The first thing to remember when cutting samples for EBSD, is to preserve the sample axes orientation. Cut the sample in such a manner that important sample directions, such as the Rolling Direction, the Transverse Direction and Sample Normal are not lost. The second thing to remember that the cutting process must not damage or change the sample as this would lead to erroneous results.
Avoid aggressive cutting methods that generate heat or cause deformation at the cut surface. Severe damage induced at this stage may extend so deep into the material that it is not removed by subsequent grinding and polishing. Heating caused during cutting may cause changes to the microstructure - phase transformations or precipitation/diffusions mechanisms may become active. Therefore heating must be avoided at all costs.
Images courtesy of Buehler.
Wet abrasive cutting machines are common in the metallurgical industry and are suited to cutting larger sections of material. The sample may be subjected to considerable force and heat if used incorrectly, good cuts can be performed with minimal damage. using excessive force with an inappropriate wheel can cause sample to overheat locally. Manufacturers of cutting equipment and cut-off wheels publish tables and diagrams to help to make the choice of wheel easier. The importance of observing the manufacturer’s recommendations cannot be over-stressed. If over-heating of the sample occurs, it is often due to using a wheel that is too ‘hard’ for the material being cut. The wheel does not wear properly which causes the abrasive to become blunt. Another possibility is that the abrasive becomes clogged. Friction then causes excessive heating and damage to the sample. These processes can result in altered surface structures, which subsequent grinding and polishing do not remove. EBSD is very sensitive to damage caused in this manner and greater care than usual is warranted to avoid generating misleading results, or compromising pattern quality. Therefore, the selection fo an appropriate cut-off wheel is important to avoid introducing unnecessary levels of damage when cutting materials.
Precision, Low Deformation Cutting Machines
There are many examples of wet abrasive cutting machines on the market designed for precision and low damage cutting. Such machines normally employ CBN (Cubic Boron Nitride) and diamond type cutting wheels, although abrasive cut-off wheels may also be available, depending on the machine. Generally, low deformation cutting machines are particularly well suited to cutting sections for EBSD.
Images courtesy of Struers.