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Ultrafast lasers let engineers weld ceramics at room temperature

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

A new ceramic welding technology could enable smartphones that don’t scratch, metal-free pacemakers and electronics for use in space.

Research by engineers at the University of California, San Diego, and published in the journal Science describes a unique welding method for ceramics that uses an ultrafast pulsed laser to melt them along the interface and fuse them together. 

It works in ambient conditions, and uses less than 50 watts of laser power, making it much more practical than current methods that require heating the parts in a furnace. 

Ceramic materials are of great interest to engineers because they are biocompatible, hard and shatter resistant, which makes them perfect for biomedical implants or as a protective casing on electronics. But current methods aren’t conducive to making those products. Furthermore, ceramics have been hard to work with because melting them requires exposing them to extreme temperature gradients that can cause them to crack. 

"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," says Javier Garay, a professor of engineering at UC San Diego, and a senior author of the paper. 

Garay and colleagues used a series of short laser pulses along the interface between two ceramic parts to create localised melting only in those areas. To make the method, which they’ve dubbed ultrafast pulsed laser welding, work properly, the team had to optimise both the laser parameters (exposure time, number and duration of pulses), and the transparency of the ceramic material. 

"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," says Guillermo Aguilar, who worked on the project alongside Garay.

By focussing the energy where they wanted it, the team were able to avoid damaging temperature gradients, enabling them to encase temperature-sensitive materials such as electronics, added Garay.

They tested the technique by welding a transparent cylindrical cap to the inside of a ceramic tube, after which tests showed that the welds created using the new method were strong enough to hold a 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," says first author Elias Penilla, who worked on the project as a postdoctoral researcher in Garay's research group at UC San Diego.

The next stage will be to optimising the technique, which has only been used on small parts less than two centimetres in size, for larger scales, as well as different materials and geometries.
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