Volume 54, Issue 8

Ambulant metallography enables microstructure determinations and surface examinations of large components without the need to take samples, thus avoiding destructive or expensive repairs. Its benefits are the universal usability, quick availability of results and economic efficiency. For 30 years now, the component metallography working group of the German Society for Materials (DGM) runs an annual vocational training where theoretical and practical metallographic working techniques are presented.

The development of welding consumables is permanently challenged with matching the increasing strength and toughness of thermomechanically treated or quenched and tempered steels. A martensitic microstructure offers promising prospects to guarantee such requirements in the all-weld metal as well. A thorough characterization of the microstructure is indispensable to understand its effects on the mechanical properties. This paper shall summarize how light optical microscopy and electron backscatter diffraction can be used to deepen the understanding of fully martensitic weld metal. It was found that electron backscatter diffraction offers a variety of information that light optical microscopy cannot deliver, particularly regarding the prior austenite grain structure. Grain sizes of the primary dendrites, the prior austenite grains and the martensitic structure can be measured with a combination of these techniques.

Aluminium-based powder metallurgy (PM) alloys have a number of advantages over cast and wrought aluminium alloys. These PM alloys can be produced using either prealloyed or elemental premixes, with the latter offering a longer die life because of their softer nature compared with prealloyed powders. It is found that the use of an Al-Cu premixed PM alloy gives green density values higher than those of Al-Cu prealloyed systems reported in the literature. Most commercial aluminium PM alloys and alloy developments are based on the Al4Cu system. The amount of liquid phase has significant effects on the microstructure and the mechanical properties of sintered products. Lack of a liquid phase results in inadequate mechanical properties, while an excess of liquid phase causes distortion and shape deformation of the compacts formed by sintering. The objective of this study is to determine the properties of an Al4Cu PM alloy produced using an elemental premix. The effects of the amount of liquid phase on microstructural features and mechanical properties are assessed through thermal analyses. It is found that the optimum transverse rupture strength is obtained by sintering at 600 °C for 2 h.

Seamless tubes of the highly corrosion resistant austenitic steel 1.4539, X1NiCrMoCu25-20-5 (Alloy 904L) were observed to exhibit signs of inter-crystalline damage to a depth of several layers of grains and in particular on their internal surface. The material had been stored and had not been put into service. A number of hypotheses had been discussed to explain the predominant cause of the damage. Using optical light and scanning electron microscopy investigation techniques, clear evidence was obtained indicating it to be inter-crystalline corrosion due to the sensitisation of the grain boundaries. The most probable cause of this was determined to be the presence of residual deposits from the rolling process, which due to poor cleaning, had not been completely removed prior to the final solution annealing treatment. This explaining why predominantly the internal surface of the tubes was affected.