New research shows why metal alloys degrade

September 24, 2008,

( -- Metal alloys can fail unexpectedly in a wide range of applications -- from jet engines to satellites to cell phones—and new research from the University of Michigan helps to explain why.

Metal alloys are solids made from at least two different metallic elements. The elements are often mixed together as liquid, and when they "freeze," into solids, tiny grains of crystal form to create a polycrystalline material. A polycrystalline material is made of multiple crystals.

Within each of the grains of crystal, atoms are arranged in a periodic pattern. This pattern isn't perfect, though. For example, some of the places atoms should be are empty. These empty spaces are called vacancies. Atoms of each element in the alloy take advantage of these holes in the lattice. In a process called diffusion, atoms hop through the material, changing its structure.

"It's kind of like musical chairs," said Katsuyo Thornton, assistant professor in the U-M Department of Materials Science and Engineering. "Diffusion happens in nearly every material, and materials can degrade because diffusion causes certain changes in the structure of the material."

Atoms of different elements tend to hop at different rates because they are bound to their surrounding atoms with varying strength. Thornton and her colleagues have demonstrated that when there's a greater discrepancy in the hop rates in the different elements in the alloy, there's a more pronounced diffusion along grain boundaries. This possibly leads to a faster degradation. Thornton's collaborators on this project are Materials Science and Engineering doctoral student Hui-Chia Yu, and Anton Van der Ven, an assistant professor in the same department.

"In some cases, the grain-boundary diffusion is 100 times higher than what was commonly expected," Thornton said.

"This is a very generic finding," she said. "That's why it's important. It applies to a wide variety of materials. It applies to polycrystalline materials including electronic materials like solder."

Conventional solder, made of tin and lead, is a common alloy that connects electronic components in computer circuit boards and gadgets. Because lead is toxic, engineers are working to design new kinds of solder without lead. But they haven't found a substitute that works as well. The team's findings may help explain why "tin whiskers" form in some of these new solders. Tin whiskers have caused damage to satellites, for example.

"We are trying to apply this theory to whisker growth in solder," Thornton said.

This finding suggests that materials scientists could make longer-lasting alloys if they use metals with similar atomic hop rates, or manipulate the intrinsic hop rates by other mechanisms.

A paper on the findings called "Theory of grain boundary diffusion induced by the Kirkendall effect" is published online in Applied Physics Letters.

Provided by University of Michigan

Explore further: Predicting a new phase of superionic ice

Related Stories

Predicting a new phase of superionic ice

March 15, 2018

Scientists predicted a new phase of superionic ice, a special form of ice that could exist on Uranus, Neptune, and exoplanets. This new type of ice, called P21/c-SI phase, occurs at pressures greater than those found inside ...

Nanostructures made of previously impossible material

March 9, 2018

Materials scientists often seek to change the physical properties of a material by adding a certain proportion of an additional element; however, it isn't always possible to incorporate the desired quantity into the crystal ...

Chemical waves guide to catalysts of the future

February 20, 2018

Spectacular electron microscope images at TU Wien lead to important findings: Chemical reactions can produce spiral-like multi-frequency waves and thus provide local information about catalysts.

Recommended for you

Neutrons help demystify multiferroic materials

March 19, 2018

Materials used in electronic devices are typically chosen because they possess either special magnetic or special electrical properties. However, an international team of researchers using neutron scattering recently identified ...

Designing diamonds for medical imaging technologies

March 19, 2018

Japanese researchers have optimized the design of laboratory-grown, synthetic diamonds. This brings the new technology one step closer to enhancing biosensing applications, such as magnetic brain imaging. The advantages of ...


Adjust slider to filter visible comments by rank

Display comments: newest first

4.8 / 5 (5) Sep 24, 2008
As a materials science major, I can say, we already knew this. For quite a long time.
5 / 5 (2) Sep 24, 2008
Ditto Rawley. This was covered in intro to materials science.

Their application to tin based solder could be huge though. They estimated a cost of going lead free is in the hundreds of billions of dollars a year. The lead free solder fails regularly, and that includes things on the ground, in the air and in outer space. A fix for this would be close to priceless.
not rated yet Sep 25, 2008
I worked at the component level as the first ICs were introduced. It was a huge headache to get the 'wrong' solder out of the supply system in my highly controlled industry. We were taught that a solder joint had had a limited lifetime (by what criteria I don't know). Then I went into operations/testing...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.