A look through the microscope: curious finds from the testing laboratory
19. July 2017
Just in time for Halloween, this little “dragon” appeared under Gabi Engler-Stollfuß's microscope. The colleagues she called over quickly named it the “little monster of Loch N’ESSEN”.
From a metallurgical perspective, this is a cross-section of a corrugated tube made from austenitic steel, as used in exhaust pipes, photographed at 10× magnification. (Image: October 2016)
For our colleagues at the ExpertCenter and MaterialtestCenter, expert reports on damage, materials analyses and metallographic examinations are generally factual, analytical tasks. Occasionally, however, a look through a reflected-light microscope or scanning electron microscope (SEM) reveals surprising structures that sometimes seem almost like something from a fairy tale.
We have put together a small collection of these “curious finds” from our accredited testing laboratory. It shows that metallography is not always a dry subject.
An apple with a bite taken out
A mischievous mind might see aggressive advertising or the logo of a well-known Californian computer and smartphone brand in this image. In fact, it is a non-metallic inclusion in steel, photographed at 500× magnification.
(Image: August 2015)
Fern on steel?!
Whether it looks like fern, dark frost patterns or algae, at first glance this image suggests plant structures rather than metal. Looking through the microscope, laboratory employee Elena Grassmann discovered these drying effects in a polished section of a steel microstructure.
(Image: October 2015)
The sad polar bear?
Perhaps it was the winter month or the lack of snow: our laboratory manager, Dr.-Ing. Lorenz Gerke, discovered this “sad polar bear” while looking through the microscope. The image actually shows a hardness indentation below a fracture surface in the thread of a screw.
(Image: February 2016)
A little elephant?
All that seemed to be missing was a trumpet call when our laboratory colleague Gabi Engler-Stollfuß examined this image under the microscope: the “ears” at the top left, the “trunk” at the top right and a small “eye”.
From a metallurgical perspective, however, this is a butt weld viewed at 6× magnification in an etched section. The “ears” and “trunk” are displaced material, while the “eye” and “nostril” are pores that happen to be in just the right places.
(Image: June 2015)
What kind of sphere is this?
Be honest: what immediately comes to mind when you see this image? In the testing laboratory, spontaneous interpretations ranged from an extraterrestrial boule to a larva in a tadpole egg and the ball joint of a prosthesis.
The image actually shows a sphere of iron oxide on a fracture surface. A fine example of how metallography can also spark the imagination.
(Image: May 2015)
Where are the Inuit?
“Where are the Inuit?” That was the thought that occurred to our ExpertCenter colleague Andreas Leitner when he discovered this “igloo” under the scanning electron microscope (SEM).
Only a closer look revealed that it was a blister-like irregularity in the zinc coating of a steel sheet, visible in cross-section under the SEM at 10× magnification.
(Image: July 2017)
The dancer
This “dancer” is showing off some lively footwork. Discovered by Evgenija Kuznecov, the image shows a microstructural constituent in a polished specimen of as-cast aluminium at a magnification of 500:1.
The Christmas star
This structure inevitably brings to mind a star or comet from outer space. In reality, the image shows white cast iron with spiky carbides at a magnification of 25:1. This image was also taken by Gabi Engler-Stollfuß, in 2014.
The apple in tungsten carbide
“A hard shell, yet a soft core”: these were the first thoughts of our colleagues at the W.S. MaterialtestCenter and W.S. ExpertCenter, when they examined an overload fracture in tungsten carbide.
More precisely, this is tungsten monocarbide, a hardmetal also known as Widia because of its extreme hardness. The structure’s coincidental resemblance to an apple with a bite taken out made the discovery all the more remarkable.
(Image: May 2018, discovered by Andreas Leitner)
The lost finger
There is probably no nail polish for this “finger”. It is actually a pin-shaped manganese sulphide inclusion measuring just 12 µm on the fracture surface of a steel. This is worth a closer look, particularly when evaluating steels: in so-called free-cutting steels, an increased concentration of manganese sulphides is actually desirable. These steels are often used in series production on automatic lathes and machining centres, as manganese sulphides improve chip breaking and thus allow higher machining speeds. In other steel grades, however, larger quantities of manganese sulphide would be undesirable because they can increase the tendency towards embrittlement.
(Image: August 2018, by Dr.-Ing. Lorenz Gerke)
When specimen preparation itself produces surprises
Preparing metallographic specimens can also produce unexpected and curious effects. Some polished sections suddenly reveal structures that look “laughing” or “Chinese” (because of the little pointed hat), for example as a result of particular reflections or specimen preparation artefacts in samples of pipes or screws. Although these images can be explained metallurgically, they are a reminder that looking through a microscope can sometimes reveal surprisingly creative shapes.
Preparing metal specimens can sometimes unintentionally produce curious results, as these “laughing” or “Chinese”-looking specimens (because of the little pointed hat) from various metal pieces, including pipes and screws, demonstrate:
