Sensors produced by powder-filled pastes

Due to the complexity of systems or products, health monitoring of devices is important to gain information about the system's status and to optimize the maintenance rate. Here different kinds of sensors are needed to e.g. detect temperature changes. Powder metallurgical sensor coatings offer the advantage of applying a sensor directly onto a device. The functional pastes can be applied to insulated stainless steel sheets, powder metallurgical parts and ceramics (e.g. alumina) via screen printing technology. The sensor is functionalized during the following heat treatment during which the properties of the sensor can be influenced by the sintering parameters. The powder-filled pastes can be produced in high material diversity and allow the use of established printing processes. The screen printing technology offers the advantages of a low cost, mass production process. The application of a sensor to a device's surface leads to new integrated functions of the device. A combination of different sensors is possible due to the possibility of a complex screen layout. Depending on the quantity to be measured - i.e. strain, temperature, rotational speed - different materials are evaluated, e.g. thermocouple standard types (as type T: Cu-CuNi) are investigated. At the Fraunhofer IFAM a variety of thick-film sensors have been developed which can be applied directly onto parts. Here investigations on the functionality of strain gauges or overload sensors, as well as thermocouples have been performed. Also the deposition of magnetic sensorial structures is possible, which exhibit either hard or soft magnetic properties. The functionality of the different sensors is tested, depending on the sintering conditions, i.e. temperature, dwell time and atmosphere. The powder metallurgical produced sensors are checked with adequate testing methods, e.g. a temperature calibration or load tests. Metallographic investigations of the sintered layers and interdiffusion zones were performed to study the formation and composition of possible phases or microstructures.