Properties of a nanostructured bainitic steel

In some recent work, we produced a nanostructured steel was produced using a clean steel-making technique. Hoping that applying VIM-VAR processing would achieve better mechanical properties by reducing tramp elements, like sulphur and phosphorous. Resulting in less problems of embrittlement by these elements and by manganese sulphide inclusions, etc.

No doubt these steels have impressive combinations of properties. We had the chance to measure many different mechanical properties of the same batch of steel. Only complicated by the fact that we were trying to develop heat treatments to improve the properties at the same time.

These results have been published in Materials Science and Technology, here: http://dx.doi.org/10.1080/02670836.2016.1271522

The maximum strength of the material recorded was 2.2 GPa at yield, with an ultimate tensile strength of 2.5 GPa, accompanied by a Charpy impact energy of 5 J, achieved by heat treatment to refine the prior austenite grain size from 145 to 20 µm. This increased the strength by 40% and the Charpy V-notch energy more than doubled. In terms of resistance of the hardness to tempering, the behaviour observed was similar to previous alloys. Despite reducing the hardness and strength, tempering was observed to reduce the plane-strain fracture toughness.

Royal Societies Inspiring Scientists

The Royal Society put together some student resources on Inspiring British scientists with minority ethnic heritage. My Supervisor Harry Bhadeshia is twice as inspiring as the rest, as you can see from the Royal Societies Tweet:

Royal Soc Inspiring Scientists

Royal Soc Inspiring Scientists

Link to resources

Overheating the i7 620M processor in my laptop (Lenovo T410)

Having fun causing my laptop to shutdown trying to run some density functional theory code (CASTEP) on my laptop. Usually firefox is the culprit.

I installed cpufreq tools which seem to make no difference.

Installing thermald seems to help.

The fist time I ran simulations with castep.serial, i.e. compiled to run on one processor core, and it ran fine. To try and speed up calculations I managed to compile using intel ifort and supporting mpi. I actually managed to slow down the calculation the first time trying to run on 4 cores… the i7-620M only has 2 cores, but supports hyper-threading to add an additional 2 virtual cores.

After that I also need to make sure I don’t do a bandstructure calculation using multi-cores again, CASTEP will happily perform the calculation on 4 cores, but the output file informs there is no parallelisation implemented yet for this task.

This command lets me know temperatures, fanspeed, cpu frequency etc.

watch -n 2 -d cpufreq-info -c 0 -fm; cpufreq-info -c 1 -fm; cpufreq-info -c 2 -fm; cpufreq-info -c 3 -fm; sensors

Running castep.serial compiled with gfortran / fftw3 ?

Pseudo atomic calculation performed for Ni 3d8 4s2

Converged in 38 iterations to a total energy of -1355.3473 eV

Charge spilling parameter for spin component 1 = 0.20%
Charge spilling parameter for spin component 2 = 0.27%

Initialisation time = 17.13 s
Calculation time = 2663.64 s
Finalisation time = 0.42 s
Total time = 2681.19 s
Peak Memory Use = 397444 kB

Running castep.mpi compiled with ifort / mkl

Pseudo atomic calculation performed for Ni 3d8 4s2

Converged in 38 iterations to a total energy of -1355.3473 eV

Charge spilling parameter for spin component 1 = 0.20%
Charge spilling parameter for spin component 2 = 0.27%

Initialisation time = 10.33 s
Calculation time = 996.47 s
Finalisation time = 1.26 s
Total time = 1008.06 s
Peak Memory Use = 430140 kB

You will notice I haven’t yet tried mpi with gfortran or serial with ifort. These are just the options I tried so far. Also thermal management was different between these two calculations. But it seems playing around with compilation, thermal management, and using parallelisation can more than double the speed of the calculations.

System details:
3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt25-2+deb8u3 (2016-07-02) x86_64 GNU/Linux

Lectures on Bainite – 2007

A blast from 2007 for Harry Bhadeshia fans. These lectures can be found on youtube. Slides can be found here http://www.msm.cam.ac.uk/phase-trans/2007/M/M.html

Prof. Bhadeshia’s new book will be available soon, you can find details here: http://www.oxbowbooks.com/oxbow/other-subjects/materials-science-engineering/bainite-in-steels-3rd-edition.html

Laser engineering to produce hydrophobic surfaces

TheEngineer has an article covering work by scientists at the University of Rochester who have achieved the surface modification of metals, by treatment with lasers, to make the surfaces hydrophilic or super-hydrophobic. In their study they used titanium, brass and platinum.

Bouncing water drops

Bouncing water drops from modified metal surface

Original paper: http://scitation.aip.org/content/aip/journal/jap/117/3/10.1063/1.4905616

Making a welded Damascus Knife

John Neeman Tools have posted a beautiful video of manufacturing a welded Damascus patterned knife.

5 layers of 3 different steels were forge-welded, folded, and forged. With each step being repeated 8 times. This produces a patterned with 320 layers. Finally twisting and forging the steel produces a more complex pattern.

Just checking the number of layers, I get their total to be different. My calculation of the number of layers is 5 × 28 = 1280, that is 4 times more than claimed (320 layers should be the result of folding 6 times (6 folds 5 × 26).

With 1280 folds, if we assume the thickness of the knife is 2 mm, that means each layer is 1.6 μm, 320 folds would be 6 μm layers. These are both lower than what can be resolved using the naked eye. It’s very close to the wavelength of visble light — if the metal were folded one more time, or the final thickness of the knife is less than 1 mm you would be there.

Audi’s audacious aluminium advertising artifice

Audi’s advert for their A6 is really beautifully made…

Suppose you could make metal do anything you wanted,
use it in ways no one thought possible,
at Audi that’s what we do,
the new Audi A6 with Aluminium-hybrid body,
engineered for a lighter touch.

The way the metal forming is done in the advert is really nice, just shaping the parts by hand, just like the clay model can be formed when producing models of the car.

The technology is interesting, and challenging, a combination of aluminium and steel parts are used to make the car body. About 20% of aluminium by weight of the car body is aluminium, that means about 40% by volume. Non-load bearing parts such as body panels are aluminium (which benefit from good stiffness/weight ratio). All of the car body is made from cold formed and warm formed steels as in conventional car body. Interesting, aluminium sections seem to be present as side impact bars and bumper. From the advert you might be left with the impression that the whole body is aluminium, or that this is something that would be desirable, especially confusing since ‘hybrid’ is also now commonly used to refer to automobiles which use combinations of different power sources for the engine.

This video shows which parts of the car body are aluminium and steel.

However these cars overall are not much lighter due to the use of aluminium. From the previous model of A6 the weight saving is 30 kg, the weight if the total car is 1575 kg unladen or 2,155 kg gross weight (figures for 4 door 2.0 diesel). I want to look up the weight of Audio A6 since they are first introduced, that’s because in all cars there has been a trends towards increasing weight, despite all the advances in decreasing the weight of the car body.