Volume 55, Issue 9

A great number of applications and technical processes is limited by the materials’ maximum load bearing capacity, while the development of new materials is inextricably linked with the availability of appropriate characterization methods. This work aims to point out methods used and fields of research worked on, in the past years and currently, at the Department of Physical Metallurgy and Material Testing of the Montanuniversität Leoben. In this context, the study aims to present the use of classic metallography as well as the benefit of high-resolution characterization methods for a comprehensive understanding of the structure of metallic materials. The examples shown range from grain boundary etchings in high strength steels, atom probe measurements on automotive steels, and the use of scattering techniques to characterize intermetallic titanium aluminide alloys, up to cases of damage on galvanized structural steels. This work furthermore demonstrates the use of ab initio calculations on a high-alloy steel for the prediction of phase preferences of alloying elements.

High-performance materials play a dominant role in modern society. Without them, modern manufacturing and transportation technologies would, for instance, be impossible. In order to purposefully improve and optimize the potential of these materials based on their properties, a multi-scale understanding of the interaction of microstructural elements and mechanical properties is essential. Such understanding can be achieved by the specific analysis of the interaction of microstructural components such as interfaces, crystal structures, precipitates, and other defects in the material, as well as of their impact on the underlying deformation processes in complex alloys. For this purpose, not only a precise metallographic preparation of the individual microstructural constituents is performed but also, and in particular, rate- and temperature-dependent plastic deformation processes are determined. On the one hand, this is done on a local scale using micromechanical examination methods such as nanoindentation or uniaxial micropillar-compression experiments. On the other hand, experiments on the global scale with compression and tensile tests are performed. These mechanical characteristics are subsequently correlated with structural and chemical high-resolution analyses based on electron microscopy and atom probe tomography methods. Thus, reliable mechanistic models of the dominating deformation mechanisms of high-performance materials can be created based on these examinations – even under harsh conditions such as elevated temperatures or aggressive environment. This targeted correlative interaction of metallography, high-resolution microstructural analysis, and mechanical deformation experiments is demonstrated by the examples of the refractory metals Mo and Cr as well as on a Mo-Hf-C alloy.

“Top-quality powder is a precondition for additive manufacturing of quality components.” This paper covers the powder characterization of high-melting and highly reactive intermetallic γ-TiAl powders by combining technological and metallographic examinations. Measurements of tap density, bulk density, flow behaviour, particle size distribution and sphericity of the powder will reveal characteristic parameters which have an effect on process stability. The subsequent analysis of the powder microstructure will show possible gas inclusions or defects which may negatively affect the mechanical properties of the manufactured component. Each of these factors presents a quality criterion, which is also applicable – irrespective of the alloy system – to other materials systems.

An explosion of a ball valve occurred during starting up a hydraulic unit. The hydraulic valve was split into several parts. The investigations and estimations of the occurring pressures and stresses reveal that the valve body was ruptured by an extreme overpressure of more than 2 000 bar. A small defect on the ball might be responsible for such a high pressure, leading to self-ignition of the hydraulic fluid. A possible scenario how this might have happened is given.