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Laser shock peening used to 'heal' cracks during additive manufacturing

Researchers at Swiss research institute EPFL have developed a technique that dramatically reduces cracking in metal components during selective laser melting (SLM).

The patented technique, which the researchers say produces metal components with unprecedented resistance to high temperature, damage and corrosion, could be used to manufacture new power-generating turbine blades or key aircraft components, for example.

During SLM, a powerful laser melts and fuses metallic powders together, gradually building a 3D component layer by layer. However, some metals and alloys cannot withstand the high temperature variations that SLM involves, causing them to crack.

In Additive Manufacturing, the researchers from EPFL's Laboratory of Thermomechanical Metallurgy describe how their new method, which involves applying a second laser treatment every few layers during the building phase, is able to 'heal' cracks on the fly during 3D printing.

The treatment, known as laser shock peening, works by periodically directing high-intensity laser pulses on the component under construction. It acts as a high-energy photonic 'hammer', sending shock waves through the material.

The method involves two lasers. The first melts the metallic powders and heats the fused material, while the second generates stresses in the component in targeted locations to eliminate cracks. 

Related article: Diode laser used to reduce residual stress in metals during additive manufacturing

'Laser shock peening is normally reserved for surface treatments,' remarked Roland Logé, who led the research team. 'But in our case, it has become a bulk treatment, in that it operates in 3D within the material itself.'

The researchers found that their technique is able to eliminate up to 95 per cent of cracking normally observed in a nickel-based superalloy. They now plan to apply the method to other crack-sensitive alloys.

'This hybrid 3D printing method has applications that go way beyond eliminating cracks,' concluded Logé. 'We’re only just beginning to understand its full potential.'

Several 3D-printing companies have already expressed an interest in the new technique, according to the researchers.

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