Quality Control of Advanced Ceramics

High-performance ceramics provide key components – but only if they are defect-free. To detect rejects at an early stage, researchers at Fraunhofer IKTS have developed an in-line inspection method based on laser speckle photometry.

×

High-performance ceramics are established in many application areas. Despite optimized manufacturing technologies, production is sometimes prone to defects. Cracks, break-outs or inclusions have a negative impact on the quality of the component. Therefore, it is important to detect these defects as early as possible in the manufacturing process, ideally before expensive sintering. Until now, there has been no satisfactory automated solution for inspecting components – from the green body to the sintered material. A sensor concept developed at Fraunhofer IKTS based on laser speckle photometry (LSP) promises a remedy. It is used to non-destructively determine defects near the surface of technical ceramic components. After excitation by a short laser pulse, the surface heats up by a few Kelvin. This creates a dynamic speckle pattern from whose characteristic change over time defects in the material can be detected without affecting the component. The system consists of laser diode, digital camera and excitation source. This small and at the same time robust setup is characterized by low costs and a very fast measurement: Depending on the resolution and computing technology, for example, a component of the size 30 x 30 mm² is tested in 60 seconds. Almost all common materials, such as Al₂O₃, TiO₂, ß-Al₂O₃, MgO or SiC, can be examined in the process. In addition to a modular demonstrator, a compatible software kit was developed at Fraunhofer IKTS in an IGF project. Robotic sensor guidance enables inspection of both planar and three-dimensional components. The system can be equipped with different objectives and has a maximum optical resolution of 10 μm. “So far, we had samples with defects of at least 70 μm at our disposal, which we detected without any problems with this demonstrator,” explains Lili Chen, scientist in the IKTS speckle-based methods group.