I.Sh. Trakhtenberg

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.

Friction, wear and service properties of i-C coatings on steel

Abstract We have developed a high-accuracy test unit that permits the testing of wear of coatings by a flux of solids. The unit features the following advantages: • - Special abrasive particle collectors are provided which enable one to determine accurately the number of particles that have caused the wear of a given specimen; • - Spatial homogeneity of the particle effect on a specimen is ensured, owing to scanning a particle jet perpendicular to the plane of its rotation. Friction studies and tests of i-C diamond-like coatings (DLCs) in a flux of solids have shown that the surface hardening effect is determined by the adhesion of coating to the substrate and by the critical degree of plastic deformation at the substrate coat interface. On the basis of the tests performed, a procedure of applying surface-hardening i-C DLCs on various tools has been developed which permits the operational life of tools to be extended considerably.

Oxygen Isotope Exchange between Gaseous Phase Enriched with 18O Isotope and Nanocrystal Oxides LaMnO3+δ Obtained by Severe Plastic Deformation

The kinetics of the isotope exchange between gaseous oxygen enriched with the 18O isotope and two LaMnO3+δ oxide samples – a nanopowder and a bulk nanocrystal – has been studied. The 18O isotope concentration has been measured by the acceleration nuclear microanalysis method. The coefficients of the volume and the nanograin boundary self-diffusion of oxygen have been evaluated at 500 °C. They are equal to 3.5·10 −20 and 1.5·10 −13 cm2/s, respectively.

Modification of amorphous diamond-like films by bombardment with low-energy ions☆

Abstract The study is concerned with the influence that bombardment with low-energy (approximately 1 keV) ions of argon, oxygen, nitrogen or hydrogen exerts on properties of the amorphous diamond-like coatings (DLCs) produced by vacuum pulse sputtering of graphite in an arc discharge. It is shown that hydrogen treatment leads to the formation of C:H films whose composition depends on specific bombardment conditions. Bombardment with the other ions results in etching and smoothing of the DLC relief, while the film composition remains unchanged. Ionic bombardment increases the share of the diamond-like component in the film structure.

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.