Volume 56, Issue 9

X-ray computed tomography (XCT) is a powerful volumetric non-destructive testing tool. In this contribution, its application for large pieces of equipment is demonstrated, after the main components of an XCT scanner are described. While the technology has been well known in the scientific community for many years, its industrial-scale use is relatively new, especially as far as very large units are concerned. In a number of case studies, the benefits to the failure analyst of readily available XCT machines will be shown. The advantages in employing non-destructive XCT for metallurgical root cause failure analysis, prior to cutting up a failed part for sectioning and opening of cracks or other imperfections, will be revealed. It will be indicated how XCT can be conveniently applied in failure cases, for the sake of both the failure analyst and the fractographer. XCT can be used as a first testing method to get an understanding of the exact location of imperfections, fields of porosity, crack systems and the like, before macro- and microstructural anomalies are opened by the fractographer. To state it more clearly, the fractographer who has a high-powered XCT, with excellent spatial resolution at his or her disposal, will never again run the risk of cutting away a crack tip that is so valuable in determining the fracture mode.

The global economic network, increasing mobility and wealth have a significant impact on energy consumption and environmental degradation, creating a serious social and political pressure on climate protection issues and a sustainable use of limited natural resources. In this context, a variety of programs are launched worldwide on a political and scientific / technical level to reduce aviation as well as automobile emissions. To meet these requirements, apart from new and improved design and lightweight construction concepts, high-temperature lightweight structural materials and their processing technologies play a key role. Due to their high specific (creep) strength and low density, intermetallic titanium aluminides have a particularly great potential, which is already being used industrially. While in the last decades, predominantly ingot metallurgical processes have been developed for the production of pre-material, which have subsequently been processed by casting and hot-working, the introduction of powder-based manufacturing technologies (e. g. additive manufacturing), with the availability of high-quality alloy powder, opens up new ways of material processing and component design. The basis of this work is the process-adapted 4 th generation TNM-alloy, which was developed at the Chair of Physical Metallurgy and Metallic Materials. Due to its reactivity, manufacturing methods used are electron beam melting and laser powder-bed fusion as well as spark plasma sintering. Furthermore, high demands are placed on the production of the powder, in particular with regard to its purity. The chemical composition of the project alloy is designed and optimized so that it is “resistant” to the characteristics of the different manufacturing processes and their physical conditions. The starting powders and the manufactured specimens are subjected to a comprehensive characterization involving microstructural investigations on several length scales as well as the examination of the mechanical properties. Moreover, in order to further optimize the mechanical properties at elevated temperatures, it is an essential goal to develop suitable heat treatments. This work will show how conventional and high-resolution metallography can be used to combine innovative alloys with new processing technologies.

The development of new materials and heat treatment concepts requires extensive structural analyses. An example for this is the development of extremely durable and deformable steels using the “Quenching and Partitioning” (Q&P) heat treatment. The aim is to achieve a balanced ratio of dispersed austenite islands in a martensitic matrix to achieve maximum strength at a moderate deformability. There is a wide range of different procedures for the microstructure characterization and phase quantification. Color etchings present an efficient alternative to time-consuming electron-microscopic examinations via EBSD. In the present work, comparative examinations regarding the reliability of light-optical analyses via color etching were carried out. It was shown that process-related factors might lead to significant misinterpreations. Especially the production conditions of the raw material are an essential influencing factor regarding the etching behaviour und thus the interpretation of the micrographs.