Strange pattern in Al Ka...

[BenjaminWade]

Hi all
I am hoping to draw on the wisdom and experience of people on the forum. I have recently done some spot analysis and mapped some Ti6Al4V alloy. From spot analysis it is quite consistent in Al content (avg 30 spots: 5.99 +/-0.12 wt%). They were looking for Fe/V rich inclusions, so I thought I would also map it which is where I have run into trouble. I have attached below two of the Al Ka maps on my TAP xtal, one from a small area of the sample, one from a larger area. The pictures are quite grainy as the Al is quite consistent at around 6wt% so I had to stretch out the constrast, but you can see a rhythmic nature to the Al maps.

Behind this I can see some "real" patchy zoning of Al, but can't explain what the artifact is. The other elements I mapped for (Ti on LPET, V and Fe on LLIF xtals) do not show this pattern, so I don't think its real, doesn't look like a discharging artifact. Some orientation effect with my TAP xtal? The sample is polished very well and very flat.

Anyone have any ideas..? 

Cheers

[Probeman]

Do you have an SE or BSE map of the same areas?
john

[BenjaminWade]

hi John
Unfortunately not of the exact same area that was mapped, but I do have some high mag BSE images from the spot analysis (one is attached). They were imaged at high beam current with contrast cranked to pull out any zoning, and I run an undersaturated filament so the image quality is not great. I would have thought they should be visible in the BSE image if it was real Al zoning.

If I quant the maps and do a vertical linescan profile, the apparent Al variation across the peaks and troughs ranges from 5.4-6.6 wt%Al, which is outside the min/max values from random spot analysis (5.8-6.2 wt%Al).

I guess the test would be to rotate the samples 90 degrees and map it again...

Cheers

[BenjaminWade]

Interestingly the student on today is running some basic garnet maps, and I am seeing some artifacts again on the same TAP xtal on Al again. Different type of artifact but very regular striping. Not sure if the problem is related at all...

[Probeman]

Interestingly the student on today is running some basic garnet maps, and I am seeing some artifacts again on the same TAP xtal on Al again. Different type of artifact but very regular striping. Not sure if the problem is related at all...

That's definitely some kind of electronic noise.  These are stage maps?   Is it only one spectrometer that you are seeing these artifacts on?

Maybe check the detector bias and see if it's too low or too high by running a bias scan in PFE.
john

[BenjaminWade]

Crap! You are dead right John. Just had a look at the garnet map settings and somehow the Gain setting on that TAP xtal that I am measuring Al on got set to 2500 and it should be up around 3000.

I don't think that explains the Al maps in the Ti alloy though, as it was on a different spectrometer and looking at the metadata the gain was what it should be for those maps. Also the "waviness" isn't uniform stripes but on a wavy diagonal.

Cheers

[Probeman]

Crap! You are dead right John. Just had a look at the garnet map settings and somehow the Gain setting on that TAP xtal that I am measuring Al on got set to 2500 and it should be up around 3000.

I don't think that explains the Al maps in the Ti alloy though, as it was on a different spectrometer and looking at the metadata the gain was what it should be for those maps. Also the "waviness" isn't uniform stripes but on a wavy diagonal.

Cheers

I agree the pattern in the Al-Ti alloy looks different.    Maybe try rotating the sample.  And do SE and BSE images also.