Wear and T.E.M. Studies of P.E.C.V.D. Diamond-like-Carbon Films

Diamond-like-carbon (D.L.C.) films are characterized by a low friction coefficient, a high wear resistance and a high corrosion resistance. D.L.C. films can be obtained by P.V.D., C.V.D. and duplex techniques with solid or gaseous precursors. Depending on the processing, hydrogen concentration ranges between 0 and 60%

In this study, hydrogenated D.L.C. has been deposited with a radio frequency system (13.56 MHz) onto a steel substrate. Wear was studied by pin-on-disc testing at room temperature with an alumina counterpart. Interrupted tests were carried out to go into wear mechanisms. Debris were collected after various given sliding times for transmission electron microscopy (T.E.M.) in addition to scanning electron microscopy (S.E.M.) applied to the wear tracks.     

Fracture toughness evaluation of a H.S.L.A. steel

The fracture toughness, J_Ic of a 3.5 Ni-Cr-Mo-V steel has been measured using the ASTM method. The results have been used to predict the stress intensity factor, K_Ic from the relationship between linear elastic and elastic-plastic fracture parameters. These predicted values were compared with K_Ic values obtained from empirical equations based on valid K_Ic tests, involving the Charpy upper shelf energy. It was found that the ASTM method for measuring J_Ic led to conservative estimates of K_Ic.     

MAS n.m.r. and e.s.r. studies of MnAlPO5

²⁷Al and ³¹P magic angle spinning (MAS) n.m.r. and e.s.r. measurements have been performed on MnAlPO5 in order to obtain direct evidence for Mn⁺² incorporation into tetrahedral sites in the framework. Two samples differing in their Mn content have been studied, and their results were compared with those obtained from impregnated Mn-AlPO5 and exchanged Mn-SAPO5 where the Mn⁺² does not occupy framework sites. The MAS n.m.r. spectrum showed a large anisotropy, manifested in numerous side bands due to the paramagnetic shifts induced by dipolar interactions between the unpaired electrons of the Mn⁺² and the ³¹P and ²⁷Al nuclei in its vicinity. On dehydration, a considerable linewidth narrowing has been observed, attributed to a decrease in the electronic relaxation time induced by increase in Mn⁺² spin-exchange interaction. Calculated³¹P MAS n.m.r spectra, where the paramagnetic shift anisotropy was obtained from X-ray diffraction data of AlPO5 and taking into account the Mn content obtained from the chemical analysis, showed qualitative agreement with the experimental spectra. Comparison of the simulated and experimental spectra indicates that, indeed, part of the Mn⁺² cations occupy framework sites; it does, however, also suggest that extraframework Mn⁺² cations are present as well. These conclusions are further supported by e.s.r. measurements. The e.s.r. spectrum of MnAlPO5 shows resolved hyperfine lines with splitting characteristics of octahedral Mn⁺², supporting the existence of extraframework Mn⁺². On dehydration, the spectrum of MnAlPO5 coalesce into a single absorption line. This coalescence is attributed to increase in the spin-exchange interaction due to migration of probably extraframework Mn⁺² toward the framework.     

Prof. Dipl.-Ing. Dr. techn. Dr. h. c. Wilhelm Schneider

Summary In order to provide a firmer foundation on which some reciprocity theorems in Eshelbian mechanics where established earlier, a nonlinear and then linearized formulation of these theorems is presented. To carry out the required operations a simple two-degrees-of-freedom system was chosen. The analysis led to mostly algebraic expressions which are also illustrated graphically. Readers will be very sad to learn of the mournful death on January 7, 2007, of Prof. Dr. sc. techn. Dr. h. c. George Herrmann. Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday     

The use of rubbers in C.F.R.P. manufacture

Manufacturing techniques are crucial to the variability of advanced composites. For this reason a number of processes have been developed to reduce the cost of producing composite structures. Some of these processes make use of the properties of rubber in self-sealing from fitting rubber vacuum bags, in pressure pads and as a hydraulic medium. Each has its advantages and disadvantages but the overall trend is to reduce the costs of advanced composites manufacturing, at times dramatically.     

International Activity of VNIIM im. D. I. Mendeleeva

On the basis of experience the institute demonstrates the possibility of effective use of international cooperation in solving many problems including improvement of the standard base, an increase in specialist qualifications, and introduction of scientific achievements. Particular attention is devoted to fulfilling obligations connected with participation in the Metric Agreement and Convention “Mutual recognition of national measurement standards and certificates for calibration and measurement issued by national metrology institutes.”__________Translated from Izmeritel’naya Tekhnika, No. 6, pp. 66–69, June, 2005.     

The spectrum of cosmic-ray electrons measured with H.E.S.S.

The measurement of very-high-energy cosmic-ray electrons is intrinsically difficult due to the very steep electron spectrum with low fluxes and an enormous background of hadronic cosmic rays. The large collection areas needed for such a measurement can be provided by ground-based imaging atmospheric Cherenkov telescopes. The High Energy Stereoscopic System (H.E.S.S.) has performed the first ground-based cosmic-ray electron measurement and thereby extended the measured range of the spectrum to several TeV. Here the H.E.S.S. measurement is presented, as well as an extension of the H.E.S.S. spectrum towards lower energies. At these energies, H.E.S.S. can probe recent ATIC measurements, which have been interpreted in terms of dark matter scenarios.     

C.V.D. Coating of Alumina Reinforcing Particles to Improve the Wear Resistance of H.S.S. Based Composites

C.V.D. coating of the reinforcing ceramic particles used in particulate metal matrix composites allows the control of reactivity at the particle/matrix interface. Wear resistant high speed steel-based composites containing uncoated A1₂0₃, uncoated TiC and C.V.D. coated A1₂0₃ were liquid phase sintered, then characterized using “pin-on-disc” wear testing. TiC or TiN C.V.D. coatings of A1₂0₃ were tested to determine die increase in reactivity of the particles with the liquid phases formed during sintering. This resulted in a porosity decrease at the particle/matrix interface in addition to a better ceramic/metal cohesion due to improved wettability. Reactivity and wettability were studied using differential thermal analysis, electron microprobe analysis, transmission electron microscopy, and image analysis. Results from pin-on-disc wear testing illustrated the role of the C.V.D. coating on the wear behavior of the studied materials. Lower wear rates were obtained with the composites containing TiC or TiN-coated Al₂0₃. These results showed that there is a relation between wettability of ceramic particles by the metallic phases and wear resistance of the composites.