Material Durability
The capability of a multi layer thin film sensor to withstand rapid and extreme temperature fluctuations without undergoing delamination or fracturing defines its reliability in harsh environments. High thermal shock resistance ensures that the active sensing grid remains bonded to the substrate during rapid heating or cooling events. This capability is required for sensors mounted on gas turbine exhaust systems.
Failure Trigger
Thermal mismatch stress is the primary cause of coating failure during rapid temperature transitions. When the thermal expansion coefficient of the deposited film differs significantly from that of the substrate, rapid heating generates high shear forces at the interface. These forces can exceed the bond strength, leading to sudden peeling and failure of the sensor.
Mitigation Design
Graded transition layers and thin film architecture are used to minimize the risk of failure during thermal cycles. By introducing a layer with an intermediate thermal expansion coefficient, the shear stress is distributed across multiple interfaces. This design prevents the concentration of mechanical energy at a single boundary and improves the thermal shock resistance of the device.
Thinner layers also accumulate less elastic strain energy, which reduces the driving force for crack propagation along the interface.
Testing Validation
Cyclic testing is conducted to evaluate the performance of the sensor under simulated operational conditions. The sensor is repeatedly exposed to high temperature gas jets and then rapidly cooled to measure its durability. This testing ensures that the sensor can survive the rapid start up and shut down cycles of turbine engines.
