Welding Ceramics with Lasers

Optical transmission through a transparent ceramic (left) vs. a traditional opaque ceramic. (Source: D. Baillot, UCSD)

Smartphones that don’t scratch or shatter. Metal-free pacemakers. Electronics for space and other harsh environ­ments. These could all be made possible thanks to a new ceramic welding tech­nology developed by a team of engineers led by the University of Cali­fornia San Diego. The process uses an ultrafast pulsed laser to melt ceramic materials along the interface and fuse them together. It works in ambient condi­tions and uses less than 50 watts of laser power, making it more practical than current ceramic welding methods that require heating the parts in a furnace.

Ceramics have been funda­mentally challenging to weld together because they need extremely high temperatures to melt, exposing them to extreme tempera­ture gradients that cause cracking, explained Javier E. Garay, a professor of mechanical engi­neering and materials science and engi­neering at UC San Diego, who led the work in colla­boration with UC Riverside professor and chair of mechanical engi­neering Guillermo Aguilar.

Ceramic materials are of great interest because they are bio­compatible, extremely hard and shatter resistant, making them ideal for biomedical implants and protective casings for electronics. However, current ceramic welding proce­dures are not conducive to making such devices. “Right now there is no way to encase or seal electronic components inside ceramics because you would have to put the entire assembly in a furnace, which would end up burning the elec­tronics,” Garay said.

Garay, Aguilar and colleagues’ solution was to aim a series of short laser pulses along the interface between two ceramic parts so that heat builds up only at the interface and causes localized melting. They call their method ultrafast pulsed laser welding. To make it work, the researchers had to optimize two aspects: the laser para­meters – exposure time, number of laser pulses, and duration of pulses – and the trans­parency of the ceramic material. With the right combi­nation, the laser energy couples strongly to the ceramic, allowing welds to be made using low laser power less than 50 watts at room tempera­ture.

“The sweet spot of ultrafast pulses was two pico­seconds at the high repetition rate of one megahertz, along with a moderate total number of pulses. This maximized the melt diameter, minimized material ablation, and timed cooling just right for the best weld possible,” Aguilar said. “By focusing the energy right where we want it, we avoid setting up tempera­ture gradients throughout the ceramic, so we can encase tempera­ture-sensi­tive materials without damaging them,” Garay said.

As a proof of concept, the researchers welded a trans­parent cylin­drical cap to the inside of a ceramic tube. Tests showed that the welds are strong enough to hold vacuum. “The vacuum tests we used on our welds are the same tests that are used in industry to validate seals on electronic and opto­electronic devices,” said Elias Penilla, who worked on the project as a post­doctoral researcher in Garay’s research group at UC San Diego.

The process has so far only been used to weld small ceramic parts that are less than two centi­meters in size. Future plans will involve opti­mizing the method for larger scales, as well as for different types of materials and geometries. (Source: UCSD)

Reference: E. H. Penilla et al.: Ultrafast Laser Welding of Ceramics, Science 365, 803 (2019); DOI: 10.1126/science.aaw6699

Link: Materials Science and Engineering, University of California, San Diego, USA

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