Shape memory alloys have the ability to “remember” their shape, meaning they can be deformed and then return to their previous shape when heated. However, existing shape memory alloys are generally only able to change from one shape to another, or in response to one specific temperature change. By developing functionally graded shape memory alloys, a team of UK researchers hopes to modify these properties at different points in the material. In this way, the material can change its shape in response to different temperatures at various points on the device.
Professor Duncan Hand of Heriot-Watt University in the UK is developing a new alloy for applications in more complex and controllable micro-robots. To produce this advanced material, the researchers are developing a new technique called functionally graded laser induced forward transfer (FG-LIFT).
- Flexible robot fingers (Nitinol shape memory alloy)
The technique uses a pulsed laser to deposit thin films of metals such as nickel, titanium or copper layered on a transparent polymer onto a substrate. So the technique can print various metal films onto the [receiver] substrate layer by layer, like an old-fashioned typewriter ribbon, so maybe three layers of titanium, four layers of nickel and one layer of copper are laid down. In this way, the process can build up three-dimensional elements, which the team describes as voxels, made up of layers of different metals. The material can then be heat-treated to carefully control the diffusion process between the metal layers in each voxel, allowing researchers to precisely control the composition of the material.
By adding voxels together, researchers can build 3D microstructures with different properties at specific points in the material. So some parts of the device might be shape memory alloys, some parts won’t have that effect, and some parts will have shape memory alloys that operate at different temperatures.