Shape memory alloys can now remember multiple shapes, according to Canadian researchers.

The patent pending Multiple Memory Material Technology (MMMT), which involves applying high-power densities to materials, is said to control the transformation temperatures at certain locations in the materials. This, the researchers claim, increases the alloys’ functionality.

Ibraheem Khan, a Research Engineer working on the project at Waterloo University in Ontario, explains that, when applying high-power densities to shape memory alloys, he  has ‘noticed a change in the differential scanning colour imagery results, or thermal results, as well as the mechanical properties. We realised that we were altering the transformation temperatures and the pseudo-elastic properties as well’.

At present, Khan, who has worked on the research with Professor Norman Zhou, is applying the technology to thermal management in cars.

He claims that, ‘There isn’t really any technology out there that will enable you to embed multiple memories into a shape memory alloy. We can control what the transformation temperatures are, or what the shape memory effect is, at a certain location. Our technology enables you to increase the functionality by embedding local memories, which are different to that of the original material (see diagram below)’.

He adds that this is important, as different applications require different speeds of transformation temperature change. The process is not said to be limited to specific types of smart materials. The researchers have applied it to nickel-copper, copper, nickel-titanium, platinum, zinc, and even polymers. ‘At this point, we haven’t noticed any discrimination towards any of the material types,’ Khan says, adding that the technology can be applied in under one second, depending on the size of the sample.

Multiple Memory Material Technology may enable industry professionals to tailor their smart materials for specific applications. For example, in industry, they could be used in dental braces, as well as in stents for heart patients. Khan mentions that, ‘We can envision a stent that can gradually open instead of opening once, which has more shock on the body’.

Professor Tony Anson, of Brunel University and Diameter Ltd, based in the UK, comments that it is difficult to give ‘a definitive opinion of the claims,’ as the researchers’ processing methods are not presented in detail.

He says, ‘Two-way memory is definitely well-known. The uniqueness here might be by zonal heat treatment, affecting a specific area’. However, he admits that this is only speculation. More details of the patent will be made available when it is published in the first quarter of next year.

Anson, however, is sceptical about the potential for progressive opening of stents, saying that it is ‘unlikely to be a practical proposition using multiple shape effects as described. The radial or hoop forces exerted by an in vivo stent are in most cases somewhat progressive – the surrounding tissue “gives” over time due to continuous pressure (very small pressure) exerted by the stent.’

In relation to future projects, Mr Khan sees potential in several different areas. He says that ‘it depends on who comes to us, but we are actively developing prototypes. It’s a platform technology, so we don’t really have any one direction that we can go’.