Pulsating laser welding technique joins ceramics

Materials World magazine
,
27 Sep 2019

An ultrafast laser technique can weld ceramic joints without the use of high-temperature furnaces. Shardell Joseph finds out more.

A new welding technique that can bind ceramics has been created, using an ultrafast pulse laser to melt the materials and fuse them together. The team of engineers, from the University of California (UC) San Diego and UC Riverside, USA, claimed the technique could broaden the material’s field of applications.

Potential uses for this technique include manufacturing shatter and scratchproof devices, metal-free pacemakers and electronics for harsh environments. Unlike other ceramic welding techniques, the laser method is able to prevent heat damage to electronic components attached to the material.

‘Even if you were not interested in electronics, you can join ceramic to ceramic just to make a high-temperature structural component,’ UC San Diego Mechanical Engineering and Materials Science Engineering Professor, Javier Garay, told Materials World.

‘As technology progresses, we will be able to join ceramics with lasers, even at a larger scale, so therefore can make ceramic structural components like one can already metals. If we did apply this technique, let’s say to our smartphones, and we wanted to have it encapsulated in ceramic, we could weld this joint using these lasers. We believe that now the smartphone will be waterproof.’

According to Garay, the technique could also provide a foundation for large-scale joining of ceramics for more general components.

The welding problem

The use of ceramics for greater applications is a growing point of interest due to its extremely hard, shatter-resistant and biocompatible material properties, with a focus on its potential for biomedical implants and protective casings for electronics.

In modern manufacturing, however, the material’s inability to be welded without conducting large amounts of heat has deterred large-scale adoption. Existing methods are unable to join ceramics that are touching, or in close proximity to temperature-sensitive materials such as polymers and electronic components, as they require high-temperature diffusion bonding.

In regards to general welding, attempting to join ceramic to ceramic by only heating the interface between the two plates would cause the material to expand and crack in other cooler areas, due to thermal shock.

‘With a metal like aluminium or steel, one can weld those pieces together and build a device or a machine up from the ground,’ Garay said. ‘Unlike with ceramics, once you have made the parts, you cannot join them after they have been made. So it has really hindered ceramics being adopted in general.

‘There are a lot of industrial uses for ceramics, but I don’t think it is as prevalent as it would be if one had a really good joining technique.’

Ultrafast pulses for joining

Tackling the ceramic welding conundrum, the team introduced the ultrafast-pulsed laser approach. They found that by using ultra short laser pulses, this leads to heat building up very quickly in a small area, which causes localised melting rather than ablation.

‘We had never really tuned the ceramic or the material to the laser, or vice versa, the laser to ceramic,’ said Garay. ‘Because we had gained a pretty good understanding of both, we thought that if we can now tune the properties of the material to the absorption where the laser puts out its power, we should be able to get a better material energy coupling.’

According to the team, the most effective speed for the ultrafast pulses was two picoseconds at the high repetition rate of 1MHz, but an overall moderate total number of pulses. ‘This maximised the melt diameter, minimised material ablation, and timed cooling just right for the best weld possible,’ said UC Riverside Mechanical Engineering Chair and Professor, Guillermo Aguilar.

The team explained in the paper, Ultrafast laser welding of ceramics, published in Science, how they tested the technique by joining both transparent ceramic with varying absorption properties and conventionally sintered ceramics that have limited light transparency – both successfully demonstrated the joining of simple geometries.

Future of ceramic fusing

Looking to integrate ceramics into industrial welding processes and capabilities, the team has since gained interest in its technique, and its large-scale potential.

‘There are lots of people who use the robotic laser welding for metals, it’s already out there,’ said Garay. ‘So I think there are lots of people who know, from the industrial side, what it would mean to bring this into the ceramic world. In fact, I have had some interest from industrial folks who plan to do some collaboration.’

The team, however, is still looking to work on the process before it is ready for commercialisation, as so far it can only be applied to small ceramic parts less than 2cm in size. The researchers now plan to scale it up for larger sizes, and looking into its cost-effectiveness and industrial applications in the future.