Materials Scientists Use Optical Microscopes to Examine Structures

Chemjobber posted earlier about this image:

I've already commented over there about the issue, but I felt the need to elaborate. You see, microscopy is a *huge* part of much of materials science. As a simulationist, no, I'm not doing it on a daily basis anymore. I'm still my group's polishing guru when they need help with sample preparation. But in my prior research life at SnowTech, optical microscopy was as important of a tool to me as tensile testing and hardness testing, and far and away the best way for me to characterize a structure.

Let's look at a few examples of what we can learn from microscopy:

Five different Zn-Al-Cu compositions, all with over 87% Zn. Scale bars represent 50 micrometers. All samples  were manufactured by die casting with rapid quenching and no additional heat treatment.

I took these images from a report I wrote as an undergrad. There are 5 different compositions of Zn-Al-Cu alloys, all made by die casting, all with fairly similar compositions (I won't frighten you with ternary phase diagrams just yet). From these images (sometimes with the help of SEM verification) I can do the following:

-Identify the major phases present
-Estimate the average grain size
-Estimate the porosity (I'm looking at you, D...)
-Identify impurities and inclusions present in the sample
-The order of solidification and phase transformations (with help from the phase diagram)

So why do I care about all of these things? Because microstructure affects macroscale properties. For this particular study, we were looking at creep, and because creep tests take *months*, we did tensile and hardness testing for kicks. The grain size and shape controls the creep mode. Large, soft primary particles allow dislocations to move rapidly, which is undesirable in this case. We can predict a significant amount about how the material will behave under elevated temperature/ stress just by looking at the microstructure, which is good, because I really didn't want to wait three years to get enough creep tests run to reach the same conclusions.

We also learn different things at different magnifications. Low magnification can show directional crystallization/deformation that would be unnoticeable at higher magnification, and is much better for quantifying porosity and primary phase fractions.

AA6082 extrusion with an AA5086 weld bead at low magnification 

This is an AA6082 aluminum extrusion with an AA5086 weld bead run through it, also my own micrograph. You'll notice this is a much lower magnification than the previous collection. The sample has been fractured, but you can distinctly identify three major regions in the sample: the weld bead, the heat affected zone (where recrystallization has occurred) and the extrusion region, where the microstructure is unaffected by the weld. I can also see how the grains grew during solidification of the weld melt metal, and there's clearly a crack from the residual stresses caused by welding. Most of this can't be seen at higher magnifications

AA6082 extrusion with AA5052 weld bead at weld toe, same sample as above at higher magnification in a different location

There are also many times when optical microscopy is *better* than electron microscopy. But ... big fancy expensive machine! It must be better! (cry the undergrads) The contrast in an SEM image comes from two things: topology and elemental contrast. If you want to look at the grain structure of, say, an Al-Si alloy, the SEM will show you very little, because Al and Si are both fairly low elemental numbers, and don't show much contrast. On the other hand, pure Al and the binary Al-Si phase look very different in an optical micrograph. In the above image, the Si-rich regions show as dark, and pure aluminum shows as bright white. And unless you want your airplane to fall out of the sky, you better hope that materials scientists are using optical microscopy for quality control checks.

And this has just been a discussion of optical microscopy in non-ferrous metals. I haven't even gotten to technical ceramics or composites, let alone steel and cast-iron. There are entire handbooks devoted to the microstructures of Fe-C alloys alone (which may be my next spiffy material).

My New Favorite Thing...

... is the Dover Chemistry/Physics series of books. They're fairly affordable paperback textbooks or reprints of classic manuscripts, so I don't feel bad about ordering them speculatively, or writing in them. I've purchased four so far on group theory/spectroscopy and mechanics, and they're all pretty fantastic. Plus, being paperbacks, I can carry them around in my purse, even though I don't have a particularly big bag. These texts typically have a pretty narrow focus, so while they may be less than perfect for undergraduates, they're exactly what I need.

Impostor Syndrome and Family

Thank you to Scicurious for hosting a carnival on this subject.

As a woman in engineering, I expected to feel impostor syndrome quite strongly, but so far, I just haven't. I can find myself in a room as the only woman, and I barely notice. Am I some magical super-confident oddity? Not really. But even if I don't think I'm the best at ___, I still feel like I deserve to be where I'm at most days.

As I've been reading some of the brilliant posts around the internet, it seems that authors largely find in one of two categories: "best students" who no longer are, or people making a large leap from their background.

I've talked before about my SciGrandmother, and my other family members in STEM fields both in and out of academia. Clearly, I'm not making a large leap away from my background. Even at GiantU, I have a family support network, in the form of an aunt who is a professor in a biological field. She helped me find a mentor in my own department to help me deal with some of the nonsense that is my advisor. Having someone who is not a formal chain-of-command mentor has been incredibly helpful. When my own advisor was editing at the rate of molasses, he was willing to read my manuscript and give me feedback about organization and writing style, even if he didn't know all of my science.

As far as the "best student" thing goes, I've never been the best student at everything, thanks to my sister. It's been a life-long competition, with me winning some subjects and her winning others. We're fairly close in age, and very even in ability. I've had years to get used to having someone who was better than me. I'm better at math, she's better at writing. I'm better at music, she's better at drawing. And eventually, I've gotten to the point where that's ok. The best days are when one of us can say to the other "It's so helpful having a sister who's better at ___ than I am".

Lastly, I'm often just too damn busy think "I need to do x, y, z, alpha..." to think I'm not good enough. If I can't do everything, it's probably because there's so much of it. Every so often, I lapse into thinking I'm incompetent because I haven't finished everything, and then I vent to a lab mate, and they remind me I'm working on 3+ projects.

So what advice can I offer others? Find and cultivate a support network of various stages and fields. Find a peer you can vent with, find a mentor who's not your advisor (admittedly, this can be very tricky), make friends in other departments and other groups. Find someone who will tell you that what you do is awesome (that isn't a family member). Have trouble reaching out to people? Join Twitter, read blogs, form a virtual support network. Seriously, the blogosphere is full of supportive people from all sorts of career stages, even if it's dominated by biologists.

Somedays, life doesn't suck

Posting has been particularly sporadic recently, as I've been spending more time than usual coding. It's amazing how much creative energy this really takes. I've also had a great time working with the undergraduate on my project. Ze's super motivated and picks things up quickly. I will be sad to lose hir this summer. However, ze will be transitioning to an experimental group, and I do think the exposure to a wider variety of types of research before graduate school is highly beneficial. Plus, this experimental group is run by SuperFamousDude, which will look a lot better on grad school applications.

But for the next few weeks, we get to finish going over all the results and figuring out what needs to be done to polish them up for inclusion in a manuscript.

I also have delicious tea, the sun is out, and I found the Query Scholar extension for Chrome by way of @highlyanne . I may even decide to eat lunch not at my desk.

Learning from (Negative) Examples: Part II

To see the first post of the series, go here.

This week's observation of management failures:

When you hire an expert in ____, have them work on ____. For example, assume you hire someone who is a preeminent scientist in shock-wave physics. You have two projects with funding: one is on polymeric structures, and the other is on simulating ion impacts. Quick, which one do you have them work on?

*buzz* Time's up! If you said ion impacts, you are clearly not my advisor.

Keep it simple or explain it clearly: you may have great reasons for adding 10 layers of complexity to what is typically a very simple process (like, say, taking a group photo). However, don't expect an enthusiastic response when something that should take 5 minutes takes an hour if you don't make clear why. Even if you can't successfully communicate it, try.

Not everyone responds to the same motivation: My advisor is a big believer that we should all be motivated to work 16 hours a day so we can graduate sooner and go out into the world an make a reasonable amount of money. This, apparently, is all the motivation we should possibly need. I don't think he comprehends that short-term praise/feedback can make a huge difference in productivity. I don't think he understands how utterly disheartening broken equipment can be. Most students don't need cheerleaders, but most students do need some outside motivation.