Laser-based interdiffusion of electroplated nickel-titanium layers for shape memory applications

Laser-based heat treatment methods are popularly used for modifying the surface properties of metals. Using a laser provides localised heating of the metal that can be used flexibly and precisely to tailor material properties. Generally, laser surface alloying is used to improve the wear resistance of materials such as aluminium by alloying with elements such as nickel, titanium, or silicon carbide [1]. The intermetallic compounds formed during the short laser interaction time strengthen the surface and improve the wear resistance. Laser-based annealing processes have also been shown to crystallise amorphous nickel-titanium (NiTi) thin films thereby demonstrating that shape memory properties can be selectively introduced [2].

We are particularly interested in understanding the interdiffusion of nickel-titanium layers at the micron scale as we intend to fabricate NiTi-based shape memory alloy components. NiTi alloys are generally manufactured by either casting or powder metallurgy techniques that are limited to wires and sheets. They are subjected to thermomechanical treatments before use to ensure homogenisation and shape setting properties. On the other hand, although NiTi-based thin films can be surface-treated using lasers, laser-based diffusion studies of nickel-titanium layers are not yet fully explored. We aim to explore this potential by using a scanning laser to locally control the microstructure of the fabricated NiTi component.

In this talk, we present the early results of laser heat treatment of an electroplated nickel layer deposited on top of a titanium foil. We experimentally study their diffusion behaviour at different energy densities and scanning speeds using a fibre-based IR laser. The morphology, phase and composition of heat-treated samples are characterised using XRD and EDX-SEM respectively.