W. Rakowski

Parylene coatings on stainless steel 316L surface for medical applications — Mechanical and protective properties

The mechanical and protective properties of parylene N and C coatings (2-20 μm) on stainless steel 316L implant materials were investigated. The coatings were characterized by scanning electron and confocal microscopes, microindentation and scratch tests, whereas their protective properties were evaluated in terms of quenching metal ion release from stainless steel to simulated body fluid (Hanks solution). The obtained results revealed that for parylene C coatings, the critical load for initial cracks is 3-5 times higher and the total metal ions release is reduced 3 times more efficiently compared to parylene N. It was thus concluded that parylene C exhibits superior mechanical and protective properties for application as a micrometer coating material for stainless steel implants.

Micromechanical and Tribological Properties of Nanocomposite nc-TiC/a-C Coatings

The nanocomposite coatings composed of nanocrystalline TiC grains embedded in hydrogen free amorphous carbon a-C matrix (nc-TiC/a-C) were deposited by magnetron sputtering on the two substrates, oxygen hardened Ti-6Al-4V alloy and heat treated VANADIS 23 steel. The Ti-6Al-4V alloy was oxygen hardened by plasma glow discharge. Micro-mechanical and tribological properties as well as coating adhesion to the substrates were investigated. Micro/nanostructure of the coatings and the substrates were examined using scanning- and transmission electron microscopy methods as well as X-ray diffractometry. Nano-, microhardness tests performed for the coated materials showed average hardness 13.4-14.7 GPa and modulus of elasticity 160 GPa. Scratch test revealed good adhesion of coatings to the both substrates. The nanocomposite coatings significantly improved tribological properties of the titanium alloy and steel, increased wear resistance and decreased friction coefficient.

Mechanical and tribological properties of carbon-based graded coatings

The paper presents research on coatings with advanced architecture, composed of a Cr/Cr2N ceramic/metal multilayer and graded carbon layers with varying properties fromCr/a-C:H to a-C:N. The microstructure of the coatings was analysed using transmission electron microscopy and Energy Dispersive Spectroscopy, the mechanical properties were tested by nanoindentation, spherical indentation, and scratch testing, and tribological tests were also conducted. The proper selection of subsequent layers in graded coatings allowed high hardness and fracture resistance to be obtained as well as good adhesion to multilayers. Moreover, these coatings have higher wear resistance than single coatings and a friction coefficient equal to 0.25.

Effect of Interfaces on Mechanical Properties of Ceramic/Metal Multilayers

Multilayers of alternate Ti/TiN coatings deposited on X20Cr13 ferritic stainless steel by pulsed laser deposition (PLD) method have been tested using instrumented indentation. The effect of bilayer period and metal/ceramic thickness ratio were studied.

THERMAL STRESS MODEL FOR POLYMER SENSORS

ABSTRACT The problems of thermal stress in a new theoretical model are discussed to help gain an understanding of the piezoresistivity in polymer composites. A new polymer matrix composite is a smart material with sensor properties and good sliding behavior for the diagnosis of plain bearings. Composites consist of a polyesterimide matrix with electrical conductor powders and lubricating additives. The theoretical model and numerical simulation of such composites, designed for the understanding of the electrical (sensor) properties, involves combined thermal, mechanical, and electrical interactions between the filler particles. Electrical conductivity of the composite is due either to the thermal stress or to the external mechanical stress, leading to a positive or negative temperature coefficient of resistivity. By comparing theoretical calculations with experimental measurements, it has been shown that the model for the piezoresistant effect can predict the composite resistance with reasonable accuracy.

Semiconductive friction node as a temperature sensor

When constructing micro- and milirobots, it is important to secure that structural elements perform also metrological functions. Silicon is used in microrobots, while for milirobots polymer composite materials are applied. These composites shall have the following features: metrological sensitivity, appropriate mechanic and tribologic characteristics. Strong piezoresistive properties of three- component composites: metal, resin, graphite make their utilization possible for diagnosis of temperature and stress. These properties have composites of composition in surrounding of critical concentration of percolation process. The authors undertake an effort to develop models of these thermosensitive and piezoresistive properties for friction pair microcontact.

Carbon Based Coatings with Improved Fracture and Wear Resistance

The paper presents the results of mechanical and tribological tests of two kinds of carbon coatings with advanced microstructures - nanocomposite CrC/a-C:H and multilayer TiN/Ti/a-C:H. The introduction of barriers for dislocation motion and microcrack propagation as CrC nanograins in nanocomposite coating or Ti and TiN interlayers in multilayer led to coatings hardening and improved fracture and wear resistance in comparison to a single amorphous a-C:H coating. It was confirmed by wide range of mechanical tests. The mechanism of microcrack deflection and splitting on CrC nanograins and Ti layers was studied using spherical indentation tests and TEM observations of indent cross-sections.

Texture and Mechanical Properties of Electrodeposited Copper Thin Films

Influence of the electrodepositing parameters e.g. applied electric current as variable on texture formation and on mechanical properties of copper thin films was studied. Experiment was done for copper deposition from sulphate bath under galvanostatic and pulse current. It was found that copper layers exhibits different texture depending on applied current conditions during electrodepositing process. Pulse and direct current conditions leads to different texture of electrodeposited copper. Texture of electrodeposited copper coatings and mechanical properties could be correlated. It was found that, texture indexes although are not complex information about texture could be used for analysis of such correlation in technological process.