Fabrication of Magnesium diboride superconductor

Bhadesha123 has posted a nice video on youtube discussing the fabrication of Magnesium diboride superconductors.

This seems an interesting metallurgical case study about developing a processing route. Advantages of swagging and drawing are discussed as well as the importance of preventing grain growth to allow processing and for control of material properties.

The video was provided by Professor Bartek Glowaki of the University of Cambridge, who filmed, directed and edited the videos.

Dyanamic test austempered ductile iron

Drs Dawid Myszka, A. Wieczorek and Tadeusz Cybula from the Warsaw University of Technology, Poland investigated the influence of microstructure on the dynamic mechanical properties of austempered ductile iron using Taylor impact testing. Austempered dictile iron means it’s a cast iron, so has graphite particles in a matrix heat treated to become bainite!. Taylor impact testing means you fire cylinders of the material at an immovable object and see how the material gets squished.

Deforming Austempered Ductile Iron

Shattering Austempered Ductile Iron

The heavily deformed volume which faced the impact has resulted in hardening and in transformation to martensite — both hardness and magnetic measurements have been used. Hardening was due to mostly strain induced austenite-to-martensite transformation, and also due to cold-work.

References
D. Myszka, L. Cybula and A. Wievzorek
Influence of heat treatment conditions on microstructure and mechanical properties of austempered ductile iron after dynamic deformation test
Archives of Metallurgy and Materials
V59, Issue 3, 2014

DOI:10.2478/amm-2014-0204

Japanese Swords are medieval nanotechnology

During Japanese sword making the steel is folded repeatedly. Each time the steel is folded the structure is refined.

The folding is a key process in sword making. Folding and striking the metal forges the surfaces back together. This process of folding, then forge welding, can be repeated as many as 16 times. The process removes impurities and helps even out the carbon content, and controls the scale of chemical segregation, and it is this which results in alternating layers of hard and ductile material.

So how can folding the steel result in a nanoscale structure?

When the steel is folded the number of layers obviously increases geometrically. 1 fold result in 2 layers, 2 folds results in 22 = 4 layers, 3 folds results in 23 = 8 layers. By the time we get to 15 or 16 layers we have 32768 layers or 65536 layers. After that the sword is forged out to have a width of around half a centimetre.

5 mm divided by 65536 = 76 nm.
(5e-3/65536=7.629e-8)

So each layer is 76 nm. So we can legitimately argue that Japanese Swords are bulk nano materials, with structure controlled on the ‘nano’ level, for metallurgists this is just routine stuff.

Edo period Forge Scene

Edo period Forge Scene

Of course Japanese swords are not true examples of nanotechnology, despite the validity of the maths the folding doesn’t really result in a controlled structure on the nanoscale due to the changes that occur during the welding process… I plan to talk more about that in a later post.

As you can see below, the laminations are typically visible on the millimetre scale.

Lamination on Japanese Sword

Lamination on Japanese Sword

Grain Boundary Allotriomorphic Ferrite and Polygonal Ferrite

Bodnar and Hansen (writing in 1994) note that Polygonal ferrite can occur as grain boundary allotriomophs and intragranular idiomorphs. They then demonstrated the similarity between grain boundary allotriomorph and polygonal ferrite  by showing the same grain boundary area at two different magnifications with different labels. In the combined image you can see that the arrow is pointing at very similar position in two figures.

Grain Boundary Allotriomorph in Figure 1 A

 

 

 

 

Polygonal Ferrite Figure 1 B

Polygonal Ferrite in Figure 1 B

 

Posiiton of Figure A in Figure B

Posiiton of Figure A in Figure B