A.P. Rubshtein

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.

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.

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.

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.

Effect of mechanical activation on the morphology and structure of hydroxyapatite

We have studied the effect of grinding in planetary mills on the phase composition, morphology, and water content of hydroxyapatite powder. The results indicate that milling for even relatively short times, which reduces the average particle size by a factor of 2, causes the monetite present in the unmilled powder to disappear and reduces the crystallite size of the hydroxyapatite. The fraction of nanoparticles in the powder is then 98% and remains constant during further milling. Milling for longer times leads to hydroxyapatite amorphization. For an average size of large particles R ≥ 1 μm, the surface area of the particles per unit volume, E (cm−1), is determined only by R (E ∼ 1/R).

The use of deuterium for examination of C:H films

Abstract The method of nuclear reactions has been exploited to determine the hydrogen composition of diamond-like C:H films. Amorphous films 1–3 × 10 3 A thick were prepared from methane enriched with deuterium to 99% via decomposition from high-frequency or d.c. plasmas. Substrates were glass, Ge, or Cu. For determination of composition, use was made of 12 C(d, p) 13 C and D(d, p)T reactions on deuterons. A Van de Graaff electrostatic accelerator produced a beam of deuterons with energy 900 keV. Nuclear reaction products (protons) were observed with a surface-barrier detector of resolution 25 keV. Concentration ratios x = C D / C C were determined in the films; the ratios were found to be within the interval x = 1.5-0.5, depending on the sputtering conditions It was found that during measurement the amount of hydrogen in the films decreases as the absorbed dose W increases up to W ⋍ 5 × 10 4 MH , after which it stabilizes. Carbon content remains unchanged. The values of ∂ x /∂ W differed at the initial irradiation stages for films condensed under various conditions. The relation x = f ( W ) for films sputtered under the same conditions is similar for different substrates. This study has shown that ion irradiation results in the breaking of C-H bonds, the appearance of mobile hydrogen, and a simultaneous increase in the concentration of hydrogen “traps”.

An electron microscopy study of irradiation and thermal effects on C:H films

Abstract This paper deals with the influence of irradiation and thermal effects on the structure of hydrogen-containing carbon (C:H) films produced by the decomposition of deuterated (99%) methane. A beam of deuterons with E = 900keV was used for irradiation. Transmission electron microscopy and electron diffraction methods were employed to examine the structures of the starting film and of films subjected to the following treatments: (1) irradiation with D + ions; (2) annealing at 300 °C; (3) annealing at 300 °C and subsequent irradiation with D + ions; (4) annealing at 500 °C. The films annealed at 300 °C and those subjected to post-annealing irradiation (T=300 °C) differ in their morphology.

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.