Merge branch 'Bernadetadk-patch-1'

collections/_tutorials/Sample preparation

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+---
+title: Sample preparation
+author: Bernadeta Karnasiewicz
+---
+
+# Metallurgical preparation of Ti6Al4V specimens for microscopic observation (B12 lab)
+
+First the specimen needs to be mounted in the resin, in hot compression mounting machine. If you are preparing the sample for EBSD examination, remember that If your sample is 
+not flat, it will be very difficult to obtain EBSD map on this sample, regardless of the faultlessness of the preparation.
+
+Turn Struers TetraPol grinder on. For griding we use the SiC abrasive papers starting from 180, 320, 600, 800, 1200, 2400 and 4000 grade, under flowing water with sliding 
+speed between 200 to 300 rpm. Regarding details of the grinding technique, people often have different methods for force and time that they grind for, these vary from couple 
+of seconds  to 10 mins on every paper with manual force adjusted to the size and state of the material of the specimen (for example CP Ti is softer and more prone to scratches 
+in comparison with Ti alloy, also the Ti64 specimen in deformed state will be more difficult to prepare than the one that has been casted or annealed at β phase temperature). 
+The rule of thumb is that after grinding on each paper you should not see any scratches from the previous one (by eye), the one with the smaller grade. You should use User
+Defined mode (you can control the speed and the water supply). When the machine is set, press the green button (by pressing the red one, you can always stop the grinder).
+Place the specimen on the disc, but not in the centre. Hold your specimen in the way that your hands are aligned with the net force on the disc but counteract it (left image).
+You can also use the designed tool to keep the sample on the rotating disc (right image). 
+
+After grinding, chemical-mechanical polishing with a mixture of colloidal silica (OP-S) and hydrogen peroxide should be performed on a polishing cloth with proportions:
+4 OP-S to 1 hydrogen peroxide. Put on the gloves. Mix the liquids in a small container, install the polishing cloth on the magnetic disc, turn the water off, adjust the speed 
+and press the green button. Pour some of the mixture onto the cloth and place your sample on the rotating disk in the same way as for grinding. Adjust the force and the time 
+of polishing to the state of material of your sample (casted, deformed, hot annealed etc) and the size of it. As in case of grinding, people often have different methods for 
+force and time that they apply for polishing too, these vary from 2 -5 mins on OPS with a “hard force” or 20 mins of “light” pressure. When you are done, apply ethanol and dry 
+up your sample. If you see any kind of residual smear from the OP-S mixture you can try to remove it by turning the water on and as remaining OP-S mixture is still on the cloth, 
+slightly press the sample on the rotating disk. 
+
+Titanium and titanium alloys should normally look very clean after polishing so you should not see any dirt or anything like that on the surface. Due to the hexagonal 
+crystal lattice of α phase, the microstructural details in titanium can be seen using cross-polarized light on a light optical microscope, without etching. This can be used as 
+rapid and easy assessment of the polish quality. Remember that highly deformed material are in general more difficult to prepare and exhibit poorer response to cross-polarized 
+light (lack of sharp detail and poor contrast).