Ultrafast pulsed laser joins ceramics

Ultrafast pulsed laser welding has been used to join ceramics, an advance that could lead to pacemakers with no metal parts and electronics for space and other harsh environments.

Ultrafast pulsed laser
Optical transmission through a transparent ceramic (left) vs. a traditional opaque ceramic (right) (Image: David Baillot/UC San Diego Jacobs School of Engineering)

Described in Science, the new ceramic welding technology has developed by engineers at the University of California San Diego and the University of California Riverside.

The process is said to use an ultrafast pulsed laser to melt ceramic materials along the interface and fuse them together. It works in ambient conditions and uses under 50W 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, said senior author 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.

Ceramics are an ideal material for biomedical implants and protective casings for electronics because they are biocompatible, extremely hard and shatter-resistant. However, current ceramic welding procedures preclude 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 in a statement.

The team’s ultrafast pulsed laser welding solution directs a series of short laser pulses along the interface between two ceramic parts so that heat builds up at the interface and causes localised melting.

To make it work, the researchers optimised the laser’s 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 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 maximised the melt diameter, minimised 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 first author 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 under 2cm in size but future work will involve optimising the method for larger scales, as well as for different types of materials and geometries.

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