E. A. Levashov

Structure and properties of CaO- and ZrO2-doped TiCxNy coatings for biomedical applications

Abstract In the present work multicomponent thin films based on the systems Ti–Ca–C–O–N and Ti–Zr–C–O–N have been deposited and evaluated. TiC 0.5 +10% CaO and TiC 0.5 +10% ZrO 2 targets were manufactured by means of the self-propagating high-temperature synthesis (SHS) method. The synthesized targets were subjected to DC magnetron sputtering in an atmosphere of argon or in a gaseous mixture of argon and nitrogen. The films were characterized in terms of their structure, surface topography, mechanical properties and tribological behavior. The films deposited on Si substrates under optimal conditions showed high hardness in the range of 36–40 GPa, low Youngs modulus 260–300 GPa and high percentage of elastic recovery 70–75%. The CaO- and ZrO 2 -doped Ti–C–N films showed significantly lower friction coefficient and wear rate against WC+6% Co alloy in comparison to conventional magnetron–sputtered TiC and TiN films. The biocompatibility of the films was evaluated by both in vitro and in vivo experiments (in mice). In vitro studies involved the investigation of the proliferation of fibroblasts Rat-1 and epithelial cells IAR-2 at the tested films and morphometric analysis of the cells cultivated on the films. Fibroblasts and epithelial cells were seeded on the coverslips, coated with examined films and incubated at 37 °C for 24, 48 and 72 h. We did not detect statistically significant differences in the attachment, spreading and proliferation of cultured cells on the coated and the uncoated substrata. The adhesion and proliferation of cells was good at all investigated films. We also did not observe any inflammatory reactions on the implants, inserted under the mouse skin.

Self-propagating high-temperature synthesis of advanced materials and coatings

ABSTRACT Self-propagating high-temperature synthesis (SHS) or combustion synthesis (CS) is a rapidly developing research area. SHS materials are being used in various fields, including mechanical and chemical engineering, medical and bioscience, aerospace and nuclear industries. The goal of the present paper is to provide a comprehensive state-of-the-art review and to analyse a critical mass of knowledge in the field of SHS materials and coatings. We also briefly discuss the history and scientific foundations of SHS along with an overview of the technological aspects for synthesis of different materials, including powders, ceramics, metal-ceramics, intermetallides, and composite materials. Application of CS in the field of surface engineering is also discussed focusing on two main routes for applying SHS to coating deposition: (i) single-step formation of the desired coatings and (ii) use of SHS-derived powders, targets or electrodes in the coating deposition processes.

Localized deformation of multicomponent thin films

A comparative analysis of fracture for various films is presented. Films of Cr–B, Ti–Si–N, Ti–B–N and Ti–Cr–B–N were deposited by DC magnetron sputtering of composite targets. The indentation of the as-deposited films on ( 001 ) Si substrates was made using Vickers microhardness tester at a load of 10, 25 and 50 g. The scanning electron microscopy and atomic force microscopy studies were fulfilled to investigate the film behavior during localized deformation. Both homogeneous and localized inhomogeneous deformations of the fracture surface were observed and described. Isolated particles located within the area of deformation were frequently observed. The films were characterized in terms of their structure, hardness, elastic modulus, elastic recovery and surface topography. The H yE ratio (i.e. resistance to plastic deformation ) was proposed to be a ranking parameter 32 for the prediction of shear banding under the localized deformation. The correlation between the surface roughness, surface relief inside indentations and columnar fracture morphology was outlined. It was suggested that column sliding is the dominant fracture mechanism resulting in the formation of breaking-away particles under unloading. 2002 Elsevier Science B.V. All rights reserved.

Characteristics and in vitro response of thin hydroxyapatite–titania films produced by plasma electrolytic oxidation of Ti alloys in electrolytes with particle additions

Enhanced incorporation of hydroxyapatite nanoparticles in porous titania coating formed by plasma electrolytic oxidation significantly increases surface osteogenic activity.

Multifunctional nanostructured coatings: Formation, structure, and the uniformity of measuring their mechanical and tribological properties

The state of the art of the studies in the field of the development and certification of novel multifunctional nanostructured coatings having a wide spectrum of applications is reviewed. The main tendencies in the optimization of the compositions and properties of the coatings are described, and the modern methods of diagnostics of the nanostructured coatings are considered.

Self-propagating high-temperature synthesis of composite targets based on titanium carbonitride, silicide, and aluminide for ion-plasma deposition of multifunctional coatings

The macrokinetic features of combustion of the mixtures in the Ti-Al-Si3N4-C system calculated for the formation of compact ceramic materials (CCMs), the composition of which is described by the general formula X(TiAl3) + (100 − X)(0.448TiC0.5 + 0.552(Ti5Si3 + 4AlN) with mixture parameter X = 10–50%, are investigated. Compact CCM samples with the main structural components in the form of TiCxNy grains and binding phases TiAl3 and Ti5Si3 are fabricated by the technology of forced self-propagating high-temperature synthesis (SHS) compaction. An increase in X promotes the formation of the Mn+1AXn phase with the composition Ti3SiC2 in the synthesis products. Complex investigations into the physicomechanical properties of the obtained ceramics are performed. Based on their results, the inverse dependence of the density and hardness of compact materials on parameter X is established. Tests of the samples for oxidation resistance showed that the obtained CCMs based on titanium carbonitride, silicide, and aluminide possess excellent resistance to high-temperature oxidation, and their oxidation rate in air at t = 900°C for 30 h does not exceed 7.8 × 10−5 g/(m2 s).

Effect of Al, Si, and Cr on the thermal stability and high-temperature oxidation resistance of coatings based on titanium boronitride

The thermal stability and resistance to high-temperature oxidation of multicomponent nanostructured coatings in the Ti-X-B-N (X = Al, Si, Cr) system have been studied using X-ray diffraction analysis, X-ray photoelectron spectroscopy, secondary-ion mass spectroscopy, and transmission electron microscopy. The hardness, elastic modulus, elastic recovery, friction coefficient, wear rate, and adhesion strength of the coatings have been determined. It has been established that Ti-B-N and Ti-Cr-B-N coatings exhibit a stable nanostructure and high stable mechanical and tribological properties up to 1000°C. The coatings with an fcc structure can be also employed as barrier layers preventing diffusion of metal atoms from the substrate. It has been shown that the high resistance to high-temperature oxidation of Ti-Cr-B-N and Ti-Al-Si-B-N coatings is connected with the fact that protective oxide layers based on (Ti,Cr)BO3 and TixAlySiOz are formed on their surface.

Structure and properties of nanocomposite Mo—Si—B—(N) coatings

Coatings in the Mo—Si—B—(N) system are obtained using the magnetron sputtering method. Control of nitrogen and silicon content in the coatings is carried out using various gaseous Ar + N2 mixtures and variation of the number of Si segments in the area of MoSiB target erosion. The structure of coatings is studied using methods of scanning and transmission electron microscopy, X-ray analysis, infrared and optical emission spectroscopy, and Raman spectroscopy. Mechanical and tribological properties of the coatings are determined using methods of nanoindentation, scratch-testing, and tribological testing at temperatures of 25, 500, and 700°C. The oxidation resistance of coatings is studied. It is established that coatings with maximum Si and N content possess the best properties: hardness of 32 GPa, elastic recovery of 66%, low friction coefficient at high temperatures, and heat resistance up to 1200°C.

The influence of Si concentrations on the oxidation resistance of Mo-Si-B-(N) coatings

The influence of the silicon concentration on the oxidation resistance of Mo-Si-B-N coatings prepared by magnetron sputtering is investigated. The Si content in them was controlled by the composite-target composition, as well as by various areas of silicon segments placed into the target-erosion zone. The composition and structure of coatings after deposition and annealing in air at temperatures of 500–1300°C are investigated using transmission and scanning electron microscopy, energy-dispersive analysis, and glow-discharge optical emission spectroscopy. It is established that oxidation resistance increases as the Si concentration in coatings increases, which is caused by the formation of a silicon oxide-based dense layer; this layer prevents oxygen propagation into the coating depth upon heating. The maximal oxidation resistance at a level of 1300°C is attained in Mo-Si-B-N coatings containing 40 at % Si.

Silicon carbide ceramics SHS-produced from mechanoactivated Si–C–B mixtures

We investigated the influence of mechanical activation (MA) and initial temperature T0 on combustion temperature Tc and burning velocity Uc for 90% (Si + C)–10% (4B + C) mixtures as well as on product morphology. Mechanical activation was found to strongly change the size and morphology of Si and graphite particles (by a factor of 6–8), lead to accumulation of micro strains, and increase the reactivity of green mixture. An increase in T0 was found to proportionally increase the values of Tc and Uc but produce little or no influence on the phase composition of product. The SiC powder consisting of 50–100 nm crystallites was obtained by diminution of combustion product and then used to prepare, by hot pressing, a ceramic PVD target for magnetron sputtering.