Examination of a cast steel with SEM (scanning electron microscopy)
Since the turbo manifolds used by Scania must withstand hard conditions with high temperatures, corrosion and loading the mechanical properties are of utmost importance. These properties are related to the microstructure of the material. The steel microstructure shown above is studied in detail with electron microscopy because of its carbides and we aim to understand if cracks follow the path of the carbides or another path. This is a way to detect the weakness of a material and understand how it can be made stronger. The picture shows the grain boundaries of the material where the carbides often are found.
The past weeks I have worked almost full time in the lab trying to make the equipment ready for low cycle fatigue testing. We have a new videoextensometer! It is a camera used for studying the sample and register the resulting strain during testing. The camera registers the distance between two white markers of aluminum oxide. These markers are sprayed on the sample using a gun and a mask and the resulting beautiful pattern can be seen to the right in the picture viewed below. Between the markers one can see the thermocouple that is used to measure the temperature of the sample, tied to the sample with a ceramic thread.
The research concerning the markers have proven to be a great step forward. In our low cycle fatigue testing procedure the sample will be strained and compressed for a constant temperature of 800 degrees celsius in the three gaseous environments air, argon and diesel. This means that the markers of aluminum oxide must be able to resist mechanical forces, high temperatures and the presence of gases. We have done several tests to verify the survival of our new markers. Soon my college, Shengmei Xiang, will join the team after her stay in China.
Scania and KTH have recently initiated a new project named CorrosionFatigueCreep. This means that the lab is in use again and that the truck manufacturer Scania can continue its research within the field of high-temperature materials at KTH. The group aims to investigate the deformation mechanisms creep and fatigue under the influence of corrosion. Moreover, the lab is being upgraded to better meet our requirements for future testing. The first step is to make the equipment ready for LCF-testing (low cycle fatigue) at 800 degrees for three different environments: argon, air and diesel gas. The materials included in this first part are a cast ductile iron, a cast stainless steel and a Ni-resist (DS5).
My name is Christian Öberg (to the left in the attached picture) and I started working as a PhD-student for KTH and Scania in the beginning of september. The plan is that Shengmei Xiang, viewed to the right in the picture, will join the research team when she is back from China. My previous degree is within nanotechnology engineering with a master in materials science, received from Lund institute of technology.
The former main attractions still work for the project! Stefan Jonsson is the professor and the former PhD-student, Madeleine Ekström, is involved as a supervisor and technical expert.
It has been a long time since I posted. Most of my time has been spent on writing my thesis. It takes a lot of energy and I struggle to find ways of getting some back. Today I took a sunny walk in the forest next to KTH. After spending so many months in darkness it is a fantastic feeling!
We are back from Argentina and ready for lab work. The machine is now finally running again after the failure! Professor Jonsson is also doing some lab work. A picosecond laser, which will be used for cutting and processing, is being installed. More to come!