A.B. Vladimirov

Porous material based on spongy titanium granules: structure, mechanical properties, and osseointegration.

A porous material has been produced by pressing spongy titanium granules with subsequent vacuum sintering. The material with porosity of more than 30% has an open system of interconnecting pores. The Youngs modulus and 0.2% proof strength have been measured for the samples having 20-55% porosity. If the porosity is between 30 and 45%, the mechanical properties are determined by irregular shape of pores, which is due to spongy titanium granules. The experiment in vivo was performed on adult rabbits. Before surgery the implants were saturated with adherent autologous bone marrow cells. The implants were introduced into the defects formed in the condyles of tibias and femurs. Investigations of osseointegration of implants having 40% porosity showed that the whole system of pores was filled with mature bone tissue in 16 weeks after surgery. Neogenic bone tissue has an uneven surface formed by lacunas and craters indicative of active resorption and subsequent rearrangement (SEM examination). The bone tissue is pierced by neoformed vessels. Irregular-shaped pores with tortuous walls and numerous lateral channels going through the granules provide necessary conditions for the formation of functional bone tissue in the implant volume and the periimplant region.

The effect of substrate and DLC morphology on the tribological properties coating

Abstract We studied the effect of the initial substrate surface roughness and as grown DLC microrelief on the tribological properties of coating. The diamond-like films were prepared by pulse arc sputtering of graphite onto R6M5 and 20Cr13 tool steel substrates. Special attention was paid to production of the DLC having increased the friction coefficients necessary for such device as printing machine valves and chuck’s jaws. The tribological properties of the deposited coatings were studied under conditions of dry sliding friction and under the action of an abrasive-particle jet. It was shown using both testing methods that the substrate surface roughness (R) is the decisive parameter for the wear resistance of the DLC to external loads. The wear resistance of coating is increased several-fold at some optimal R-value as compared to the smoother surface. The optimal R-value depends on the coating thickness, h. The optimal R/h value should not deviate largely from the ratio R/h∼0.2–0.3.

The analysis of microhardness measurement approach for characterization of hard coatings

Abstract The analysis of problems concerning thin film (1–5 μ) microhardness measurement by means of different techniques is conducted in case of diamond-like carbon coatings. It is shown experimentally that the extrapolation of the lg( H m − H s ) vs. d dependence to zero d values, where H s is microhardness of the film substrate, H m is formal microhardness of the substrate with coating and d is Berkovich pyramid depth, leads to reliable coating microhardness values H f independent on substrate properties and characterizing the properties of the coating itself. This approach is used to obtain the average H f values of multilayer coatings. It is found that the surface roughness of the coatings impedes the correct determination of the coating microhardness by means of nano-indentor techniques. The coating surface smoothening (mechanical or by ion etching) provides the conditions for correct microhardness measurement. It is concluded that the real H f values of diamond-like carbon coatings obtained by pulse arc graphite sputtering exceeds 100 GPa.

Effect of adhesion strength of DLC to steel on the coating erosion mechanism

Abstract The wear of DLCs deposited onto steel substrates using a graphite arc-pulse sputtering technique in a corundum particle jet was studied. Two sample sets had different adhesion strength to the substrate due to different adhesive sublayer structures. It was found that the DLC itself does not wear, so that coating destruction occurs due to peeling. Analysis of the wear results for coatings having different (0.4–2.6 μm) thickness revealed that peeling is a result of two basic crack systems: (i) from the DLC surface inside the coating; and (ii) along the DLC–substrate interface.

The effect of additional treatment on tribological properties of amorphous carbon coatings on metals

Abstract We have developed the effect of additional treatment on improvement of tribological properties of diamond-like coatings (DLCs) on steels. It is shown that a maximum realization of the strengthening properties of DLCs is possible either through preliminary hardening of the substrate with ion implantation and additional thermal treatment or using etching of the coating surface with ions of active gas.

Practical use of strength and anticorrosion properties of amorphous carbon thin films

Abstract A study was made of the protective properties of amorphous C thin films deposited by the method of pulse sputtering of graphite on substrates having a temperature of approximately 175°C. It is shown that the films can be successfully used to improve the service properties of audio or video heads and surgical cutting instruments.

Service properties of cutting tools hardened with a diamond-like coating☆

Abstract Mill-type cutting tools with and without a hardening amorphous-carbon coating were tested for wear and serviceability. The feed rate, speed, and cutting width were varied. Mathematical processing was used to determine wear and service life as a function of the cutting parameters. It was found that the cutting edge may be blunted during coating application. The calculated dependences allow choice of the most favorable operating conditions for tools hardened with a carbon coating. The inferences made from the study were checked under actual conditions of operation. The results are reported.

Elastic properties of a porous titanium-bone tissue composite.

The porous titanium implants were introduced into the condyles of tibias and femurs of sheep. New bone tissue fills the pore, and the porous titanium-new bone tissue composite is formed. The duration of composite formation was 4, 8, 24 and 52 weeks. The formed composites were extracted from the bone and subjected to a compression test. The Youngs modulus was calculated using the measured stress-strain curve. The time dependence of the Youngs modulus of the composite was obtained. After 4 weeks the new bone tissue that filled the pores does not affect the elastic properties of implants. After 24 and 52 weeks the Youngs modulus increases by 21-34% and 62-136%, respectively. The numerical calculations of the elasticity of porous titanium-new bone tissue composite were conducted using a simple polydisperse model that is based on the consideration of heterogeneous structure as a continuous medium with spherical inclusions of different sizes. The kinetics of the change in the elasticity of the new bone tissue is presented via the intermediate characteristics, namely the relative ultimate tensile strength or proportion of mature bone tissue in the bone tissue. The calculated and experimentally measured values of the Youngs modulus of the composite are in good agreement after 8 weeks of composite formation. The properties of the porous titanium-new bone tissue composites can only be predicted when data on the properties of new bone tissue are available after 8 weeks of contact between the implant and the native bone.

Mechanical properties and the structure of porous titanium obtained by sintering compacted titanium sponge

Mechanical properties and characteristics of the porous material obtained by sintering of compacted granules of titanium sponge of grade TG-OP-01 have been investigated with the purpose to develop a technology of production of biocompatible orthoimplants. The content of pores θ was from 20 to 60%. As θ increased from 20 to 50%, the Brinell hardness HB, maximum bending strength σbend, and impact toughness Kc decreased, following the empirical dependences HBθ = const, σbend × θ2 = const, and Kc × θ1.5 = const, respectively. At θ > 50%, there was observed a stronger drop in these values. The experiments on the absorption of water by the pores and an analysis of the filtration properties of the material made it possible to establish that the basis of the system of pores connected with the surface is composed by the gaps between the pressed granules 0.1–0.2 cm sintered during annealing rather than by the small (∼ 100 μm) pores in the granules.

Nanocomposite films prepared by arc-plasma deposition of titanium and carbon

The composition, structure, and properties of films prepared by depositing both titanium and carbon have been investigated. It was found that the films consist of an amorphous carbon matrix with uniformly distributed therein nanoparticles of titanium carbide (less than or equal to 20 nm in size). With increasing carbon concentration above 20 wt %, the film density decreases and the microhardness of the films increases, which reflects the diamond-like nature of the amorphous constituent of the composite film.