Using of laser ablation to fabrication nanocrystalline multilayer coatings for biomedical and tribological application
Publication from Materials
Proc. International Society for Optical Engineering (SPIE) 6598, pp. 659807.1-659807.12, 2007
Titanium nitride (TiN) is regarded as a potential biomaterial for blood-contact applications. TiN thin films were fabricated by pulsed laser deposition with the Nd:YAG laser on biologically applied polyurethane. Transmission electron microscopy (TEM) study of 350 nm thick films revealed columnar structure. Such films were observed to be brittle. In order to improve the coatings elasticity, the thickness was reduced to 50nm, which limited the deposition mechanism operation to the early stage. A biological test showed that TiN surface film produced on polyurethane is characterized by good biocompatibility and decreased surface affinity for cell adhesion. The physical explanation of TEM images was based on the performed finite element calculations of the temperature and stress distribution using the ADINA program. Boron nitride thin layers were produced by means of the pulsed laser deposition technique from hexagonal boron nitride target. Two types of laser i.e. Nd:YAG with Q-switch as well as KrF coupled with RF generator were used. Influence of deposition parameters on surface morphology, phase composition as well as mechanical properties is discussed. There are an increasing number of applications in tribology where the properties of a single material are not sufficient. One way to surmount this problem is to use a multilayer coating. Application of metallic interlayers improves adhesion of nitride hard layer in multilayer systems. Tribological coatings consisted of 4, 8 and 32 layers of Cr/CrN and Ti/TiN types were fabricated with the PLD technique. It is found in transmission electron examinations on thin foils prepared from cross-section that both nitride-based multilayer structures studied are characterized by small columnar crystallite sizes and high defect density, what might raise their hardness but compromise coating adhesion. The intermediate metallic layers contained larger sized and less defective columnar structure compared to the nitride layers, which should improve the coatings toughness. Switching from single layer to multi-layer metal/nitride composition improved resistance to delamination.