The work presents a computer simulation realized with the ADINA program concerning nanoindendation test. A shape of nanoindenter was proposed to be similar to the real surgical tools. The theoretical model was used to predict phenomena which would appear in practice. The contribution of the TiN coating thickness to the implant rigid properties was simulated. Three types of extortion conditions could be considered, i.e., short contact with surgery tool (i); long continuous contact with natural tissue (ii); long cyclic contact with natural tissue (iii). In the first part of the work, the authors focused on the first type of extortion (i). The second part of the work is dedicated to the calculations of temperature impact to layer behaviour. Two layer thicknesses are considered i.e., 250 nm and 50 nm. The examined coatings find serious practical applications as a blood-contacting material in medicine. The coatings were subjected to transmission electron microscopy investigations. Columnar mechanism of film growth controlled by kinetic process is stated to operate for the considered range of layer thickness. Plasma temperature is observed to influence the substrate behaviour. Examinations of thinner layers, i.e. under 100nm, revealed higher degree of smoothness and uniformity, which could be related to the operation of the surface diffusion mechanism at the early stage of deposition. The physical explanation of TEM images was based on the finite element calculations of the temperature distribution using the ADINA program .
Biocompatible coatings produced on the basis of the chemically extracted natural hydroxyapatite (HAp) from the animal bones were deposited using multiplex method comprising glow discharge nitriding (GDN) of the titanium alloy substrate and pulsed laser deposition (PLD) of HAp on the formerly fabricated titanium nitride layer (TiN). The TiN interlayer plays an important role improving adhesion of HAp to substrate and preserves the direct contact of the tissue with metallic substrate in the case of possible cracking of HAp coating. Surface morphology of deposited layers, crystallographic texture and residual stress were studied in relation to the type of laser applied to ablation (Nd:YAG or ArF excimer), laser repetition, temperature of substrate and atmosphere in the reactive chamber.
Hybryd PLD method was used for deposition high quality thin Ti, TiN, Ti(C,N) and DLC coatings. The kinetic energy of the evaporated particles was controlled by application of variation of di#11;erent reactive and non reactive atmospheres during deposition. The purpose was to improve adhesion by building a bridge between the real ceramic coating and the substrate. A new layer composition layout was proposed by application of a bu#11;er, starting layer. Advanced HRTEM investigation based on high resolution transmission electron microscopy was used to reveal structure dependence on specific atmosphere in the reactive chamber. New experimental technique to examine the crystallographic orientation based on X-ray texture tomography was applied to estimate contribution of the atmosphere to crystal orientation. Using Dictyostelium discoideum cells as a model organism for specific and nonspecific adhesion, kinetics of shear flow-induced cell detachment was studied. For a given cell, detachment occurs for critical stress values caused by the applied hydrodynamic pressure above a threshold. Cells are then removed from the substrate with an apparent first-order rate reaction that strongly depends on the stress. The threshold stress depends on cell size and physicochemical properties of the substrate, but it is not a#11;ected by depolymerization of the actin and tubulin cytoskeleton.
Mechanical components and tools in modern industry are facing increasing performance requirements leading to the growing need for advanced materials and thus, for modern frictional systems. In the last decades, the Pulsed Laser Deposition (PLD) has emerged as an unique tool to grow high quality mono- as well as multilayers surfaces in metallic/ceramic systems. Building up a knowledge base of tribological properties of industrially-scaled, room temperature deposited PLD hard coatings are the most important step for the application of these coatings in engineering design. Although single-layer coatings find a range of applications, there are an increasing number of applications 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, which has been used in PVD processes for many years, however, the PLD technique gives new possibilities to produce system comprising many bilayers at room temperature. Tribological coatings consisted of 2, 4 and 16 bilayers of Cr/CrN and Ti/TiN type were fabricated with the Pulsed Laser Deposition (PLD) technique in the presented work. 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 rise 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.
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. Results obtained using Fourier Transformed Infrared Spectroscopy, Transmission and Scanning Electron Microscopy, Atomic Force Microscopy are presented. Micromechanical properties measured during microindentation, scratch and wear tests are also shown.
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 250 nm thick films revealed columnar structure. Such films were observed to be brittle, which led to crack formation and secondary nucleation of microcolumn. TEM studies showed a kinetic mechanism of growth (columnar) in films of 250 nm thickness. It was stated that thinner films were much smoother and uniform than the thicker ones, which could be associated with the surface diffusion mechanism to appear. In order to improve the coatings elasticity, the thickness was reduced to 50 nm, which limited the deposition mechanism operation to the early stage. TEM cross-section observation revealed elastic properties of thin films. A biological test showed that TiN surface film produced on polyurethane is characterized by good biocompatibility and decreased surface affinity for cell adhesion. Films of 0.25 and 0.5 1m thick of TiN were selected for theoretical finite element modelling (FEM) using ADINA program. The micro cracks formation predicted in simulation was verified by phenomena observed in microstructure examinations.
Pulsed laser deposition technique was applied for covering elastic cast-polyurethane membranes with titanium nitride and boron nitride layers. The deposition process was realized using a Nd:YAG laser with Qswitch in stages; firstly the membranes were coated with ultra-thin titanium nitride layer (TixN) by evaporation of a metallic titanium disk in nitrogen gas atmosphere and then a layer of boron nitride (BN) was deposited by ablation of hexagonal h-BN target in argon atmosphere. The surface morphology was observed by scanning electron microscopy. Chemical composition was analyzed by energy dispersive X-ray spectrometry. The phase analysis was performed by means of grazing incidence X-ray diffraction and attenuated total reflection infrared spectroscopy. The crystallographic texture was measured. The wear test was performed by pin-on-disk method. Hexagonal boron nitride layers with (0001)[uvtw] texture with flake-like grains were fabricated. The structure and texture of boron nitride was identical irrespectively of substrate roughness or BN thickness. Pin-on-disk wear tests showed that the coatings effectively decreased the friction coefficient from two to even four times comparing to pure polyurethane and polyurethane covered with graphite. This proved that deposited layers can replace graphite as a lubricating material used to protect polymer surfaces.