Shock compaction of cubic boron nitride powders

C-BN powders with different grain sizes were dynamically compacted by explosive shock loading using approximate peak pressures from 33 to 77G Pa. The density and the microhardness of the resulting c-BN compacts were strongly dependent upon the grain size of the c-BN powders used as the starting materials. The best c-BN compacts, with 98% of the theoretical density and microhardness of 51.3G Pa, were obtained from the coarse c-BN powder (40 to 60m). In the compacted fine c-BN powder (2 to 4m) conversion of the c-BN to low density forms of BN at a residual temperature degraded the interparticle bonding significantly. X-ray line-broadening analysis of the compacted c-BN powders indicated that the residual lattice strain increased with the increase in grain size of the starting powder, while the crystallite size was independent of the grain size.     

Lubrication in steel strip rolling in Japan

Research into, and the state of technology for, lubrication in steel strip rolling in Japan are reviewed. Both cold and hot strip rolling are discussed. Subjects covered include coefficient of friction and oil film thickness, friction pick-up, and roll wear.     

Effect of the specimen geometry on wear - combination of polyacetal (POM) and carbon steel for machine structures

Engineering plastics which have been shown to have good mechanical properties are now frequently used as materials for various machine elements. Engineering plastics are combined with other engineering plastics and metallic materials for machine construction. These machine elements are fabricated with contact surface forms, such as convex, concave, and plane surfaces. Therefore, when designing machines with a combination of materials containing engineering plastics, it is useful to know the wear and friction characteristics for various contact surface forms. In the present research, polyacetal (POM), an engineering plastic, and carbon steel, a metal often used for machine structures, were chosen as materials to study wear and friction. Wear tests were performed in the combination of a convex surface and a plane, and in the combination of a plane and a plane. As a result, some features of the wear and friction characteristic are clarified. (1) The worn mass when the flat specimen made of POM is rubbed by the POM pin specimen is larger than when with the pin specimen made of carbon steel. (2) When the flat specimen made of POM is rubbed by the POM or the carbon steel pin specimen, the same grade of wear is observed regardless of the pin specimen material. (3) The worn length of the steel spherical pin specimen on the steel flat specimen becomes close to the initial radius of the curvature of the pin specimen when the sliding distance is large. The initial condition of the spherical tip pin specimen on the flat specimen evolves toward a condition of the flat tip pin specimen on the flat specimen. So, the comparison between the two geometries is non-relevant. Such problem did not occur in POM pin specimen.     

Effects of Co content and WC grain size on wear of WC cemented carbide

WC cemented carbides are used extensively to improve abrasion resistance. Co content and WC grain size influence the mechanical properties of the cemented carbides. In this study, the effects of Co content and WC grain size of cemented carbide on wear were examined. We prepared 13 different cemented carbides with different Co content and WC grain size. Wear tests were carried out against 0.45% carbon steel under dry condition at 98 N and 232 mm/s. From the results, we found that wear increased with both Co content and WC grain size. Specific wear rate of the cemented carbides tested was in the range of 10⁻⁷ mm³/(N m). We discussed the wear properties with hardness and the mean free path of the cemented carbide. These two parameters alone cannot explain the wear property.     

Tribology of helical scan tape drive systems

The future direction of the designs of the metal evaporated tape for higher density recording in the helical scan tape drives which use MR heads was investigated. Static friction force between a tape and a roller guide increases the force with which the tape edge is pressed against the flange of the roller guide and wear debris is produced from the tape edge. The wear debris is driven to the recording area on the tape and increases a rewrite ratio, which indicates the ratio of failure of reading data. A solid lubricant at operating temperature was found to reduce the coefficient of static friction. However, the combination between the solid lubricant and MR heads which are heated by sense current may cause tape damage in dwell tests at low temperature. The increase in a melting temperature of the solid lubricant was found to improve the durability in dwell tests at low temperature.     

Tribological characteristics of bonded MoS2 films evaluated in rolling-sliding contact in a vacuum

Tribological characteristics of bonded MoS₂ films have been evaluated in air, nitrogen and vacuum using a two-roller type rolling-sliding friction apparatus. Two conventional space-proven films, polyamideimide-bonded and sodium silicate-bonded, designated as film A and film B respectively, were tested at a speed of 998 rev min^-1 under a load of 100 N at slip ratios of 1–100%, the slip ratio being defined as (V₁ - V₂)/ V₁ × 100%, in which V₁ and V₂ was rotational speed of each roller.

The wear life of the film A was more slip ratio dependent than that of the film B. The wear life of the film A tested in a vacuum was the longest at 10% slip ratio but it reduced significantly at 1%. On the contrary, the best durability of the film B was obtained at 100% slip ratio (pure sliding). The wear life of the film A shortened considerably in air and nitrogen.

In general, a solid lubricant film applied to spur gears is subjected to rolling-sliding friction of 0-10% slip ratios. To improve the endurance life of the film A at 1% slip ratio, films prepared by changing content of pigments (MoS₂ and Sb₂0₃) were evaluated. The films with a pigment content of 5-15% showed a marked improvement in wear life at a slip ratio of 1%, while maintaining excellent durability at 10%.

The wear process of an improved film was monitored using a gap sensor. It appears to be dominated by fatigue.     

Application of high-resolution scanning electron microscopy to biological macromolecules

The development of ultrahigh-resolution scanning electron microscopes (SEMs) has made the observation of biological macromolecules feasible, but adequate preparation methods have not yet been established. Although it has been possible to observe some molecules after they have been spread on a carbon substrate, this method has not proved suitable for other molecules which exhibit lower contrast, or are more susceptible to damage by the electron beam. In this study we have applied heavy-metal impregnation methods using phosphotungstic acid, uranyl acetate, or osmium tetroxide mordanted by tannic acid. In addition, contamination due to the electron beam was reduced by improving the vacuum in the specimen chamber, and by the use of a heated specimen stage. Using these measures, haemocyanin, ferritin, apoferritin, thyro-globulin and immunoglobulin M were successfully imaged. Ultrahigh-resolution SEM seems likely to become an important means for studying the morphology of biological macromolecules.     

Effects of substrate surface finish and substrate material on durability of thermally sprayed WC cermet coating in rolling with sliding contact

In this study, using a two-roller testing machine, the authors examined the surface durability of thermally sprayed WC-Cr-Ni cermet coating in lubricated rolling with sliding contact conditions. The coating was formed onto the axially ground, blasted and circumferentially ground roller specimens made of a thermally refined carbon steel or an induction hardened carbon steel by means of the high energy type flame spraying (Hi-HVOF) method. The WC cermet coated roller finished to a mirror-like condition was mated with the carburized steel roller without coating having a surface roughness of Ry=3.05.0 μm. In the experiments, a maximum Hertzian stress of P_H=0.6 or 0.8 GPa was applied for the thermally refined carbon steel roller and P_H=1.4 GPa was applied for the induction hardened carbon steel roller in line contact condition. As a result, it was found that in the case of induction hardened steel substrate, the coated roller generally exhibits a long life without any serious damage and the surface durability is hardly affected by the substrate surface finish, while in the case of thermally refined steel substrate, the durability of coated roller is lowered and the life to flaking is very short particularly when the substrate surface is circumferentially ground and the mating surface is rough. The surface durability of coated roller was also compared with the durability of steel roller without coating. Finally, in order to discuss the durability of coated roller, the elastic-plastic behavior of the subsurface layer under repeated rolling with sliding contact was analyzed using a finite element method (FEM).     

Development of precise cylindrical grinding by ball centers: effect of dynamic stiffness on work profile

In high-precision cylindrical grinding, it is known that the accurate and inexpensive steel balls used instead of the cone centers enable accurate grinding of the work without the misalignments and the geometrical deviations of the center holes. The purpose of this study is to explain the supporting characteristics of these ball centers. In this article the work profile, supporting stiffness, and grinding force in grinding only are measured to investigate the stiffness effects on the ground profile. Moreover, the generation process of the work profile is addressed via both experimental and simulation analyses. The obtained main results are as follows: (1) The ball center enables detailed observation of the work profile, displacement, and grinding force during grinding. (2) The radial compliance of the work supporting system correlates well with the center hole profile. (3) The compliance has a strong influence on the work profile in grinding. (4) The amplitudes and the phases of the work profile components are formed at the beginning of the spark-out states.