plated films had (200) orientation and (111) orientation. Both plated coatings contained impurities that originate from chemicals used in the plating baths. The surface of the sputtered coatings reflects the substrate surface, while the electroplated samples on the same substrate (type A coatings) show a smooth mirror like surface and the type B electroplated coatings show a rough surface. Technique II sputtered coatings showed the highest hardness in the amount of 13 GPa, followed by electroplated type A coatings with a hardness of about 9 GPa while the Technique I coatings showed hardness of 6-8 GPa. All sputtered coatings exhibited compressive stress while the electroplated type A coatings exhibited tensile stress of almost twice the magnitude. In this study it is shown that sputtered nickel based coatings sputtered nickel based coatings are a promising more environmental friendly alternative to electroplated nickel coatings.

Contatos elétricos são aplicados na área de geração, manuseio e distribuição de energia elétrica, sendo fabricados em metais condutores como: cobre eletrolítico e suas ligas. Através de alguns métodos de brasagem, pastilhas com propriedades de condutividade, elétrica e térmica, mais apuradas são brasadas sobre estas bases condutoras. Em função da substituição do cádmio por um elemento menos nocivo ao homem e ao meio ambiente, o estanho vem se difundindo com rapidez, apoiado por iniciativas internacionais. O objetivo deste trabalho é avaliar a brasabilidade de um metal de adição na liga 40%Ag-21%Zn- 20%Cd-19%Cu, sobre metais de base em: cobre eletrolítico, latão (65%Cu-35%Zn), prata pura e prata-óxido de estanho (90%Ag-10%SnO2) através dos ensaios da gota séssil e da cunha. As amostras foram caracterizadas metalograficamente. Os resultados mostraram que a brasabilidade para todos os substratos empregados estava dentro de valores de ângulo de contato menores que 10o, com exceção do substrato prata-óxido de estanho. Para este material ocorreu o demolhamento, dificultando a caracterização da sua molhabilidade. / Electrical contacts are manufactured with conductive metals, like electrolytic copper and its alloys. These products are used in electric circuits to manage the electrical energy. Electrical contacts assemblies can be built up by brazing joining methods, which improves electrical and thermal conductivity in non-ferrous substrates. The cadmium oxide, present into electrical contact alloys, has been replaced by tin oxide due to environmental issues, to meet the actual internationals agreements. The objective of this work is to evaluate the brazeability of a filler metal 40%Ag-21%Zn-20%Cd-19%Cu, on non-ferrous substrates, like: electrolytic copper, brass (65%Cu-35%Zn), silver and silver tin-oxide (90%Ag- 10%SnO2) using sessile drop and edge tests. The results showed that the brazeability of all non-ferrous substrates depicted contact angles less than 10º, except for the silver-tin oxide substrate. For silver-tin oxide substrate dewetting took place and the measurement of contact angles was impossible.

Simultaneous measurement of electrical contact resistance (ECR) and coefficient of friction (COF) at the sliding interface is essential to assess the performance of selected material contact pairs for the transfer of current from stationary member to moving member (or vice-versa). Low and stable values of ECR and COF are desirable during the intended operating life of the contact members. These parameters may change with respect to time as a consequence of change in the surface properties of contact members due to their relative movement. Hence experimental investigations have been conducted to study the variation of ECR and COF while different riders sliding on copper and brass flat samples in different environments. As a part of the experimental investigation, a reciprocating sliding setup is designed and developed to study the variation of ECR and COF in terms of normal force, sliding speed, current and environment. The details of the experimental setup are described along with its construction and operation. The sample preparation, instrumentation, data acquisition and presentation are explained in detail. The variations of ECR and COF at different normal forces, currents and sliding speeds by moving OFHC copper, brass, silver, Ag10Cu and Ag20Cu riders on OFHC copper and brass flat samples in vacuum, argon, nitrogen and air are studied in detail. Studies are also conducted to evaluate the performance of metallic contacts under lubricated condition using general purpose lubricating oils of different viscosity. Metallic contacts show a decrease in ECR with increase in normal force at all sliding speeds in all media. Sliding metallic contacts show a significant decrease in both ECR and COF during the initial sliding cycles at constant normal force in all media. Surface roughness of flat sample is found to have a significant effect on both ECR and COF in all media. Wear of rider is found to be significant as compared to wear of flat samples. Metallic contacts show an inverse relationship between ECR and COF in all media under mild wear regime (0.2< COF≤ 0.4). ECR and COF of sliding metallic contacts are independent of current (≤ 4A) in mild wear regime in all media. Reasonably low values of ECR and COF are observed for prolonged duration with lubricants having low viscosity. The presence of wear fragments at the sliding zone is found to have significant effect on both ECR and COF in all media. Low values of ECR are observed while copper rider sliding on brass sample as compared to silver rider under same operating conditions. Significant amount of metal transfer is observed with silver based riders sliding on copper and brass flat samples in different media. The present investigations are useful in understanding the contact behaviour of copper and brass flat samples for similar and dissimilar riders sliding on them in various environments.

The master thesis deals with the phenomena called electro-dynamic force in the electrical apparatus. Nowadays, there are high requirements for electrical devices. The devices and especially their contacts are subject to high demands on reliability, reliability and mechanical durability. The electro-dynamic forces caused by the passage of electric current mechanically deform the current path. The design of the electrical apparatus must take these forces into account. Equations for electro-dynamic forces calculation are presented. In master thesis, individual parts of the current path are derived and described. Various configurations and designs of the current path are solved. The thesis also deals with the issue of forces in electrical contacts. Individual theoretical equations are then applied to a particular disconnector QAK, made by company IVEP, a.s. Parts of the disconnector were redrawn into 3D program SolidWorks. The model was analysed in program ANSYS Maxwell. The thesis compares the achieved results of analytical equations and numerical simulations.