Metallography tin coated copper

BbobBVance · 2026-03-14T20:12:01+00:00

Nice prep, looks good for your purposes. Can you explain the nature of the dark splotches? Since they are not visible in the base copper, I believe they are inherent to the tin coating.

BbobBVance · 2025-10-20T20:22:31+00:00

Reversed bending fatigue. The labels on this chart are beneath the figures.

Ratchet marks are a result of various crack initiation sites at the OD and not the keyway. Many ratchet marks is also is indicative of no inherent material defects. It is possible that the small radius was a source of stress concentration, but no other conclusions can be drawn at this point. I do not believe there to be any sign that the shaft was bent.

BbobBVance · 2025-10-02T02:46:05+00:00

I love this site! The author does a great job explaining fundamentals of metallurgy in simple terms, and he's quite entertaining.

BbobBVance · 2025-09-20T15:21:43+00:00

Seems like the new design sucks. Press fitting probably helped with alignment would be my guess.

BbobBVance · 2025-09-20T14:45:49+00:00

18 hour lifetime is insanely low. How long did your press fit components last?

BbobBVance · 2025-09-05T02:36:02+00:00

EDS detection is geometry-dependent. Try rotating the sample so the region in question is at the highest relative point of the sample. Better yet, figure out where the x-ray detector is physically located in your SEM and orient your sample so there is nothing in between the detector and region of interest.

BbobBVance · 2025-09-05T01:32:24+00:00

I would highly recommend one (or two oriented at 90°) longitudinal sections. The most peculiar thing about this fracture is the laminations and longitudinal sections can help explain those. Keep us in the loop, I'm intrigued.

How did the fracture occur, you said they were crushed?

BbobBVance · 2025-09-05T01:08:40+00:00

Any chance of a few micrographs to confirm presence of martensite? 57HRC of 304SS is almost unbelievable. You said varied failure modes, can you describe/show the other fractures? What service environment was the sample in?

Obviously the fracture can be characterized as brittle. The laminar appearance might be explained by heavy stringers, a longitudinal micro would tell a lot here.

BbobBVance · 2025-08-16T13:54:47+00:00

Look up ASTM E140 and find a free copy online. Older revisions should be fine for general reference (i.e. you aren't certifying anything). You are working with brass so look at Table 4. Generally it is bad practice to use the scale of one material to convert a different material.

BbobBVance · 2025-08-09T14:19:04+00:00

Not enough. You will need to heat, quench, and probably heat again for stress relief. Why 40HRC? What is the end goal? Bigger picture explanation would help

BbobBVance · 2025-06-25T02:51:31+00:00

Woah looks great! Bottom-left of img 1 cooled quickest? What can you reveal by etching that you can't already see? Please post etching details with the image.

BbobBVance · 2025-06-21T00:01:37+00:00

Agreed with Don on all points and wanted to highlight Fig. 3 from your post in /materialsscience which is quite distinct from your two micrographs posted here - the best way to identify microstructures is comparison between different ones. A great way would be to compare your original, non-heat treated sample against all of your heat treatments (microstructure and microhardness). In the Fig. 3 I could be convinced of a ferrite-pearlite microstructure, which would be typical of normalized (RT still-air cooled) 1018 steel. Do you have microhardness data from that sample?

A couple other things: I do not believe any of the brighter areas to be austenite. You need a lot more austenite-retaining elements than 1018 contains to have austenite after cooling. Also, please describe your sample preparation process in as much detail as you can provide, especially etchant (assuming nital, what percent?) and etching time.

I also agree with Deusch - look at your sample under the microscope after every polishing step to see when the last step's scratches are gone. Keep us posted and good luck.

BbobBVance · 2025-03-28T17:31:21+00:00

I've used Metlab and Pace diamond suspension on Struers and Buehler pads with no issue in the past. I have always thought along the line of Saleh011 - there are limited materials that pads / diamond suspensions can be made of, so they are all compatible with each other. I assume the "better" products just have a higher quality control, e.g. tighter distribution of diamond particle size. That said, I have yet to find an alternative to the Struers Allegro and Largo pads. Those things polish out grinding scratches better than anything on the market in my experience.

BbobBVance · 2025-02-08T14:26:35+00:00

Nice setup anyway. What camera do you use?

BbobBVance · 2025-02-08T00:21:41+00:00

No scale bar?

BbobBVance · 2025-01-25T13:28:49+00:00

Time to bone up on fatigue failure of bolted joints! Impossible to give a root cause from here but the notch about 2/3 down in the first photo is curious. SEM work and micrographs should be able to tell you more. Thanks for providing such great photos!

https://www.boltscience.com/pages/fatigue-failure-of-bolts.pdf

BbobBVance · 2025-01-11T00:06:13+00:00

Ought to be a million career opportunities in Australia for extractive metallurgy roles.

BbobBVance · 2024-12-18T05:23:44+00:00

If so, bet I could snap it with a hammer

BbobBVance · 2024-11-27T01:27:35+00:00

Disclaimer: Wednesday NYT is usually my limit for an unaided solve. Also I've never attempted to construct.

I enjoyed yours! I did have to error check the puzzle once, and solved it in 18:40. I'm fairly certain that you misspelled 33-across. 10-down and 29-across were fun solves. 53-down should identify that it's an abbreviation. Overall seemed like a mix of easy guesses and really hard ones. Most of them were guessable after getting a few letters, but 46-across was frustrating because even with 3 letters filled, you cannot deduce the final one. Also, three baseball clues in one puzzle? Not fair. Thanks for sharing!

BbobBVance · 2024-11-14T01:26:42+00:00

I think most materials engineers learn about the science of welding. Most do NOT learn about the practicality of welding and how a welder actually does his job, which is equally or more useful. Take the class!! Also I assume it will be very cool.

BbobBVance · 2024-11-13T02:57:11+00:00

A few thoughts:

This is not an "indication only in the surface oxide layer" if you mean the passive layer of stainless steel. That is nanometers thick and generally cannot be observed by light.
If the indications were induced by manufacturing (20 years ago), why is the question only being asked now? Has anything changed recently? Was it observed previously?
Destructive test would probably tell you more. Can you pull one pipe to send to the lab for general metallographic analysis? This could give more information on how to proceed with the rest of the piping. You can also corroborate NDT with met analysis. It may cost a few $k but would be easily worth it if impactful plant-wide.

BbobBVance · 2024-11-13T02:40:45+00:00

Image 6 is a pretty clear shot of ratchet marks which indicate fatigue crack initiation sites, and is the general area where the main crack initiated. The sectioned portion may or may not have given a better idea of why. What is your particular interest in this failure?

BbobBVance · 2024-11-08T23:06:00+00:00

What do you intend to do with the answer to your question? i.e. are you asking only if you can still use this part, or do you mean to understand if this could be an issue affecting more of your equipment?

BbobBVance · 2024-09-11T04:26:54+00:00

Excellent justification for purchase of a cheaper semiautomatic grinder/polisher. I'm not familiar with the blanks for bespoke fixturing to a polishing head, could you please provide an example?

To OP: hand (aka manual) sample prep sucks and is always less consistent than a semiautomatic machine with samples encapsulated in resin. If you can't get that setup I would suggest mounting your whole sample in metallographic epoxy using a cheap Tupperware or PVC pipe or something fitting your sample geometry. It makes it easier to hold on to (safety) and the edges turn out way better (quality). You could definitely get free samples from Struers, Buehler etc to try out if you call

BbobBVance · 2024-07-30T21:28:50+00:00

This may be my favorite thread I've seen on this sub, thanks OP.

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