Gutierrez and Raabe have reported amazingly low dislocation density in Fe-3Si (wt.%) alloy after deforming to 500 MPa, using electron channeling contrast imaging in SEM-EBSD. In their paper “Dislocation density measurement by electron channeling contrast imaging in a scanning electron microscope“, published in Scripta Materialia, Vol 66, Issue 6, 2012. They report dislocation density of 10 ± 4 × 10-13 and 17 ± 6 × 10-13 m-2.
Just for fun… lets imagine shortest dislocation to be 3 unit cells long and calculate the volume it would be found in (any shorter and we might be considered out dislocation to be some sort of point defect, but I wonder if there is criteria for shortest length?). 3 unit cells, so 2.8 * 3 = 9 nm. Volume = length/ density. 9 × 10-9 / 10 × 10-13 = 9000 m3. So one of our short dislocations would be found in a block 20 m × 20 m × 20 m.
A more usual dislocation density would be 10 × 1013. That means a length of 1014 m of dislocations in 1 cubed meter. That is equivalent to 100,000 km of dislocations in a 1 cm cube (a block of 1 cm × 1 cm × 1 cm). Or 100 km of dislocations in 1 mm cube. — A distance that would take more than 1 hour to ride on a motorbike, although it would be balance on the dislocations travelling at that speed.
The distance to the moon is 385,000 km, so we can only go 1/4 of the way there using the dislocation density I started with, also dislocations are space, and space is space too, so there are already dislocations there. It makes more sense to dig a tunnel with them…
The radius of Earth varies from 6,353 km to 6,384 km (Wikipedia), so there is a long enough length of dislocations in 1 cm cube of steel (if we take dislocation density to be 114 m/m3 still) to stretch to the centre of the earth 16 times, or to go all the way through the earth and come out the other side 8 times.