Volume 61, Issue 11

Laboratory X-ray microscopy and nano X-ray computed tomography (nano-XCT) have the unique capability to combine sub-100nm resolution and high object penetration. Therefore, these are appropriate non-destructive inspection techniques for the detection of flaws with a size of 100 nm and below in opaque objects and bulk materials. Another advantage of X-ray microscopy – as opposed to destructive failure analysis methods – is that kinetic processes such as microcrack evolution can be imaged. The unique combination of micromechanics and high-resolution 3D imaging allows to study degradation and failure mechanisms in opaque 3D nanopatterned structures, and it allows to provide essential information for fracture mechanics in small dimensions. The high-resolution in-situ/operando imaging of microcrack propagation in microelectronic products and in battery electrodes is demonstrated.

In the past 20 years or so, atom probe tomography has gone from a niche technique in physical metallurgy to a well-established method in many parts of materials science and beyond. This is owing to the improvement in both instrumentation and specimen preparation. Given the availability of instruments, successful specimen preparation is often the bottleneck in atom probe projects. In this article, the authors want to give an overview of the types of preparation techniques that are available and which challenges they pose. This includes basic electropolishing, which was dominant until the introduction of focused ion beam-based preparation some 25 years ago. Nowadays, focused ion beam-based preparation methods possibly represent the largest share, as they allow for site-specific specimen preparation, non-conductive specimens and often a higher throughput. They are continuously improved, i. e., through higher current plasma ion columns, cryo preparation for sensitive materials and room temperature liquids and ‘additive’ techniques for nanomaterials. This steadily increases the types of materials that can be analyzed using atom probe tomography.

FIB/SEM tomography is a serial sectioning method in which the cross-sectional area of the sample is stepwise removed with a focused ion beam (FIB) and the exposed cross-sectional area is imaged with a scanning electron microscope (SEM). All imaging techniques of the SEM can be used, which allows the application to a wide range of materials science questions. On the one hand, resolutions of a few nm can be achieved, and on the other hand, volumes with edge lengths of 100 μm and more can be examined. This article gives an overview of the current state of the art and the practical implementation of FIB/ SEM serial sectioning. The special aspects of the integration of energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) are also discussed.

Bulkhead ring fasteners, four in total, were found fractured in a large gas turbine engine after 1700 operating hours and a high number of engine starts and shut-downs for such a relatively short time in service. A metallurgical failure investigation was ordered by the client for determining the metallurgical cause of the cracking. The subject bolts failed due to high-stress low cycle fatigue fracture.