Second dendrite arm is easily visible but nothing happens when switch to PLM. Keller and Barker's reagent were used.
Are you using a color filter as well when switching to PLM? This should help greatly with grain contrast if the etch is sufficient. See the attached image for an example of the color contrast. This was produced with a Barker's etch (20 s pre-etch + 90 s with applied voltage) on Al 6061.
Ethan Michael Sullivan Thank you for your quick reply. Your picture is exactly what I want to achieve. I used the lambda plate on my microscope and was able to get dark field pictures which is basically the same image as the one I posted but with a dark background. The etching procedure I used was grinding, polishing (down to 0.06 um), Immersion in Keller's (20 sec), electro-etching in Barker's (4 min, 20V). And the material I am dealing with is Al 4043.
Zhongjia Gao In addition to the lambda plate, which polarizes the light coming from the light source, you must also insert an analyzer (recombines the light waves after interference with the sample) and a color filter (to provide color contrast that complements the interference contrast. Your microscope may or may not have these components. See the schematic here: https://www.microscopyu.com/techniques/polarized-light/polarized-light-microscopy
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