Properties of Carbon Fiber Materials Coated with Thin NiTi Films

Smart materials offer exciting possibilities for new applications, in particular when small-scale parts and devices are of interest. For the design and fabrication of novel functional materials such as smart textiles, coated single glass or carbon fibers may be a favorable alternative to using solid NiTi wires. The present study explores how thin NiTi coatings can be produced under these conditions. We deposited NiTi as a 300 micron thin film on different  (glass and carbon) fibre substrates by a PVD magnetron sputter process. The single fibre diameters are in the range of 8 to 20 microns. Moreover, we compare the shape memory characteristics of these films with thin coatings produced on a plane carbon substrate by first sputtering Ti and then Ni, followed by an annealing treatment at 500 °C. We discuss how different annealing temperatures and times, and additional processing parameters affect the formation of thin NiTi films that actually exhibit shape memory characteristics. The phase transition behavior and thermo-mechanical properties of the thin films are characterized by nanoindentation; microstructures are characterized by X-ray diffraction and electron microscopy. The different microstructural features are directly related to distinct processing parameters. Our investigations indicate that coating single fibers with NiTi is a promising approach for the fabrication of smart small-scale structures.