Where science meets art

Posted: May 7, 2014 - 5:23pm | Y-12 Report | Volume 10, Issue 2 | 2014

You could say being a metallographer was a matter of destiny for one Y‑12 employee. She’s the third member of her family to examine the microscopic structure of metals at the site. “It’s an honor to do what my aunt and cousin did,” she said.

It’s also an essential step in ensuring the quality of Y‑12’s Defense Programs work for the National Nuclear Security Administration.

For one ongoing project, the metallographer and other technicians in her group analyze the integrity of welds in stainless steel tubes. The tubes are used to sample mock weapon components, which serve as surrogates to assess the quality of weapon components in the stockpile. After sampling, the tubes must be welded shut.

Some tubes, which are less than an inch long and about a quarter inch in diameter, have multiple welds to be examined. So that a proper crimp and seal on each weld can be verified, the metal is removed layer by layer to allow examination of grain size and structure, porosity and voids, and defects.

“You can’t see what’s going on inside until you break through those layers,” the metallographer said. “The outside of a tube doesn’t give you the whole picture. At each plane, we want to see how well the crimp is sealed. I call it controlled tearing apart.”

This methodical approach involves mounting a tube in epoxy for stability, grinding it with grit paper, polishing with diamond and silica solutions to get a smooth mirror finish, and, if a void is found, doing some electro-etching (a metal etching process that uses electricity and oxalic acid) to better view the area. The metallographers take measurements at specified locations and enter the dimensions and other information into a database. Engineers review the data to determine whether the welding parameters need adjustments. Low- and high-magnification digital images called micrographs capture the process, which typically takes two to three days for each tube.

Another metallographer uses jeweler’s glasses to do the precision work. “There’s a lot of hand/eye coordination,” he said. “There aren’t machines to automate this fine work. You have to apply the right balance of pressure and dexterity because you don’t want to mess up.”

The consequences of messing up are serious: A weapon component in the nuclear arsenal may be deemed unacceptable. To date, the metallographers have never destroyed a tube.

“There are a lot of gotchas here, so you’ve got to be careful,” said Steve Dekanich, an engineer in Quality Assurance. “We have only one shot per tube, and it’s important because the inspection and data give you a good idea of whether you’ve got your welding parameters correct. Our metallographers are spot on. What they do is probably 20 percent knowledge and 80 percent art.”

In recognition of their vital national security work, the metallographers were part of a team that received a 2012 Defense Programs Award of Excellence. But for the honoree following in her family’s footsteps, knowing that her aunt and cousin are proud of her is enough. “When I first started at Y‑12, I had some big shoes to fill,” she said. “But now I’ve achieved a certain skill level, and I honor them by doing my job well.”