SLM techniques could enable manufacture of complex parts

By experimenting with various blends of relatively cheap, coarse powders, the team at Exeter University was able to create extremely hard metal matrix composites with underlying reinforcing microstructures.

SLM essentially involves a laser that scans back and forth over the surface of a powder, melting it in the shape of the first layer. The work surface then drops by the thickness of the layer and another layer of powder is distributed over the surface.

Generally, research has focused on blending extremely fine (and expensive) powders before sintering to achieve novel components. The research team at Exeter, however, began experimenting in a trial-and-error fashion with various aluminium alloys mixed with iron oxide.

‘Although we use a mixture of relatively coarse and cheap powders, the laser-assisted chemical reaction allows the production of new constituents that are different from primary ones,’ Dr Sasan Dadbakhsh of Exeter told The Engineer. ‘These new constituents have been formed under laser rapid solidification, which abundantly restricts their growth, leading to their ultrafine and nanoscale sizes.’

This in-situ reaction between constituents releases energy, which also means materials can be produced at a higher rate using less power. The team had particular success blending aluminium oxides with silicon and magnesium crystals plus around 15 per cent iron oxide.

Analysis with computed tomography (CT) scanning revealed microstructures that act as reinforcements, creating composites that are significantly harder than those conventionally manufactured with casting.

‘The ultrafine dendritic features and matrix are the results of rapid solidification in conjunction with abundant nucleation sites,’ said Dadbakhsh. ‘This is very different from the grain structures that usually appear in aluminium alloys.’

Because of the distributed strength of the components, the method that produces it has the potential to manufacture aluminium composite parts as pistons, drive shafts, suspension components, brake discs and almost any structural components of cars or aircraft.

The work was carried out at Exeter University’s Centre for Additive Layer Manufacturing (CALM), a £2.6m investment in innovative manufacturing for the benefit of businesses in the south west and the rest of the UK in collaboration with EADS UK.