Junji Sugishita

The effect of cast iron graphites on friction and wear performance I: Graphite film formation on grey cast iron surfaces

Abstract Cast iron is assessed as a self-lubricating metal-base composite material. The formation of cast iron graphite films and the effective surface treatment of grey cast iron are discussed. It was found that the friction and wear behaviour of cast iron are influenced by the formation of a graphite surface layer. When cast iron surfaces are etched with Nital, they are found to be covered with a graphite film during the sliding friction process. This contributes to the protection of metallic contact points. The formation of graphite films during testing is assumed to be due to the non-elastic deformation of surface graphite. The effects of applied load, sliding velocity and lubricant are also discussed. The coefficient of friction increases with applied load and sliding velocity, and therefore lubrication becomes more important. These phenomena are discussed in terms of the formation of graphite films during the friction process.

The effect of cast iron graphites on friction and wear performance: II: Variables influencing graphite film formation

Abstract Cast iron may be classed as a self-lubricating metal-base composite material. The cast iron graphites have an excellent lubricity which is similar to that of a solid lubricant and contributes to the decreases in the wear loss and the friction coefficient. Factors affecting graphite film formation are discussed. The coefficient of friction increases with substrate hardness because graphite film formation is influenced by the relative difficulty of substrate deformation. Although adhesive wear and the friction coefficient increase with decreasing air pressure, the cast iron graphites contribute to the decrease in wear rate in the region of 10−2 Torr. Water vapour pressure has a direct effect on film formation and film hardening, particularly above 16 Torr. The lubricity of cast iron graphites was confirmed at temperatures below 100°C. The friction coefficient increases with the temperature rise owing to hardening of the graphite film. The effect of cast iron graphites on rolling wear resistance is discussed.

The effect of cast iron graphite on friction and wear performance III: The lubricating effect of graphite under rolling-sliding contacts

Abstract The formation of nodular cast iron graphite films and the factors affecting squeeze film formation during rolling-sliding contact are discussed. The lubricating effect of the graphite is confirmed by roller tests and by practical gear tests. The frictional torque behaviour and wear change with surface treatments such as etching and hardening. The wear loss of ground specimens is greater than that of etched specimens because of differences in the substrate hardness and the microstructure. The formation of cast iron graphite films on hardened ground surfaces covered with a plastic flowed layer is difficult because of the small plastic deformation of the substrate, and severe wear occurs. The lowest values of the frictional torque and of the wear rate are obtained for ground surfaces with a substrate hardness of about 300 HV. This is due to the ease of formation of a graphite film as a result of the combined effects of fatigue failure of the surface and a squeeze phenomenon. The size of the spherical graphite particles affects film formation. If the size is doubled, the wear rate is halved. The grinding of tooth surfaces has a detrimental effect on the fatigue wear life.

A study of cast alloys with partially dispersed graphite: I: The process of partial dispersion with uncoated carbon microballoons

Abstract A study of cast alloys with partially dispersed graphite was carried out to improve the mechanical properties as well as to retain excellent wear resistance. Uncoated carbon microballoons (carbospheres) instead of graphite were only dispersed by a centrifugal casting machine to surfaces requiring wear resistance or lubrication. With pure aluminium, aluminium alloys and tin-based Babbitt metal, carbonized layers extended to a height of 30 mm from the bottom of the specimens and they had a maximum thickness of 1.2 mm. Partial dispersion is due to the poor affinity between the carbon and the molten metal. The casting alloys developed have a smooth surface and no shrinkage from solidification. Factors affecting the mechanism of partial dispersion and remaining problems are discussed: some successful examples are presented.

Influence of M (M=Zn and Ni) Substitution for Cu on Microwave Dielectric Characteristics of Yb2Ba(Cu1-xMx)O5 Solid Solutions

The effects of M (M=Zn and Ni) substitution for Cu on the microwave dielectric properties and the crystal structure of Yb2Ba(Cu1-xMx)O5 solid solutions were investigated. Yb2Ba(Cu1-xNix)O5 (x=0 to 1) solid solutions are a single phase, whereas the limit of Yb2Ba(Cu1-xZnx)O5 solid solutions is x=0.75. The formation of the solid solutions is caused by the difference of ionic radii between Yb3+ and M2+ ions. The ?r values of Yb2Ba(Cu1-xZnx)O5 (x=0 to 0.75) solid solutions vary from 7.9 to 14.9, depending on the composition x. This variation is interpreted as an increase in the volume of the Yb2O11 polyhedron induced by an expansion of the bottom plane with M substitution for Cu. Moreover, the Q?f values of the solid solutions are extremely improved by M substitution for Cu, and the maximum Q?f values with Zn and Ni substitutions for Cu are 52815 and 50042 GHz, respectively.

Effects of Dy substitution for Y on microwave dielectric properties of High-Q R2O3-BaO-ZnO (R=Y and Dy) system

Abstract The (Y 2− x Dy x )BaZnO 5 solid solutions were synthesized and studied, this paper focused on the relationships between the crystal structure and the improvements in temperature coefficients of resonant frequency (τ f ) caused by Dy substitution for Y. The dielectric constants ( e r ) were slightly increased with increasing the composition x ; this result was attributed to the increase in the ionic polarizabilities caused by Dy substitution for Y. The quality factors ( Q · f ) were extremely decreased from 165,500 to 29,600 GHz with increasing the composition x . The τ f values were increased from −44.5 to −1.6 ppm/°C, whereas the temperature coefficients of the dielectric constant (τ e ) varied from positive to negative values.

Grinding performance of an aluminium-bonded diamond wheel on ceramics and glass

Abstract Grinding tests were conducted using a straight type diamond wheel, the bond of which is an aluminium alloy containing an inter-metallic compound such as TiAl3 phase. Workpiece materials were two kinds of ceramics and one float plate glass. The results of tests are as follows: the aluminium-bonded wheel showed a better grinding ratio and lower power consumption compared to a conventional bronze-bonded wheel, particularly in grinding float plate glass; the change of shape of the grinding wheel due to wear is smaller and the life of the wheel was found to be doubled compared to a conventional bronze-bonded wheel.

A study of cast alloys with partially dispersed graphite II: The process of partial dispersion with uncoated flake graphites

Abstract The mechanism of partial dispersion of uncoated flake graphite particles was investigated and compared with that of carbon microballoons (carbospheres) investigated earlier. Two types of flake graphite particles and the same base metals as previously used were investigated. The dispersive power of uncoated flake graphites was relatively small compared with that of spherical carbon balloons. For dispersion a temperature of 50 – 100 °C above the melting point with G = 1500 (where G is a non-dimensional gravity variable) is required with pure aluminium and its alloys. The variation in surface roughness of cast aluminium alloys containing flake graphites is due mainly to the magnitude of the centrifugal forces; the roughness decreases with increase in the acceleration (expressed in terms of G ). The dispersive width of the graphitic layers and the clearance ratio are related; the width increases with ratio up to D / d = 2.5.

a study of cast alloys with partially dispersed graphite III: Characterization of high density dispersed surfaces

Abstract The characteristic features of cast alloys with partially dispersed graphite are wear resistance and toughness. The friction and wear performance, hardness and other surface characteristics of the cast alloys with a high dispersive density of 60% at the casting surfaces were studied. The reciprocating sliding wear volume of aluminium alloy AC7A containing dispersants decreases with an increase in the gravity variable G = 2 π 2 DN 2 /60 2 g , where D (cm) is the diameter of rotation, N (rev min −1 ) is the rotational speed and g (cm s −2 ) is the acceleration due to gravity, but depends on the nature of the dispersants. The effect of casting temperature on the wear loss was not significant. The dispersive density at the near-surface regions which is susceptible to the magnitude of G has a direct effect on the wear loss. A dense dispersant has an adverse effect on wear resistance and lubricity. A relation between surface roughness and casting temperature is also reported.

Relationship between crack growth and wear mechanism of brittle materials during sliding contact

Abstract Effects of crack growth on wear mechanisms of brittle materials such as ceramics were evaluated using a testing apparatus having a reciprocal movement at a constant frequency with various normal loads in air. Soda lime glass bars and alumina spheres were mainly used for specimens. The friction and wear behavior showed that the wear of the glass depended on the crack growth near the wear scar and that the coefficient of friction was greater corresponding to the wear rate. Critical stresses for crack growth in sliding contact were determined from indentation damage technique. The crack growth below the wear scar was estimated from inert strength measurements after the friction experiment. The maximum stress at the trailing edge in sliding contact was calculated from elastic contact theory. It was confirmed that the tangential traction at the interface had great influence on the stress at the trailing edge and that crack growth occurred during sliding contact when the stress exceeded the critical value for crack growth.