Ultrafast lasers used to weld ceramics without furnace
Researchers at the University of California San Diego have successfully welded ceramics together using an ultrafast laser, a process that usually requires the extreme temperatures of a furnace to achieve.
The new technique, described in an August issue of Science, works in ambient conditions and uses less than 50W of laser power. It enables the melting and fusing of ceramic materials without causing cracking, an issue often faced when welding ceramics with a furnace due to the extreme temperature gradients involved.
Ceramic materials are of great interest to multiple industries 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,’ explained Professor Javier Garay of UC San Diego, who led the work in collaboration with UC Riverside professor Guillermo Aguilar.
The researchers’ technique instead uses an ultrafast laser to generate a series of ultrashort laser pulses, which are aimed along the interface between two ceramic parts so that heat builds up only at the interface and causes localised melting. The method has been named ‘ultrafast pulsed laser welding’.
To make it work, the researchers had to optimise 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 50W) 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,’ said Aguilar. ‘This maximised the melt diameter, minimised material ablation, and timed cooling just right for the best weld possible.’
Garay added: ‘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.’
As a proof of concept, the researchers have welded a transparent cylindrical cap to the inside of a ceramic tube, with tests confirming that the welds are strong enough to hold vacuum.
So far the new technique has only been used to weld small ceramic parts that are less than two centimetres in size, however future plans involve optimising the method for larger scales, as well as for different types of materials and geometries.
The researchers’ work was funded by Defense Advanced Research Projects Agency (DARPA), the National Science Foundation (NSF) and the UC Riverside Office of Research and Economic Development.
Paper in Science: Ultrafast laser welding of ceramics